Replacement OEM 737-500 Throttle & Center Pedestal - Conversion to NG Style

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737-300 throttle quadrant with old style paddle-style stab trim levers

The last few months have seen quite a bit of activity regarding the throttle quadrant and center pedestal, which has culminated in me selling my former 737-300 series throttle quadrant and pedestal and replacing it with an another unit from a late series 737-500 aircraft.

Brief Recap

In late 2012, I decided to convert the 737-300 throttle to full automation.  A dilemma I faced was whether to keep the throttle unit as a 300 series throttle with the attached two-bay pedestal, or do a full conversion to make it similar to the Next Generation. 

After careful consideration, it was decided convert the throttle quadrant.so it appeared as close as possible to the Next Generation.

Stab Trim Switches

One of the biggest differences, apart from thrust lever handles, between early model throttle units and the Next Generation units is the stab trim cut out switches.  On the earlier 300 series units, the switches are paddle / lever style switches while the Next Generation uses toggles and T-Locks.  T-Locks are a safety feature and sit beneath the toggle switches and are spring loaded; the pilot must push down the T-Lock to activate the toggle.  

To convert the trim switches requires cutting out the old switches and fitting new reproduction Next Generation switches.  This is a major task requiring precision work.  Although reproduction switches can be made, the reproduction T-Locks don't operate as the real T-Locks should.  I did search for some genuine T-Locks and toggles, however, my search was fruitless as these parts appear to be reused by airlines (or recycled).

Replacement 500 Series Throttle Quadrant & Three-Bay Center Pedestal

A friend of mine informed me that a late model 737-500 throttle quadrant was for sale.  This unit was in better shape than my existing throttle, included the genuine Next Generation style stab trim switches complete with T-Locks, and also had a three-bay center pedestal.  It appears provenance was shining on me as the new throttle appeared for sale a day before the stab trim switches were about to be removed (with a metal cutter...)

The throttle and center pedestal were purchased (you only live once!) and the 300 series throttle sold to an enthusiast in Sweden.

Next Generation Conversion

To bring an earlier style throttle and center pedestal to appear similar to a Next Generation throttle quadrant requires, at a minimum:

  • Attachment of a Next Generation style throttle lever shroud to existing aluminium levers;

  • Removal of TOGA buttons and relocation to bring design in-line with a Next Generation (the buttons are identical, but the housing is different);

  • Possible replacement of the stab trim switches;

  • Painting of throttle housing and center pedestal from Boeing grey to Boeing white; and,

  • Painting of all throttle knobs from Boeing grey to Boeing white.

The biggest hurdle is usually replacing the trim stab switches, however, as these are already present on the new throttle, and are the Next Generation, considerable time and expense was saved in not having to replace them.

Main Differences - Next Generation & Classic

The Boeing airframe that most people associate with today begins with the 737-200 and ends with the 737 Next Generation.  In between we have the classics which refer to the 737-300, 400 & 500 series airframes. The 737 Next Generation series includes the 737-600, 700, 800 & 900 series airframes.

The main differences between a classic and Next Generation throttle quadrant are:

  • The stab trim switches are slightly different; the classics having two flat levers while the Next Generation has toggle-style buttons with T-locks;

  • The throttle thrust lever handles; the classics are bare aluminium and the Next Generation is white aluminium that is ergonomically-shaped.  The TO/GA buttons are also positioned in a different place on the Next Generation.  The knobs (handles) on the levers are also coloured white rather than off-grey;

  • The method that the throttle thrust levers move during automation.  The classics move both thrust levers together when auto throttle is engaged.  The Next Generation moves each lever individually in what often is termed the throttle dance (this is due to the computerised fuel saving measures incorporated in the Next Generation);

  • The spacing (increments) between each flap lever position is identical in the Next Generation, but is different in the earlier series throttles;

  • The center pedestal in the classics is either a two-bay pedestal (early 300 series and before), but more likely a three-bay pedestal.  The Next Generation always has a three-bay pedestal.  Base materials for the center pedestal are also different - aluminium verses a plastic composite material;

  • The speedbrake knob is very slightly more elongated on the Next Generation unit; and,

  • The telephone, circuit breakers and mike assembly differ in type and location

Next Generation Skirt - Thrust Levers

Boeing when they designed the Next Generation style throttle didn’t design everything from new; they added to existing technology.  All Next Generation throttles utilise thrust levers which are identical to those of earlier units.  

