Journal Archive (Newest First)


Flight Controls - General Information

Second to the yoke, a throttle quadrant (TQ) is probably the next important item in the simulator.  How ever there is more to a TQ than thrust levers - a TQ includes functionality for thrust levers, reverse thrust, idle cut outs, flaps, speedbrakes, park brake, trim wheels, horn cut out, stabilizer trim cut out and trim tab indicators.  As with the yoke, if possible it's best to not scrimp in this area as the TQ will be used constantly on all flights.

I have used several  throttles in the past.  At the 'dawn of time' I used a keyboard (FS1) prior to migrating to a throttle manufactured by CH Products, and then to a more higher-end unit manufactured by Precision Flight Controls (PFC).   The TQ used in the simulator currently is an Original Equipment Manufacturer (OEM) Boeing 737-500 throttle unit converted for use in Flight Simulator.

The B737-800 Project uses the following flight controls:

  • OEM B737-500 dual yokes and columns (identical to NG)
  • OEM B737-500 Throttle Quadrant (revamped to NG style)
  • OEM B737-400 Rudder Pedals with custom-made rudder pedal assembly
  • OEM B737-400 Steering Tiller (identical to NG)

OEM is an acronym for Original Equipment Manufacturer (meaning a 'real' aircraft part).

Throttle Quadrants - Historical Perspective

There are several  throttle units commercially available for use in flight simulator, and selecting one is predominately based on what level of realism is sought.

At an early stage, I was moving towards a reproduction throttle quadrant produced by one of several companies such as ThrottleTec or Revolution-Sim. Without going into great detail, I was not convinced that the reproduction throttles provided consistent reliable service for the amount of expenditure required (over $5000.00 USD).

The more downmarket throttles, such as that produced by ThrottleTec did provide consistent operation, however, lacked realism and authenticity. It didn't take much imagination to finally decide on a reconditioned OEM B737 throttle from a real aircraft.

To Avoid Confusion - Throttle Conversions

To date, two OEM throttle quadrants have been converted.  The first throttle converted was from a B737-300 with a two-bay center pedestal.  This was converted  for manual use only by Northern Flight Sim in 2011.  The unit was subsequently sold and replaced, in 2013, by a B737-500 quadrant with a three-bay center pedestal.  This TQ has been converted to NG style with full automation. 

In 2014, this TQ was further modified to improve the automation amongst other improvements.  This final 'rebuild' will be completed in January 2015.

On this website you will find mention of two (2) throttle quadrants and their respective conversions. 

  1. The B737-300 TQ (converted by Northern Flight Simulations and subsequently sold);
  2. The B737-500 TQ converted to NG style; and,
  3. The advanced conversion (rebuild) of the above-mentioned NG style quadrant.

The conversion of the throttle unit has been an 'evolutionary process' and the latest advanced conversion has incorporated high-level mechanical and software engineering.  The design and operation duplicates the systems in the real aircraft and those used in high-level commercial simulators used for pilot training.

First TQ - B737-300 Throttle Quadrant (2011)

I was fortunate to find a throttle quadrant for sale in a tear down yard in Arizona. The throttle came from retired Boeing 737-300 series aircraft and included the full throttle quadrant and center pedestal complete with DZUS rails. The TQ belonged to a South West 737 that plied the continental US for many years.

LEFT:  First TQ - B737-300 throttle quadrant.  This quadrant was not converted to full automation and motorization; therefore, conversion after basic refurbishing wasn't overly difficult.


Historically, autothrottle use has always posed more challenges and problems than what is was worth; however, technology goes forward and the development of specialist interface cards, that superceeded the standard-issue Phidget card, and the continued development of advanced avionic suites such as ProSim737 and Sim Avionics has allowed automation to be improved upon several-fold.

The first TQ, since sold, was not converted for automation as at that time (late 2012) automation was in its infancy.

Second TQ - B737-500 - Full Automation and NG Conversion (2013)

In late 2013, I upgraded the throttle to a throttle that came from a B737-500 series aircraft.  Because of the improvements to automation, this unit was refitted for full automation and motorization.

