E-mail Subscription

Enter your email address:

Delivered by FeedBurner

Syndicate RSS

Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.


Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).


All funds are used to offset the cost of server and website hosting (Thank You...)

No advertising on this website - EVER!


Find more about Weather in Hobart, AU
Click for weather forecast






If you see any errors or omissions, please contact me to correct the information. 

Journal Archive (Newest First)

Entries in OEM Aviation Parts (5)


V1-Avionics, ARINC 429 Protocol & SIM429-11 Interface - Interfacing OEM Aviation Parts

There’s nothing like using a genuine aviation part in Flight Simulator.  Real parts are made to last, cannot be upgraded, and offer a level of immersion rarely attributable to a reproduction part.  There is also the historical perspective knowing what airframe the part was removed from.  This said, although OEM parts are not difficult to find, a solid level of ability is needed to successfully convert many parts to use in Flight simulator.  

Conversion of an OEM part can involve  re-wiring, determining the pin-outs for each function of the part, interfacing with an appropriate card such as a PoKeys or Phidget card and connecting to a suitable power supply.  OEM parts that are more complicated in nature may involve further work to determine functionality and necessitate several interface cards and relays for correct operation.

ARINC 429 Protocol & SIM429-11 Interface

Put very simply, ARINC 429 is a data communication protocol used on most higher-end commercial, military and transport aircraft.  The protocol defines the physical and electrical interfaces to support an aircraft’s avionics instruments.  

LEFT:  SIM 429 enclosure by V1-Avionics - compact and easy to install (image copyright V1 Avionics).

With knowledge of the protocol, many instruments can be converted for flight simulator use if an appropriate avionics interface is used between the simulator and the OEM part.  

V1 Avionics has developed a low-cost interface called the SIM429-11 Interface.  This interface will allow easy connection of OEM instruments avoiding the necessity of rewiring and conversion.

Whilst the Protocol is used by many OEM parts, it is not used by all; therefore, if the Protocol is not supported, conversion of that part to Flight Simulator will still be the traditional way using an interface card.


V1-Avionics is the company behind the development of the SIM429-11.  The project team comes from a background in telecommunications, engineering and aerospace applications and is ideally positioned to unravel the intricacies of the ARINC 429 Protocol, to develop, and eventually release the SIM429-11 interface for public use.

Once the interface is released, conversion of OEM avionics instruments will become easier, more streamline, and within the reach of all flight simulator enthusiasts.

I'll post additional information as this technology unfolds.

For further information on the interface, additional photographs, diagrams and videos - navigate to the V1-Avionics website.


OEM - Original Equipment Manufacture (real aviation parts)


B737 Throttle Quadrant - Automated Thrust Lever Movement

In this final post dealing with the conversion of the throttle quadrant, we will discuss the automation and movement of the throttle thrust levers and look at some of the teething problems encountered during the throttle conversion.  We will also briefly discuss the use of potentiometers.  Part of this post will be repetitive as I briefly discussed automation in an earlier post.

LEFT:  The Autothrottle arming switch is a solenoid operated switch clearly identified on the main Instrument Panel (MCP).  The switch is linked to the IAS/MACH speed window (adjacent) and to two A/T disconnect buttons located either side of the throttle lever handles.

Avoiding Confusion - Automation

To avoid confusion, automation refers only to the movement of the two throttle thrust levers in relation to the %N1 output.  These N1 limits and targets are provided by the Flight Management Computer (FMC) and normally are used by the Autopilot Flight Director System (AFDS) and the Auto Throttle (A/T) to maintain airspeed and/or thrust setting.  

Automation and Movement - Interface Cards

Essentially, automation is the use of CMD A or CMD B (autopilot) to control the %N1 outputs from the Autothrottle (logic), and motorization is the moving of the throttle levers in unison with %N1 output.  To acheive this seemlessly, two interface and one controller card are used.

Alpha Quadrant Cards (2):  Each  motor controller card has the automation logic programmed directly to the card (via propiety software).  One card controls Auto Pilot CMD A while the other card controls Autopilot CMD B.

Phidget Advanced Servo Card (2):  This card acts as an interface and bridge between the Alpha Quadrant cards and the flight simulator platform used.

The card does not provide movement for the throttle thrust levers; this is controlled by a Phidget Motor Controller card.

Leo Bodnar BUO 836 A Joystick Controller Card:  This card will register in Windows the movement of levers, buttons and switches on the TQ.  Calibration of this card is done first in Windows, then in Flight Simulator (FSX/P3D), FSUPIC or the avionics suite used; for example, ProSim737.

The interface cards are mounted forward of the MIP within the Throttle Interface Module (TIM) and are connected to the throttle unit by custom VGA cables and to the computer by a single USB cable.

Main Controller Cards

The controller card I have used is not a Phidget card but a specialist card often used in robotics (Alpha Quadrant card).  The software to program the card has been independently developed by a software engineer and does not utilize Phidgets.

