August 27, 2015

10 Mile ARC to VOR 30 Approach - Hobart, Tasmania Australia (YMHB)

August 27, 2015/ Flaps 2 Approach

Approach chart depicting VOR 30 Approach to YMHB. Important points to note are: initial approach courses to intercept the arc (295 & 334), the D10 HB arc, the altitude increments of 4000, 3000 and at 7 miles, 2400, and the Initial Approach Fix (IAF) and speed of 210 kias

Recently, I flew from Brisbane to Hobart and the pilot flying made a different style of approach to what normally is made at this airport. After landing, I approached the pilots and queried the approach. The Captain stated that he had decided to fly a semi-automated VOR approach along an arc to land at runway 30.

The reason being, that Air Traffic Control (ATC) had warned them of turbulent conditions near the airport. He commented that in such conditions, he felt more confident using the older style arc approach using LNAV/VNAV with Speed Intervention (SPD INTV) engaged, with a transition to Vertical Speed and VOR once on final.

The First Officer stated that this was the first time he had seen an arc being used to set-up for a VOR approach. He said that usually they use ILS into RWY 12 or RNAV into RWY 30. He commented that the only time he had made a VOR approach was during simulator training, and then he would probably only use such an approach, if the ILS was inoperative or there was an issue with RNAV.

The use of this approach is a prime example of the variation offered to pilots in relation to how they fly and land the Boeing 737.

Screen Images

Several screen captures from the Instructor Station, CDU and Navigation Display (ND) which I hope will make it easier to understand this post. The avionics suite used is ProSim737 distributed by ProSim-AR. Note that some of the mages are not sequential as I captured the images over two simulator sessions.

How To Set-Up An Arc

To set-up an approach using an arc is very easy.

The following example is for Hobart, Tasmania Australia (YMHB). The instructions assume that you are conversant with operating the CDU and have a basic understanding of its use.

Essentially, an arc is using a Place/Bearing/Waypoin t to define an arc around a point at a set distance. The distance between each of the generated waypoints along the arc, is at the discretion of the flight crew.

Approach Charts

To determine the correct distance to create the arc, the approach chart for the airport should be consulted. The chart, in addition to providing this information, will also aid you in decided where to place the final waypoint (if wanted) along the approach course.

In this example, the YMHB VOR 30 approach states that the aircraft must fly an arc 10 miles from the airport between an altitude of 4000 and 3000 feet before descending to be at 2400 feet 7 miles from the runway threshold.

The approach chart depicted is provided by Lufthansa Systems (LIDO/FMS) distributed by Navigraph.

Navigraph Charts 4 Review.

CDU Instructions

(i) Open the FIX page and type in the scratchpad the airport code (YMHB). After uploading, type the distance (/10 miles). This will create a green-dotted citcle around YMHB with a radius of 10 miles.

(ii) Open the LEGS page and type into the scratchpad the airport code (YMHB). Immediately following YMHB, type the required radial1 (in degrees) from the airport that you wish the initial waypoint to be generated. Follow this with a slash and type in the distance from the airport (YMHB340/10).

This will generate a waypoint 10 miles from YMHB on the 340 radial. This is the waypoint from which you will begin to build your arc.

Obviously, the radial you use to define the location of your first waypoint will depend upon the bearing that you are flying toward the airport.

(iii) To Generate the ARC you must repeat the above process (ii) changing the radial by 10 degrees (or whatever you believe is needed) to generate the required waypoints around the arc at 10 miles from the airport. As an example: YMHB320/10, YMHB340/10, YMHB000/10 and so forth until the arc is built.

As you upload each of the radials you will note that the name for the waypoint is changed to a sequential number specific to each waypoint. As an example; the above waypoints will each be named YMH01, YMH02 and YMH03.

If you make a mistake, you can delete a waypoint and start again; however, realize that the sequential numbers will not be in order. This is not an issue (it is only a number) but it is something be aware of.

In our example, the VOR approach is for runway 30. Therefore; your final waypoint on the arc will be YMHB121/10. Prior to reaching this waypoint, if flying manually, begin the right hand turn to intercept the approach on the 121 radial (bearing 300 degrees).

A Note About /-+

The more observant will note that the distances in the example above do not utilise the /+ key before the distance (YMHB340/+10). When entering the distance it can be with or without the + key.

Variation

Before going further, there are many ways to fly the B737. The method selected is at the discretion of the pilot in command and is dependent upon airline preferences, environmental conditions, and pilot experience. This statement was stressed to me when I spoke with the Captain of the aircraft.

Often an approach will incorporate a number of automated systems including VNAV, LNAV, Vertical Speed, Level Change, VOR Localizer and old fashioned manual VFR flying. In most cases the particular approach will be programmed into the CDU, at the very least for situational awareness. However, the CDU does not have to be used and often a step down approach is a good way to maintain flying skills and airmanship.

Handy Hints

The following hints will assist with situational awareness and in allowing the aircraft to be guided by the autopilot to a point to which manual flight can commence.

If you carefully study the approach chart for YMHB VOR 30, you will note that the altitude the aircraft should be at when at 7 miles from the threshold should be 2000 feet. The chart also depicts the letter D at this point meaning that a continuous descent can be made this point.

Hint One - visual descent point (VDP)

To make the transition from the arc to the approach easier, create a waypoint at the 7 mile point from the airport along the radial used for the approach (YMHB121/7). Using a waypoint allows the aircraft’s Lateral Navigation (LNAV) to be used. This type of waypoint is usually referred to as a Visual Descent Point (VDP).

When the waypoint at 7 miles from the threshold is reached, a transition to manual flying can commence, or Vertical Speed can be used to maintain a 3 degree glidepath (GP) while following the VOR. Remember to change the EFIS from MAP to VOR so you can use the VOR indicator during the approach.

Hint Two - extend runway line

Assuming you have not inserted an approach into the CDU, an aid to increase situational awareness is to select the correct runway from the CDU and enter a distance that the runway line is to be extended from the threshold.

To do this, select runway 30 from the ARRIVALS (ARR) page in the CDU (RWY30) and type the numeral 7 (or whatever distance you require) into the scratchpad and upload. This will extend the green line from the runway threshold to the previously generated waypoint at 7 miles. Ensure you clean up any discontinuity (if observed) in the LEGS page.

This enables three things:

The generation of a 3 degree glidepath (GP) from the distance entered (example is 7 miles) to the runway threshold.
It enables LNAV (even if the autopilot is not engaged) to continue to provide the Flight Director (FD) with heading information during the approach, and
It enables the Navigation Performance Scales (NPL) on the Pilots Flight Display (PFD) to provide glidepath (GP) guidance (assuming that the correct runway or approach is selected in the CDU and NPL is enabled within the ProSim737 avionics suite).

UPPER LEFT: Screen capture from the instructor station PFD and ND for the approach into YMHB. The aircraft, after turning right from the 10 mile arc, is aligned with the 121 radial approaching the waypoint YMH07 (the WP entered at the 7 mile point). LNAV is engaged and the aircraft is being controlled by the autopilot. As RWY 30 was inserted into the route, the Navigation Performance Scales (NPS) show Glidepath (GP) data in the Primary Flight Display (PFD). Note that the EFIS is still on MAP and is yet to be turned to VOR. In real life, VOR would have been selected earlier (click to enlarge).

LOWER LEFT: The transition from LNAV to VOR has occurred and the autopilot and autothrottle are not controlling the aircraft. The aircraft is on short final with gear down, flaps 30 and the airspeed is slowly decaying to VREF+5.

The EFIS has been changed from MAP to VOR to allow manual tracking using the VOR needle. The NPS show good vertical alignment with a lateral left offset; the VOR indicator confirms this. The Flight Mode Annunciator (FMA) displays LNAV (although the autopilot is disengaged) and the Flight Director (FD) and NPS show glidepath (GP) data. The Flight Path Vector (FPV) symbol shows a continuous descent at roughly 3 degrees. The altitude window and heading on the MCP has been set to the appropriate missed approach (4200/300). Click image to enlarge.

Do Not Alter Constraints

As alluded earlier, there are many ways to accomplish the same task. However, DO NOT alter any constraints indicated in the CDU if an approach is selected and executed. CDU generated approaches have been standardised for a reason.

Finding the Correct Radial/Bearing to Build Your Arc

Finding the correct bearing to use on the arc can be challenging for those less mathematically inclined. An easy method is to use one of the two MCP course selector knobs.

Rotate the knob until the green dotted line on he Navigation Display (ND) lies over the area of the arc that you wish the waypoint to be created. Consult the MCP course selector window - this is the figure you place in the CDU. Next, rotate the knob a set number of degrees and repeat the process. You can also consult the data displayed along the course indicator line on the Navigation Display (ND).

When you build the arc, ensure you have set the EFIS to PLN (plan). PLN provides more real estate to visualize the approach on the Navigation Display (ND). You can use STEP in the LEGS page to cycle through the waypoints to ensure you have an appropriate view of the surrounding area.

Important Points

Always double check the Place/Bearing/Waypoint entries in the CDU and in the ND (PLN) before executing. It is amazing how easy discrepancies can occur.
Always check the approach plate for the approach type you are intending to make. Once again, mistakes are easy to make.
If using VNAV, double check all speed and altitude constraints to ensure compliance with the approach chart and situation (some airlines promote the use of the speed intervention button (SPD INTV) to ensure that appropriate speeds are maintained).
If need be, select the approach (ARR) in the CDU to provide added situational awareness.

Images

The following are screen captures from the instructor station CDU and Navigation Display (ND). Ignore altitude and speed constraints as these were not set-up for the example. Click each images to enlarge.

LEFT: Circular FIX ring has been generated around YMHB at 10 mile point. The arc waypoints will be constructed along this line.

LEFT: Various waypoints have been generated along the 10 mile fix line creating an arc. The arc ends at the intersection with the 212 radial for the VOR 30 approach into YMHB. The route is in plan (PLN) view and is yet to be executed.

LEFT: The constructed arc as seen in MAP view. From this view it is easy to establish that the aircraft is approaching TTR and once reaching the 10 mile limit defined by the 10 mile FIX (green-coloured dotted circle), the aircraft will turn to the left to follow the arc waypoints until it intersects with the 121 radial.

LEFT: This image depicts the waypoint generated at 7 mile from the threshold (YMHB121/7). This waypoint marks the point at which the aircraft should be on the 121 radial to VOR 30 and at 2400 feet altitude (according to the VOR 30 approach plate.

LEFT: RWY 30 has been selected from the arrivals (ARR) page. This displays the guidepath (GP) assistance. it also generates a runway line extending from the threshold to 7 miles out; the same distance out from the threshold that the final waypoint was generated.

The course line is coloured pink indicating that LNAV is enabled and the aircraft is following the programmed route.

At the final waypoint (YM10) the autopilot (if used) will be disengaged and the aircraft will be flown manually to the runways using the VOR approach instrumentation and visual flight rules (VFR). The EFIS will be changed from MAP to VOR. LNAV will remain engaged on the MCP to ensure that the NPL indications are shown on the PFD. The NDL indicators provide glidepath (GP) guidance that is otherwise lacking on a VOR approach.

Final Call

I rarely use automated systems during landing, unless environmental conditions otherwise dictate. I prefer to hand fly the aircraft where possible during the approach phase, and often disengage the autopilot at 5000 feet. If flying a STAR and when VNAV/LNAV is used, I always disengage the autopilot no later than 1500 feet. This enables a safe envelope in which to transition from automated flight to manual flight.

Using an arc to fly a VOR approach is enjoyable, with the added advantage that it provides a good refresher for using the Place/Bearing/Waypoint functionality of the CDU.

Additional articles that address similar subjects are:

Glossary

CDU – Control Display Unit (aka Flight Management Computer (FMC).
EFIS – Electronic Flight Instrument System.
LNAV – Lateral navigation.
RADIAL/BEARING – A radial radiates FROM a point such as a VOR, whilst a bearing is the bearing in degrees TO a point. The bearing is the direction that the nose of the aircraft is pointing.
VNAV – Vertical Navigation.

February 17, 2015

Autobrake System - Review and Procedures

February 17, 2015/ Flaps 2 Approach

air berlin 737-700 - autobrake set, flaps 30, spoilers deployed, reverse thrust engaged (Marcela, GFDL 1.2 www.gnu.org/licenses/old-licenses/fdl-1.2.html, via Wikimedia Commons)

The autobrake, the components which are located on center panel of the Main Instrument Panel (MIP), is designed as a deceleration aid to slow an aircraft on landing. The system uses pressure, generated from the hydraulic system B, to provide deceleration for pre-selected deceleration rates and for rejected takeoff (RTO). An earlier post discussed Rejected Takeoff procedures. This article will discuss the autobrake system.

General

The autobrake selector knob (rotary switch) has four settings: RTO (rejected takeoff), 1, 2, 3 and MAX (maximum). Settings 1, 2 and 3 and RTO can be armed by turning the selector; but, MAX can only be set by simultaneously pulling the selector knob outwards and turning to the right; this is a safety feature to eliminate the chance that the selector is set to MAX accidentally.

When the selector knob is turned, the system will do an automatic self-test. If the test is not successful and a problem is encountered, the auto brake disarm light will illuminate amber.

The autobrake can be disengaged by turning it to OFF, by activating the toe brakes, or by advancing the throttles; which deactivation method used depends upon the circumstances and pilot discretion. Furthermore, the deceleration level can be changed prior to, or after touchdown by moving the autobrake selector knob to any setting other than OFF. During the landing, the pressure applied to the brakes will alter depending upon other controls employed to assist in deceleration, such as thrust reversers and spoilers.

The numerals 1, 2, 3 and MAX provide an indication to the severity of braking that will be applied when the aircraft lands (assuming the autobrake is set).

In general, setting 1 and 2 are the norm with 3 being used for wet runways or very short runways. MAX is very rarely used and when activated the braking potential is similar to that of a rejected take off; passenger comfort is jeopardized and it is common for passenger items sitting on the cabin floor to move forward during a MAX braking operation. If a runway is very long and environmental conditions good, then a pilot may decide to not use autobrakes favouring manual braking.

Often, but not always, the airline will have a policy to what level of braking can or cannot be used; this is to either minimize aircraft wear and tear and/or to facilitate passenger comfort.

The pressure in PSI applied to the autobrake and the applicable deceleration is as follows:

Autobrake setting 1 - 1250 PSI equates to 4 ft per second squared.
Autobrake setting 2 - 1500 PSI equates to 5 ft per second squared.
Autobrake setting 3 - 2000 PSI equates to 7.2 ft per second squared.
Autobrake setting MAX and RTO - 3000 PSI equates to 14 ft per second (above 80 knots) and 12 ft per second squared (below 80 knots).

Conditions

To autobrake will engage upon landing, when the following conditions are met:

The appropriate setting on the auto brake selector knob (1, 2, 3 or MAX) is set;
The throttle thrust levers are in the idle position immediately prior to touchdown; and,
The main wheels spin-up.

If the autobrake has not been selected before landing, it can still be engaged after touchdown, providing the aircraft has not decelerated below 60 knots. Setting the autobrake usually forms part of the approach cehcklist.

To disengage the autobrake system, any one of the following conditions must be met:

The autobrake selector knob is turned to OFF (autobrake disarm annunciator will not illuminate);
The speed brake lever is moved to the down detent position;
The thrust levers are advanced from idle to forward thrust (except during the first 3 seconds of landing); or,
Either pilot applies manual braking.

The last three points (2, 3 and 4) will cause the autobrake disarm annunciator to illuminate for 2 seconds before extinguishing.

Important Facet

It is important to grasp that the 737 NG does not use the maximum braking power for a particular setting (maximum pressure), but rather the maximum programmed deceleration rate (predetermined deceleration rate). Maximum pressure can only be achieved by fully depressing the brake pedals or during an RTO operation. Therefore, each setting (other than full manual braking and RTO) will produce a predetermined deceleration rate, independent of aircraft weight, runway length, type, slope and environmental conditions.

Autobrake Disarm Annunciator

The autobrake disarm annunciator is coloured amber and illuminates momentarily when the following conditions are met:

Self-test when RTO is selected on the ground;
A malfunction of the system (annunciator remains illuminated - takeoff prohibited);
Disarming the system by manual braking;
Disarming the system by moving the speed brake lever from the UP position to the DOWN detente position; and,
If a landing is made with the selector knob set to RTO (not cycled through off after takeoff). (If this occurs, the autobrakes are not armed and will not engage. The autobrake annunciator remains illuminated amber).

The annunciator will extinguish in the following conditions:

Autobrake logic is satisfied and autobrakes are in armed mode; and,
Thrust levers are advanced after the aircraft has landed, or during an RTO operation. (There is a 3 second delay before the annunciator extinguishes after the aircraft has landed).

Preferences for Use of Autobrakes and Anti-skid

When conditions are less than ideal (shorter and wet runways, crosswinds), many flight crews prefer to use the autobrake rather than use manual braking, and devote their attention to the use of rudder for directional control. As one B737 pilot stated - ‘The machine does the braking and I maintain directional control’.

Anti-skid automatically activates during all autobraking operations and is designed to give maximum efficiency to the brakes, preventing brakes from stopping the rotation of the wheel, thereby ensuring maximum braking efficiency. Anti-skid operates in a similar fashion to the braking on a modern automobile.

Anti-skid is not simulated in FSX/FS10 or in ProSim737 (at the time of writing).

To read about converting an OEM Autobrake.

February 01, 2015

Rejected Takeoff (RTO) - Review and Procedures

February 01, 2015/ Flaps 2 Approach

The Rejected Takeoff is part of the Auto Brake Selector Panel located on the Main Instrument Panel (MIP). RTO can be selected by turning the selector knob to the left from OFF by one click. The knob is from a classic 737-500 knob

A takeoff may be rejected for a variety of reasons, including engine failure, activation of the takeoff warning horn, ATC direction, blown tyres, or system warnings. For whatever reason, Boeing estimates that 1 takeoff in every 2000 will be rejected (Boeing Corporation).

This is an OEM (Original Equipment Manufacture) autobrake assembly that has been converted for use in the simulator. Note that the selector knob is not NG compliant but is from a 500 series airframe. In time this knob will be replaced. (click image to enlarge)

Performed incorrectly, an RTO can be a dangerous procedure; therefore, protocols have been are established that need to be followed.

This is the first of two consecutive posts that will discuss components of the autobrake system. In this post RTO procedures will be explained. In the second post the auto brake will be examined.

Rejected Takeoff (RTO)

The Auto Brake and Rejected Takeoff (RTO) are part of Auto Brake System, the components which are located on center panel of the Main Instrument Panel (MIP). An RTO is when the pilot in command makes the decision to reject the takeoff of the aircraft.