Controlling Throttle Automation - Controller Cards, Phidgets, DC & Electric Motors

Throttle Automation & Bridging

Automation of the throttle unit is controlled by two Alpha Quadrant motor controller interface cards.  The cards are programmed with logic to automate the operation of the thrust levers when either CMD A or CMD B is selected on the MCP.   The software used is very similar, if not identical to that used to program robotic engineering for mass production as observed in automobile and other factories.  NASA also use similar technology to control the lunar robots used in the space industry.

ABOVE:  The second TQ - A NG style quadrant, still in the crate after delivery.  The various VGA cables and D-Sub plugs can be seen forward of the throttle unit.

A major benefit of using these cards is that it removes the need for the FS2Phidgets library.  In the past with my 300 series throttle the Phidget library caused minor glitches., this being especially evident when using a USB hub.

A high current Phidget motor controller servo card is then used to act as a "bridge" between the two Alpha Quadrant motor controller interface cards and the avionics suite (in this case ProSim737). 

The controller cards are the software behind the automation. 

Phidget, Relay  & Leo Bodnar Cards

Phidget and relay cards have been used to control many of the functions of the throttle unit, such as the accurate movement of the trim tab indicators, Runaway stab trim toggles, movement of the flaps, fire handle operation, and several other functions.  Other buttons and switches located on the throttle are controlled by a Leo Bodnar BU0836X joystick controller card, and FSUIPC is used to assign functionality and calibrate if necessary.

Controlling Trim Wheel Spinning & Movement of Throttle Levers

A Phidget motor controller advanced servo card and high current motor controller card is used to power two DC pump motors that control the movement of the trim wheels (when the aircraft is being trimmed either manually or by the autopilot CMD A or CMD B). 

LEFT:  Backlighting is impressive as the light plates are in excellent condition.

The speed that the trim wheels spin is dictated by the logic supplied by the avionics suite (ProSim737); this logic is identical to that of the real aircraft.  To change the revolutions of the trim wheels, the Phidget card has been set-up using two channels, each channel controls a specific speed.  The speed used is dependent on the level of automation set from the MCP.

An electric motor, previously used to power and move automobile electric windows, is used to power the smooth movement of the throttle levers.   

Logic for Speed Brake and Flaps

Speed Brake

The operation of the speed brake, which replicates the logic observed in the real aircraft, can be either controlled by the logic within the Alpha Quadrant cards or by the flight avionics (ProSim 737). 

LEFT:  New TQ installed and operational.

To enable the speed brake lever to engage at the correct position, a number of micro buttons have been strategically located beneath the plate of the speed brake lever.  Movement of the lever over the switch sends a signal which activates or deactivates four relays that trigger the speed brake logic. 

The mechanical circuit is simplistic in design and allows accurate and trouble free operation that is a mechanical solution to a normally software driven operation.

Speed of Lever Movement

The speed that the lever moved when the spoilers are deployed was an issue on my earlier throttle (it was snail slow).  To solve this problem, a high torque DC motor identical to that used for the movement of the throttle levers has been used.  The motor provides enough power to move the lever at a similar speed observed in the real aircraft.

The DC motors for both the speed brake and the throttle lever movement is mounted forward of the throttle unit.


The flaps lever in most throttle units is controlled by a potentiometer that is calibrated via FSUPIC.  Calibrating with FSUIPC can be troublesome and often the calibration is not very accurate due to the minimal throw of the potentiometer.  Contamination and variance in potentiometer manufacturer (+- tolerances) can also be problematic.

A solution was developed that replaces the potentiometer with a series of micro buttons.  The micro buttons have been correctly positioned on a custom-made bracket that is mounted immediately below the flap arc beneath the flaps lever. The micro buttons are on/off and are activated as the flaps lever is lifted or dropped into the flaps detent position. 

Calibration of the flaps is done directly through ProSim737, FSUIPC is not required.  This method is very accurate and does not require any calibration, tweaking or maintenance.  The use of buttons to replace the minimal throw of a potentiometer allows a complete range of movement from flaps up to flaps 40.