The technology used in the controller card is very similar to that utilized by NASA to control their robotic landers used in the space industry.  The technology is also used to control robots used in the car industry and in other mass production streams.  One of the benefits of the card is that it utilizes a software chip (firmware) that can be easily upgraded ore replaced.  

The Alpha Quadrant cards provide the logic from which the automation of the throttle unit operates.  The cards act a 'bridge' between the card and the avionics suite - "call it a language transfer if you will."

Being able to program each card allows replication of real aircraft logic and systems.  Whenever possible, these systems and their logic have been faithfully reproduced.

CMD A/B Autopilot - Two Independent Systems

Most throttle units only use one motor controller card which controls either CMD A or CMD B; whichever autopilot you select is controlled by the same card.  

In the real aircraft to provide for redundancy, each auto pilot system is separate.  This redundancy has been duplicated by using two Alpha Quadrant controller cards, rather than a single card.  Each controller card has been independently programmed and wired to operate on a separate system.  Therefore, although only one CMD is operational at any one time, a completely separate second system is available if CMD A or B is selected on the MCP.

Synchronized or Independent Lever Motorization

Synchronization refers to whether the two throttle thrust levers, based upon separate engine %N1 outputs, move in unison with each other (together) or move independently.

In the real aircraft, on earlier airframes (B707, B727 & some B737 classics), the levers were synchronized; however, the NG has a computer-operated fuel control system which can minutely adjust the %N1 of each engine.  This advanced fuel management can be observed in a real aircraft whereby each throttle lever creeps forward or aft independent of the other lever.

Programming flight simulator to read separate %N1 outputs for each engine and then extrapolating the data to allow two motors to move the throttle levers independently is possible; however, the outputs are often inaccurate (for varying reasons).  This inaccuracy can often be observed on reproduction throttle units that exhibit a gap between lever one and lever two when automating %N1 outputs.  

It was decided to maintain the older system and have both levers synchronized.  Although this is not replicating the NG system, it does make calibration easier.  If in the future incremental thrust lever movement is required, then it’s a matter of adding another 12 Volt motor to the front of the throttle bulkhead to power the second thrust lever.  

Be aware that although both thrust levers are synchronized, the throttle handles may still show a slight difference in position in relation to each other.  This is caused by the varying tension that needs to be maintained on the fan belt connecting the 12 Volt motor to the mechanical system beneath the thrust levers.

LEFT:  Autothrottle activation will advance both thrust levers in unison to a defined %N1 output.

Another aspect to note is that the position of the thrust levers during automation is arbitrary and is a visual representation of the %N1 output; it may or may not reflect the exact position on the throttle arc that the thrust lever would be placed if moved manually (by hand with Autothrottle turned off).  

Although the TQ is automated, manual override (moving the thrust levers by hand) is possible at any time as long as the override is within the constraints of the real aircraft logic and that provided by the flight avionics (ProSim737).  

Power Requirements and Mechanics

To provide the power to move the throttle thrust levers, a 12 Volt motor previously used to power electric automobile windows, is mounted forward of the throttle bulkhead (see image at bottom of post).  Connected to the motor's pulley is a fan belt that connects to the main pulley located beneath the thrust levers.  To enable the thrust levers to move in unison, a slip clutch, which is part of the main pulley assembly, is used.  

ProSim737 Limitations - TO/GA and Auto Throttle Override

Unfortunately, concerning automation the ProSim737 is deficient in two areas: TO/GA and A/T Override (see postscript below).

LEFT:  Captain-side TO/GA button is clearly seen below lever handles.  The button at the end of the handle is the Auto Throttle disconnect button.

(A)  TO/GA

In the real aircraft, the flight crew advances the thrust levers to power 40%N1 (or to whatever the airline policy dictates), allows the engines to spool, and then pushes the TO/GA button/s.  Pressing TO/GA causes the throttle to go on-line and to be controlled by the AFDS logic.  The throttle levers then advance automatically to whatever %N1 the logic deems appropriate based on takeoff calculations.

As at the time of writing. If you're using ProSim737, this will NOT occur.  Rather, you will observe the thrust levers retard before they advance (assuming you have moved the thrust levers to %40 N1).  The reason for this is nothing to do with how the throttle is calibrated, FSUPIC or anything else.  ProSim737 software controls the %N1 outputs for the automation of the thrust levers and the developer of the software has not fine-tuned the calibration in the software to take into account real-world avionics logic.  This thread located on the ProSim737 forum provides additional information. 

I have not tested Sim Avionics, but have been told this issue doesn't occur in their avionics suite.

There are two workarounds:  Engage TO/GA from idle (hardly realistic) or push the thrust levers to around 80% N1, allow the engines to spool, then push TO/GA.  Anything less that around 80% N1 will cause the thrust levers to retard before advancing.


The latest version of ProSim (V-133) has provided improvement to the above issue.  Throttles can now be advanced to ~60% N1 and TOGA engaged without the throttle levers retarding.  This is possible ONLY if you calibrate the throttle levers within ProSim and allow ProSim to control the throttle output logic.  if you calibrate within FSUPIC then the same issue will apply.

