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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).


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Journal Archive (Newest First)

Entries in Boeing 737-300 (5)


"Sticky" Auto Throttle Button - Repaired

I noticed soon after the TQ arrived that the engine number one auto throttle button was a bit “sticky”.  Depressing the button, it would stay pressed in for a few seconds even though pressure had been released.  The A/T buttons are one-way buttons meaning that they are click buttons – click in, release, and click out.  It’s probable that after many hours of service, sweat, dead skin cells and dirt has built up on the inner button behind the spring mechanism; a friend suggested that DNA analysis of the built up debris would probably provide a list of suspect pilots!

Whilst the button was still in place, I attempted to loosen the built up material using a can of pressurised electronic cleaner fluid.  The fluid, I hoped would dislodge any loose material before evaporating.  Unfortunately, this didn’t work in the long run, although once lubricated with the evaporative solvent, the button operated correctly for a short time.


The button is held in place within the throttle handle by a ½ inch circlip.  Beneath the circlip and button there is a spring mechanism that pushes the button out after being depressed.  Using a pair of specialised circlip pliers, I very carefully removed the circlip making sure that the spring mechanism of the circlip didn’t propel my A/T button out the window and into the garden! 

With the circlip removed, the inner portion of the throttle handle slides out revealing the button and attached wiring.  The button is a modular design (shaped to fit inside the thorottle handle) and unfortunately cannot be disassembled further, Therefore, I reassembled the button and sprayed a small amount of silicone spray around the button, allowing the silicone solution to penetrate around the the edge of the button. 

The silicon lubricant (which is non conductive, so there is no issue with power shorting) seems to have solved the problem as the button no longer sticks, however, this is only an interim solution.  I'll search for a replacement button module.  Sometimes the most simple solution will fix your problem!!

No doubt I can purchase a new replacement from Boeing for errr $800.00....  I think not.  Eventually I'll find a disused button module in my travels.   If you find a B737 on the line and note the captain side A/T button has been removed - you know who "stole" it  :)


Throttle Teething & Calibration Issues - It Was Expected

The throttle quadrant works well and I’m pleased with the outcome; however, as anticipated there are a few minor teething issues that require sorting.  There is a background “hum” noise, The engine one auto throttle switch is "sticky", and there are some minor issues with the calibration of throttle reversers and the speed brake. 

Background “Hum”

When the phidget software is turned on with FSX there is an annoying background “hum”.  Initially, I thought this background hum to be the low frequency AC noise, but then realized that everything is DC – so there shouldn’t be any noise.  After consultation with my technical engineers, I believe the cause to be either of the following issues:

1: When the phidget software is turned on it’s activating power to the servo motor to deploy the speed brakes.  The servo motor is ready and waiting for a command, but as there is no command for movement and the  servo motor has power running to it, it’s humming.  If this is the reason, then the installation of the Phidget 004 card (pictured left) will solve this issue. 

A Phidget 004 card has four relays which allow for three situations – on, off and always on.  When connected, the relays will tell the servo motor to “switch off “until activated by movement of the speed brake.

2: All power to the TQ is via 400 watt computer power source and a bench-top voltage reducing board (see last post).  I’ve been told that because all the power requirements are coming from a singular source, then this maybe a cause of noise.  The easiest method to solve this is to use two or three independent power sources.

I’ll have a better indication to root of the “noise hum” problem, once a Phidget 0/0/4 card arrives in the mail.

Speed Brake Calibration - Auto Deployment of Handle

Calibration is always an issue when simulating a complex piece of machinery such as TQ.  Calibration must take into account the various positions and operational requirements of the speed brake.  The speed brake must be recognised by the flight software in the following positions: off, armed and part/full detent.  It must also be configured to automatically activate (deploy) upon flare and touch down when the landing wheels touch the ground. 

The Boeing Operations Manual states: the thrust reverser can be deployed when either radio altimeter senses les than 10 feet altitude, or when the air/ground safety sensor is in ground mode.  Movement of the reverse thrust levers is mechanically restricted until forward thrust levers are in idle position.

Once touch down in achieved, the mechanical speed brake arm on the throttle quadrant will move automatically to the deployment position (full detent).  This is done by programming a squat switch.  A squat switch is standard on/off relay that tells the brake to either deploy or remain in the non deployment position.