The Boeing Flight Crew Training Manual (FCTM) states:

‘A flight crew should be able to accelerate the aircraft, have an engine failure, abort the takeoff, and stop the aircraft on the remaining runway'; or,
'accelerate the aircraft, have an engine failure, and be able to continue the takeoff utilizing one engine’.

Two important variables of pre-flight planning need to be established for an RTO to be executed safely - V speeds and runway length.

V Speeds and Runway Length

There are three V speeds that are critical to a safe takeoff and climb out: V1, Vr and V2.

V1 is the speed used to make the decision to ‘abort or fly’. Vr is the rotation speed, or the speed used to begin the rotation of the aircraft by smoothly pitching the aircraft to takeoff attitude. V2 is the speed used for the initial climb-out, and is commonly called the takeoff safety speed. The takeoff safety speed ensures a safe envelope for single engine operations.

It stands to reason, that the runway must be long enough to cater towards the V speeds calculated from the weight of the aircraft and outside temperature.

Rejected Takeoff - Conditions and Procedure

In general, the protocol used to execute an RTO, is to:

Abort the takeoff for ‘cautions’ below 80 knots; and,
Between 80 knots and V1 speed, abort only for ‘bells’ (fire warning) and flight control problems.

If a problem occurs below V1 speed, the aircraft should be able to be stopped before reaching the end of the runway. After exceeding V1 speed, the aircraft cannot be safely stopped and the only option is to takeoff, and after reaching a safe minimum altitude and speed, troubleshoot the problem.

Before takeoff, a flight crew will position the auto brake selector knob to RTO. This action will trigger the illumination of the auto brake disarm annunciator, which will illuminate amber for 2 seconds; this is a self-test to indicate that the system is working. After 2 seconds the annunciator will extinguish.

To arm the RTO prior to takeoff, the following conditions must be met:

The auto brake and anti-skid systems must be operational;
The aircraft must be on the ground;
The auto brake selector must be set to RTO;
The forward thrust levers must be in the idle position; and
The wheel speed must be less than 60 knots.

Once armed, the RTO system only becomes operative after the aircraft reaches 80 knots ground speed (some manuals state 90 knots). If an ‘abort’ is indicated below 80 knots, the aircraft will need to be stopped using manual braking power.

The auto brake will remain in the armed mode if the RTO abort was executed prior to 80 knots (the auto brake disarm annunciator does not illuminate).

To engage the RTO the following conditions must be met:

The auto brake must be set to RTO;
The thrust levers must be retarded to idle position;
The aircraft must have reached 80 knots; and,
The autothrottle must be disconnected.

When an RTO is executed and the auto brake system engages, the system will apply 3000 PSI to the brakes to enable the aircraft to stop. Additionally, if the aircraft has reached a wheel speed in excess of 60 knots, and one or two of the reverse thrust levers are engaged, the spoiler panels will extend automatically to the UP position (deploy), and the speed brake lever on the throttle quadrant will move to the UP position.

The auto brake will disengage, if during the RTO either pilot:

Activates the toe brakes;
Turns the selector knob of the auto brake from RTO to off.

If the reversers have been engaged and the speed brake lever is in the UP position, then the lever will abruptly move to the DOWN detente position. When this occurs, the speed brake annunciator will illuminate amber for 2 seconds before extinguishing. Braking will then need to be accomplished manually.

RTO Procedure

Pilot flying calls ‘STOP’, ‘ABANDON’ or ‘ABORT’
Pilot flying closes thrust levers and disengages autothrottle.
Pilot flying verifies automatic RTO braking is occurring, or initiates manual braking if deceleration is not great enough, or autobrake disarm light is illuminated.
Pilot flying raises speedbrake lever.
Pilot flying applies maximum reverse thrust or thrust consistent with runway and environmental conditions.
Once stopped, pilot flying engages parking brake and completes RTO checklist.

Important Point:

Point 4 is important as although the spoilers deploy automatically when the reverse thrust is engaged, the speedbrake lever must be extended manually by the pilot flying (prior to application of reverse thrust). This is to minimise any delay in spoiler extension, as extension is necessary for efficient wheel braking.

What Circumstances Trigger An RTO

Prior to 80 knots, the takeoff should be rejected for any of the following:

Activation of the master caution system;
Unusual noise and vibration;
Slow acceleration;
Takeoff configuration warning;
Tyre failure;
Fire warning;
Engine failure;
Bird strikes;
Windshear warning;
Window failure; and/or,
If the aircraft is unsafe or unable to fly.

After 80 knots and prior to V1, the takeoff should be rejected for any of the following:

Fire warning;
Engine failure;
Windshear warning; and/or,
If the aircraft is unsafe or unable to fly.

After V1 has been reached, takeoff is mandatory.

Important Points:

Important points to remember when performing a Rejected Takeoff are:

Engage the RTO selector knob before takeoff;
Retard throttles to idle;
Disengage the autothrottle (A/T);
Engage one or both reverse thrust levers;
Monitor RTO system performance, being prepared to apply manual braking if the auto brake disarm light annunciates;
Manually raise speed brake lever if not already in the UP position BEFORE engaging reverse thrust; and,
Remember that RTO functionality engages only after the aircraft has reached 80 knots ground speed, and remains armed if the RTO has been executed below 80 knots.

Procedural Variations

A successful RTO is dependent upon the pilot flying making timely decisions and using proper procedures. Whether an RTO is executed fully or partly is at the discretion of the pilot flying (reverse thrust engaged to deploy spoilers).

It should be noted that If the takeoff is rejected before the THR HLD annunciation, the autothrottles should be disengaged as the thrust levers are moved to idle. If the autothrottle is not disengaged, the thrust levers will advance to the selected takeoff thrust position when released. After THR HLD is annunciated, the thrust levers, when retarded, remain in idle.

For procedural consistency, disengage the autothrottles for all rejected takeoffs.

Figure 1 provides a visual reference indicating the distance taken for an aircraft to stop after various variations of the Rejected Takeoff are executed (copyright, Boeing Flight Crew Training Manual FCTM).

figure 1: distance taken for an aircraft to stop after various variations of the Rejected Takeoff are executed (copyright, Boeing Flight Crew Training Manual FCTM)

This post has explained the basics of a Rejected Takeoff. Further information can be found in the Flight Crew Training Manual (FCTM) or Quick Reference Handbook (QRH).

In the next post the autobrake system will be discussed.

January 19, 2015

Direct-To-Routing, ABEAM PTS and INTC CRS - Review and Procedures

January 19, 2015/ Flaps 2 Approach

In an earlier post, a number of methods were discussed in which to create waypoints ‘on the fly’ using the Control Display Unit (CDU). Following on a similar theme, this post will demonstrate use of the Direct-To Routing, ABEAM PTS and Course Intercept (INTC CRS) functionality.

CDU use an appear very convoluted to new users, and by far the easiest way to understand the various functionalities is by ‘trial and error and experimentation’.

The software (Sim Avionics and ProSim737) that generates the math and formulas behind the CDU is very robust and entering incorrect data will not damage the CDU hardware or corrupt the software. The worst that can happen is having to restart the CDU software.

Line Style and Colour

The style and colour of the line displayed on the Navigation Display (ND) is important as it provides a visual reference to the status of a route or alteration of a route.

Dashed white-coloured lines are projected courses whilst solid magenta-coloured lines are saved and executed routes. Similar colour schemes apply to the waypoints in the LEGS page. A magenta-coloured identifier indicates that this is the next waypoint that the aircraft will be flying to (it is the active waypoint).

Direct-To Routing

A Direct-To Routing is easily accomplished, by selection of a waypoint from the route in the LEGS page, or by typing into the scratchpad (SP) a NAVAID identifier and up-selecting this to LSK 1L. Once up-selected, the Direct-To route will be represented on the Navigation Display (ND) by a dashed white-coloured line. Pressing the EXEC button on the CDU will accept the route modification and precipitate several changes:

The route line displayed on the ND, previously a white-coloured dashed line will become solid magenta in colour;
The previous displayed route will disappear from the ND;
All waypoints on the LEGS page between the aircraft's current position and the Direct-To waypoint in LSK 1L will be deleted; and,
The Direct-To waypoint in LSK 1L will alter from white to magenta.

Once executed the FMS will direct the aircraft to fly directly towards the Direct-To waypoint.

ABEAM PTS

Following on from the Direct-To function is the ABEAM PTS function located at LSK 5R.

ABEAM points (ABEAM PTS) are one or more fixes that are generated between two waypoints from within a programmed route. The ABEAM PTS functionality is found in the LEGS page of the CDU at LSL 5R and is only visible when a Direct-To Routing is being modified, within a programmed route (the LEGS page defaults to MOD RTE LEGS). Furthermore, the ABEAM PTS dialogue will only be displayed if the the up-selected fix/waypoint is forward of the aircraft's position; it will not be displayed if the points are located behind the the aircraft.

If the ABEAM PTS key is depressed, a number of additional in-between fixes will be automatically generated by the Flight Management System (FMS), and strategically positioned between the aircraft’s current position and the waypoint up-selected to LSK 1L. The generated fixes and a white-coloured dashed line showing the modified course will be displayed on the Navigation Display (ND).

To execute the route modification, the illuminated EXEC button is pressed. Following execution, the white-coloured line on the ND will change to a solid magenta-coloured line, and the original displayed route will be deleted. Furthermore, the LEGS page will be updated to reflect the new route.

Nomenclature of Generated Fixes

The naming sequence for the generated fixes is the first three letters of the original waypoint name followed by two numbers (for example, TTR will become TTR 01 and CLARK will become CLA01). If the fixes are regenerated, for instance if a mistake was made, the sequence number will change indicating the next number (for example, TTR01, TTR02, etc).

Technique

Up-select a waypoint from the route in the LEGS page to LSK 1L, or type into the scratchpad a NAVAID identifier. This is a Direct-To Routing; when executed the waypoints between the up-selected waypoint and LSL 1L are deleted.
Press ABEAM PTS in LSK 5R to generate a series of fixes along a defined course from the aircraft’s current location to the up-selected waypoint. The fixes can be seen on the ND.
Pressing the EXEC button will accept and execute the ABEAM PTS route.

Example and Figures

The below figures are screen captures using ProSim737 avionics suite. The programming of the CDU has been done with the aircraft on the ground. Click any image to enlarge.

**FIGURE 1:** The LEGS page shows a route HB-TTR-CLARK-BABEL-DPO-WON. The route is defined by a solid magenta-coloured line

**FIGURE 2:** The Route is altered to fly from HB to BABEL. Note that in the LEGS page, the title has changed from ACT to MOD RTE 1 LEGS. The ND displays the generated ABEAM PTS and projected course (white-coloured dashed line), beginning from the aircraft’s current position and traveling through HB01, TTR01, CLA01 to BABEL. The EXEC light is also illuminated

**FIGURE 3:** When the EXEC light is pressed, the ABEAM PTS and altered route (Figure 2) will be accepted. The former route will be deleted and the white-coloured dashed line will be replaced by a solid magenta-coloured line. The magenta colour indicates that the route has been executed. The LEGS page will also be updated and display the new route, with the waypoint HB01 highlighted in magenta

The Intercept Course (INTC CRS)

To understand the INTC CRS, it is important to have a grasp to what a radial and bearing is and how they differ from each other. For all practical purposes, all you need to know is that a bearing is TO and a radial is FROM. For example, if the bearing TO the beacon is 090, you are on the 270 radial FROM it.

The Intercept Course (INTC CRS) function is located beneath the ABEAM PTS option in the LEGS page of the CDU at LSK 6R. Like the ABEAM PTS function, the INTC CRS function is only visible when a when a Direct-To Routing, is being modified within a programmed route (the LEGS page defaults to MOD RTE LEGS).

The function is used when there is a requirement to fly a specific course (radial) to the fix/waypoint. By default, the INTC CRC displays the current course to the fix/waypoint. Altering this figure, will instruct the FMS to calculate a new course, to intercept the desired radial towards the fix/waypoint (1) The radial will be displayed on the ND as a white-coloured dashed line, while the course to intercept the radial (from the aircraft’s current position) will be displayed as a magenta-coloured dashed line.

Visual Cues

An important point to note is that, if the course (CRS) is altered, is that the displayed (ND) white-coloured line will pass directly through the fix/waypoint, but the line-style will be displayed differently dependent upon what side of the fix/waypoint the radial is, in relation to the position of the aircraft. The line depicted by sequential long and short dashes (dash-dot-dash) shows the radial TOWARDS the fix/waypoint while the line showing dots, displays the radial AWAY from the fix/waypoint.

It is important to understand, that for the purposes of the FMS, it will always intercept a course TO a fix/waypoint; therefore, the disparity in how the line-style is represented provides a visual cue to ensure a flight crew does not enter an incorrect CRS direction.

Intercept Heading

However, the flight crew may wish not fly directly to the fix/waypoint, but fly a heading to intercept the radial. In this case, the flight crew should select the particular heading they wish to fly in the MCP heading selector window, and providing LNAV is armed, the aircraft will fly this heading until reaching the intercept course (radial), at which time the LNAV will engage and the FMS will direct the aircraft to track the inbound intercept course (radial) to the desired fix/waypoint.

Technique

Up-select a waypoint from the route in the LEGS page to LSK 1L, or type into the scratchpad a NAVAID identifier and up-select. This is a Direct-To Routing and will delete all waypoints that the aircraft would have flown to prior to the up-selected identifier.
Type the course required into INTC CRS at LSK 6R.
This will display on the ND a white-coloured long dashed line (course/radial). Check the line-style and ensure that the course is TOWARDS the waypoint. The line, closest to the aircraft should display sequential long and short dashes.
Prior to pressing the EXEC button to confirm the route change, check that the intended course line crosses the current course line of the active route (solid magenta-coloured line).
If wishing to fly a heading to intercept the radial, use the MCP heading window. If LNAV is armed the FMS will direct the aircraft onto the radial.

Example and Figures

The below figures are screen captures using ProSim737 avionics suite. The programming of the CDU has been done with the aircraft on the ground. Click any image to enlarge.

**FIGURE 1:** The LEGS page shows a route HB-TTR-CLARK-BABEL-DPO-WYY-WON. The route is defined by a solid magenta-coloured line. ATC request ‘QANTAS 29 fly 300 degrees until intercepting the 345 degree radial of BABEL; fly that radial to BABEL then remainder of route as filed

**FIGURE 2:** From the LEGS page, locate in the route the waypoint BABEL (LSK 4L). Recall that the INTC CRS will only function in Direct-To Routing mode. Up-select BABEL to LSK 1L. Note that a dashed white-coloured line is displayed on the ND showing the new course from HB to BABEL. The original course is still coloured magenta and the EXEC light is illuminated

**FIGURE 3:** Type the radial required (345) into INTC CRS at LSK 6R. This action will generate (fire across the page) a white-coloured dashed line displaying the 345 course to BABEL (the 165 radial). Check the line-style and ensure the radial crosses the aircraft’ current course which is 300. Recall that this line style indicates that the radial to TO BABEL

**FIGURE 4:** Press EXEC to save and execute the new route. The dashed line alters to a solid magenta-coloured line and joins with the remainder of the route at BABEL. The magenta colour indicates this is now the assigned route. Note that the magenta line continues across the ND away from the aircraft and BABEL. This is another visual cue that the radial is traveling TO BABEL
If the aircraft continues to fly on a course of 300 Degrees, and LNAV is armed, the FMS will alter course at the intersection and track the 345 course to BABEL (165 radial). The LEGS page is also updated to reflect that BABEL is the next waypoint to be flown to (BABEL is coloured magenta

Final Call

Direct-To Routings and ABEAM Points are usually used when a flight crew is required to deviate, modify or shorten a route. Although the use of ABEAM PTS can be debated for short distances, the technology shines when longer routes are selected and several fixes are generated. The Intercept Course function, on the other hand, is used whenever published route procedures (STAR and SID transitions), or ATC require a specific course (radial) or heading to be followed to or from a navigation fix.

Caveat

The content of this post has been checked to ensure accuracy; however, as with anything that is convoluted minor mistakes can creep in (Murphy, aka Murphy's Law, reads this website). If you note a mistake, please contact me so it can be rectified.

Acronyms and Glossary

ATC – Air Traffic Control
CDU – Control Display Unit
Direct-To Routing – Flying directly to a fix/waypoint that is up-selected to LSK 1L in the CDU. All waypoints prior to the u-selected waypoint will be deleted
DISCO – refers to a discontinuity between two waypoints loaded in a route within the LEGS page of the CDU. The DISCO needs to be closed before the route can be executed
DOWN-SELECT - Means to download from the CDU LEGS page to the scratchpad of the CDU)
FIX – A geographical position determined by visual reference to the surface, by reference to one or more NAVAIDs
FMC – Flight Management Computer
FMS – Flight Management System
Identifiers – Identifiers are in the navigation database and are VORs, NDB,s and published waypoints and fixes
LSK 5L – Line Select: LSK refers to line select. The number 5 refers to the sequence number between 1 and 6. L is left and R is right (as you look down on the CDU in plan view)
MCP – Mode Control Panel
NAVAIDS – Any marker that aids in navigation (VOR, NDB, Waypoint, Fix, etc.). A NAVAID database consists of identifiers which refer to points published on routes, etc
ND – Navigation Display
RADIALS – A line that transects through a NAVAID representing the points of a compass. For example, the 045 radial is always to the right of your location in a north easterly direction (Bearings and Radials Paper)
ROUTE – A route comprising a number of navigation identifiers (fixes/waypoints) that has been entered into the CDU and can be viewed in the LEGS page
SP - Scratchpad
UP-SELECT – Means to upload from the scratchpad of the CDU to the appropriate Line Select (LSK)
WAYPOINT – A predetermined geographical position used for route/instrument approach definition, progress reports, published routes, etc. The position is defined relative to a station or in terms of latitude and longitude coordinates.

1: The FMS will calculate the new course based on great circle course between the aircraft’s current location and the closest point of intercept to the desired course. This course is displayed on the ND as a white dashed line.

January 04, 2015

Integrated Approach Navigation (IAN) - Review and Procedures

January 04, 2015/ Flaps 2 Approach

Japanese airlines nearly always gravitate to new technology. ANA landing RJAA (Narita, Japan). Maarten Visser from Capelle aan den IJssel, Nederland, JA02AN B737 ANA gold cs landing (7211516992), CC BY-SA 2.0

Increased navigational accuracy obtained from software and hardware improvements have led to several enhanced approach types being developed for the Boeing 737. These augmented approach types provide a constant rate of descent, follow an approximate 3 degree glide path, and eliminate the traditional step-down style of approach.

This improves landing capability in adverse weather conditions, in areas of difficult terrain, and on existing difficult to fly approach paths. Not to mention, the benefits that a stabilized and safer approach bring: greater passenger comfort, less engine wear and tear, and lower fuel usage while bringing less workload for the flight crew.

