B737 Throttle Quadrant - Parking Brake Mechanism

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oem 737-500 parking brake lever and light

This post we will briefly discuss the conversion of the parking brake mechanism, and a video will demonstrate the solenoid engaging to move the lever within the mechanism.   The function of the parking brake is self-explanatory.

Parking Brake - Solenoid Auto Release

The parking brake can be engaged or disengaged by either engaging (lifting) or disengaging (pushing down) the park lever, or by depressing the toe brakes located on the rudder pedals. 

In the real aircraft, mechanical linkages and a cam disengage the parking brake.  A solenoid has been installed to replicate this in the simulator.

Interfacing with Flight Simulator

To use the solenoid, a relay card (on/off) and standard toggle-style switch is used.  The relay card is mounted in the Trial Interface Master Module (IMM) and connection from the throttle to the IMM is via a straight-through custom VGA cable. Any brand relay card will do this job.

Red Bulb

The red light is illuminated by a 28 Volt bayonet-style light bulb.  The bulb can be downgraded to 12 Volts; however, the illumination produced will not be as bright as if a 28 volt bulb was used. 

Spring, Solenoid and Toggle

The operation of the park brake lever revolves around four items:

  1. A long rod that connects from the lower section of the park lever to the toggle switch;

  2. A standard on/off toggle-style switch;

  3. A solenoid;

  4. A high tensile spring; and,

  5. A relay card.

parking brake Solenoid attached to port side firewall of throttle unit

When the park brake lever is pushed down or pulled up a corresponding movement of the long rod occurs.  Connected to the lower part of the rod is a standard-style toggle switch and a spring.  The spring is attached to the base of the throttle unit.  Movement of the rod causes the toggle to either be switched on or off (up/down), while the spring provides the tension for the automatic movement of the park lever to occur when the solenoid is energized (the lever is pulled downwards to the disengaged position).  A relay card is connected to the solenoid to control the timing that the solenoid receives power.

Toe Brakes Activation of Park Brake

As in the real aircraft, the parking brake can be released by the pilot depressing the toe brakes. 

There are  two methods commonly used to connect the toe brakes to the release of the park brake lever and parking brakes.  

The first (and easiest) method uses a Phidget 0/0/4 (1014_1) relay card and logic from within FSX or the avionics software (ProSim737), while the second method is a standalone closed system that can be implemented using a double-throw relay and a momentary switch; the switch being specific to the park brake.  For simplicity, I have incorporated the first method into the simulator as ProSim737 and FSX already provide a software solution to release the parking brakes.

Below is a short video showing how the parking brake mechanism operates.

 

737 throttle parking brake mechanism

 

In the next and final post regarding the throttle conversion, we will inspect the movement of the thrust levers during engagement of the Autothrottle (A/T) and discuss some of the teething issues with the throttle conversion.

Update

on 2017-06-26 06:40 by FLAPS 2 APPROACH

In June 2015, this mechanism was replaced with a more reliable system that replicates how the system operates in the real Boeing aircraft.  The system now in place is purely mechanical and does not rely on ProSim-AR for operation (other than registration of the movement of the parking brake lever).