Throttle Improvements / Retrofitting The Last Build (evolution) - Advanced Conversion of B737-500 Throttle Quadrant (2014/15)

Two major alterations to the simulator have occurred.  The first concerns the throttle quadrant and the second is the replacement of the trial Interface Master Module with a more permanent modular solution.  The changes will be documented in the near future after final testing is complete.

LEFT:  The throttle quadrant has been completely rebuilt from the ground up.  Although the outside may appear identical to the earlier quadrant, the rebuild has replaced nearly everything inside the quadrant and the end product is far more reliable than its predecessor.

The throttle unit, in its previous revision, worked well, but there were several matters which needed attention.  The automation and functionality was adequate, but could be improved upon.  There were also 'niggling' issues with how the clutch assembly operated - it was somewhat loose which caused several flow-on problems.

Initially, some minor improvements were to be made; however, one thing lead to another and as 'fate would have it' the throttle unit has been rebuilt from the bottom up.


The improvements have primarily been to the automation, the autothrottle and the speedbrake system.  However, during the rebuild other functionality have been improved: the synchronised movement of the thrust levers is now more consistent and reliable,  and an updated system to operate the parking brake has also been devised.  This system replicates the system used in the real aircraft in which the toe brakes must be depressed before the parking lever can set or disengaged.

Furthermore, the potentiometers controlling the movement of the flaps and thrust levers have been replaced with string potentiometers which increases the throw of the potentiometer and improves accuracy.  The calibration of the flaps and speedbrake is now done within the system, removing the need for 'tricky' calibration in FSUIPC. 

In the previous throttle version there was an issue with the speedbrake not reliably engaging on landing.  This in part was caused by a motor that was not powerful enough to push the lever to the UP position with consistent reliability.  This motor has been replaced with a motor more suitable to the power requirement needed.  The speedbrake is mechanical, mimics the real counterpart in functionality, and does not require software to operate.

This throttle conversion has maintained the advanced servo card and motor that was used to control the movement of the stab trim tabs (trim indicators); however, the motor that provides the power to rotate the trim wheels has been replaced with a more reliable motor with greater power and torque.  The replacement motor, in conjunction with three speed controller interface cards, have enabled the trim wheels to be rotated at four independent speeds.  This replicates the four speeds that the wheels rotate in the real B737.

Finally, the automotive fan-belt system/clutch system which was a chapter from the 'Dark Ages' has been replaced with two mechanical clutch assemblies that has been professionally designed to operate within the throttle unit - this will completely remove any of the  'niggles' with the previous clutch assembly becoming loose and the fan belt slipping.  Each thrust lever has a dedicated slipper-clutch and separate high powered motor. 

The conversion of the throttle quadrant has been a learning process, and the changes that have been done improve the unit's functionality and longevity - not too mention accuracy, far beyond what it was previously.

Dedicated Interface Modules

The throttle previously interfaced with the Interface Master Module (IMM).  The IMM was developed as a trial module to evaluate the modular concept.

The throttle quadrant will now directly interface with two dedicated modules called the Throttle Interface Module (TIM) and Throttle Communication Module (TCM).  Both of these modules contain only the interface cards, relays and other components required to operate the throttle and automation.  Additionally, the system incorporates a revised Interface Alert System which evolved from the original concept used in the IMM.

Navigate to Interface Modules in the main menu to learn more...

Flight Testing (March 2015)

The throttle and replacement interface modules are currently being evaluated and minor issues rectified.

Once testing is complete, the alterations undertaken during the rebuild process will be documented in separate posts and, to facilitate ease of searching, links will be added to the section below.

Journal Posts

The posts that document the conversion of the Boeing 737 throttle to Flight Simulator have generated considerable interest.  To consolidate the posts for retrieval, I’ve provided links to those posts that deal with the conversion of the throttle quadrant.  These links only relate to the B737 NG throttle and do not relate to the B737-300 throttle sold in early 2012.  Any post from 2013 onwards deals ONLY with the new quadrant.

The following links are to posts on this site that relate only to the B737-500 throttle quadrant (converted to NG style).

The links below relate ONLY to the rebuild of the immediately above discussed throttle quadrant.