According to ProSim developers, this issue is probably related to the calibration of the ProSim servo output. When you press TO/GA, the current N1 is taken and calculated back to a throttle percentage. This throttle percentage, when combined with the servo calibration data from ProSim results in a servo output. The servo calibration at the moment only has 2 calibration points, which are 0 and 100%. This results in a linear behavior between the two points, while depending on the construction of the throttle, the relationship might be non-linear. This would require a multi point calibration which is hard to do at the moment, because a throttle does not have exact readouts of the current position, so it will be hard to calibrate a 50% point.

This may need improvement in the code to auto calibrate the throttle system.

It's hoped that fuutre relase of ProSim will rectify this issue.

(B) Autothrottle Manual Override

In the real aircraft, manual override is available to a flight crew and the thrust levers can be retarded with the Autothrottle engaged.  When the flight crew release pressure on the thrust levers the Autothrottle will take control again and return the thrust levers to the appropriate position on the throttle arc dependent upon the speed indicated in the speed window of the MCP.

ProSim737 will not temporarily disconnect (manual override) the Autothrottle.  

At the time of writing, there is no workaround to solve this.

Potentiometers - Two Types; Which is Best

There are two types of potentiometers.  The first type, (I will call them standard potentiometers) are inexpensive, often have a +- percentage variance, are compact, have a minimal throw depending upon the size of the device and are not contaminate free.  

The last point is worth mentioning as it is wrongly assumed that a potentiometer will remain correctly calibrated for the life of the unit.  General wear and tear, dust and other debris will accumulate on the potentiometer; any of which may cause calibration and accuracy problems.  Keeping the potentiometers free of dust is important.

The second type of potentiometer is called a string potentiometer (strings).  Contrary to the standard type, strings are very accurate, are in a sealed unit presenting zero contamination, are manufactured to exacting standards, are larger in size and are expensive.

The difference in size between the two potentiometer types is often the reason for using the smaller standard type.  The strings are very long requiring quite a bit of real estate either forward of the throttle bulkhead or within the center pedestal.  In contrast, the standard potentiometers are quite compact; finding a position to install them is not problematic.

Calibration of Potentiometers

The main method of calibrating the position of the thrust levers is by calibrating the potentiometer in Windows, then in FSX followed by fine-tuning in FSUPIC (if needed).  

Standard potentiometers are used in the simulator; therefore, at some stage cleaning or replacement of a potentiometer maybe necessary.   The 737 throttle quadrant is not cavernous and only certain sized potentiometers will fit into the unit; this combined with other parts and wiring means that the potentiometers are often inaccessible without removing other components.  

To allow speedier access to the potentiometers, a Quick Assess Mounting Plate was designed.

Quick Access Mounting Plate (QAMP)

The potentiometers are mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws.   To access the plate, the side inspection cover of the throttle is removed (a few screws) followed by turning the thumb screws on the access plate.  This releases the plate.

LEFT:  QAMP secured to base of throttle unit.  Thumb screws are visible on each corner of the plate.  A possible add on modification to reduce the risk of dust contamination to the potentiometers is a plastic cover that fits over the plate (a lunch box).

A similar plate has been designed and constructed for use with the stand-by potentiometer that controls the flaps.  A more detailed picture of the QAMP can be seen here in an earlier post.

Below is a video showing the movement of the thrust levers with the Autothrottle (A/T) engaged.  The movement of the thrust levers is in real time according to flight parameters during the test flight and has not been instigated by overriding the servo. 

Teething Issues with the Throttle Conversion

It was envisaged that more problems would have surfaced than have occurred.  The major issues are outlined below:

(A) Trim Wheels

An early problem encountered was that the trim wheels when engaging generated considerable noise.  After checking through the system, it was discovered that the two-speed rotation of the trim wheels were causing the two nuts that hold each of the trim wheels in place to become loose.  This in turn caused the trim wheels to wobble  slightly generating undue noise.  


Tighten the two nuts at the end of the rod that holds the two trim wheels in place.

(B) Flaps 5 Not Engaging

The problem with the flaps 5 micro-button has been discussed in an earlier post.  To summarize, when you moved the flaps lever to flaps 5 the correct flaps were not selected on the aircraft or registered on the PoKeys 55 interface card.  Several hours were spent checking connections, micro-buttons, wiring and the custom VGA cables that connect the flaps section of the quadrant to the appropiate interface module; the problem could not be discovered.  


One of the two Belkin powered hubs located within the IMM had been replaced with another powered unit.  It appears the problem was that the replacement hub had too low a voltage, as a replacement with a higher voltage solved the problem.

(C) Throttle Thrust Levers Not Synchronizing (A/T on)

The two thrust levers of the quadrant did not synchronize when the Auto Throttle (A/T) was engaged; one lever would always be ahead or behind of the other.  At other times they would split apart (do the splits) when A/T was engaged.  