Squat Switch & FSUPIC Programming

To program a squat switch I used  Phidget 0/0/4 card and programmed the F2Phidgets software to read "squat switch" in the interface.

To ensure that the speed brake was calibrated to FSX correctly I used FSUPIC.  One important aspect of the calibration is to ensure that the speed brake handle matches more or less the same movement of the virtual speed brake handle within the throttle of the B737 in FSX.  To check this you must open the throttle in FSX and actually observe  the virtual movement of the handle while manipulating the real handle.

Using FSUPIC, open the Axis Assignment tab and move the speedbrake handle checking that the arm and detent positions are correct.  Select "send to FSUPIC" and tick (check) the spoilers in the call out box.  Finally save the adjustments.

If you have not done so already, it's a good idea to have a FSUPIC profile set up to ensure that your changes are saved to specific aircraft.  For example my FSUPIC profile is called B737 Project.


Once a Phidget 0/0/4 card is installed and the card relays calibrated appropriately to the speed brake, it’s hoped that the calibration of engine 1 and engine 2 reversers through detent position 1 and 2 will be straightforward.

After consulting with others and solving these issues, I'll post an update to this thread (here).  Perhaps the information may benefit someone else doing a similar throttle retrofit.


Powering, Wiring & Configuring the B737 Throttle Quadrant

The picture shows the front of the throttle quadrant with the attached 0064 and 0066 phidget cards and the BUO 836X Leo Bodnar card.  I thought this to be the best location for attaching the cards rather than having them either sit loose or be mounted on a separate board.  The wiring and cards will not be visible when the quadrant is sealed against the front of the main instrument panel (MIP). However, if servicing is required, access to the cards and wiring can easily be achieved via the front of the MIP.

LEFT:  Front of Throttle quadrant showing wiring and card installation.

The Phidget cards are required to provide functionality to the trim indicator, motorizing of the trim wheels (via a servo motor), and to allow the deployment of the auto speed brake.

Different Voltages Required

The throttle quadrant requires different voltages to operate correctly.  Apart from the obvious USB power through the USB cable connected to the cards, external power is supplied via a standard style computer power source, rated to 400 watts.  To reduce the main power, which is 240 volts in Australia, to that required by the phidget cards and integrated back lighting (IBL); I installed a benchtop power board kit.  This small kit comes unassembled in a box direct from China.  Assembling the kit and card isn’t difficult but it does taken considerable time to solder all the terminals in place.  The benchtop kit allows the power from the computer power source box  to be reduced to: 3.3 V, 5 V, +12 V and -12V.  Each power selection is protected by a 5 amp in-line fuse.  In an attempt to try and maintain neatness I mounted this card directly to the power source box. 

Functions on the throttle quadrant that require power are:

  • Integrated back lighting (IBL – aircraft bulbs) – 5 volts
  • Main parking brake light – 12 volts
  • Fire suppression module backlights and handle lights – 5 volts
  • Speed brake servo.  Phidget controlled servo motor - 5 volts & 12 volts
  • Trim wheels (spin when electric trim is activated from yoke) Phidget controlled servo motor – 12 volts
  • Lighting on/off switch (TQ IBL only) – 5 volts
  • Hobbs meter (to indicate length of time TQ has been operational) – 24 volts (12V + 12V)

The other avionics that will be installed into the avionics bay are powered directly via USB (unless real aircraft modules are used)

I wasn’t exactly sure what the amperage draw was from the servo motor (that spins the trim wheels and activates the speed brake).  Therefore, to connect the external power through the benchtop power kit, I decided to use 10 amp wire. I have a sneaky suspicion that 10 amp rated wire is overkill for the task, but at least I know it won’t melt.

If you want to view more detailed images, please navigate to the image gallery and select construction

Phidget & Leo Bodnar Card Programming

Most of the buttons and levers located on the throttle are assignable to standard FS controls through the windows joystick controller (or Leo Bodnar card).  But, those throttle functions that are controlled by a Phidget card, initially require mapping through a registered version of FSUPIC, so that they can be seen within the Phidget's interface to allow assignment and configuration.  I used a FSUPIC profile to map the functions controlled by Phidget cards, which were: the trim indicators, trim wheels and speed brake. 