Boeing designed a shroud or skirt that attaches over the existing thrust levers encapsulating the older thrust levers and sandwiching them between two Next Generation pieces.  The assembly is made from aluminium and is painted white.

The TO/GA buttons are located in a different position on the Next Generation units, although the buttons used are identical.

To alter the position of the TO/GA buttons you must detach  the small aluminium box from the 300 series thrust levers, remove the TO/GA buttons, and then re-solder the buttons in the appropriate location on the new unit.

I did not make the Next Generation skirt for the thrust levers, but rather had fabricated, from design specifications, a reproduction skirt.  The skirt is produced from aluminium and replicates the dimensions of the Boeing part.

Time-line, Functionality and Conversion

The throttle is initially being converted in the United States.  The advanced work (automation) will be done by a good friend in California, and then I will follow on with more mundane tasks.

The replacement unit will feature several improvements which will allow: full motorized functionality, full speed brake capability, accurate trim tab movement, alternate trim wheel spin speeds, correct park brake release, trim wheel braking and several other features. 

I want the functionality of the throttle to be as close as possible to that found in the real aircraft; therefore, the methods used to ensure this functionality will be slightly different from the norm.

When the throttle is fully functional and tested, I'll publish a post providing further information and detailed photographs of the various functions.

It is hoped everything will be completed, and the throttle and pedestal installed by late May 2013.  The next month or so will be quite exciting.

Two-bay Pedestal Will Be Missed

I know I will miss the narrower two-bay center pedestal.  A major advantage that will be lost is the ease in climbing into and out of the flight deck; the two-bay provided more room between the pedestal and the seats.  At some stage, I probably will need to install J-Rails because the seats I'm using are fixed-claw feet Weber pilot seats; J-Rails will be needed to allow lateral seat movement.

BELOW:  Montage of several images showing main visual differences between 737-300 classic series throttle quadrants and the 737 Next Generation. The 737-300 throttle is my old throttle but, the Next Generation throttle quadrant belongs to a mate of mine.

Montage of several images showing main visual differences between 737-300 classic series throttles and the 737 NG style throttle units. The 300 series TQ is my old throttle unit but, the NG Throttle quadrant belongs to a mate of mine

B737-300 Throttle Full Automation Upgrade

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oem 737-300 throttle formally used by South West Airlines. Note grey coloured throttle levers and raw aluminum handles. The boxes that contain the TOGA buttons can just be seen

The throttle quadrant installed in the simulator is from a 737-300.  When I initially  converted the throttle for flight simulator use, I choose to not have full automation included; automation being at the time fraught with issues in relation to correct and accurate operation.  

Technology rarely remains stationary and after one year of operation I’ve been reliably informed that automation can now be implemented without the problems previously experienced.  Therefore, I’ve crated the throttle quadrant and it’s now on its way to the US via DHL courier for conversion to full automation.  A process I am told that will take a few weeks.

Automation will include, at the minimum, the following:

  • 4 speed trim wheels dependent upon aircraft status (as in the real aircraft)

  • Accurate trim tab movement

  • 9 point speed brake (speed brake operation as in the real aircraft)

  • Full automation of throttle thrust handles as per MCP speed window and/or CDU

  • Hand brake release by depressing brake pedals (as in the real aircraft)

I don’t mind admitting that that my building abilities don't include complete knowledge on how to convert a 737 throttle correctly - especially in relation to automation; therefore, this task has been outsourced.

The method in which automation will be achieved is slightly different from the usual way throttles are converted, and includes some magic programming of chip sets and machining of parts to allow compatibly with ProSim737.  Taking into account Christmas and New Year, I'm hoping that the machining, installation, configuration and testing will be completed by January (2013) and the throttle will be re-installed into the simulator by February.

In a future post, I will explain the process of conversion, and how automation has been achieved with minimal use of add-on software.