The problem was easily solved by altering the tension on the slip clutch nut.  When the nut was  tightened, both levers moved together as one unit.  The secret was finding the appropriate torque.

(D) Throttle Thrust Levers Difficult To Move in Manual Mode (A/T Off)

The ability to move the thrust levers in manual mode (Autothrottle turned off) was not fluid and the levers occasionally snagged or were sticky when trying to move them.  

This is caused by the fan belt not moving smoothly through the groove of the pulley wheel.   The Autothrottle when engaged overrides any stickness due to the power and torque of the Auto Throttle motor.


Unfortunately, there isn’t a lot you can do to rectify this issue as it’s a by-product of using a mechanical system in which the fan belt is central to the consistent operation of the unit.  

LEFT: The fan belt is barely visible linking the pulley of the motor to the main pulley inside the quadrant.

The conundrum is that if you tighten the fan belt too much you will be unable to manually move the thrust levers as they will be exceptionally stiff and difficult to move (as you are pushing against the tension of the fan belt); however, if you loosen the fan belt too much, although the levers will move fluidly by hand, the fan belt may not have enough tension to move the levers when Auto throttle is engaged.  It’s a matter of compromise; selecting an appropriate in-between tension to allow acceptable manual and Autothrottle operation.

A more reliable method is to use a small gearbox, a simple slip clutch and a coupler to connect to the spur gear.  Another option is to use an electrical system.

Further thought needs to be done in this area before a decision is made to replace the fan belt system.  If a new system is incorporated, the change-out will be documented in a future post.


This brings us to the end of the throttle conversion.  The following links will take you to other posts regarding the conversion.  

B737 TQ - General Overview
B737 TQ - Speedbrake Conversion and Use
B737 TQ - Flaps UP to 40; Conversion and Use
B737 TQ - Trim Wheels and Trim Indicator Tabs
B737 TQ - Parking Brake Mechanism

Despite some of the shortcomings to this conversion, in particular the mechanical fan belt system, the throttle unit shows a marked improvement on the earlier 300 series conversion.

Technology and innovation rarely stand still and there is little doubt other ways will evolve to achieve similar results with greater efficiency.

Acronyms and Glossary 

AFDS - Autopilot Flight Director system
A/T – Autothrottle
CMD A/B - Autopilot on/off for system A or system B
Flight Avionics Software - Sim Avionics, ProSim737 or similar
FMC - Flight Management Computer
MCP - Main Control Panel
QAMP – Quick Access Mounting Plate
Throttle Arc – The arc of the thrust levers from the end of the blocks to fully forward.  The term refers to the curved piece of aluminum that the throttle levers are moved along
TO/GA - Takeoff Go-around switch
%N1 -  Very simply explained, %N1 is throttle demand and as N1 (and N2) spin at absurdly high speeds, it is easier to simply reference a percentage and display that to the crew. It's much easier for our brains to interpret a value on a scale of 0-100% rather than tens of thousands of RPM 


B737 Throttle Quadrant - Speedbrake Conversion and Use


The speedbrake serves three purposes: to slow the aircraft in flight (by incurring drag), to slow the aircraft immediately upon landing, and to assist in the stopping of the aircraft during a Rejected Takeoff (RTO).  

There are four speedbrake settings: Down (detent), Armed, Flight Detent and Up. 

In addition, there are three speedbrake condition annunciators (lights), located on the Main Instrument Panel (MIP), that annunciate speedbrake protocol.  They are: Speedbrake Armed, Speedbrakes Do Not Arm and Speedbrakes Extended.  These annunciators (lights) illuminate when certain operating conditions are triggered.

This post is rather long as I've attempted to cover quite a bit of ground.  The first part of the post relates to technical aspects while the second portion deals with conversion.  Hopefully, the video at the end of this post will help to clarify what I have written.

Technical Information

Speedbrakes consist of flight spoilers and ground spoilers. The speedbrake lever controls a 'spoiler mixer', which positions the flight spoiler power control unit (PCU) and a ground spoiler control valve.   The surfaces are actuated by hydraulic power supplied to the power control units or to actuators on each surface.

Ground spoilers operate only on the ground, due to a ground spoiler shutoff valve which remains closed until the main gear strut compresses on touchdown (this is activated by the squat switch).

In Flight Operation

Actuation of the speedbrake lever causes all flight spoiler panels to rise symmetrically to act as speedbrakes.  The lever can be raised partly or fully to the UP position.  This causes the extension of the flight spoilers to the equivelent full up (ground spoiler) position.

Ground Operation

All flight and ground spoilers automatically rise to full extension on landing, if the speedbrake lever is in the ARMED position and both throttle thrust levers are in IDLE. When spin-up occurs on any two main wheels, the speedbrake lever moves to the UP position, and the spoilers extend.

When the right main landing gear shock strut is compressed, a mechanical linkage opens a hydraulic valve to extend the ground spoilers.  If a wheel spin-up signal is not detected, the speed brake lever moves to the UP position, and all spoiler panels deploy automatically after the ground safety sensor engages in the ground mode.