I'll be the first to admit that my knowledge of Phidgets is lacking; Until recently I couldn't spell the word.  With the help of a very kind person from northern California who is exceptionally knowledgeable on Phidgets my worries were soon overturned - at least for the time being.  During a two hour telephone hook-up, the correct computer drivers and Phidget libraries were installed on the computer and the attached Phidget cards on the TQ were programmed to the required throttle quadrant fields with various FS variances and offsets (after they were mapped in FSUPIC). 

As with many software related products, there was a bit of troubleshooting and configuration that needed to be done, but nothing too drastically complicated.  It all seems quite easy when you know how.

The throttle now has full functionality with the exception of the automatic deployment of the speed brake on flare and touch down.  This requires an additional Phidget card (004 card) which has four relays that can be computer controlled.  The relay is needed to activate the squat switch to turn off the servo motor allowing the speed brake to deploy.  This additional Phidget card will be installed shortly.

It was quite amusing when we programmed the Phidgets to the trim wheel movement.  I hadn't expected the movement and was leaning on the trim wheel while discussing the issue on the phone.  BANG WHIRL as the trim wheel began to spin at a high number of revolutions.  The movement and noise startled me and I almost fell from my perch!  The TQ shook madly as the trim wheel rotated (as it isn't yet screwed to a platform) - I can now understand how real world pilots spill their coffee!

LEFT:  Phidget 1064 card attached to recess panel on front of TQ.

Programming the Leo Bodnar card was straightforward; this card follows the standard for windows joystick controllers.  Basically, you just follow the screen prompts and allocate button functions to whatever devices you choose.

One aspect that required careful attention is to check that the FS controls are not duplicated in either the  phidgets, Leo Bodnar, yoke, or other joystick controller settings.  duplicate settings will cause problems.

Throttle Functionality Includes:

  • Independent forward and reverse thrust to engine 1/2 throttles
  • Speed brake arming
  • Speed brake flight deployment (spoilers)
  • Speed brake deployment on flare & touch down (requires another Phidget card)
  • Trim wheel rotation/revolution when trim applied
  • Trim wheel indicator functional and moving when electric trim is activated from yoke
  • Park brake and light
  • Cut off Levers (fuel idle & cutoff)
  • Flaps
  • TO/GA button functional (to go around)
  • A/T disengage functional (auto throttle)
  • All IBL backlighting functional

The stab trim switches I have had wired in such a way to stop the trim wheels from spinning.  Although the spinning trim wheels are accurate to the real aircraft, they can be annoyingly noisy, especially at night when others are trying to sleep.  To disengage the trim wheel motor from the spinning trim wheels,  I flick the stab trim switch.  To activate the them again, I reverse the process.

The horn cut out switch is currently not connected to throttle functionality, however, can be allocated to another FS function if required.

Fire Suppression Module (FSM)

A communication error with my friend, who was converting this modue to FS use, means a little more work is required to add FS functionality.  At the moment I have power running to the handles causing the lamps to be lit all the time, and some of the module buttons to be back lit.  To my knowledge, the handles should only light when the backlighting is switched on or when they are activated.  I still have the original Boeing circuit boards and solinoid switches, and athough I haven't given the matter a lot of thought, I believe that it should be possible to connect a Phidget 004 card, which has relays, to allow activation of APU and fire handles via the original solinoid switches.  I'm not quite sure on how to activate the buttons and switches - perhaps FS offsets and phidget software.  Rome wasn't built in day, so more on this later.

Link to Phidget cards

Link to Leo Bodnar cards


B737-300 Throttle Quadrant & Center Pedestal - Arrived at Last

A big orange truck from TNT Express parked outside the house this afternoon and the driver began to offload a large wooden crate that weighed around 80 kilograms.  I could be only one thing – the Boeing throttle quadrant and avionics box (center pedistal) had finally arrived.   

Together, the driver and I manhandled the crate through the hallway of the house to the room in which construction of the simulator is taking place.  Removing a heavy piece of machinery from a wooden crate can be tricky, and the only method was to disassemble the box screw by screw – WOW what beauty!