In this article, I will discuss the concept of Integrated Approach Navigation (IAN) and explain the procedures recommended by Boeing to successfully implement IAN.

The Boeing Flight Crew Training Manual (FCTM) has an excellent section addressing IAN, and I recommend you read it to gain a greater understanding of how the IAN system functions.

The Navigation Performance Scales (NPS), which augment IAN, will not be discussed. NPS will form part of a future article. Information in this article relates to FMC software U10.8A.

Overview

Integrated Approach Navigation (IAN) derives information from an approach type selected from the Flight Management Computer (FMC) database to generate a 3 degree glide path from the Final Approach Fix to the threshold of the runway. In so doing, it displays visual cues similar to the Instrument Landing System (ILS). Flight path guidance is derived from the FMC, navigational radios, or combination of both.

To use IAN, an approach with a glide path must be selected from the FMC database. The approach must include a series of waypoints that depict a vertical profile that includes a glide path.

An IAN approach may be flown with a single autopilot, raw data, or by following the visual cues displayed on the Flight Director (FD).

IAN is an airline option, and although not every airline carrier will have IAN as part of their avionics suite, the technology is becoming more popular as the safety and economic benefits of IAN are understood by airline carriers.

Geometric Path (Glide Path)

An IAN Approach approximates a 3 degree glide path (descent profile) from the Final Approach Fix (FAF) to approximately 50 feet above the runway threshold. Although, the glide path may not comply with altitude constraints in the FMC prior to the FAF, the generated glide path will always be at or above the altitude constraints between the FAF and the Missed Approach Point (MAP) displayed in the FMC.

Critically, an IAN approach is a Category I Non Precision Approach (NPA) and is not to be confused with an ILS Precision Approach. Therefore, NPA procedures must be adhered to when initiating an approach using IAN.

Although the automation provided by IAN will guide an aircraft (in most cases) to the threshold of the runway, IAN has not been designed to do this. Rather, IAN has been designed to guide the aircraft to the MAP published on the approach chart. The flight crew will then disengage IAN by disengaging the autopilot and autothrottle and fly the remainder of the approach manually as per NPA protocols.

In some instances, the final approach course (FAC) is offset from the runway center line and manoeuvring the aircraft for direct alignment will be necessary, whilst following the glide path angle.

Although the final approach is very similar to an ILS approach, IAN does not support autoland; if the aircraft is not in a stable configuration and you are not visual with the runway at or beyond the MDA, a missed approach procedure (Go-Around) should be executed.

Consistency in Procedures (eighteen approach types to one)

The introduction of IAN has condensed the number of approach types (and differing procedures) to one consistent procedure; minimising the amount of time an airline needs to train pilots in numerous approach types. Time is money and utilising advanced technology such as IAN can increase airline productivity and safety.

Approach Types

IAN can be used for the following approach types:

RNAV
RNAV (RNP) – (provided there are no radius to fix legs)
NDB and VOR
GPS & GNSS
LOC, LOC-BC, TACAN, LDA SDF (or similar style approaches)

Note that if using IAN to execute a Back Course Localiser approach (B/C LOC), the inbound front course must be set in the MCP course window.

During the approach you must monitor raw data and cross check against other navigational cues. Furthermore, although the use of IAN is recommended only for straight-in approaches, line use suggests that flight crews routinely engage IAN up to, but not exceeding 45 degrees from the runway approach course.

IAN is compatible with several approach types, however, being compatible does not necessarily mean that every approach type in the FMC is suitable.

Since IAN was introduced, additional approaches have been developed and added to the RNAV family; in particular, RNAV (RNP) approaches, that use ‘radius to fix’ (RF) to generate a curved path that terminates at a location where an approach procedure begins. These approaches have been designed to optimise airspace and usually have tight separation requirements; to fly these approaches an aircraft is required to have additional on-board navigation performance monitoring and alerting equipment.

These approach charts are identified by the title RNAV (RNP) RWY XX and the letters AR (Authorisation Required) in the description of the chart.

These approaches and are not suitable to use with IAN; they should be flown with LNAV/VNAV.

Recommended Approach Types

The best approach to use with IAN are straight-in or near straight-in approaches. VOR, LOC, NDB, RNAV and RNAV (GNSS) approaches work especially well as these approaches usually provide relatively long straight-in legs.

IAN can be used on an RNP (AR) approaches as long as there are no RF turns involved (straight-in approach only). If flying such an approach you should be aware that the legs can be quite short and IAN may arm and engage quite late in the approach profile.

Important Point:

The use of IAN is not authorised for a RNAV (RNP-AR) approach.

Using IAN – General

IAN does not need to be specifically ‘turned on’ for it to function; the functionality, if installed in the aircraft, is always operational. When the aircraft is within range of the designated approach, the runway data and/or Deviation Pointers will annunciate and be displayed on the PFD. At any time after this point has been reached, IAN can be armed and or engaged by pressing the APP button on the MCP.

Navigation Radios and Radio Frequencies

For an IAN approach to function, an approach procedure with a glide path must be selected from the FMC database. Although selection of navigation radios is not mandatory, selection is recommended, as correct tuning of the radios can provide increased visual awareness and redundancy, should a CDU failure occur, or there be a corruption of the data in the FMC.

Boeing strongly advise to tune the radios to the correct localiser frequency for the approach. This eliminates the possibility of the radio picking-up another approach from a nearby airport (and providing erroneous data to the crew). The ILS frequency must never be used with an IAN approach (unless the glideslope is inoperative). In the case of an inoperative glideslope, the G/S prompt in the CDU must be selected to OFF to ensure that the FMC generated glide path is flown.

Minimum Descent Altitude (MDA)

As mentioned, an IAN approach is a NPA, and when authorised by the Regulatory Authority non-ILS approaches can be flown to a published VNAV Decision Altitude/Height (DA/H) or to a published MDA (the MDA is used as a decision altitude). If not authorised to use the MDA as a decision altitude, crews must use the MDA specified for the approach flown.

To comply with the MDA protocols during a constant angle approach where a level off is not planned at the MDA, it is necessary to add +50 feet to the published MDA. This enables an adequate buffer to prevent incursion below the MDA and adhere to the NPA protocols.

Important Points:

IAN uses the FMC database to generate a 3 degree glide path from the FAF to the runway threshold. IAN does not require the navigation radios to be tuned. However, it is recommended to tune the radios.
Some approaches in the FMC database have a number of glide paths displayed with differing altitudes. When presented with this scenario, always select the first glide path and altitude.

IAN approach to RJAA **ILS X** or **LOC X** Rwy 16L. The localiser has been captured and the FMA displays FAC in green, while G/P is armed (FMA G/P white). The vertical Deviation Pointer is displayed as an outlined magenta-coloured diamond (anticipation pointer) while the localiser is displayed as solid magenta (because FAC has been captured). The source of the runway data is from the FMC (ProSim737 avionics suite)

Using IAN - IAN Annunciations and Displays

IAN can display several visual cues to alert you to the status of the IAN system. The cues are triggered at various flight phases and are displayed on the attitude display of the Primary Flight Display (PFD) and on the Flight Mode Annunciator (FMA).

Runway Data: Runway data (runway identifier, approach front course, approach type and distance to threshold) is displayed in the top left area on the PFD when either the localiser or the selected FMC approach is in range of the runway.

IAN approach to RJAA **ILS X** or **LOC X** Rwy 16L. The localiser and glide path have been captured. The FMA displays FAC and G/P in green and SINGLE CH is displayed. The Deviation Pointers, previously in outline (Figure above), are now solid filled. The aircraft will descent on the glide path to the threshold of the runway (ProSim737 avionics suite)

If the source of the runway data is the navigation radio, then this information will be displayed when the radio is in range of the localiser. However, if the primary data source is from the FMC (radio not tuned) the runway data will be displayed only after IAN has engaged. When IAN engages, the runway data will be sourced from the FMC. This will be evident as the approach type will be displayed on the PFD.

The approach type (LNAV, FMC, LOC, ILS etc) displayed will depend on what type of approach has been selected from the FMC database.

Approach Guidance: Approach guidance (Deviation Pointers) are displayed on the PFD whenever IAN is in range of the runway. When the Deviation Pointers are displayed, IAN can be used.

Final Approach Course (FAC): The letters FAC are displayed on the center FMA when IAN is armed.

It stands to reason, that FAC (lateral guidance) usually annunciates prior to G/P (vertical guidance), but depending on the position of the aircraft when APP in pressed, both annunciations may be displayed at the same time.

Glide Path (G/P): The letters G/P are displayed on the right FMA when IAN is armed.

FMA FAC and G/P Colours: Two FMA colours are used. White indicates that the FAC or G/P is armed. The colour of the FMA display will change from white to green when the aircraft captures either the localiser or glide path.

Mode Control Panel (MCP): Arming IAN (pressing the APP button on the MCP) will cause the letters APP on the MCP to be illuminated in green. The APP light will extinguish when IAN captures the glide path.

Lateral and Vertical Guidance Deviation Pointers: Deviation Pointers display the lateral and vertical position of the aircraft relative to the final approach course of the selected runway. The lateral pointer represents the localiser while the vertical pointer represents the glide path. The pointers are displayed whenever IAN is in range of the runway.

The pointers will initially be displayed as either magenta or white-coloured outlined diamonds. When the aircraft captures either the localiser or glide path, (2 1/2 dots from center) the pointer (s) will change from an outline, to a solid-filed magenta-coloured diamond.

Whether the initial colour of the diamonds is magenta or white depends on which pitch/roll mode has been selected when the aircraft comes into range.

Although the correct name for the pointers is Deviation Pointers, they are often called anticipation pointers, anticipation cues or ghost pointers (ghost pointers being an 'Americanism').

During an IAN approach:

The deviation alerting system will self-test when passing through 1500 feet radio altitude. The self-test will generate a two-second FAC deviation alerting display on each PFD (the pointers will flash in amber); and,
If the autopilot is engaged, and at low radio altitudes, the scale and Deviation Pointers will turn amber and begin to flash if the deviation from either the localiser or glide path is excessive.

SINGLE CH: SINGLE CH will be displayed in green, when the aircraft captures the glide path (both the localiser and glide path). At this time, the Deviation Pointers will change from white-coloured outlines to solid magenta-coloured diamonds. FAC and G/P on the FMA will also be in green. Additionally, the illuminated APP button on the MCP will extinguish. At this point, the aircraft will be guided automatically along the glide path.

Flight Mode Annunciations (FMA): The FMA display will vary depending on the source of the navigation guidance used for the approach.

For localiser-based approaches (LOC, LDS, SDF and ILS (glideslope OUT), the FMA will display VOR/LOC and G/P. For B/C LOC approaches, the FMA will display B/CRS and G/P.

If lateral course guidance is derived from the FMC (RNAV, GPS, VOR, NDB and TACAN approaches), the FMA will display FAC and G/P.

Ground Proximity Warning System (GWPS) Aural Warnings and Displays: GWPS warnings will annunciate if at any time the aircraft deviates below the glide path, and failure to disengage IAN at the appropriate altitude will trigger a GPWS aural warning alert ‘autopilot autopilot’ at 100 feet radio altitude. This is in addition, to the words ‘autopilot’ being displayed on the PFD.

Using IAN – At What Distance Does IAN Work

IAN is not designed to navigate to the airport and its functionality will only be available when the aircraft is in range of the airport runway; for a straight-in approach, this is at approximately 20 nautical miles. However, this distance can be considerably less if the aircraft is not on a straight-in course to the runway.

Important Point:

To give you the longest time from which to transition to an IAN approach, try to choose a suitable approach type (from the FMC) that exhibits a ‘more or less’ straight-in approach.

Using IAN – When to Arm and Engage IAN

IAN can be armed at anytime after the Deviation Pointers are displayed on the PFD.
To arm/select IAN, the flight crew press the APP button on the Mode Control Panel (MCP) similar to performing an ILS approach.
IAN is armed only after clearance for final approach has been received from Air Traffic Control (ATC). By this time, the aircraft is probably on a straight-in approach.
IAN cannot be used for STARS and is not designed to be engaged when the aircraft is ‘miles’ from the designated runway. Transition to an IAN approach can be from any of several pitch/roll modes.
IAN (if armed) engages automatically when the either the localiser or glide path is captured.

IAN should only be armed or engaged when:

The guidance to be used for the final approach is tuned and identified on the navigation radio;
An approach has been selected from the FMC database that has a 3 degree glide path;
The appropriate runway heading is set in the course window in the MCP;
The aircraft is on an inbound intercept heading;
ATC clearance for the approach has been received; and,
The approach guidance information is displayed on the PFD along with the lateral and vertical Deviation Pointers.

Disengaging IAN

IAN is either armed, engaged or not engaged.

If you want to disarm IAN from the arm mode, it is a matter of pressing the APP button on the MCP; the light on the APP button will extinguish and the Deviation Pointers on the PFD will not be visible.

If you want to disengage IAN after it has captured either the localiser or glide path (or both), pressing the APP button on the MCP will do nothing. In this scenario, to disengage IAN you will need to conduct a Go-Around by selecting TOGA, or change the pitch/roll mode (i.e. Level Change).

Disconnecting the autopilot and flying manually will also disengage IAN; the upside being that the Deviation Pointers will remain displayed on the PFD, until a different pitch/roll mode is selected.

Important Points:

If the navigation radio is not tuned to the localiser, the runway data will not be displayed until IAN is engaged, however, the Deviation Pointers will be displayed.
IAN can be armed whenever the aircraft is in range of the runway - in other words whenever the Deviation Pointers are displayed on the PFD.
When IAN is armed, the FAC and G/P display on the FMA is coloured white.
When IAN is engaged (localiser or glide path) the FAC and G/P on the FMA is coloured green.
IAN will only engage after capture of either the lateral (FAC) or vertical glide path (G/P).
When IAN has captured the glide path, SINGLE CH will be displayed in green in the PFD.

Using IAN - Set-Up and Procedure

The following procedures used for an IAN approach are derived from ILS procedures and are consistent for all approach types.

Select the appropriate approach to use from the FMC database. Ensure that the selected approach has a glide path. Do not alter any of the approach constraints.
Set the altitude of the glide path (from the FMC) in the MCP altitude window.
Fly the aircraft in whatever pitch/roll mode to the Initial Approach Fix (IAF). Remember straight-in approaches are best, although offsets between 25 and 45 degrees may be used but not recommended.
Configure the navigation radios to the correct frequency based on the approach type you have selected from the FMC database. Do not use an ILS frequency.
Set the barometric minimums to the altitude published on the approach chart. Add 50 feet to avoid breaking NPA protocols.
Set the correct runway approach course in the MCP course window.
Do not select IAN (press the APP button) until the aircraft is in the correct position relative to the approach course.
When approximately 2 miles from the FAF - GEAR DOWN, FLAPS 15, SPEED CHECK.
At glide path capture (FAF) – FLAPS 25/30 (landing flaps), SPEED CHECK.
At 300 Feet below glide path capture, reset the MCP altitude window to the missed approach altitude. Failure to wait until the aircraft descends 300 feet will cause the ALT HOLD annunciation to display and the aircraft levelling off.
At minima – Disengage autopilot and autothrottle, manually align aircraft to the runway, and follow the Deviation Pointers and Flight Director (FD) cues to the runway threshold. Maintain the glide path to the flare and do not descend below the displayed glide path.

Although glide path guidance can be used as a reference once the aircraft descends below the MDA, the primary means of approach guidance is visual. If not visual at the MDA, execute a Go-Around. Remember, using IAN is a NPA.

Important Points:

When using IAN the aircraft should be configured approximately 2 nautical miles from the FAF (this is one of the fundamental differences between an IAN approach and an ILS approach).
Often, the runway may not be aligned with the FMC generated course. The FCTM states; ‘If the final approach course is offset from the runway centreline, manoeuvring to align with the runway centreline is required. When suitable visual reference is established, continue following the glide path angle while manoeuvring to align with the runway.
Flying an IAN approach is an NPA; it is important to fly visually after passing the MDA.
The approach mode (APP on center CTR knob) on the EFIS can be selected when using IAN. This will display the IAN approach on the Navigation Display as if it is an ILS approach.

Transitioning to an IAN Approach

A flight crew will usually transition to an IAN approach 2 nautical miles prior to the Initial Approach Fix (IAF).

At this distance from the runway there is not a lot of time to configure the aircraft for landing, and if IAN engages when the aircraft is either above or below the glide path, there is a possibility that the aircraft will abruptly and unexpectedly ascend or descend as the automation attempts to capture the glide path. Therefore, you must be in diligent that the aircraft’s altitude roughly matches the position of the Deviation Pointers when close to the FAF.

Techniques to Transition Smoothly to an IAN Approach

There are several techniques that can be used to ensure a smooth transition to an IAN approach.

By far the easiest technique to ensure a seamless transition without any abrupt lateral or vertical deviation, is to position the aircraft ‘more or less’ within one dot deviation of the localiser or glide path (Deviation Pointers) prior to selecting IAN.

In this way you can follow (‘fly’) the Deviation Pointers and engage IAN when the aircraft is more or less aligned with the position of the pointers (similar to how an ILS approach is carried out).

Another technique, is to fly the aircraft until ALT HOLD is displayed in the FMA (assuming that the altitude set in the altitude window in the MCP is approximately 2 nautical miles from the FAF). Then select IAN. This should enable the aircraft to smoothly capture the glide path when reaching the FAF.

Importantly, if transitioning to IAN from VNAV, it is prudent to engage SPD INTV to manually control MCP speed.

**FIGURE 1:** Visual representation of an IAN approach and transition from roll mode. (*Copyright Boeing FCTM).*

Increased Spatial Awareness

Any approach can be busy and it is easy to forget something. Therefore, it is wize to create a circle at 2 miles from the FAF that can be displayed on the Navigation Display (NP).

One way to accomplish this is by using the FIX page in the CDU.

In the LEGS page copy to the scratchpad the FAF (click the line on which the FAF is located). Open the FIX page and upload the FAF (from the scratchpad) to the FIX entry. To create a dashed circle at 2 nautical miles from the FAF, enter /2 to Line Select Left 1.

Important Points:

Maintaining the correct approach speed and altitude is paramount to a successful IAN approach. If the aircraft is travelling too fast, slowing down after IAN has engaged can be difficult. Likewise, if the aircraft is too high and IAN engages, the vertical descent can be steep as the aircraft attempts to follow the FMC generated glide path.
You must be vigilant and anticipate actions and events before they occur.

Using IAN - Situations To Be Attentive Of

Automation can have its pitfalls and IAN is no different. However, once potential shortcomings are known, it is straightforward to bypass them. The most common mistake, especially with virtual pilots, is not following the correct procedure.