After touchdown, all spoiler panels retract automatically if either throttle thrust lever is advanced. The speedbrake lever will move to the DOWN detent.

All spoiler panels will extend automatically if take-off is rejected (RTO) and either reverse thrust lever is positioned for reverse thrust. Wheel speed must be above 80 knots in order for the automatic extension of the spoilers to take place.

A failure in the automatic functions of the speedbrakes is indicated by the illumination of the SPEEDBRAKE DO NOT ARM Light. In the event the automatic system is inoperative, the speed brake lever must be selected manually placed in the UP position after landing by the pilot not flying.

Speedbrake Lever Movement

The logic relating to the position of the speedbrake lever is:

DOWN (detent)

  • All flight and ground spoiler panels are in the closed position.


  • Automatic speedbrake system armed.
  • Upon touchdown and activation of the squat switch, the speedbrake lever moves to the UP position and all flight and ground spoilers are deployed.


  • All flight spoilers are extended to their maximum position for inflight use.


  • All flight and ground spoilers are extended to their maximum position for ground use.

Illumination of Speedbrake Condition Annunciators (lights)

The logic relating to the illumination of the annunciator condition lights is:

Speedbrake Armed Annunciator

  • The light will not illuminate when the speedbrake lever is in the DOWN position.
  • The light illuminates green when the speedbrake is armed with valid automatic system inputs.

Speedbrake Do Not Arm Annunciator

  • The light will not illuminate when the speedbrake lever is in the DOWN position.
  • The light indicates AMBER if there is a problem (abnormal condition).
  • The light will illuminate during the landing roll following through 64 KIAS provided the speedbrake lever has not been stowed.  The light will extinguish when the aircraft stops or when the speedbrake lever is stowed.

Speedbrakes Extended Light

  • The annunciator illuminates AMBER pursuant to the following conditions.

In Flight

  • Amber light illuminates if speedbrake lever is positioned beyond the ARMED position, and
  • TE flaps are extended more than flaps 10, or
  • Aircraft has a radio altitude (RA) of less than 800 feet .

On The Ground

  • Amber light if the speedbrake is in the DOWN (detent) position.
  • Amber light if the ground spoilers are not stowed.

It is important to remember that the speedbrakes extended annunciator will not illuminate when the hydraulic systems A pressure is less than 750 psi.

Simulator Operation - What Works

Note that the following has since been replaced with more reliable system.

Throttle Quadrant Rebuild - Speedbrake Motor and Clutch Assembly Replacement.

  1. Rejected Take Off (RTO) after 80 knots called - Activation of either reverse thrust lever and throttle to idle will extend spoilers (if RTO armed).  Lever moves to UP position on throttle quadrant.
  2. Spoilers extend on landing when squat switch activated, throttles are at idle and lever is in armed position (3 requirements).  Lever moves to UP position on throttle quadrant automatically
  3. Spoilers extend automatically when reverse thrust is applied (if not previously armed - see above)
  4. Engaging thrust after landing automatically closes spoilers.  Lever moves to DOWN position on throttle quadrant.
  5. Speedbrakes extend incrementally in air dependent upon lever position (flight detent).

Speedbrake Logic - Alpha Quadrant Card and Closed System

The logic for the speedbrake, which is identical to the real B737 aircraft, is “hardwired” into the Alpha Quadrant card which is located in the Interface Master Module (IMM) and connected to the throttle quadrant by a custom wired VGA cable.  Programming the Alpha Quadrant card is by stand-alone software.

The speedbrake system is a closed system, meaning it does not require any interaction with the avionics suite software (ProSim737); however, the illumination of the condition lights does require configuration within the avionics suite as they are not part of the closed system (a future update will include all annunciators within the system). 


A common method to convert the speedbrake is to use a potentiometer and then calibrate using FSUIPC ( Flight Simulator Universal Inter-Process Communication).   Whilst this method is valid, it relies very much on FSUIPC to determine the accuracy of the visual position of the speedbrake lever.  The longevity of the system also very much depends upon the potentiometer used, its +- variance at time of manufacture and its cleanliness.  I wanted to move away from potentiometers and FSUIPC and develop a more reliable and robust system.

Micro-buttons Replace Potentimeter - Goodbye FSUIPC

A series of micro buttons are attached to a half-moon shaped arc made from aluminum.  The arc is installed directly beneath the speedbrake lever’s range of movement.  There are six micro buttons installed and each button corresponds with the exact point that a function will be activated when the speedbrake lever moves over the button.  A further two buttons are used forward of the throttle bulkhead and are associated with arming of the speedbrake.

The benefit of using buttons rather than a potentiometer is accuracy and reliability.  A button is on or off and there is little variance.  A potentiometer on the other hand has considerable variance in both accuracy and reliability.