Idle Time

Although the throttle quadrant and pedestal will be absent from the simulator for a short time, work will not be idle.  The conversion of the twin real B737 yokes and columns has been completed and I'm finalising installation of the second platform which incorporates linked 737 rudder pedals.  I am hoping this will be completed by mid-November.  I have discussed the new platform in a previous post.

Throttle Thrust Problem - Loosing Thrust at N1 - The Solution

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oem 737-300 throttle

The throttle installed into the simulator is a converted genuine B737-300 throttle.  Lately, I have observed inconsistent power thrust issues during the take off roll and climb out. 

As I begin the take off roll, engage TO/GA and rotate, but before acceleration altitude or acceleration height is reached, one of the throttles looses or gains power.  Moving the throttle handle reinstates throttle power, but the power is dependent on where the actual throttle lever is physically positioned. 

When the aircraft is above thrust reduction altitude (1500 radio altitude) the problem rectifies itself.  The problem cannot be replicated when flying above 1500 feet.  I also noted, and this may also be part of the issue, that the power indicators located on the EICAS display fluctuate (twitch) a little as I moved the throttle levers.

This problem only began to occur after I transferred the avionics software to ProSim737.

Process of Elimination

Problems like this are not uncommon when interfacing real aircraft parts and the challenge is finding the cause of the problem.  The only method to determine solutions to problems such as this is to systematically, through the process of elimination, identify the problem area.

My first thought was that one of the potentiometers in the throttle quadrant maybe damaged, although I considered this to be unlikely as the units are still relatively new.  The throttle has four potentiometers: throttle 1, throttle 2, flaps and spoilers. Flight testing indicated that the power loss alternated between engine 1 and engine 2; therefore, the likelihood of two potentiometers failing at the same time was minimal. 

The next step involved checking the wiring within the throttle quadrant, to ensure there wasn’t damage to the outer coating of the wires.  A damaged or loose wire can easily short on the throttle frame and generate a spike.  However, if the wiring was loose or damaged, the problem would also occur when flying at altitude, and I had clearly demonstrated that the problem only occurred during the take off roll and climb out to thrust reduction altitude. 

The next step was to ensure that calibration of the throttle unit was correct.

Re-Calibration Using FSUIPC

I decided to re-calibrate the throttles using FSUIPC rather than FSX.  This process isn’t difficult and FSUIPC allows you to fine tune each throttle with greater accuracy than is possible with FSX. 

After re-calibration, the “twitching” of the power indicators ceased, but the initial problem remained.

The Cause of the Problem

The only culprit I could think of to cause this problem was ProSim737.

To check whether ProSim737 was actually the cause of the problem, it is necessary to remove any input from the ProSim737 software.  This is straightforward.  Either use another avionics software package or use FSX itself.  I did twenty trial flights using both Sim Avionics and FSX and the problem did not replicate. 

ProSim737 Excellent Support and Advice

I contacted the developers at ProSim737 explaining my problem in detail, and I received a response to my questions within a few hours.  Marty was especially helpful and we discussed several potential reasons for this issue and possible workarounds.  I must stress that the response I received from ProSim737 was absolutely 100% top notch. 

Marty genuinely wanted to help resolve the issue – whether it be with ProSim737 or otherwise.

Real B737 Throttle Operation

Now this where the comment “as real as it gets” does have meaning…. 

The developers of ProSim737 have designed their software to replicate the logic used by the real B737 auto throttle.  The software (ProSim737) is doing exactly what it’s supposed to do in relation to power thrust, and the issue I was experienced is caused by using a real aircraft throttle without automation.  Let me explain.

In the real aircraft, when TO/GA is enabled, the auto throttle logic has control of the aircraft.  The throttles are off-line and power thrust cannot be manipulated by the pilot.  The flight mode annunciator (FMA) illuminates N1. 

As 84 knots is passed the FMA changes from N1 to THR HOLD.  At this time, the actual throttles come back on-line, meaning that you can manually alter throttle power by moving the levers.  After rotation and at 800 radio altitude the auto throttle system is ready to change from take off power to climb power and the FMA changes from THR to ARM.  When in ARM mode the throttles are still on-line. 