Possible 'surprises' associated with an IAN approach are:

1. Failing to configure the aircraft prior to IAN engaging in FAC and G/P mode.

Unlike an ILS approach, where configuration for landing is initiated when the aircraft captures the glideslope (usually some distance from the runway) during an IAN approach configuration for landing is initiated approximately 2 nautical miles from the FAF.

If you have not configured the aircraft for landing prior to the capture of the glide path, there may be insufficient time for you to complete recommended actions and checklists.

If you believe this will occur, there is no reason why configuration cannot occur at an earlier stage.

2. Forgetting to set the Missed Approach Altitude (MAA) in the MCP.

Failing to wait until the aircraft has descended 300 feet below the glide path capture altitude to reset the MCP altitude to the MAA. Failure will cause the ALT HOLD annunciation to display and the aircraft leveling off.

3. Approaching the runway while not on the correct intercept course.

IAN operates flawlessly with straight-in approaches and to a certain extent with approaches up to 45 degrees from the main approach course, however, IAN will not engage if you approach the assigned runway at 90 degrees. Nor will IAN engage if you are attempting to fly a STAR.

4. Forgetting to set the initial glide path altitude in the MCP (from the FMC).

A common mistake is not setting the glide path altitude (from the FMC) in the MCP window when configuring the aircraft for an IAN approach.

ProSim737 and IAN

Installing IAN to ProSim-AR Avionics Suite

IAN forms part of the avionics suite, however, for IAN to function it needs to be selected (turned on) in the ProSim-AR IOS (Instructor Operator Station). The same is for the Navigation Scales (if required).

To turn on IAN, open IOS: Settings/Cockpit Setup Options/Options and place a tick in the appropriate box beside IAN. A restart of the ProSim-AR main module may be required for the change to take effect.

IAN was introduced to the ProSim737 avionics suite in December 2014. For the most part, the functionality is reliable and operates as it should (see note 1).

As at writing, known issues are as follows (this may change with Version 3 software updates):

ProSim737 does not display the IAN runway data immediately following the engagement of TO/GA during the take-off roll.

This is incorrect. In the real aircraft, this information is displayed immediately following the engagement of TO/GA during the take-off roll while. (further research required)

The colour of the approach guidance display (LNAV/VNAV) after TO/GA is engaged is currently white. This is incorrect. The colour should be green.
At 100 feet AGL, if IAN is engaged and the autopilot remains selected, a flashing AUTOPILOT warning in amber colour will be displayed on the PFD. This is correct. However, an audible ‘autopilot’ callout should also be heard. This is not simulated.

Important Point:

ProSim737 users should also note, that for IAN to function within the avionics suite, it must be selected in the cockpit set-up page of the Instructor Station (IOS).

Note 1: IAN works flawlessly for straight-in approaches (or approaches that are slightly offset). However, the ProSim software when using some RNAV (RNP) approaches has trouble maintaining the correct vertical profile.

When a RNAV (RNP) approach (not AR) is selected, IAN arms and engages very late in the approach profile (after the FAF). The altitude that IAN engages is well below the profile used in VNAV; this results in the aircraft diving to capture the IAN glide path. Once the aircraft is established on the glide path IAN works as it is supposed to.

The above scenario does not occur with every VNAV (RNP) approach; only those that exhibit a curved radius to fix (RF) profile or short leg profile to the runway threshold.

In the real aircraft (depending on operator and country of operation) IAN can handle all RNAV (RNP) approaches with the exception of RNAV (RNP-AR) approaches.

In comparison, Precision Manuals Development Team (PMDG) NGX and NGXu can fly the above approaches in IAN. This has been achieved by artificially replicating the approach using various hidden ‘waypoints’ that their software can read. In effect, what you are seeing is the aircraft flying over the waypoints that have been overlaid onto the curves in the approach.

I do not believe ProSim has replicated PMDG’s methodology in their software.

Therefore, if flying an RNAV (RNP) approach using IAN, select only those approaches that are ‘more or less’ straight-in without RF curves or turns; otherwise, use LNAV/VNAV.

BELOW: Montage of four screen captures of the PFD showing some of the displays generated during an IAN approach (images upper left to right then bottom left to right). Images 1-3 are sequential. Image 4 is standalone.

Image 1: Aircraft is LNAV/VNAV approaching the IAF. The aircraft is too far from the runway for IAN to be in range to operate (RJAA VOR Rwy 16R).

Image 2: Aircraft is in range of RJAA localiser (tuned in the navigation radio). Runway data is displayed from localiser and Deviation Pointers are displayed in outlined white-coloured diamonds (anticipation pointers). The Deviation Pointers will change from white (outline) to magenta (either outline or solid) when either the localiser or glide path is captured. FAC and G/P are displayed on the FMA in white indicating that IAN has been armed. Note that if IAN was not armed, only the runway data and Deviation Pointers would be displayed (RJAA VOR Rwy 16R).

Image 3: IAN has captured the localiser and the lateral Deviation Pointer is displayed as a solid magenta-coloured diamond. FAC (in green) is displayed on the FMA. The vertical Deviation Pointer is still in outline and in white (anticipation pointer), as is the G/P on the FMA. IAN is tracking the localiser (RJAA VOR Rwy 16R).

Image 4: IAN has engaged. The runway data is now sourced from the FMC and not the localiser (as in the above examples). The FMA displays FAC and G/P in green colour, SINGLE CH is displayed, and both Deviation Pointers are solid magenta-coloured diamonds. IAN has captured the Glide Path (RJAA ILS X or LOC X Rwy 16L).

Montage of four screen captures of the PFD showing some of the displays generated during an IAN approach (images upper left to right then bottom left to right). Images 1-3 are sequential. image 4 is standalone
**Image 1:** Aircraft is LNAV/VNAV approaching the IAF. The aircraft is too far from the runway for IAN to be in range to operate (RJAA VOR Rwy 16R).
**Image 2:** Aircraft is in range of RJAA localiser (tuned in the navigation radio). Runway data is displayed from localiser and Deviation Pointers are displayed in outlined white-coloured diamonds (anticipation pointers). The Deviation Pointers will change from white (outline) to magenta (either outline or solid) when either the localiser or glide path is captured. FAC and G/P are displayed on the FMA in white indicating that IAN has been armed. Note that if IAN was not armed, only the runway data and Deviation Pointers would be displayed (RJAA VOR Rwy 16R).
**Image 3:** IAN has captured the localiser and the lateral Deviation Pointer is displayed as a solid magenta-coloured diamond. FAC (in green) is displayed on the FMA. The vertical Deviation Pointer is still in outline and in white (anticipation pointer), as is the G/P on the FMA. IAN is tracking the localiser (RJAA VOR Rwy 16R).
**Image 4:** IAN has engaged. The runway data is now sourced from the FMC and not the localiser (as in the above examples). The FMA displays FAC and G/P in green colour, SINGLE CH is displayed, and both Deviation Pointers are solid magenta-coloured diamonds. IAN has captured the Glide Path (RJAA ILS X or LOC X Rwy 16L)

Videos of IAN Approach

IAN APPROACH IN SIMULATOR

IAN APPROACH IN REAL 737-800 AIRCRAFT

Final Call

The use of Global Positioning Systems has enabled stabilised approaches at many airports, and the IAN system can take advantage of this technology to provide intuitive displays that support stabilised approaches on a consistent basis.

Aircraft fitted with IAN are capable of using the APP button located on the MCP to execute an instrument ILS-style approach based on flight path guidance from the FMC. This makes Non Precision Approaches easier to execute with increased safety. It also enables a constant descent angle, less engine spooling, wear and tear, and improved passenger comfort. Furthermore, IAN uses a standardised and consistent procedure, that in addition to improved displays and alerts, can be used in place of LNAV/VNAV.

Nevertheless, a flight crew must be vigilant when using any automation, especially during the critical approach phase where there is little margin for error. First and foremost is the innate ability to fly the airliner manually, and although automation such as IAN can enhance safety, it does so at the detriment of manual flying skills.

References

Several sources were used to obtain the information documented in this post, including: personal communication with a B737-800 pilot, the Boeing Flight Crew Training Manual and the Boeing 737 Technical Guide by Chris Brady.

If any discrepancies are noted in this article, please contact me so they can be rectified.

Acronyms and Glossary

AGL – Above Ground Level
APP – Approach button located on MCP
CDU – Control display Unit (glorified keyboard)
EFIS – Electronic Flight Instrument Display
FAC – Final Approach Course
FAF – Final Approach Fix
FMA – Flight Mode Annunciator
FMC – Flight Mode Computer
FMS – Flight Management System
G/P – Glide Path (Non Precision Approach / NPA)
G/S – Glideslope (Precision Approach / PA)
IAF – Initial Approach Fix
IAN – Integrated Approach Navigation
ILS – Instrument Landing System
IMC – Instrument Meteorological Conditions
MAP – Missed Approach Point
MCP – Mode Control Panel
MDA - Minimum Descent Altitude
ND – Navigation Display
PFD – Primary Flight Display
RA – Radio Altitude
RF – Radius to fix
RNAV (RNP-AR) Approach - RNP-AR is a subset of an RNAV approach that requites authorization (RA) to fly
Select – To select , arm or engage something
STAR - Standard Terminal Arrival Route

Review and Updates

25 August 2017 - Review and content updated.
03 December 2019 - Review and content updated.
29 October 2019 - Review and content updated.
28 April 2021 - Review and content updated. Release of .pdf.
21 December 2022 - Updated to latest procedure changes.

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December 01, 2014

Cost Index (CI) Explained

December 01, 2014/ Flaps 2 Approach

Screengrab from CDU screen showing the Cost Index page in *PERF INIT*

The Cost Index (CI) function of the Flight Management Computer (FMC) is an important and often misunderstood feature of a modern airliner. Apart from real-world cost savings in fuel, differing CI values alter airspeeds used during the climb, cruise and descent phase of a flight. Certainly, the CI value is not a pressing issue for a virtual pilot flying a simulator, but to an operating airline in a fuel-expensive environment, differing CI values can equate to thousands of dollars saved.

CDU showing Cost Index. A CI of 11 will generate significant savings as opposed to a value of 300. FMC is produced by Flight Deck Solutions (FDS)

Simply explained, the CI alters the airspeed used for economy (ECON) climb, cruise and descent; it is the ratio of the time-related operating costs of the aircraft verses the cost of fuel. If the CI is 0 the FMC calculates the airspeed for the maximum range and minimum trip fuel (lower airspeed). Conversely, if the CI is set to the highest number, the FMC will calculate higher airspeeds (Vmo/Mmo) and disregard any cost savings.

In practice, neither of the extreme CI values is used; instead, many operators use values based on their specific cost structure, modified if necessary to the requirements of individual flight routes. Therefore, the CI values will typically vary between airline operators, airframes, and individual routes.

Access to the CI is on page 1 of 2 in the ‘ACT PERF INIT’ page of the Control Display Unit (CDU) of the Flight Management Computer (FMC). It is on the left hand side lower screen and displayed ‘COST INDEX’. The range of the CI is 0-200 units in the Boeing 737 Classics and 0-500 units in the Next Generation airframes.

Fuel Verses Time and Money

There is a definite benefit to an airline’s fuel cost when the CI is used correctly. Bill Roberson in his excellent article ‘Fuel Conservation Strategies: Cost Index Explained’ states the difference between a CI value of 45 verses a CI value of 12 for a B737-700 can be in the order of $1790 - $1971 USD depending upon the price of fuel; the time gained by selecting the higher CI value (CI-12) is in the area of +3 minutes. Although these time savings appear minimal, bear in mind that airlines are charged by the minute that they remain at the gate.

Granted fuel savings are important, but so is an airline’s ability to consistently deliver on time, its passengers and cargo. It is a fine line between cost savings and time management, and often the CI will be changed before a flight to cater towards unscheduled delays, a change in routing, short or long haul flights, cost of fuel, aircraft weight, or favourable in-flight weather conditions (i.e. tailwind).

A higher CI value may be used by airlines that are more interested in expediency than fuel cost savings; the extra revenue and savings generated by an airline that consistently meets its schedule with less time spent at the gate may be equal to, or greater than any potential fuel savings. Boeing realizes that as fuel costs increase, airlines are reticent to only expend what is absolutely necessary; therefore, Boeing works with its clients (airlines) to determine, based upon their operating style, the most appropriate CI value to use.

Changing CI on The Fly'

Although not standard practice, the CI value can be changed during the flight. Any change in the CI will reflect on climb, descent and cruise speeds, which will be updated in the CDU and can be monitored via the 'progress' page of the CDU.

**Figure 1:** compares the cost index values against climb, cruise, descent and recommended altitudes for the Boeing 757 air frame. Although these figures do not relate to the Boeing 737-800 NG, they do provide an insight into the difference in calculated CI values for climb, cruise, descent and recommended altitude

Is the Cost Index Modelled in all Avionics Suites

The CI is modelled by the avionics suite, and whether it is functional depends on the suite used. ProSim737 and Sim Avionics have the CI modelled and functional, as does Project Magenta (PM), Precision Manuals Development Group (PMDG) and I-Fly.

Airline Cost Index Values

As stated above, the inputted CI value is variable and is rarely used at either of the extreme ranges. The following airline list of B737-800 carriers is incomplete, but provides guidance to CI values typically used. Note that the CI is variable and the values below may alter dependent upon airlines operations. A more detailed list can be found on the AVSIM website (Thanks Dirk (ProSim737 forum) for the link).

Air Baltic CI – 28
Air Berlin CI – 30
Air France CI – 35
Air Malta CI – 25
Air New Zealand CI – 45
Austrian CI – 35
Fly GlobesSpan CI – 13-14
Fly Niki CI – 35
Hamburg International CI – 30
KLM CI – 15/30
Nord Star CI – 30
Norwegian CI – 15
QANTAS CI – 40
Ryanair CI – 30
SAS CI – 45-50
South African CI – 50
South West CI – 36
Thomson Airways CI – 9
Ukraine International Airlines CI – 28
WestJet CI – 20-25

The CI is an important feature of the avionics suite that should not be dismissed. Whilst real-world fuel savings are not important during simulator flying, the altered airspeeds that a different CI value generates can have consequences for the distance able to be flown, climb, descent and cruise speeds.

Acronyms

CDU – Control Display Unit
CI – Cost Index
FMC – Flight Management Computer
Mmo – Maximum operating speed
Vmo – Maximum operating limit speed

September 18, 2014

B737-800 NG Flight Mode Annunciator (FMA)

September 18, 2014/ Flaps 2 Approach

Automatic Flight System - Background

The Boeing 737-80 has a relatively sophisticated Automatic Flight System (AFS) consisting of the Autopilot Flight Director System (AFDS) and the Autothrottle (A/T).

The Boeing 737-800 NG has a relatively sophisticated Automatic Flight System (AFS) consisting of the Autopilot Flight Director System (AFDS) and the Autothrottle (A/T). The system is as follows:

The N1 target speeds and limits are defined by the Flight Management Computer (FMC) which commands airspeeds used by the A/T and AFDS;
The A/T and AFDS are operated from the AFDS Mode Control Panel (MCP), and the FMC from the Control Display Unit (CDU);
The MCP provides coordinated control of the Autopilot (A/P), Flight Director (F/D), A/T and altitude alert functions; and,
The Flight Mode Annunciator (FMA), located on the Captain and First Officer side of the Primary Flight Display (PFD), displays the mode status for the AFS.

If you read through the above slowly and carefully it actually does make sense; however, during in-flight operations it can be quite confusing to determine which system is engaged and controlling the aircraft at any particular time.

Reliance on MCP Annunciations

Without appropriate training, there can be a reliance on the various annunciations and lights displayed on the Mode Control Panel (MCP). While some annunciations are straightforward and only illuminate when a function is on or off (such as the CMD button), others can be confusing, for example VNAV.

Do not reply on the MCP. Always refer to the FMA to see what mode is controlling the aircraft.

Flight Mode Annunciator (FMA)

All Boeing aircraft are fitted with an FMA of some type and style. The FMA on the Next Generation is located on the Captain and First Officer side Primary Flight Display, and is continuously displayed. The FMA indicates what system is controlling the aircraft and what mode is operational. All flight crews should observe the FMA to determine operational status of the aircraft and not rely on the annunciators on the MCP that may, or may not indicate a selected function.

The FMA is divided into three columns and two rows. The left column relates to the Autothrottle while the center and right hand column display roll and pitch modes respectively. The two rows provide space for armed and selected annunciations to be displayed. Selected modes that are operational are always coloured green while armed modes are coloured white.

Below the two rows are the Autopilot Status alerts which are in larger green-coloured font, and the Control Wheel Steering (CWS) displays which are coloured yellow. The Autopilot Status alerts are dependent upon whether a particular system has been installed into that aircraft. For example, Integrated Approach Navigation (IAN), and various autoland capabilities.

When a change to a mode occurs (either by by a flight crew or by the Automatic Flight System), a mode change highlight symbol (green-coloured rectangle) is displayed around the changed mode annunciation. The rectangle will be displayed for 10 seconds following the change in mode.

Unfortunately, not all avionics suites have the correct timing (10 seconds) and some displays the rectangle for only 2 seconds. According to the Boeing manual the default time should be 10 seconds.

**figure 1:** common mode annunciations that the FMA can display. FMA annunciations may differ between airframes depending upon the software installed to the aircraft (and avionics suite used in your simulation). G, W and Y indicates the colour of the annunciation (green, white, or yellow). the pitch mode FOR column and CWS display are not populated.
**ERRATUM:** ILS, SINGLE CH and IDLE HAVE NOT BEEN INCLUDED WHEN THEY SHOULD HAVE

Important Points:

An annunciation that is green-coloured indicates a selected mode.
An annunciation that is white-coloured indicates an armed mode.
If there is some confusion to what mode is currently flying the aircraft, the FMA should be what you look at - not the MCP.

Video

Boeing 737 ILS CAT IIIa Autoland PFD demonstrating FMA.

September 02, 2014

B737 Autothrottle (A/T) - Normal and Non-Normal Operations

September 02, 2014/ Flaps 2 Approach

Mode Control Panel (MCP) showing A/T on/off solenoid switch and speed window. The MCP shown is the Pro model manufactured by CP Flight in Italy

The Autothrottle (A/T) is part of the Automatic Flight System (AFS) comprising the Autopilot Flight Director System (AFDS) and the autothrottle. The A/T provides automatic thrust control through all phases of flight.

The autothrottle functionality is designed to operate in unison with the Autopilot (A/P), Nevertheless, a flight crew will not always adhere to this use, some crews preferring to fly manually or partially select either the autopilot or autothrottle.

A search on aviation forums will uncover a plethora of comments concerning the use of the autothrottle which, combined with autopilot use and non-normal procedures, can be easily be misconstrued. An interesting discussion can be read on PPRuNe.

This post will examine, in addition to normal A/T operation, some of the non-normal conditions, their advantages and possible drawbacks. Single engine operation will not be addressed as this is a separate subject.