Relay Card

The micro buttons are connected to a Phidget 0/0/8 relay card (4 relays) that, depending upon the position of the speedbrake lever, turn on or off the programmed speedbrake logic.  The Phidget 0/0/8 relay card is located in the Interface Master Module (IMM). 

Basically, the system is a mechanical circuit controlled by micro switches that reads logic programmed into the Alpha Quadrant cards.  Because it’s a closed system, the logic from the avionics suite (ProSim737) software is not required.  Nor, is calibration by FSUPIC.

Arming the Speedbrake - The Detail

To arm the speedbrake, two micro-buttons, located forward of the throttle bulkhead and attached to a solid piece of metal are used.  Connecting the lower end of the speedbrake lever to the clutch assembly is a green coloured rod.  The rod is the linkage that moves the speedbrake lever.  Adjacent to this rod is a cylinder made from aluminum used to open or close the arming circuit.

As the speedbrake lever is brought into the arm position, the cylinder is moved until it touches either of the arming on/off button-switches.  

The cylinder will stay in the armed position until voltage is provided to the motor to move the speedbrake lever, which in turn moves the rod and cylinder. 

Power is sent to the motor in only two circumstances: when the aircraft lands and the squat switch is activated, or during a Rejected Takeoff (RTO).

LEFT & BELOW LEFTDetail of the speedbrake mechanism (click picture for larger view).  

The motor powering the movement of the lever is the angled motor. The two arming button switches can be seen, one is red the other black, while the rod, clutch assembly and cylinder can easily be identified.


Most enthusiasts use a servo motor to control the movement of the speedbrake lever.  I used a servo motor on my first TQ and was never satisfied at the speed the lever moved; it was always VERY slow and seemed to lack consistent power.

In this conversion a DC electric motor, previously used to automobile power electric windows was used.   The advantage in using a motor of this type is its small size, strong build quality and high torque output.  This translates to more than enough power to mobilize the speedbrake lever.  The motor is mounted to the front of the throttle bulkhead.

Clutch Assembly

The purpose of the clutch is to enable the movement of the motor’s internal shaft to be transferred to the rod which moves the speedbrake lever.  The clutch is fitted with a synthetic washer and a torque nut either loosens or tightens the clutch to either increase or decrease the drag pressure on the speedbrake lever (see photograph).  

Speedbrake Lever Movement - Variable Voltage to Control Speed

The speedbrake lever in the real B737 moves rather slowly when the lever is powered.  Traditionally, this slow movement has been cumbersome to replicate, the movement of the lever either being too slow or too fast.  

Below is a short video showing the speed that the speedbrake lever moves on a real Boeing 737-800 (courtesy & copyright to 737maint U-Tube).  Apologies for the adverts which I can not remove from the embed code.

Altering the Speed of Lever Movement

You will note that the lever movement is speed-controlled in both directions (forward and aft).  Whilst controlling the speed of the lever during landing is relatively easy, controlling the speed of the lever as it is stowed (down) is more difficult.  At this time I have not attempted to control the later speed.

Variable Voltage - 12 Volts

If you provide 12 volts directly to the motor, the lever will move very fast in a movement I have coined the 'biscuit cutter'.  However, if you lower the voltage that is provided to the motor, the speed of the lever will slow.  The crux of the issue is if you provide a voltage that is too low the lever will not move and if the voltage is too high you have a 'biscuit cutter'.   There has to be enough voltage for the motor to provide power to start the movement of the lever and rod. Further, the power must be strong enough to be able to push the cylinder past the on/off switch when the speedbrake is armed and deployed (down), or is being closed (up) when throttles are advanced (after touchdown).

Two Methods  & Troubleshooting Potemtial Problems

I examined two methods to reduce the speed of the lever movement.

The first method uses a commercially manufactured reducer to lower the voltage, to a level that allows the lever to move more slowly than if full voltage was supplied to the motor.  This is the more expensive, but probably the better method to use, as you know exactly what voltage the motor is receiving after the reducer is connected.  Reducers can be purchased that reduce voltage by a known amount.

The second method takes advantage of voltage-reducing diodes and resisters to minimize the voltage coming directly from the relay card (the power connects directly to the relay card).  Although simplistic and less expensive than a reducer, it can be troublesome to determine the correct voltage reduction after the diodes or resisters are installed.  

As stated above, 'too little voltage and the lever will not move or move at a snail’s pace; too fast and your cutting biscuits… '

Although diodes and resisters were used, I believe using a reducer is probably more effective.  Using the former method involves educated "guesswork"  to how much voltage is needed to start the movement of the lever.  I believe a reducer may provide a more measurable approach.

The speed that the lever moves is not "perfect", but is adequate in comparison to the speed that the lever moves in the real aircraft.  I'd like to implement the correct noise that can be heard when the speedbrake is moving.  The noise (heard in the above video) emanates from the hydraulic actuator that pushes the lever mechanism.