When the aircraft reaches 1500 RA which is the thrust reduction altitude, the throttles go off-line and the AT logic is controlling the power thrust of the throttles.  The FMA changes from ARM to N1.

Throttle Anomaly

The B737 does not have a manual throttle, but an automated throttle.  The software is programmed to move the throttle levers to the correct position mimicking the actual power thrust called for by the auto throttle logic.

If you use a manual throttle (genuine or otherwise) the connection to the automated physical movement of the throttle levers is missing; you must counter this by moving the levers yourself.  This issue should not occur with a correctly calibrated automated throttle.

Using an Auto-throttle

If you have an auto throttle, the levers will automatically and physically move to the indicated thrust position as determined by the auto throttle logic (90%N1 at TO/GA).  When the FMA illuminates THR HOLD at 84 knots, and the throttles come back on-line for possible pilot intervention, the auto throttle logic will not sense any change in the throttle lever position, and power thrust (90%N1) will be maintained.   This is because the automated system placed the throttle levers in the correct position when TO/GA was initiated.

Using as Manual Throttle

However, if you’re using a manual throttle, the throttle levers MUST be physically positioned at the correct location on the throttle quadrant, otherwise the auto throttle logic will sense a change in position of the levers and alter the power thrust accordingly to this new level. 

This is what was occurring in my situation.  I was resting my hand on the throttle and only advancing the levers 3/4 of the way forward.  TO/GA indicated 90%N1, but when the throttles came on-line at 84 knots, the auto throttle logic noted that the position of the throttle levers was not at 90%N1 and subsequently altered the power thrust accordingly.

The reason the issue was inconsistent is that I didn’t always advance the throttle levers to the same position, and if I did the problem did not occur.

LEFT:  B737-300 throttle quadrant converted to Flight Simulator use.  The TQ is a manual throttle meaning that the thrust levers are not automated and must be moved manually.  I have used a pencil to lightly mark the metal adjacent to the most commonly used N1 settings.  This ensures the levers are moved the correct location during take off.  Lever position is set to 90%N1 and flaps 5.

Solution – Change in Procedures

The solution to this anomaly of using a real “manual” throttle is relatively simple.

You must determine where on the throttle quadrant the various N1 power settings are and then ensure, after engaged TO/GA that you move the throttle levers to the correct position (90%N1).  In my situation, the procedure is to advance the throttle to 40%N1, engage TO/GA, and then manually push the throttle levers to 90%N1.

Thank you

I’d like to thank Marty at ProSim737.  Marty worked with me to solve the issue, which ultimately was not really a problem with either ProSim737 or my set-up, but is an anomaly of using a genuine throttle unit without automation.

Possible Update

I may update the throttle quadrant to enable automation of the throttle levers and speed brake, however, for the time being the throttle quadrant will not include automation.

Update

on 2013-04-23 23:56 by FLAPS 2 APPROACH

 

diagram 1: a clear diagram that helps explain the problem discussed in the article (thanks to frazier @ prosim737 forum)

 

OEM 737-300 Throttle Quadrant

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oem 737-300 throttle quadrant in tear down yard

I was surprised to find an OEM throttle quadrant, at more or less the same time that I was about to purchase a reproduction throttle.

The throttle quadrant was used in a South West 737-300 series airframe and has a two-bay center pedestal.  The two-bay pedestal will suffice until a three-bay pedestal can be found.

The pedestal still has undamaged DZUS rails so it should be an easy matter to drop in avionics panels (radios, etc).

Proposed Conversion

The Throttle quadrant will be completely dismantled, cleaned and serviced.  Parts that are not required for simulation will be removed.  The lower section of the throttle and center pedestal will be removed as this is not necessary when installing the items to flat platform.

Any cards and other items needed to convert the throttle for flight simulator will be either mounted forward of the throttle on the forward bulkhead, or be hidden from sight in the center pedestal.  USB cabling will be routed along the lower side of the throttle to emerge from the forward bulkhead, and then will be connected to a computer.

The throttle will be converted using Phidget cards and servo motors.