Additional Information:

737 Automatic Systems Review (Smart Cockpit).

Autothrottle (A/T) Use

The autothrottle is engaged whenever the A/T toggle is armed and the speed annunciator is illuminated on the Mode Control Panel (MCP). Either of these two functions can be selected together or singularly.

The autothrottle is usually engaged during the takeoff roll by pressing the TO/GA buttons located under the thrust lever handles. This is done when %N1 stabilises for both engines at around 40%N1. This will engage the autothrottle in the TO/GA command mode. The reason the autothrottle is used during takeoff is to simplify thrust procedures during a busy segment of the flight.

FMA Captain-side PFD showing TO/GA annunciated during takeoff roll

Once engaged, the TO/GA command mode will control all thrust outputs to the engines until the mode is exited, either at the designated altitude set on the MCP, or by activating another automaton mode such as Level Change (LVL CHG). When TO/GA is engaged, the Flight Mode Annunciator (FMA) will announce TO/GA providing a visual cue.

The use of the autothrottle is at the discretion of the pilot flying, however, airline company policy often dictates when the crew can engage and disengage the A/T.

The Flight Crew Training Manual (FCTM) states:

‘A/T use is recommended during takeoff and climb in either automatic or manual flight, and during all other phases of flight’.

When to Engage / Disengage the Autothrottle

A question commonly asked is: ‘When is the autothrottle disengaged and in what circumstances’ Seemingly, like many aspects of flying the Boeing aircraft, there are several answers depending on who you speak to or what reference you read.

In the FCTM, Boeing recommends the autothrottle be used only when the autopilot is engaged (autopilot and autothrottle coupled).

In general, a flight crew should disengage the autothrottle system at the same time as the autopilot. This enables complete manual input to the flight controls and follows the method recommended by Boeing.

My preference during an approach is to disconnect the autothottle and autopilot no later than 1500 feet AGL. This corresponds to the altitude that the aircraft must be in landing configuration, gear down, flaps 30 and within vertical and lateral navigation constraints with landing checks completed. Disconnecting the autothrottle and autopilot earlier in the approach provides additional time to transition from automated flight to manual flight, and establish a 'feel' for the aircraft before landing.

It's not uncommon that flight crew will manually fly the aircraft, especially 'old school' pilots who are very conversant with hand flying. I know some crews that will fly from 10,000 feet to landing using the Flight Director (FD), ILS, VNAV and LNAV cues on the Primary Flight Display (PFD) for guidance and the information displayed on the Navigation Display (ND) for situational awareness. Many pilots enjoy hand-flying the aircraft during the approach phase.

Important Point:

Whenever hand flying the aircraft with the autothottle not engaged, it's very important to monitor the airspeed. This is especially so during the final approach, when thrust can easily decay to a speed very close to stall speed.

The Autothrottle is Designed to be used Coupled with the Autopilot

The autothrottle is a sophisticated automated system that will continually update thrust based on minor pitch and attitude changes, and operates exceptionally well when coupled with the autopilot. But, when the autopilot is disengaged and the autothrottle retained, its reliability can be questionable.

Some crews believe that if a landing is carried out with the autopilot off and the autothrottle engaged, and a fall in airspeed occurs, such as during the flare, then the autothrottle will apply thrust causing the potential for a tail strike. Likewise, if during the approach there are excessive wind gusts, pitch coupling (discussed below) may occur.

The advantages of using the autothrottle and autopilot together are:

(i) Speed is stabilized;

(ii) Speed floor protection is maintained;

(iii) Task loading is reduced; and,

(iv) Flight crews can concentrate on visual manoeuvring and not have to be overly concerned with wind additives

The disadvantages of using the autothrottlewithout the autopilot engaged are:

(i) Additional crew workload and possible loss of situational awareness (due to workload);

(ii) Potential excessive and unexpected throttle movement caused by pitch and attitude changes;

(iii) Potential excessive airspeed when landing in windy conditions with gusts;

(iv) The potential for pitch coupling to occur (discussed below); and,

(v) A loss of thrust awareness (out of the loop).

Important Point:

The autopilot and autothrottle should not be used independent of one another.

Boeing 737 Design

The design of the 737 airframe is prone to pitch coupling because of its under wing mounted engines. The engine position causes the thrust vector to pitch up with increasing thrust and pitch down with a reduction in thrust.

The autothrottle is designed to operate in conjunction with the autopilot, to produce a consistent aircraft pitch under normal flight conditions. If the autopilot is disengaged but the autothrottle remains engaged, pitch coupling may develop.

Pitch Coupling

Pitch coupling is when the autothrottle system actively attempts to maintain thrust based on the pitch/attitude of the aircraft. It occurs when the autopilot is not engaged and manual inputs (pitch and roll) are used to control the aircraft.

If the pitch inputs are excessive, the autothrottle will advance or retard thrust in an attempt to maintain the selected MCP speed. This coupling of pitch to thrust can be potentially hazardous when manually flying an approach, and more so in windy conditions.

Scenario - pitch coupling

For example, imagine you are in level flight with autothrottle engaged and the autopilot not engaged, and a brief wind change causes a reduction in airspeed. The autothrottle will slightly advance the throttles to maintain commanded speed. This in turn will cause the aircraft to pitch slightly upwards, triggering the autothrottle to respond to the subsequent speed loss by increasing thrust, resulting in further upward pitch. The pilot will then correct this by pushing forward on the control column to decease pitch. As airspeed increases, the autothrottle will decrease thrust causing the aircraft to decrease more in pitch.

The outcome is that a coupling between pitch and thrust will occur causing a roll-a-coaster type ride as the aircraft increases and then decreases pitch, based on pilot input and autothrottle thrust control.

A/T ARM solenoid, N1 and speed button. The N1 and speed button illuminate when either is in active mode. In the image, the A/T is armed; however, the speed option is not selected (the annunciator is extinguished). This enables thrust to be controlled manually

Autothrottle Non-Normal Operations (Arm Mode)

The primary function that the A/T ARM mode is to provide minimum speed protection. A crew can ARM the throttle but not have it linked to a speed. To configure the autothrottle in ARM mode, the A/T toggle solenoid on the MCP is set to ARM, but the SPEED button is not selected (the annunciator is not illuminated).

Scenario - speed button not selected during approach

Some flight crews prefer during an approach, to arm the autothrottle, but not have the speed option engaged (speed annunciator extinguished).

By doing this during a non-precision approach, it enables a Go-Around to be executed more expediently and with less workload (the pilot flying only has to push the TO/GA buttons on the thrust lever and the autothrottle will engage).

If the approach proceeds smoothly and a Go-Around is not required, the crew will prior to landing, disengage the A/T solenoid switch on the MCP by either manually 'throwing' the toggle or pressing the A/T buttons located on the thrust levers. Although favoured by some flight crews, this practice is not authorized by all airlines, with some company policies expressly forbidding the ARM A/T technique.

The recommendation by Boeing in the B737 Flight Crew Training Manual (FCTM) states:

‘The A/T ARM mode is not normally recommended because its function can be confusing. The primary feature the A/T ARM mode provides is minimum speed protection in the event the airplane slows to minimum maneuvering speed. Other features normally associated with the A/T, such as gust protection, are not provided’. (When the A/T is armed and the speed button option not selected).

Autothrottle Speed Protection and Vref in Windy, Gusty and Turbulent Conditions

To provide sufficient wind and gust protection, when using the autothrottle during an approach in windy conditions, the command speed should set to the correct wind additive based on wind speed, direction and gusts (between Vref+5 and Vref +20).

The use of an additive creates a safety envelope that takes into account potential changes in wind speed and minimises the chance of the autothrottle commanding a speed that falls below Vref. Remember, that as wind speed varies the autothrottle will command a thrust based on the speed.

During turbulence, the autothrottle will maintain a thrust that is higher than necessary (an average) to maintain command speed (Vref).

Important Points:

When the autothrottle is not engaged, or the speed option on the MCP deselected, minimum speed protection is lost.
Always add a wind additive to Vref based on wind strength and gusts. Doing so provides speed protection when the autothrottle is engaged.

Refer to Crosswind Landings Part 2 for additional information on Vref.

A/T disengage button on throttle thrust lever. This is an OEM throttle from a B737-300 series. The button is identical to that used in the NG with the exception that the handles are usually white and not grey in colour. Depressing this button will disengage the autothrottle and disconnect the A/T solenoid switch on the MCP

Manual Override - Engaging the Clutch Assembly

Occasionally, for any number of reasons, the flight crew may need to override the autothrottle.

The Boeing autothrottle system is fitted with a clutch assembly that enables the flight crew to either advance or retard the thrust levers whilst the autothrottle is engaged. By moving the thrust levers, the clutch assembly is engaged and the autothrottle goes offline whilst the levers are moved.

The clutch is there to enable the autothrottle to be manually overridden, such as in an emergency or for immediate thrust control.

ProSim737 does not (as at 2018) support manual autothrottle override.

Simulation Nuances

The above information primarily discusses the systems that operate in the real aircraft. Whether these systems are functional in a simulation, depends on the avionics suite used (Sim Avionics, Project Magenta, etc).

For example, the autothrottle may not maintain the speed selected in the MCP during particular circumstances (for example, turns in high winds). If this occurred in the real world, a crew would manually override the autothrottle. However, if the avionics suite does not have this functionality, then the next best option is to either:

(i) Disengage the autothrottle and manually alter thrust; or,

(ii) Deselect the speed annunciator on the MCP.

Deselecting the speed annunciator will cause the throttle automation to be disengaged; however, the autothrottle will remain in the armed mode. The second option is a good way to overcome this shortfall of not having manual override. By deselecting the speed option, the thrust levers can be jiggled forward or aft to adjust the airspeed. When the speed has been rectified by manual input, the autothrottle can be engaged again by depressing the speed button.

It's important if the autothrottle is not engaged, or is in the ARM mode, that the crew maintains vigilance on the airspeed of the aircraft. There have been several incidents in the real world whereby crews have failed to observe airspeed changes.

Manual Flying (no automation engaged)

The benefit of flying with the autothrottle and autopilot not engaged is the ease that the aircraft can be maneuvered. The crew sets the appropriate %N1 that produces the correct amount of thrust to maintain whatever airspeed is desired; gone are the thrust surges as the autothrottle attempts to maintain airspeed.

Granted, it does take considerable time and patience to become competent at flying manually in a variety of conditions, but the overall enjoyment increases three-fold.

Company Policies

Airline policies often dictate how a flight crew will fly an aircraft, and while some policies are expedient, more often than not they are based on economics (cost savings) for the company in question.

Policies vary concerning autothrottle use. For example, Ryanair has a policy to disconnect the autothrottle and autopilot simultaneously, as does Kenya Airways. Air New Zealand and QANTAS have a similar policy, however, define an altitude that disconnection must occur at or before. If an airline doesn't have a policy, then it's at the discretion of the flight crew who should follow Boeing's recommendation in the FCTM.

Confusion and Second Guessing - Vref with A/T Engaged or Disengaged

There is considerable confusion and second guessing when it comes to determining the Vref to select dependent on whether the autothrottle is engaged or disconnected at landing. To simplify,

If the autothrottle is going to be disconnected before reaching the threshold, the command speed should be adjusted to take into account winds and gusts (as discussed above and refer to Crosswind Landings Part 2). It's vital to monitor airspeed when the autothrottle is not engaged as during the approach the speed can decay close to stall speed.
If the autothrottle is to remain engaged during the landing (as in an autoland precision approach), the command speed should be set to Vref +5. This provides speed protection by keeping the engine thrust at a level that is commensurate with the Vref command speed. If wind and gust indicate a higher additive speed, then this should be added to Vref.

Refer to Wind Correction Function (WIND CORR) for information on how to use the Wind Correction function in the CDU.

Final Call

There is little argument that the use of the autothrottle is a major benefit to reduce task loading; however, as with other automated systems, the benefit can come at a cost, which has lead several airlines to introduce company policies prohibiting the use of autothrottle without the use of the autopilot; pitch coupling, excessive vertical speed, and incorrect thrust can lead to hard landings and possible nose wheel collapse, unwanted ground effec t, or a crash into terrain.

Ultimately, the decision to use or not use the autothrottle and autopilot as a coupled system is at the discretion of the pilot in command, and depends upon the experience of the crew flying the aircraft, the environmental conditions, and airline company policy. However, the recommendation made by Boeing preclude autothrottle use without the autopilot being engaged.

Disclaimer

The content in this post has been proof read for accuracy; however, explaining procedures that are convoluted and often subjective, can be challenging. Occasionally errors occur. If you observe an error, please contact me so it can be rectified.

Acronyms and Glossary

A/P – Autopilot (CMD A CMD B).
A/T – Autothrottle.
AFDS – Autopilot Flight Director System .
Command Speed - In relation to the Autothrottle, Command Speed is Vref +5 knots.
FCTM – Flight Crew Training Manual (Boeing Corporation).
FMA – Flight Mode Annunciator.
Manual Flight – Full manual flying. A/T and A/P not engaged.
MCP – Mode Control Panel.
Minimal Speed Protection – Function of the A/T when engaged. The A/T has a reversion mode which will activate according to the condition causing the reversion (placard limit). (For example, flaps, gear, etc).
Pitch Coupling – The coupling of A/T thrust to the pitch of the aircraft. A/T thrust increases/decreases as aircraft pitch and attitude changes. Pitch coupling occurs when the A/P is not engaged, but the A/T is enabled.
Selected/Designated Speed – The speed that is set in the speed window of the MCP.
Take Off/Go Around (TO/GA) – Takeoff Go-around command mode. This mode is engaged during takeoff roll by depressing one of two buttons beneath the throttle levers.
Vref – Landing reference speed.

Updated and Amended 04 July 2019

August 04, 2014

Boeing 737-800 Takeoff Procedure (simplified)

August 04, 2014/ Flaps 2 Approach

One aspect novice virtual pilots find difficult to grasp is the correct method of flying the aircraft, especially the takeoff, climb and transition to cruise.

The sheer volume of information available on the Internet often results in information overload and it’s understandable that many become bewildered as the boundaries between fact and fiction blur. Add to this that many articles on the Internet have not been peer reviewed, and you have a recipe set for disaster!

In this article, I will instruct on the basic procedures used to takeoff, climb, and transition to cruise. I’ll also provide some insight into how flight crews fly the aircraft, and discuss some of the more important concepts that should be known.

I will not discuss before and after takeoff checklists, the overhead, how to determine aircraft weights, or how to use of the Control Display Unit (CDU). I will assume all essential elements of pre-flight have been completed. Also, the following procedures assume both engines are operational. I will not be addressing engine-out procedures.

Please take note that some procedures are dependent upon what software is used in the Flight Management System (1). Furthermore, the display of specific items, such as the speed reference indicators on the Primary Flight Display (PFD), will only be displayed if the CDU is correctly set-up prior to takeoff.

I have attempted to try and simplify the procedure as much as possible. However, the automated systems that can be used on the Boeing aircraft are complicated, can be used fully or in part, and can easily generate confusion. Add to this that some procedures are different between an automated and manual takeoff, and some procedures are dictated by airline policy.

It is a challenge to simplify what in the first place is convoluted and technical.

I have set out the content in three parts:

Section One refers to a simplified generic procedure for takeoff (numerical sequence 1–20). Below each numerical number are important points (summarized as dot points). Although this section primarily refers to hand flying the aircraft, some automation concepts are discussed.
Section Two discusses takeoff procedures using automation.
Section Three provides additional information concerning important points mentioned in Section One and Two.

To minimise wordiness in this article, I have for the most part, used acronyms and footnotes. Refer to the end of the article for a list of acronyms and their meaning.

Peer Review

The information in this article has been peer reviewed by 737 Captain and First Officer.

Automation and Variability

The Boeing 737-800 can be flown with, without, or partly with automation. The combinations that can be used, how they work, and more importantly when to use them, can fill a book. Indeed, there is a book (two books) – they’re called the Flight Crew Operations Manual and the Flight Crew Training Manual.

The first point to take on board is that there is no absolute correct method for takeoff and climb. Certainly, there are specific tasks that need to be completed, however, there is an envelope of variability allowed. This variability may relate to how a particular flight crew flies the aircraft, environmental considerations (ice, rain, wind, noise abatement, obstacles, etc.), flight training, or a specific airline policy.

Whenever variability is injected into a subject, individuals who think in absolutes - black and white - will have difficulty. If you are the kind of person who likes to know exactly what to do at a particular time, then I suggest you find a technique that fits with your liking and personality.

SECTION ONE: Takeoff Guideline (1-20)

The following procedures assume essential elements of pre-flight have been completed (for example, correct set-up of CDU).

1. Using the Mode Control Panel (MCP), dial into the altitude window an appropriate target altitude, for example 13,000 feet.

2. Command speed is set in the MCP speed window. The speed is set to V2. V2 is determined by calculations made by the Flight Management Computer (FMC) based on aircraft weight, environmental conditions and several other parameters.

Important Points:

V2 is the minimum takeoff safety speed and provides at least 30° bank capability with takeoff flaps set. This speed provides a safe envelope to fly with one engine (if an engine failure occurs).
You can fly either +15 or +20 knots (maximum +25 knots) above the V2 command speed. This is done for a number of reasons: to lower or increase pitch due to the aircraft's weight, or to take into account other environmental variables (this assumes both engines operational), or it is dictated by airline policy.
A white-coloured airspeed bug is displayed at V2 +15/20 on the speed tape (part of the PFD). V2+15 knots provides 40° bank capability with takeoff flaps set. The bug is a visual aid to indicate the correct climb-out speed (bug is discussed later on).

3. Toggle both Flight Director (FD) switches to the O’ position (pilot flying side first).

4. Set flaps 5 and using the electric trim switch on the yoke, trim the aircraft to the correct trim figure for takeoff. The trim figure is shown on the CDU (for example, 5.5 degrees) and is calculated dependent upon aircraft weight with passengers and fuel. Normally the trim figure will place the trim tabs somewhere within the green band on the throttle quadrant. Takeoff should not occur if the trim tabs are outside of the green band.

5. Arm the autothrottle (A/T) by moving the toggle on the MCP to ARM. This may differ between airlines (when to arm the A/T) Consult the FCOM & FCTM.

6. Release the parking brake and manually advance the thrust levers to around 40%N1. %N1 can be airline specific with some airlines recommending 60%N1. Consult the FCOM & FCTM.

7. Monitor the EGT on the EICAS and when there is a decrease in EGT and the throttles are stabilised, either:

Advance the thrust levers to takeoff thrust (if hand flying); or,
Press one or both TOGA buttons if wishing the autothrottle system to be selected. If the autothrottle system has been selected for takeoff, both thrust levers will automatically begin to advance to the correct %N1 output calculated by the Flight Management System.