Illumination of Speedbrake Condition Annunciators on MIP

As outlined earlier, there are specific operational conditions that dictate the illumination of annunciators on the MIP

It’s not difficult to connect the condition lights on the MIP, to the actual position that the speedbrake lever is in.  To do so requires re-routing the wiring from the lights so that they illuminate at the correct setting as determined by the on/off micro buttons.   Connecting the condition lights completes the speedbrake circuit (movement and illumination) in a closed system separate to the avionics suite.

I have chosen not to do this; therefore, whilst the movement of the lever is a closed system the illumination of condition lights is dictated by the flight avionics.  This said, if the micro buttons have been positioned correctly, synchronization between illumination of the condition lights and the speedbrake lever position will not be problematic.

Upgrading Condtion Annunciators to Closed System

Sometime in the future, I’ll probably opt to attach the condition lights to the speedbrake closed system.   The advantage of this being, that if the developers of the avionics suite alter their speedbrake logic, it will not interfere with the closed system logic I am using.

Power Supply

The speedbrake motor is powered by a Meanwell S150 12 Volt 12.5 amp power supply.

Below is a video showing the movement and speed of the speedbrake lever.  The video also shows how the mechanism operates.  Please ignore the lack of lower display panel and GoFlight panel.  The later is for testing purposes until I have installed a fully functional overhead panel.


B737 Center Pedestal Completed and Installed - Flight Testing Begins

After spending the best part of two weeks wiring the various panels into the center pedestal I am now pleased with the result. 

LEFT:  B737-500 center pedestal and custom panels.  The center pedestal from the 500 series is very similar to that of the NG (600 & above) (click image to see larger).

The center pedestal is from a Boeing 737-500 and is made from fibreglass.  The earlier series two-bay pedestals were made from aluminium.  The three bay pedestal allows much more room inside the pedestal to mount interface cards and house the wiring for the various panels (modules). 

However, as with every positive there often is a drawback.  In this case there are two drawbacks.  The first is a few spare holes must be covered with OEM blanking plates, and the second is the three bay pedestal is considerably wider than a two bay pedestal.  Whilst climbing into the flight deck is easy at the moment, once a shell is fitted, J-Rails will need to be fitted to the seats to allow easy access. 


Taking advantage of the extra internal space of a three bay, I have constructed a small shelf that fits inside the lower section.  The shelf is nothing fancy - a piece of wood that fits securely between the two sides of the pedestal.  Attached to this shelf are bus bars, a Leo Bodnar interface card and a FDS interface card.  A Belkin powered hub also sits on the shelf.  The power supply for the hub resides beneath the platform to the rear ( for easy access).

The bus bars provide power for the various OEM panels and backlighting, while the Leo Bodnar card provides the interface functionality for the two ACP units.  The FDS card is required for operation of the three FDS navigation and communication radios I am currently using.

My aim was to minimise cabling from the pedestal forward to the throttle unit.  The reason for this is the throttle is motorized and moving parts and USB cables do not work well together.  I have two cables that go forward of the pedestal to the computer; one USB cable from the powered Belkin hub and the other the cable required to connect the CP Flight panels.  Both cables have been carefully routed along the inner side of the throttle quadrant so as to not snag on moving internal parts.

Pedestal Colour

The original pedestal was painted Boeing grey which is the correct colour for a B737-500.  The unit was repainted Boeing white to bring it into line with the colour of the B737-800 NG pedestal.


The backlighting for the throttle quadrant and center pedestal is turned on or off by the panel knob located on the center pedestal.  Power is from a dedicated S-150 5 Volt power supply rated to 30 amps. 

LEFT:  On the Seventh day, GOD created backlighting and the backlighting was said to be good. (click image to see larger).

The light plates are mostly aircraft bulbs; however, a few of the panels, such as the phone and EVAC panel, are LEDS and operate on 28 Volts rather than the standard 5 Volts.

Size Does Matter...

It's important when you install the wiring for backlighting that you use the correct gauge (thickness) wire.  Failure to do this will result in a voltage drop (leakage), the wire becoming warm to touch, and the bulbs not glowing at their full intensity.  Further, if you use a very long wire from the power supply you will also notice voltage drop; a larger than normal wire (thickness) will solve this problem.  There is no need to go overboard and for average distances (+-5 meters) standard automotive or a tad thicker wiring is more than suitable to cater to the amp draw from incandescent bulbs.

To determine the amperage draw, you will need to determine how many amps the bulbs are using.  This can be problematic if you're unsure of exactly how many light plates you have.  There are several online calculators that can be googled to help you figure out the amperage draw.  Google "calculation to determine wire thickness for amps".

At the moment, I am not using a dimmer to control the backlighting, although a dimmer maybe installed at a later date.

Minor Problem - Earth Issue

A small problem which took considerable time to solve was an earth issue.  The problem manifested by arcing occurring and the backlighting dimming.  I attempted to solve the problem by adding an earth wire from the pedestal to the aluminium flooring; however, the issue persisted.  The issue eventually was tracked down to an OEM radar panel which was "earthing" out on the aluminum DZUS rails via the DZUS fasteners.  To solve the problem, I sealed the two metal surfaces with tape.