Although the throttle is not going to be motorised (the thrust levers will not move automatically), the use a a DC motor will enable the trim wheels to rotate and the trim tab indicators to move.

Finally, a fresh coat of paint will be applied to the throttle and pedestal and any damaged transfers replaced.

oem 737-300 throttle quadrant in tear down yard

Original Equipment Manufacture (OEM)

A major advantage when using an OEM component such as a throttle is the added realism and immersion, not too mention that it's almost impossible to break an OEM throttle. 

One thing that I found interesting when searching for the throttle quadrant, was the number of throttles that are superficially damaged or are in poor condition.  Often the throttle and pedestal is scratched, dented and stained.  Investigating this further, I learnt that it's not so much the pilots that are doing this, but the dismantling crews.  Throttles are heavy and unwieldy and a dismantling crew has little time to worry about scratching a throttle that is probably going to scrap.

I have been fortunate in that the throttle and pedestal had been removed from the scrapped aircraft relatively carefully.

The pictures shown here were sent to me by the company who dismantled the aircraft.

Update

on 2020-07-14 23:24 by FLAPS 2 APPROACH

I've just received an e-mail from Florida stating the TQ has landed safely and in good order.  Next will be the transition from a scraped throttle quadrant to a working unit.  The timeline for the conversion is around 3-4 weeks.  If everything works out as anticipated, and freight is not delayed, I am expecting delivery to Australia sometime in early October.  Everything is green for go!  :)

Update

on 2020-07-14 23:27 by FLAPS 2 APPROACH

737-300 series throttle dismantled for cleaning.  You will immediately notice the massive internal cogs that control the internal mechanism; it makes a Swiss watch mechanism dim by comparison

After returning from a work trip to east Africa, I have been told that the throttle quadrant has been refurbished and wired to connect to flight simulator.  All that's remaining is to repaint it to Boeing grey.

Rather than repaint the actual throttle levers and knobs in white to replicate the colour scheme used by a Next Generation throttle, I have opted to leave the colour of the handles as they are.  The levers and knobs of the throttle (after cleaning) were in exceptionally good condition, and it seems a shame, almost criminal to repaint them.

Therefore, although the MIP is a simulation of a Next Generation airframe, the throttle quadrant will remain as a 300 series quadrant.  In many respects, simulation is about compromise, and to destroy an historical 300 series throttle to replicate a Next Generation throttle doesn't seem the right thing to do. 

Update

on 2020-07-14 23:32 by FLAPS 2 APPROACH

Not long now...   I spoke with my friend in Florida this morning and he informed me the throttle conversion has been completed. 

The throttle will soon be travelling as cargo to Australia either by United Airlines or Qantas for I hope a late October delivery.

Update

on 2011-10-16 07:10 by FLAPS 2 APPROACH

The throttle quadrant is finished and is finally in the air winging its way from the US to Australia.  After a stint in Australian Customs, it will then be send across Bass Straight and on to Hobart - its new home.  The next phase will then be the addition of avionic panels to the pedestal and connection and configuration to flight simulator.

Genuine 737 Throttle Quadrant - Found One

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oem 737-300 throttle quadrant as removed from aircraft

After considerable research I've learnt there are very few reproduction throttles that match the functionality and robustness of the OEM throttle.

Revolution-Sim, a company in France appears to produce an exceptionally well designed quadrant, however, not with an inexpensive price tag.  Contacting Revolution-Sim is also difficult as they do not respond to e-mails.  ThrottleTec produce a very good intermediate throttle that is reasonably priced, however, the throttle's appearance is different to the OEM throttle and it looks like a toy.

Fortunately, I have been able to find an OEM 737 throttle from a aircraft tear down yard.

If I manage to purchase this throttle, my intention is to refurbish the throttle and have it retrofitted, using Phidgets, to function with flight simulator.  How this will be done eludes me for the time being.

Although motorizing the throttle so that the autothrottle moves the thrust levers is the holy grail I have been reliably informed that attempting to do so will probably cause more problems than it's worth.  Therefore, the throttle will not be motorized.   This doesn't concern me greatly as most of my virtual flying is done manually (hand flying).

I must confess that the feel of a real throttle in your hand leads no limit to the imagination!