Interesting Point:

After takeoff configuration is complete, and with the parking brake in the OFF position, some flight crews quickly advance and retard the thrust levers. The purpose being to check for errors in the takeoff configuration. An error will trigger the audible configuration horn when the thrust levers are advanced.
Become conversant with derates. Using a particular derate is normal practice, but in particular will help control over-pitching and high vertical speeds, which are a common occurrence when the aircraft is light (minimal fuel load, passengers and/or cargo).

Important Points:

You do not have to stop the aircraft on the runway prior to initiating 40%N1. A rolling takeoff procedure is often recommended, as this expedites the takeoff (uses less runway length) and reduces the risk of engine damage from a foreign object being ingested into the engine (engine surge/stall due to a tailwind or crosswind).
When the thrust has reached 40%N1, wait for it to stabilise (roughly 2-3 seconds). Look at the N1 thrust arcs and the EGT gauge (on the EICAS display). Both N1 arcs must be stable and the EGT values decreasing slightly. In the real aircraft, the EGT should reduce between 10C-20C after N1 has stabilised at 40%. If the engines are NOT allowed to stabilise, prior to advancing the thrust levers, the takeoff distance can be adversely affected.
There is considerable confusion around when to actually press the TOGA buttons. As stated, %40N1 is common, but some airline procedures indicate 60%N1, while others recommend a staged approach – meaning, initially advance the thrust levers to 40%N1, allow the thrust to stabilise, and then advance the thrust levers to 70-80%N1 and press TOGA.
Do not push the thrust levers forward of the target %N1 - let the autothrottle do its job (otherwise you will not know if the autothrottle system has failed). See Point 10 concerning hand placement.
Ensure the autothrottle has reached the target %N1 by 60 knots ground speed. If not, execute a Rejected Takeoff (RTO).
Unless you select a different mode, the TOGA command mode that was engaged at takeoff (assuming you used the autothrottle system), will remain engaged until you reach the assigned altitude indicated on the MCP.
Selecting N1 on the MCP does not disengage TOGA mode. If you want to disengage TOGA mode, the Flight Director switches must be toggled to the OFF position, or another vertical mode selected.
In some simulators that use ProSim737 software (Version 2 & 3), you will notice that when throttle arm is displayed on the PFD, the throttle will retard slightly (%N1). This is NOT normal and is a ProSim737 software glitch. The issue is easily resolved by moving the thrust levers forward slightly. This glitch does not appear to cause other problems.

8. Maintain slight forward pressure on the control column to aid in tyre adhesion to the runway. Focus on the runway approximately three-quarters in front of the aircraft. This will assist you to maintain visual awareness and to keep the aircraft on the centreline. Use rudder and aileron input to control any crosswind.

9. During the initial takeoff roll, the pilot flying should place their hand on the throttle levers in readiness for a rejected takeoff (RTO). The pilot not flying should place his hand behind the throttle levers. Hand placement facilitates the least physical movement should an RTO be required.

10. The pilot not flying will call out 80 Knots Pilot flying should slowly release the pressure on the control column so that it is in the neutral position. Soon after the aircraft will pass through the V1 speed (this speed is displayed on the speed tape). Takeoff is mandatory at V1, and Rejected Takeoff (RTO) is now not possible. The pilot flying, to reaffirm this decision, should remove his or her hands from the throttles; thereby, reinforcing the must fly rule. (see important points below).

11. At Vr (rotation), pilot not flying calls Rotate. Pilot flying slowly and purposely initiates a smooth continuous rotation at a rate of no more than 2 to 3 degrees per second to an initial target pitch attitude of 8-10 degrees (15 degrees maximum).

Important Points:

Normal takeoff attitude for the 737-800 is between 8 and 10 degrees. This provides 20 inches of tail clearance at flaps 1 and 5. Tail contact will occur at 11 degrees of pitch (if the aircraft is still on or close to the ground).
Takeoff at a low thrust setting (low excess energy, low weight, etc) will result in a lower initial pitch attitude target to achieve the desired climb speed.
The correct takeoff attitude is achieved in approximately 3 to 4 seconds after rotation (depending on airplane weight and thrust setting).
Point 10 (above) discusses hand placement during the takeoff roll. Another method used differentiates responsibility between the Captain and First Officer. The Captain as Pilot in Command (PIC) will always have control of the thrust levers, while the pilot flying (First Officer) will concentrate solely on the takeoff with both hands on the control column. Removal of the hand after V1 is a standard operational procedure (SOP). This assumes that the First Officer will be pilot flying.

12. Following takeoff, continue to raise the aircraft’s nose smoothly at a rate of no more than 2 to 3 degrees per second toward 15 degrees pitch attitude. The Flight Director (FD) cues (pitch command bars) will probably indicate approximately 15 degrees.

Be aware that the cues provided by the Flight Director may on occasion be spurious; therefore, learn to see through the cues to the actual aircraft horizon line.

The Flight Director pitch command is NOT used during rotation.

13. At this stage, you most likely will need to trim the aircraft to maintain minimum back pressure (neutral stick) on the control column. The 737 aircraft is usually trimmed to enable flight with no pressure on the control column. It is quite normal, following rotation, to trim down a tad to achieve neutral loading on the control column. Do not trim during the actual rotation of the aircraft.

14. When positive rate has been achieved, and double checked against both the actual speed the aircraft is flying at (see speed tape on PFD), and the vertical speed indicator, the pilot flying will call Gear Up and the pilot not flying will raise the gear to minimize drag and allow air speed to increase. The pilot not flying will also announce Gear Is Up when the gear has been retracted successfully (green lights on the MIP have extinguished).

15. The Flight Director will command a pitch to maintain an airspeed of V2 +15/20. Follow the Flight Director cues (pitch command bar), or target a specific vertical speed. The vertical speed will differ widely when following the FD cues as it depends on weight, fuel, derates, etc. If not using the FD, try to maintain a target vertical speed (V/S) of ~2500 feet per minute.

Important Points:

V2 +15/20 is the optimum climb speed with takeoff flaps (flaps 5). It results in maximum altitude gain in the shortest distance from when the aircraft left the runway.
If following rotation the FD cues appear to be incorrect, or the pitch appears to be too great, ignore the FD and follow vertical speed guidance.
Bear in mind that vertical speed has a direct relationship to aircraft weight - if aircraft weight is low to moderate, use reduced takeoff thrust (derates) or Assumed Temperature Method to achieve a recommended vertical speed.
If LNAV and VNAV were selected on the MCP prior to takeoff, LNAV will provide FD inputs at 50 feet and VNAV will engage at 400 feet.
When VNAV is engaged, the speed of the aircraft will be automatically updated on the speed tape and the speed window on the MCP will become blank.
If LNAV and VNAV have not been selected prior to takeoff, it is common practice to manually select a roll mode (LNAV) at 400 feet. VNAV is usually selected after flaps UP.
If LNAV and VNAV has been selected prior to takeoff. LNAV is advisory. VNAV will automatically update the autothrottle system. The aircraft will not fly the LNAV course or the VNAV vertical profile until the autopilot is selected (CMD) on the MCP.

16. Follow and fly the cues indicated by the FD (automation), or maintain a command speed at V2 +15/20 (hand flying) until you reach Acceleration Height (AH). AH is often stipulated by company policy and is usually between 1000-1500 feet ASL. AH can be changed in the CDU.

17. At or when passing through Acceleration Height (~1500 Feet RA), a number of tasks may need to be completed. These tasks will cause the PFD display to change.

The nose of the aircraft is to be lowered (pitch decreased). This will increase airspeed and lower vertical speed. A rough estimate to target is half the vertical speed used at takeoff.
The flaps should be retracted as per the Flaps Retraction Schedule. If noise abatement is necessary, flaps retraction may occur at the Thrust Reduction Height.
Retract flaps as per the Flaps Retraction Schedule. Retract each degree of flaps as the aircraft's speed passes through the next flap increment détente. The flaps increment détente is displayed in green on the PFD speed tape. For example, as the aircraft passes through the flaps 1 designation you would select flaps 5 to flaps 1. Then, when the airspeed passes through the flaps UP position you would select flaps 1 to flaps UP. You do not want to exceed the flaps limit speed. (See Interesting Points (second dot point) regarding the Speed Trend Vector).
Do not retract flaps unless the aircraft is accelerating, and the airspeed is at, or greater than V2 +15/20 - this ensures the speed is within the manoeuvre margin allowing for over-bank protection. Do not retract flaps below 1000 feet RA.
When flaps retraction commences, the airspeed bug will disappear from the speed tape on the PFD.
If hand flying (VNAV not selected), at Acceleration Height set the speed in the speed window of the MCP to a speed that corresponds to the flaps UP speed. The flaps UP speed can be found displayed on the speed tape on the PFD. This is often referred to as Bugging Up.
Some flight crews when reaching Acceleration Height call Level Change, Set Top Bug. This ensures that TOGA speed is disengaged (by selecting another mode).
If VNAV has been selected prior takeoff, the flaps UP speed will be automatically populated and displayed on the speed tape on the PFD. However, the speed will not be displayed in the MCP speed window (the window will be blank).

18. When the aircraft flies through the flaps UP speed, and after the flaps have been fully retracted, the desired climb speed is dialed into the speed window of the MCP (If VNAV is not selected). If VNAV has been selected, the climb speed will be automatically populated and displayed on the PFD (as will the cruise speed when the aircraft reaches cruise altitude).

Important Points:

If VNAV is selected, the speed window in the MCP is blank. However, if VNAV is not selected the speed window is open.
If automation and the autothrottle system (TOGA) is not being used, and you are hand flying the aircraft, Press N1 on the MCP (if desired) at Acceleration Height and follow FD cues to flaps UP speed.
When N1 is selected, the autothrottle will control the speed of the aircraft to the N1 limit set by the FMS. Selecting N1 ensures the aircraft has maximum power (climb thrust) in case of a single engine failure.
If the autothrottle system (TOGA) has been used during takeoff, N1 is automatically selected (by the FMS) at Thrust Reduction Altitude (usually ~1500 feet RA). There is no need to press the N1 button on the MCP.
N1 mode doesn’t control the aircraft’s speed - it controls thrust. The autothrottle will set the maximum N1 thrust (power). The aircraft’s speed is controlled by the pitch attitude.
Selecting N1 on the MCP does not provide any form of speed protection.
Acceleration Height can be changed in the CDU.
The auotpilot should NOT be engaged prior to flaps UP. This is often stipulated by airline policy,

19. The aircraft is usually flown at a speed no faster than 250 KIAS to 10,000 feet. At 10,000 feet, speed is usually increased to 270 KIAS. Environmental factors and/or ATC may result in differing speeds being set.

At this stage, the aircraft can be hand flown with or without VNAV and/or the autothrottle. You can either:

Continue to hand fly the aircraft to altitude. Appropriate climb and cruise speeds will need to be dialed into the MCP; or,
Select a suitable pitch and roll mode (LVL CHG, V/S, LNAV & VNAV) and engage the autopilot or select CWS. If a pitch and roll mode is selected and the autopilot not selected, the FD will provide visual cues.

20. At 10,000 feet, dial 270 KIAS into the MCP speed window and then at 12,000 feet dial in 290 KIAS. Follow the Flight Director cues, or if the FD is not being used, maintain roughly 2000-2500 fpm vertical speed. At cruise altitude, transition to level flight and select on the MCP speed window 290-310 KIAS or whatever the optimum speed is (see CDU).

Interesting Points:

Many pilots had fly the aircraft to 10,000 feet before engaging the autopilot. To enhance situational awareness, it is common practice, if hand flying, to have LNAV and VNAV selected. This enables the pilot to follow the navigation cues displayed on the PFD.
Located on the speed tape on the PFD, is a green coloured line called a Speed Trend Vector (STV). The Speed Trend Vector will display an upwards, neutral or downwards facing arrow. During climb-out, the Speed Trend Vector arrow can be used to determine how long it will take for the aircraft, at the current thrust setting, to reach the speed that the arrow is pointing at (usually around 10 seconds). Therefore, when the upward arrow reaches the flaps indicator, the aircraft will pass through this flaps détente in approximately 10 seconds. The Speed Trend Vector can be used to help know when to initiate retraction of the flaps.

Summary

The above procedures are general. Specific airline policy for a particular airline may indicate otherwise. Likewise, there is considerable latitude to how the aircraft is flown, whether it be without automation selected, or with part or full automation selected.

It is very easy to become confused during the takeoff phase - especially in relation to automation, V speeds, acceleration heights, and how and when to change from hand flying to automation The takeoff phase occurs quickly, there is a lot to do, and quite a bit to remember - there is little time to consult a manual or cheat sheet.

SECTION TWO: Takeoff Guideline (LNAV, VNAV & autopilot selected prior to takeoff)

Although I have mentioned some of the VNAV procedures in the above discussion, I though it pertinent to include this section which will address a takeoff with LNAV and VNAV selected (points 1-10 below). This information relates to FMS software U10.8A.

Important Point:

The aircraft requires information from the FMS when automation (LNAV & VNAV) is used. For the takeoff to be successful, the PERF INIT and navigation data must be inputted into the CDU.

The following 10 points outline a VNAV selected takeoff:

Select from the CDU a Standard Instrument Departure (SID) and press the illuminated annunciator (EXEC) on the CDU.
Verify the Flight Director switches are selected to the ON.
ARM LNAV and VNAV on the MCP (press the LNAV & VNAV buttons on the MCP).
ARM the Autopilot (press CMD A/B) and set the Command Speed in the speed window of the MCP to V2 (The V2 speed can be found in the takeoff page of the CDU).
Takeoff (as discussed earlier).
VNAV will engage at 400 feet and the Flight Director will command V2 +15/20. The appropriate bugs on the PFD speed tape will be populated automatically. The speed should always be crosschecked against the actual speed that the aircraft is flying and the white bug on the speed tape.
At Acceleration Height (between ~1000-1500 feet RA or as indicated in the CDU) the Flight Director will command a speed 10 knots above the FLAPS UP speed.
Lower the aircraft’s nose and follow the FD cues (command pitch bars).
Commence FLAPS retraction and follow the Flaps Retraction Schedule (Point 18 above).
As the FLAPS retract into the UP position the Flight Director will command 250 knots.
Select CMD A/B (autopilot) or fly to 10,000 feet or cruise altitude and select autopilot.

SECTION THREE: Additional Information - Summarised Important Points

Understanding %N1

To understand the various levels of automation it is important to have a relative understanding of %N1.

N1 is a measurement in percent (%) of the maximum RPM of an engine, where maximum RPM is certified at the rated power output for the engine (most simple explanation). Therefore, 100%N1 is maximum thrust, while 0%N1 is no thrust. (%)N1 will be at a percentage commensurate with the settings that have been inputted to the CDU (aircraft weight, fuel, derates, etc).

Important Points:

The autothrottle logic when TOGA selected controls the aircraft’s thrust (%N1). The aircraft’s speed is controlled by pitch (attitude).
To clarify what automated system is controlling the aircraft, always refer to the Flight Mode Annunciations (FMA) in the PFD (Refer to Table 1 for a quick overview of annunciations displayed during the takeoff).

Common Practice - What to Select For Takeoff

It is not the purpose of this article to rewrite the FCOM or FCTM. Needless to say, there are several combinations, that can be selected at varying stages of flight. All are at the discretion of the pilot flying, or are stipulated as part of airline policy.

After Acceleration Height has been reached, the aircraft’s nose lowered to increase speed, and the flaps retracted, it is common practice to use LVL CHG, V/S, or LNAV and VNAV, and either hand fly the aircraft, select CWS, or select the autopilot (usually at or above 3000 feet, but certainly after flaps UP) and fly to cruise altitude.

If the takeoff does not use LNAV and VNAV (not selected on the MCP) LNAV can be selected at, or after 50 feet RA and VNAV can be selected at, or after 400 feet RA. After either of these two modes have been selected, the Flight Director cues will automatically update to reflect the data that has been inputted into the CDU.

Theoretically, a crew can hand fly the aircraft following the FD cues at V2 +15/20 to the altitude set in the MCP. However, there will be no speed protection, and if the pitch cues recommended by the FD are not followed, then the airspeed may be either below or above the optimal setting or safety envelope. Selecting an automation mode (not V/S) is what engages the speed protection (speed protection will be discussed shortly).

In the above scenario (assuming the aircraft is being hand flown), unless another vertical mode is selected, the aircraft will remain in TOGA command mode (thrust controlled by N1) until the altitude set in the MCP is reached. To deselect (cancel) TOGA as the command mode, another mode such as LVL CHG, VNAV or V/S will need to be selected. Altitude Hold (ALT HOLD) also deselects TOGA as does engaging the autopilot.

Flight crews typically hand fly the aircraft until the flaps are retracted (flaps UP) and the aircraft is in clean configuration. A command mode is then selected to continue the climb to cruise altitude. CWS or the autopilot may or may not be engaged.

Important Point:

It is important to understand what controls the various command modes. For example, LVL CHG is controlled by N1 and pitch. In this mode, the autothrottle will use full thrust, and the speed will be controlled by pitch.

**TABLE 1:** N1 MCP annunciation and FMA displays for common time events during takeoff and climb

**TABLE 2:** Throttle command modes for common time events during takeoff and climb. The flight crew can manually override the autothrottle logic by advancing or retarding the thrust levers by hand. This can only be done at certain phases of flight. Throttle online means that the crew can override the autothrottle logic, while Throttle offline means that the logic cannot be overridden

Speed Protection

One of the advantages when using the automated systems is the level of speed protection that some of the systems provide. Speed protection means that the autothrottle logic will not allow the aircraft’s speed to be degraded to a value, by which the aircraft can stall or be below maneuvering speed.

Speed protection is not active with every automated system. Whether speed protection is active depends upon the U version of the FMS software in use, the automation mode selected, and whether the flaps are extended or fully retracted.

The following examples indicate whether speed protection is available;

Level Change (LVL CHG): When you select LVL CHG, the speed window will open allowing you enter a desired speed. LVL CHG is speed protected, meaning that the aircraft's speed will not increase beyond the speed inputted into the MCP. This is because LVL CHG is controlled by N1 (thrust) while the aircraft’s speed is controlled by pitch.

VNAV: VNAV has active speed protection for the leading edge devices (U10.8A and above) . This is why VNAV can be selected on the ground.

Vertical Speed (V/S): V/S provides no speed protection. This is because V/S holds a set vertical speed. In V/S, if you are not vigilant, you can easily encounter an overspeed or under speed situation.

N1: Selecting N1 by pressing the N1 button on the MCP (without any other mode selected) does not provide speed protection. Using the N1 mode, only ensures maximum thrust is generated.