Initial Thoughts

The throttle and avionics bay is a genuine aircraft part so there wasn’t much to not like; you can’t “immerse” yourself or get a more authentic experience than by using a real aircraft part.  The throttle originally was in use in a Boeing 737-300 with South West livery.  Unfortunately, the guy at the tear down yard didn’t document the tail number of the aircraft it was removed from.  It would have been nice to have a photo of the actual aircraft to place on the Blog.

The first aspect I noticed about the throttle was the build.  It’s a solid piece of engineering built to withstand the neglect of pilot use and now simulator use.  I don’t believe the throttle will ever be damaged from neglect my end – its’ solidly constructed.  The feel when you push the two power levers forward is - well – you just have to be here!  Manoeuvring the flap lever through the various indents is equally rewarding.  Knowing that the throttle was once used in a real aircraft by real pilots adds a completely new dimension to flight simulation.

Retrofitting & FS Connectivity

During the refurbishment of the throttle, I had decided to not bastardize the throttle to try and replicate the appearance a throttle from a Boeing NG.  Therefore, the throttle remains a 300 series throttle.  It has been repainted only where necessary and decals have been replaced only when they were unreadable.  The internal mechanism of the throttle has been completely striped, cleaned and serviced.  Parts, such as the huge cog wheels and unnecessary internal wiring have been discarded as these are not required for simulation use. 

To allow the throttle to connect correctly with flight simulator, three Phidget cards (0066 & 0064) & a Leo Bodnar card (BUO 836X) have been used.  The cards are connected directly to the front of the throttle casing and will not be visible once the throttle casing is connected to the centre stage of the main instrument panel (MIP). 

All the functions of the throttle operate with the exception of the stab trim switches, which can be linked to another FS function if required.  Trim wheels are functional with the use of a servo motor and the trim spins when electric trim is activated on the yoke.  Back lighting is integrated back lighting (IBL) using genuine Boeing 5 volt bulbs.

Current Status

At the moment I’ve only taken delivery and am in the process of connecting a Benchmark card to an external power source to allow power to reach the 5 volt lighting bulbs and servo motors.  I have little doubt that there will be teething issues with software as I configure everything for correct functionality, but I believe that this extra effort is worthwhile to be able to use a real throttle instead of a replica.

Avionics Bay

The avionics bay is a two-bay type.  Two-bay types were mainly used on the earlier Boeing classic series jets up to the 200 series, however, a number of 300 series aircraft used them as well as 400 series.  The bay was attached to the throttle when I bought it, so rather than dump it and replicate a NG three-bay; I’ve decided to use it to maintain authenticity.  I may at some stage in the future replace it with three-bay – I’ll see how things develop once I begin to populate the bay with avionics instruments.  One benefit of using a two-bay style is that once Weber seats are fitted to the flight deck there will be more room to squeeze past to get into the seat!

An interesting feature to the unit is the positioning of two oddly shaped aluminium pull downs.  At first, I had no idea what these were used for.  Then it dawned on me – they are pull-down coffee cup holders.  What more can you ask for (laughing).  See the image gallery for a snap.

Fire Suppression Module

The fire suppression module was an afterthought.  A second hand unit was available and I decided to retrofit this with limited functionality to flight simulator.  At the moment IBL works, and when pulled, each fire handle does what it’s supposed to do.  At some stage in the future I may activate the fire bell.  But, at the moment it’s early days with regard to this.  Basically it’s a module that has to be installed into the avionics bay for aesthetics; a TQ without a fire suppression module looks a slightly naked.

More on the actual avionics bay at a later stage when I begin to populate the bay with instruments - much kmore interesting than looking at "naked bay"

  • To see a selection of detailed images of the TQ, check out the Gallery Section

Boeing 737-300 Series Throttle Quadrant - UPDATE

The refurbishing of the Boeing 737-300 throttle quadrant is almost completed and delivery to Australia should be in a week or so.  The work involved converting this throttle quadrant to flight simulator use has been quite lengthy, however, I believe the end result will justify the wait.  As with everything in flight simulation - one has to have patience.....

Read more about the TQ and see some additional pictures which have been sent to me, in the updated section of the original thread (under the original post).  Click the blue aircraft icon to read the update.