The panels I am currently using are a mixture of Flight Deck Solutions (FDS), CP Flight, 500 and NG series. 

  • NAV 1/2 (FDS)
  • M-COM (FDS)
  • ADF 1/2 (CP Flight)
  • Light Panel (OEM)
  • Radar Panel (OEM)
  • EVAC Panel (OEM)
  • Phone Panel (OEM)
  • Rudder Trim Panel (CP Flight)
  • ATC Transducer Radio (CP Flight)
  • ACP Panel x 2 (OEM)
  • Fire Suppression Panel (fire handles) (OEM)

In time a ACARS printer will be added and some of the non NG style panels (namely the ACP panels) will be replaced with OEM NG style ACP panels.  The OEM panels installed are fully operational and have been converted to be used with Flight Simulator and ProSim737.  I will discuss the conversion of the panels, in particular the Fire Suppression Panel, in separate journal posts.

The more observant readers will note that I am missing a few of the "obvious" panels, namely the cargo fire door panel and stab trim panel.  Whilst reproduction units are readily available, I'm loathe to purchase them preferring to wait; eventually I'll source OEM panels.  Rome was not built in a day.

Panel Types

If you inspect any number of photographs, it will become apparent that not all airframes have exactly the same type or number of panels installed to the pedestal.  Obviously, there are the minimum requirements as established by the relevant safety board; however, after this has been satisfied it's at the discretion of the airline to what they order and install (and are willing to pay for...).  It's not uncommon to find pedestals with new and old style panels, incandescent and LED backlighting, colour differences and panels located in different positions.

Telephone Assembly

Purists will note that the telephone is not an NG style telephone and microphone.  I have keep the original B737-500 series telephone and microphone as the pedestal looks a little bare without them attached. 

LEFT:  500 series telephone assembly.  Although not NG style the assembly completes the pedestal (click image to see larger).

If at some stage I find a NG communications assembly I'll switch them, but for the time being it will stay as it is.

More Pictures (less words...)

To see further pictures, navigate to the Image Gallery (tabs on main menu at top of page).

Flight Testing - Replication

The throttle quadrant and center pedestal are more or less finished.  The next few weeks will be spent testing the unit, it's functionality, and how well it meshes with ProSim737 in various scenarios.  This process always takes an inordinate amount of time as there are many scenarios to examine, test and then replicate. 

Replication is very important as, oddly, sometimes a function will work most times; however, will not work in certain circumstances.  It's important to find these "gremlins" and fix them before moving onto the next level. 

KIS - Keep It Simple

Although everything is relatively simple in design (OEM part connects to interface card then to ProSim737 software), once you begin to layer functions that are dependent on other functions working correctly, complexity can develop.   It's important to note that the simulator is using over a dozen interface and relay cards, most mounted within the Interface Master Module (IMM) and wired to an assortment of OEM parts configured to operate with ProSim737's avionics suite. 


Full-time Construction - Light at the end of the Tunnel

It's been three weeks since my oversized box arrived from the United States and the time has not been spent idle. 

LEFT:  Revealed after removing the lid of the crate - an OEM NG style throttle unit.   The three bay center pedestal was packed to the gunnels with OEM parts!

The first morning was spent attempting to drag, carry and push a rather large and heavy (110 kilos) crate from the side garden, up five sets of cement stairs, through the door and then into the flight simulator room. 

The only way one person could move the crate was to unpack whatever was possible into the garden, then construct a  pulley system to drag the crate and its remaining contents up the stairs.  The crate then had to be pushed along the carpet, using cardboard as a slide (to protect the carpet).  It was a relief to note that the crate had a few centimeters clearance between the sides of the crate and the door edges! 

This worked out well, although it took most of the morning, as unpacking the throttle unit outside the simulator room and  moving it to the room would have been problematic.

Fork Lift Damage

My concerns about fork lifts and delicate cargo came to fruition.  A fork lift had rammed one side of the crate leaving the tell-tale evidence - a fork shaped hole!  Fortunately, most of the delicate items were not damaged and for the most part the fork only pushed air.  A book that was included in the crate received much of the brunt and saved the fork from travelling further.  But, so much for my book which now has a hole in it....

Construction Mode

I've been in construction mode attempting to get as much done before I return to my job.  The days have been long and the wire clippers are becoming blunt from endless use!  Many hours have been spent thinking how to do things and then implementing decisions - some successful and others requiring a re-think.  The telephone has been "running hot" as I discuss options with my friend (who also has a B737 simulator) on the best methods to use.

There has been  challenges both in construction and in software development; however, after almost three solid weeks, the light can now be seen at the end of the tunnel.  Hopefully, I'll have some time spare soon to collate some photographs  with words and make a few detailed posts.

I have uploaded several photographs to the Image Gallery (Interface Master Module, Throttle Unit & Conversion of Real B737 Parts).  You will also note a new tab in the main menu called Interface Master Module.