Important Points:

Speed protection is armed only for some levels of automation.
It is imperative that you observe the Flight Mode Annunciator (FMA) to check that the aircraft is flying the mode intended.

ryanair taking off from bristol airport england (Adrian Pingstone)., Ryanair Boeing 737-800 (EI-DWO) takes off from Bristol Airport, England, 23Aug2014 arp, marked as public domain, more details on Wikimedia Commons)

Always Think Ahead

As stated, the takeoff phase happens quickly, especially if the aircraft’s weight is light (cargo, passengers and fuel).

Soon after rotation (Vr), the aircraft will be at Acceleration Height and beyond… It’s important to remain vigilant and know what’s happening, and to think one step ahead of the automated system that is controlling the aircraft. You do not want the automation to get ahead of you and hear yourself thinking what’s it doing now.

Aircraft Weight

Although briefly discussed earlier, I would like to enlarge upon how the weight of the aircraft can have an affect on takeoff and climb. An aircraft’s weight is altered by the volume of fuel on board, the number of passengers, and the amount of cargo carried in the holds.

In some respects, a heavily laden aircraft, although requiring higher thrust settings and longer runway length, will be more stable than the same aircraft at a lighter weight. A lightly laden aircraft will use less runway and, unless thrust settings are managed accordingly, will be prone to an excessive rate of climb (high vertical speed and high pitch angle). This can lead to tail strike and uncomfortably high rates of ascent.

To manage this, flight crews often limit the takeoff thrust by using one of several means. Typically, a thrust derate is used with either CLB 1 or CLB 2 set in the CDU, or an assumed temperature thrust reduction is used. Selecting either option will cause a longer takeoff roll (less thrust) and delay the rotation point (Vr), however, the climb-out will be less aggressive and more manageable.

Final Call

Reiterating, the above guidelines are generalist only. Flight crews use varying methods to fly the aircraft, and often the method used will be chosen based on company policy, crew experience, aircraft weight, and other environmental factors, such as runway length, weather and winds.

Additional Information:

Future Articles

Time permitting, other articles will be published dealing with: descent, initial approach, and landing (ILS, VNAV, Circle to Land and RNAV).

Disclaimer

The content in this post has been proof read for accuracy, however, explaining procedures that are convoluted, technical, and somewhat subjective can be challenging. Errors on occasion present themselves. If you observe an error (not a particular airline policy), please contact me so it can rectified.

Footnotes

(1): For example, there are different protocols between FMC U10.6 and FMC U10.8 (especially when engaging VNAV and LNAV prior to takeoff). I have purposely not addressed these differences because they can become very confusing (another article will do this). As at writing (2020), ProSim737 uses U10.8A.

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Acronyms and Glossary

AFDS – Autopilot Flight Director System
AH - Acceleration Height. The altitude above sea level that aircraft’s nose is lowered to gain speed for flap retraction. AH is usually 1000 or 1500 feet and is defined by company policy. In the US acceleration height is usually 800 feet RA
CDU, FMC & FMS – Control Display Unit / Flight Management Computer (term often used interchangeably). The visual part of the Flight Management System (FMS) that enables input of variables. FMS is the system and software (U10.8A). FMC is the actual computer, and the CDU is the hardware.
CLB 1/2 – Climb power
Command Mode – The mode of automation that controls thrust
EICAS – Engine Indicating and Crew Alerting System
F/D – Flight Director (Flight Director cues/crosshairs)
FMA – Flight Mode Annunciation located upper portion of Primary Flight Display (PFD)
KIAS – Knots Indicated Air Speed
LNAV – Lateral Navigation
LVL CHG – Level Change Command Mode
MCP – Mode Control Panel
N1 & N2 – N1 and N2 are the rotation speeds of the engine sections expressed as a percentage of a nominal value. ... The first spool is the low pressure compressor (LP), that is N1 and the second spool is the high pressure compressor (HP), that is N2. The shafts of the engine are not connected and they operate separately. Often written N1 or %N1.
RTO – Rejected Take Off
T/O Power – Takeoff power
Throttle On & Offline – Indicates whether the throttle is being controlled by the A/T system
TOGA – To Go Around Command Mode
TRA - Thrust Reduction Altitude. The altitude that the engines reduce in power to increase engine longevity. The height is usually 1500 feet; however, the altitude can be altered in CDU
V/S – Vertical Speed Command Mode
V1 – is the Go/No go speed. You must fly after reaching V1 as a rejected take off (RTO) will not stop the aircraft before the runway ends
V2 – Takeoff safety speed. The speed at which the aircraft can safely takeoff with one engine inoperative (Engine Out safe climb speed)
VNAV – Vertical Navigation
Vr – Rotation Speed. This is the speed at which the pilot should begin pulling back on the control column to achieve a nose up pitch rate
Vr +15/20 – Rotation speed plus additional knots (defined by company policy)

Updated April 2021.
Updates March 2024.

July 01, 2014

Crosswind Landing Techniques Part Two - Calculations

July 01, 2014/ Flaps 2 Approach

crosswind landing with right main gear touching first (Jeroen Stroes Aviation Photography from Netherlands, EI-FIZ (27608888537), CC BY 2.0

Determining Correct Landing Speed (Vref)

Vref is defined as landing speed or the threshold crossing speed, while Vapp is defined as the approach speed with wind/gust additives.

When landing with a headwind, crosswind, or tailwind the Vref and Vapp must be adjusted accordingly to obtain the optimal speed at the time of touchdown. Failure to do this may result in the aircraft landing at an non-optimal speed causing runway overshoot, stall, or floating (ground affect).

Mathematical calculations can be used to determine Vref and Vapp based on wind speed, direction, and gusts.

This is the second segment of a two-segment post. The first segment dealt with methods used to land in cross wind conditions - Crosswind Landing Techniques Part One Crab and Sideslip.

Normal Conditions

When using the autothrottle, position command speed to Vref+5 knots.

If the autothrottle is disengaged or is planned to be disengaged prior to landing, the recommended method of approach speed correction to obtain Vapp (approach speed), is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed.

One half of the reported steady headwind component can be estimated by using 50% for a direct headwind, 35% for a 45-degree crosswind, zero for a direct crosswind, or interpolation between.

When making adjustments for wind additives, the maximum command speed should not exceed Vref+20 knots or landing flap placard speed minus 5 knots, whichever is lower.

The minimum command speed setting with autothrottle disconnected is Vref+5 knots. The gust correction should be maintained to touchdown while the steady headwind correction should be bled off as the airplane approaches touchdown.

It is important to note that Vref+5 knots is the speed that is desired when crossing the threshold of the runway - it is NOT the approach speed. The approach speed (Vapp) is determined by headwind with/without gusts. If the wind is calm, Vref+5 knots will equal Vapp.

When landing in a tailwind, do not apply wind corrections. Set command speed at Vref+5 knots (autothrottle engaged or not engaged).

Non-Normal Conditions

When Vref has been adjusted by the non-normal procedure, the new Vref is called the adjusted Vref and is used for the landing. To this speed is added the wind component (if necessary).

For example, if a non-normal checklist specifies 'Use flaps 15 and Vref 15+10 for landing', the flight crew would select flaps 15 and look up the Vref 15 speed (in FCTM or QRH) and add 10 knots to that speed. The adjusted Vref does not include wind corrections and these will need to be added.

If the autothrottle is disengaged, or is planned to be disengaged prior to landing, appropriate wind corrections must be added to the adjusted Vref to arrive at command speed. Command speed is the safest speed used to fly the approach (Vapp). If the speed is above command speed then it will need to be bleed off prior to touchdown.

Autoland Limitations

If using autoland (CAT II & CAT IIIA) the autothrottle remains engaged and the command speed is set to Vref+5.

The following autoland limitations must be complied with:

Glide slope angle tolerance - maximum 3.25 degrees / minimum 2.5 degrees;
Engines 1/2 operational;
Maximum tailwind - 15 kts;
Maximum headwind - 25 kts;
Maximum crosswind - 20 kts ;
Maximum tailwind at flaps 30 - 12 knots (winglets); and,
Landing in gusty wind or windshear conditions is not approved during CAT II and CAT IIIA operations.

Guideline (an easy way to remember the above - cheat sheet)

This information assumes the autothrottle will be disengaged prior to landing.

Headwind less than 10 knots: Vref+5
Headwind greater than 10 knots: Vref +headwind / 2 (half your headwind) - This is your Vref
If Vref is > 20 knots, then: Vref+20 (as per placard guide)

With Gusts

Formula (Wind < 10 knots): Vref+5 + gust – headwind
Formula (Wind > 10 knots): Vref + headwind/2 (half your headwind) + gust – headwind

Calculating Directional Wind

A wind component will not always be at 90 Degrees or straight on to your landing direction. The following calculation is often used to determine the directional component. One half of the reported steady headwind component can be estimated by using 50% for a direct headwind, 35% for 45 degree crosswind, zero for a direct crosswind and interpolation in between.

Tail Winds

Tail winds are very challenging for conducting a stabilized approach. Because of the increased ground speed caused by a tail wind, Boeing does not publish Vref correction factors for tail winds.

Typically, to maintain the proper approach speed and rate of descent while maintaining glide slope, thrust must be decreased which minimizes the available safety envelope should a go-around be required. If a go-around is required, precious seconds might be lost as the engines accelerate; the aircraft would continue to descend and might touch down on the runway before the engines produce enough thrust to enable a climb.

The International Civil Aviation Organization (ICAO) recommends that the tail wind component must not exceed 5 knots plus gusts on a designated runway; however, adherence to this recommendation varies among members. Several airlines have been certified for operation with a 15 knot tailwind.

In the United States, Federal Aviation Administration (FAA) sets the tail wind component limit for runways that are clear and dry at 5 knots, and in some circumstances 7 knots, however FAA allows no tail wind component when runways are not clear and dry. Note, that many manuals subscribe to the 10 knots no tailwind rule (see table below).

Crosswind components can be variable dependent upon flight crew discretion and airline policy; therefore, the above is to be used as a 'guide' only.

The below table (limitations) summarizes much of what has been written above.

**table 1:** wind limits for 737-800. the table provides a good summary of what has been written in the article

The CDU if configured correctly can provide information concerning wind components. Press the key on the CDU named 'PROG' followed by 'PREV PAGE'. This page provides an overview of the wind component including head, tail and crosswind.

Wind Correction Field (WIN CORR)

The approach page in the CDU has a field named WIN CORR (Wind Correction Field or WCF). Using this field, a flight crew can alter the Vref+ speed (additive) that is used by the autothrottle. The default reading is +5. Any change will alter how the FMC calculates the command speed that the autothrottle uses; changes are reflected in the LEGS page. It's important to update the WIND CORR field if VNAV is used for the approach, as VNAV uses data from the FMC to fly the approach. If hand flying the aircraft, it's often easier to to add the Vref additive to the speed window in the MCP.

WIND CORR Explained

The WCF is a handy feature if a flight crew wishes to increase the safety margin the autothrottle algorithm operates.

Boeing when they designed the autothrottle algorithm programmed a speed additive that the A/T automatically adds to Vref when the A/T is engaged. The reason for adding this speed is to provide a safety buffer to ensure that the A/T does not command a speed equal to or lower than Vref. (recall that wind gusts can cause the autothrottle to spool up or down depending upon the gust strength).

A Vref+ speed higher than +5 can be inputted when gusty or headwind conditions are above what are considered normal. By increasing the +speed, the speed commanded by the autothrottle will not degrade to a speed lower than that inputted.

Important Points:

During the approach, V speeds are important to maintain. A commanded speed that is below optimal can be dangerous, especially if the crew needs to conduct a go-around, or if winds suddenly increase or decrease. An increase or decrease in wind can cause pitch coupling.
If using VNAV, it's important to update the WIND CORR field to the correct headwind speed based on conditions. This is because VNAV uses the data from the FMC.

If executing an autoland (rarely done in the B737), the WIND CORR field is left as +5 knots (default). The autoland and autothrottle will command the correct approach and landing speed.

June 17, 2014

Crosswind Landing Techniques Part One - Crab and Sideslip

June 17, 2014/ Flaps 2 Approach

This video very clearly illustrates my point that landing in a strong crosswind can be a challenging and in some cases downright dangerous (Video © CargoSpotter (with thanks); courtesy U-Tube).

Generally, flight crews use one of two techniques or a combination thereof to approach and land in crosswind conditions. If winds exceed aircraft tolerances, which in the 737-800 is 33 knots (winglets) and 36 knots (no winglets), the flight crew will divert to their alternate airport (Brady, Chris - The Boeing 737 technical Guide).

crab approach. Wind is right to left at 16 knots with aircraft crabbing into the wind to maintain centerline approach course. Just before flare, left rudder will be applied to correct for drift to bring aircraft into line with centerline of runway. This technique is called 'de-crabbing’. During such an approach, the right wing may also be lowered 'a tad' (cross-control) to ensure that the aircraft maintains the correct alignment and is not blown of course by a 'too-early de-crab'. Right wing down also ensures the main gear adheres to the runway during the roll out

Maximum crosswind figures can differ between airlines and often it's left to the pilot's discretion and experience. Below is an excerpt from the Landing Crosswind Guidelines from the Flight Crew Training Manual (FCTM). Note that FCTMs can differ depending on date of publication.

There are several factors that require careful consideration before selecting an appropriate crosswind technique: the geometry of the aircraft (engine and wing-tip contact and tail-strike contact), the roll and yaw authority of the aircraft, and the magnitude of the crosswind component. Consideration also needs to be made concerning the effect of the selected technique when the aircraft is flared to land.

Crosswind Approach and Landing Techniques

There are four techniques used during the approach and landing phase which center around the crab and sideslip approach. The crab and sideslip are the primary methods and most commonly used while the de-crab and combination crab-sideslip are subsets that can be used when crosswinds are stronger than usual.

It must be remembered that whatever method is used it is at the discretion of the pilot in command.

Crab (to touchdown).
Sideslip (wing low).
De-crab during flare.
Combination crab and sideslip.

1: Crab (to touchdown)

Airplane maintains a crab during the final approach phase.
Airplane touches down in crab.
Flight deck is over upwind side of runway (Main gear is on runway center).
Airplane will de-crab at touchdown.
Flight crew must maintain directional control during roll out with rudder and aileron.

With wings level, the crew will use drift correction to counter the effect of the crosswind during approach. Drift correction will cause the aircraft to be pointing in a direction either left or right of the runway heading, however, the forward energy of the aircraft will be towards the centerline. This is called the crab because the aircraft is crabbing at an angle left or right of the aircraft's primary heading.

Most jetliners have the ability to land in a crab, however, it must be remembered that landing in a crab places considerable stress on the main landing gear and tyre side-walls, which in turn can cause issues with tyre and wheel damage, not too mention directional control.

The later is caused by the tandem arrangement of the main landing gear that has a strong tendency to travel in the direction that the nose of the aircraft is pointing at the moment of touchdown. This can result in the aircraft travelling toward the edge of the runway during the roll out. To counter this, and align the nose of the aircraft with the centreline of the runway, the pilot flying must apply rudder input when lowering the nose wheel to the runway surface.

A reference to the maximum amount of crab that can be safely applied in the B737 was not found, other than maximum crosswind guidelines must not be exceeded. The crab touchdown technique is the preferred choice if the runway is wet.

2: Sideslip (wing low)

Upwind wing lowered into wind.
Opposite rudder (downwind direction) maintains runway alignment.
In a sideslip the aircraft will be directly aligned with the runway centerline using a combination of into-wind aileron and opposite rudder control (called cross-controls) to correct the crosswind drift.

The pilot flying establishes a steady sideslip (on final approach by applying downwind rudder to align the airplane with the runway centerline and upwind aileron to lower the wing into the wind to prevent drift. The upwind wheels should touch down before the downwind wheels touch down.

The sideslip technique reduces the maximum crosswind capability based on a 2/3 ratio leaving the last third for gusts. However, a possible problem associated with this approach technique is that gusty conditions during the final phase of the landing may preempt a nacelle or wing strike on the runway.

Therefore a sideslip landing is not recommended when the crosswind component is in excess of 17 knots at flaps 15, 20 and 30, or 23 knots at flaps 40.

The sideslip approach and landing can be challenging both mentally and physically on the pilot flying and it is often difficult to maintain the cross control coordination through the final phase of the approach to touchdown. If the flight crew elects to fly the sideslip to touchdown, it may also be necessary to add a crab during strong crosswinds.

3: De-crab During Flare(with removal of crab during flare)

Maintain crab on the approach.
At ~100 foot AGL the flight crew will de-crab the aircraft; and,
During the flare, apply rudder to align airplane with runway centreline and, if required slight opposite aileron to keep the wings level and stop roll.

This technique is probably the most common technique used and is often referred to as the 'crab-de-crab'.

The crab technique involves establishing a wings level crab angle on final approach that is sufficient to track the extended runway centerline. At approximately 100 foot AGL and during the flare the throttles are reduced to idle and downwind rudder is applied to align the aircraft with the centerline (de-crab).

Depending upon the strength of the crosswind, the aircraft may yaw when the rudder is applied causing the aircraft to roll. if this occurs, the upwind aileron must be placed into the wind and the touchdown maintained with crossed controls to maintain wings level (this then becomes a combination crab/sideslip - point 4).

Upwind aileron control is important, as a moderate crosswind may generate lift by targeting the underside of the wing. Upwind aileron control assists in ensuring positive adhesion of the landing gear to the runway on the upwind side of the aircraft as the wind causes the wing to be pushed downwards toward the ground.

Applied correctly, this technique results in the airplane touching down simultaneously on both main landing gear with the airplane aligned with the runway centerline.

4: Combination Crab and Sideslip

De-crab using rudder to align aircraft with runway (same as point 3 de crab during flare).
Application of opposite aileron to keep the wings level and stop roll (sideslip).

The technique is to maintain the approach in a crab, then during the final stages of the approach and flare increase the into-wind aileron and land on the upwind tyre with the upwind wing slightly low. The combination of into-wind aileron and opposite rudder control means that the flight crew will be landing with cross-controls.

The combination of crab and sideslip is used to counter against the turbulence often associated with stronger than normal crosswinds.

As with the sideslip method, there is the possibility of a nacelle or wing strike should a strong gust occur during the final landing phase, especially with aircraft in which the engines are mounted beneath the wings.

**FIGURE 1**: Diagram showing most commonly used approach techniques *(copyright Boeing)*

Operational Requirements and Handling Techniques

With a relatively light crosswind (15-20 knot crosswind component), a safe crosswind landing can be conducted with either; a steady sideslip (no crab) or a wings level, with no de-crab prior to touchdown.

With a strong crosswind (above a 15 to 20 knot crosswind component), a safe crosswind landing requires a crabbed approach and a partial de-crab prior to touchdown.

For most transport category aircraft, touching down with a five-degree crab angle with an associated five-degree wing bank angle is a typical technique in strong crosswinds.

The choice of handling technique is subjective and is based on the prevailing crosswind component and on factors such as; wind gusts, runway length and surface condition, aircraft type and weight, and crew experience.

Touchdown Recommendations

No matter which technique used for landing in a crosswind, after the main landing gear touches down and the wheels begin to rotate, the aircraft is influenced by the laws of ground dynamics.

Effect of Wind Striking the Fuselage, Use of Reverse Thrust and Effect of Braking

The side force created by a crosswind striking the fuselage and control surfaces tends to cause the aircraft to skid sideways off the centerline. This can make directional control challenging.

Reverse Thrust

The effects of applying the reverse thrust, especially during a crab ‘only’ landing can cause additional direction forces. Reverse thrust will apply a stopping force aligned with the aircraft’s direction of travel (the engines point in the same direction as the nose of the aircraft). This force increases the aircraft’s tendency to skid sideways.

Effects of Braking

Autobrakes operate by the amount of direct pressure applied to the wheels. In a strong crosswind landing, it is common practice to use a combination of crab and sideslip to land the aircraft on the centerline. Sideslip and cross-control causes the upwind wing to be slightly down upon landing and this procedure is carried through the landing roll to control directional movement of the aircraft.

The extra pressure applied to the ‘wing-down’ landing gear causes increased auto-braking force to be applied which creates the tendency of the aircraft to turn into the wind during the landing roll. Therefore, a flight crew must be vigilant and be prepared to counter this unwanted directional force.

If the runway is contaminated and contamination is not evenly distributed, the anti-skid system may prematurely release the brakes on one side causing further directional movement.

**FIGURE 2:** Diagram showing recovery of a skid caused by crosswind and reverse thrust side forces *(source: Flight Safety Foundation ALAR Task Force)*

Maintaining Control - braking and reverse thrust

If the aircraft tends to skew towards the side from higher than normal wheel-braking force, the flight crew should release the brakes (disengage autobrake) which will minimize directional movement.

To counter against the directional movement caused by application of reverse thrust, a crew can select reverse idle thrust which effectively cancels the side-force component. When the centerline has been recaptured, toe brakes can be applied and reverse thrust reactivated.

Runway Selection and Environmental Conditions

If the airport has more than one runway, the flight crew should land the airplane on the runway that has the most favourable wind conditions. Nevertheless, factors such as airport maintenance or noise abatement procedures sometime preclude this.

I have not discussed environmental considerations which come into play if the runway is wet, slippery or covered in light snow (contaminated). Contaminated conditions further reduce (usually by 5 knots) the crosswind component that an aircraft can land.

Determining Correct Landing Speed (Vref)

Vref is defined as landing speed or threshold crossing speed.

When landing with a headwind, crosswind, or tailwind the Vref must be adjusted accordingly to obtain the optimal speed at the time of touchdown. Additionally the choice to use or not use autothrottle must be considered. Failure to do this may result in the aircraft landing at a non-optimal speed causing runway overshoot, stall, or floating (ground affect).

This article is part one of two posts. The second post addresses the calculations required to safety land in crosswind conditions: Crosswind Landing Techniques Part Two Calculations.

May 17, 2014

Approach Tools: Vertical Bearing Indicator, Altitude Range Arc and Vertical Deviation Scale

May 17, 2014/ Flaps 2 Approach

qantas 737 (Aero Icarus from Zürich, Switzerland, Qantas Boeing 737-400; VH-TJI@SYD;31.07.2012 666im (7863511354), CC BY-SA 2.0)

On 12 February 2012, the flight crew of a Boeing 737 aircraft, registered VH-TJS and operated by Qantas Airways Limited, was conducting a scheduled passenger service from Sydney, New South Wales to Canberra, Australian Capital Territory. Due to scheduled maintenance the instrument landing system at Canberra was not available and the crew prepared for an alternate instrument approach that provided for lateral but not vertical flight path information. The flight was at night with rain showers and scattered cloud in the Canberra area.

Shortly after becoming established on the final approach course with the aircraft’s automatic flight system engaged, the flight crew descended below the minimum safe altitude for that stage of the approach. The crew identified the deviation and leveled the aircraft until the correct descent profile was intercepted, then continued the approach and landed. No enhanced ground proximity warning system alerts were generated, as the alerting thresholds were not exceeded.

During those phases of flight when terrain clearance is unavoidably reduced, such as during departure and approach, situation awareness is particularly crucial. Any loss of vertical situation awareness increases the risk of controlled flight into terrain. This occurrence highlights the importance of crews effectively monitoring their aircraft’s flight profile to ensure that descent is not continued through an intermediate step-down altitude when conducting a non-precision approach (Australian Transport safety Bureau, 2013).

Determining the correct rate of descent (RoD) or vertical speed (V/S) is a critical attribute if an aircraft is to arrive at the correct altitude and avoid excessive descent rates. Control of the vertical path uses two different methods: the step-down method and the constant descent method. Both methods assume that the aircraft is being flown in landing configuration at the final approach speed (VaPP) from the final approach fix (FAF) to the landing initiation of the missed approach.

Non Precision Approaches (NPA)

Historically non precision approaches reference ground navigation aids that exhibit a degree of inaccuracy, which is often enhanced by the poorly defined vertical path published on an approach chart; NPA charts typically provide only an assigned altitude at the FAF and the distance from the FAF to the MAP. Thus, flight crew awareness of the aircraft’s vertical position versus the intended vertical path of the final approach can be quite low when executing traditional style step-down approaches.

To determine the best vertical speed to use during a non precision approach, flight crews use a number of 'back of the envelope' calculations.

Rate of Descent & Glideslope Calculations

There are several calculations that can be used determine rate of descent – some more accurate than others. Search ‘determine descent rate’ in Google. Some of the more commonly used rules of thumb are:

Divide your ground speed by 2, then add a zero (120 kias / 2 = 60, add 0 = 600 fpm).
Rate of descent (RoD) in ft/min should be equal to 5 times the ground speed in knots (same as above but different calculation).
To maintain a stabilized approach, add a zero to your indicated air speed and divide by two (150 kias + 0 = 1500 / 2 = 750 fpm).
To determine distance from threshold to start a 3 degree glideslope, take the height above ground level and divide by three hundred (600 ft AGL / 300 = 2 nm).
To maintain a 3 degree glideslope (ILS), multiply your ground speed by 5. The resulting number is the rate of descent to fly (110 kias x 5 + 550 fpm on 3 degree glideslope).
If the glideslope is not operational on an ILS approach with DME, multiply the distance ‘to go’ by 300. This will provide the height in feet above the threshold of the runway (4 nm to the threshold; multiply x 300 = 1200 ft).

Flight crews today, especially those flying in and out of busy intercity hubs, rarely execute step down approaches as computer and GPS-orientated systems have replaced traditional methods of navigation. However, as the flight into Canberra revealed, the best system may at times be inoperative or fail and it is good airmanship to understand and be able to remember one or more of the above equations.

Today's systems provide a high level of redundancy and the Boeing 737-800 NG incorporates a number of integrated aids to assist a flight crew during descent and approach. In this post some of less commonly understood aids will be discussed.

CDU showing DES Page, waypoint/altitude and VBI interface (*Key RSK3 & RSK4*)

Vertical Bearing Indicator (VBI))

A tool often overlooked with regard to positional awareness is the Vertical Bearing Indicator (VBI). The VBI display is accessed and displayed in the CDU.

The VBI can calculate an accurate rate of descent to a particular spatial point. It is basically an angle calculator that provides ‘live’ vertical speed information based upon a desired descent angle, the current speed of the aircraft and an end location.

A flight crew enters into the VBI the final altitude that the aircraft should be at (for example, the Final Approach Fix or runway threshold). This figure is determined by consulting the appropriate approach chart for the airport. The CDU will then calculate the descent rate based on flight variables. As the aircraft descends, the VBI readout will continually update the descent rate based upon aircraft speed and rate of descent.

The flight crew can either manually fly the descent rate or use part or full automation to maintain the rate of descent. A common method is to use the Vertical Speed (V/S) function on the MCP.

It is important to understand that the VBI has nothing to do with VNAV. The VBI takes the raw distance between the aircraft and a selected altitude point and calculates a vertical bearing to that point. If that point is part of a route in the CDU, then the next altitude constraint will be displayed, unless the user changes this.

Accessing the VBI

Navigate to Descent page on the CDU by pressing the DES key.

At lower right hand side of the DES page you will see the following: FPA, V/B, V/S. This is the Vertical Bearing Indicator.

Key RSK3 (right line select 3) allows manual entry of a waypoint and altitude or altitude restriction. Type the waypoint and altitude separated by a / slash symbol into the scratchpad of the CDU and upload to the correct line. (for example, MHBWM/200).

The VBI provides three fields:

FPA (Flight Path Angle). This is the vertical path in degrees (angle of descent) that the aircraft is currently flying.
V/B (Vertical Bearing). This is the computed vertical path in degrees that the aircraft SHOULD be flying to reach the CDU waypoint or altitude restriction.
V/S (Vertical Speed). This is the vertical bearing (V/B) converted into a vertical speed (RoD) for easy input into the MCP. The V/S is the vertical speed (RoD in feet per minute) required to achieve the displayed vertical bearing (VB).

Observe the vertical bearing. The idle descent in a 737 is roughly 3.0 degrees. Wait until the V/B moves between 2.7 and 3.0 degrees (or whatever descent angle you require based upon your approach constraints) and note the descent rate (V/S). At its simplest level, the V/S can be entered directly into the MCP and is the rate of descent required to achieve the computed vertical path.

If using automation, it will attempt to follow the vertical bearing calculated and displayed on the CDU. For example, if a VNAV descent is activated before the Top of descent (ToD) is reached, the Flight Management System (FMS) commands a 1250 fpm descent rate until the displayed V/B is captured. This is done while maintaining a VNAV connection.

Important Points:

The VBI can be used for any waypoint, fix and altitude and acts in conjunction with the AFDS
The vertical bearing when the aircraft is on final approach calculates data from the Final Approach Fix (FAF) to the runway threshold.

To read an earlier post concerning the Vertical Bearing Indicator.

737-800 Altitude Range Arc and Vertical Deviation Scale and Pointer

Other Approach Aids

Altitude Range Arc (ARA)

A handy feature often overlooked is the Altitude Range Arc (ARA). The ARA is a green coloured half semicircle which can be viewed on the Navigation Display (ND). The ARA indicates the approximate map position where the altitude, as set on the mode control panel is expected to be reached. Once the aircraft is well established on the vertical bearing (V/B) calculated by the CDU, the ARA semicircle should come to rest on the targeted waypoint.

Vertical Deviation Scale and Pointer (VDS)

The Vertical Deviation Scale is another feature often misunderstood. The scale can be found on the lower right hand side of the Navigation Display (ND).

The VDI will be displayed when a descent and approach profile is activated in the CDU (such as when using VNAV). However, the tool can be used to aid in correct glideslope for any type of approach (RNAV, VNAV, VOR, etc). To display the VDI, an appropriate approach be selected in the CDU; however, the flight crew fly a different type of approach without VNAV engaged).

The Vertical Deviation Scale presents the aircraft’s vertical deviation from the flight management computer’s determined descent path (vertical bearing) within +- 400 feet. It operates in a similar way to the Glideslope Deviation Scale on the Instrument Landing System (ILS).

The VDS is a solid white-coloured vertical line with three smaller horizontal lines at the upper, lower and middle section, on which a travelling magenta-coloured diamond is superimposed. The middle horizontal line represents the aircraft’s position and the travelling diamond represents the vertical bearing (V/B).

When the aircraft is within +- 400 feet of the vertical bearing the diamond will begin to move, indicating whether you are above, below or on the V/B target. When the aircraft is on target (middle horizontal line) with the indicated vertical bearing, the FMA will annunciate IDLE thrust mode followed by THR HLD as the aircraft pitches downwards to maintain the V/B.

In some literature this tool is referred to as the Vertical Track Indicator (VTI).

Vertical Development (VERT DEV)

The Vertical Development (VERT DEV) is the numerical equivalent of the vertical deviation scale and is found on the Descent Page of the CDU. The VERT DEV allows a flight crew to cross check against the VBI in addition to obtaining an accurate measurement in feet above or below the targeted vertical bearing. The VERT DEV will display HI or LO prefixed by a number which is the feet the aircraft is above or below the desired glideslope.

The Vertical Deviation Scale and pointer (VDS) will remain visible on the Navigation Display (ND) throughout the approach, and in association with the Vertical Development display on the CDU are important aids to use for Non Precision Approaches (NPA).

Final Call

The traditional method of a step down approach, which was the mainstay used in the 1970s has evolved with the use of computer systems and GPS. In the 1980s RNAV (area navigation) approaches with point to point trajectories began to be used, and in the 1990s these approach procedures were further enhanced with the use of Required Navigational Performance (RNP) in which an aircraft is able to fly the RNAV approach trajectory and meet specified Actual Navigation Performance (ANP) and RNP criteria. From the 1990s onward with the advent of GPS, the method that non precision approaches are flown has allowed full implementation of the RNP concept with a high degree of accuracy.

Although the nature of non precision approaches has evolved to that of a 'precision-like' approach with a constant descent angle, their are operators that widely use these techniques, despite their flaws, weaknesses and drawbacks. Even if modern navigational concepts are used in conjunction with traditional methods, aids such as the VBI, ASR and VDI should not be overlooked. Appropriate cross checking of the data supplied by these aids provides an added safety envelope and avoids having to remember, calculate and rely on ‘back of the envelope’ calculations.

The flight crew landing in Canberra, Australia did not use all the available aids at their disposal. If they had, the loss of vertical situational awareness may not have occurred.

Abbreviations

ANP - Actual Navigation Performance
ARA - Altitude Range Arc
CDU – Control Display Unit (used by the flight crew to interface the with the FMC)
FAF - Final Approach Fix
FMS – Flight Management System
FMA – Flight Mode Annunciation
FMC – Flight Management Computer (connects to two CDU units)
ILS – Instrument Landing System
KIAS - Knots Indicated Air Speed
MAP - Missed Approach Point
MCP – Mode Control Panel
ND – Navigation Display
NPA – Non Precision Approach
RoD – Rate of Descent
RNP - Required Navigation Performance
RNAV - Area Navigation
ToD – Top of Descent
V/B – Vertical Bearing
VBI – Vertical Bearing Indicator
V/S – Vertical Speed
VDS – Vertical Deviation Scale and pointer (also called Vertical Track Indicator)
VERT DEV – Vertical Development

February 07, 2014

Changing Pilot Automation Dependency

February 07, 2014/ Flaps 2 Approach

Although this website primarily discusses construction and flying techniques of the Boeing 737, I believe it's pertinent to include articles that relate to flying in general and have merit to both real-time aviators and virtual pilots.

This article supplements an article that discusses the Speed, VNAV and Altitude Intervention (INTV) system .

Rather than create a link to an interesting article which may at some stage be removed, I’ve copied the article verbatim below. The article which came from Aviation Week Space and Technology is a little long, but well worth a read.

How To End Pilot Automation Dependency

It is foolhardy to draw hasty conclusions about accidents. The investigation into the cause of the Asiana 214 Boeing 777-200ER crash at San Francisco International Airport on July 6 is still in its early stages. While it is not clear exactly how crew performance figured into the accident that claimed three lives, we believe that there is no excuse for landing short on a calm, clear day in a fully functioning jetliner. If the NTSB determines that the 777-200ER ‘s engines and systems were working properly, then how could the Asiana pilots have gotten themselves into that jam?

It may be that the crew was acting primarily as “automation managers” and not remaining sufficiently engaged in actively flying the airplane. It would not be the first time that this has been a factor in an accident . In the final 2.5 min. of the flight, the NTSB says, “multiple autopilot modes and multiple autothrottle modes” were inputted—all while airspeed was allowed to drop far below the 137-kt. target. It also may turn out that software rules governing interaction of the autopilot and autothrottle in the 777 are not intuitive under some settings and problematic for landing (see page 25). But that would be no excuse for flying into the ground.

On balance, automation has been a major contributor to the safer, more efficient operation of airliners. But automation has not reached the point where it can handle all contingencies. We have not arrived at the point alluded to in the joke about the crew of the future being a pilot and a dog (the pilot is there to feed the dog, the dog is there to bite the pilot if he touches the controls). So humans must be prepared to hand-fly an aircraft at any point .

For years now, concern has been growing that airline pilot's basic stick, rudder and energy management skills are becoming weak due to over-reliance on automation systems. Pilots have become, in the words of Capt. Warren VanderBurgh of American Airlines dependent upon computers that generate the purple-pink cues on cockpit displays.

There is nothing inherently risky about using automation, he explains in a famous lecture, but there is a paradox about automation that crews must be aware of: In most situations, automation reduces workload. But in some situations, especially when time is critical, automation increases workload. For example, it is harder to rapidly and correctly reprogram a flight-management computer to avoid a midair collision than it is to turn off automated systems, grab the controls and take evasive action on one’s own.

This addiction to automation is particularly troubling because of the rapid growth of the international airline industry in the last two decades, notably in Asia and the Middle East. Many nations, including South Korea, do not have robust general aviation, light air freight and commuter airline sectors where pilots can amass hundreds of hand-flown takeoffs and departures, arrivals and landings before graduating to the cockpit of an Airbus or a Boeing airplane carrying scores of passengers.

In the wake of the Asiana crash , Tom Brown, a retired United Airlines 747-400 standards captain and former instructor of Asiana pilots , said in an email to friends that while he worked in South Korea, he “was shocked and surprised by the lack of basic piloting skills.” Requiring pilots “to shoot a visual approach struck fear into their hearts.”

Other expatriate training pilots who have worked in Asia and the Middle East tell similar stories about lack of basic head-up airmanship skills and preoccupation with head-down button pushing. They can perfectly punch numbers into the flight-management computer but if something unexpectedly crops up late in the flight, such as an air traffic control reroute close to the airport or a runway change, crews may not have time to punch, twist, push and flick all the controls required for the automation to make critical changes to the aircraft’s flight path. And head-down, they risk losing situational awareness.

This pitfall is not peculiar to developing regions, of course. Advanced automation can lull any crew into becoming mere systems monitors.

So what should be done? The automation dependency paradigm must be changed now. Crews must be trained to remain mentally engaged and, at low altitudes, tactility connected to the controls —even when automation is being employed. They should be drilled that, at low altitudes, anytime they wonder “what’s it doing now?” the response should be to turn automation off and fly by hand.

Aviation agencies need to update standards for certifying air carriers. There needs to be a new performance-based model that requires flight crews to log a minimum number of hand-flown takeoffs and departures, approaches and landings every six months, including some without autothrottle use. Honing basic pilot skills is more critical to improving airline safety than virtually any other human factor.

BELOW: Capt. Warren VanderBurgh’s 'children of the magenta' lecture (also viewable on VIMEO and UTube).