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 Original Equipment Manufacturer (3)


Throttle Quadrant Rebuild - Flaps Lever Uses String Potentiometer 

There are several ways to enable the flaps lever to register a particular flaps détente when the flaps lever is moved to that position on the flaps arc.

LEFT:  Flaps lever set to Flaps 30.  The throttle quadrant is from a Boeing 737-500 airframe. The flaps lever arc is the curved piece of aluminium that has has cut-out notches that reflect the various flap positions.  It was beneath this arc that micro-buttons had been installed (click to enlarge).

In the earlier conversion, the way I had chosen worked reasonably well.  However, with constant use several inherent problems began to develop.

In this article, we'll examine the new system.  But before going further, I'll briefly explain the method that was previously used.

Overview of Previously Used System

In the earlier conversion, nine (9) micro-buttons were used to register the positions of the flaps lever when it was moved (Flaps UP to Flaps 40). 

The micro-buttons were attached to a half moon shaped piece of fabricated aluminium.  This was mounted beneath the flaps lever arc and attached to the quadrant.  Each micro-button was then connected to an input on a PoKeys 55 interface card.  Each input corresponded to an output.

Calibration was straightforward as each micro-button corresponded to a specific flaps position.


The system operated reasonably well, however, there were some problems which proved the system to be unreliable.  Namely:

(i)    The vertical and lateral movement of the chain located in the OEM throttle quadrant interferred with the micro-buttons when the trim was engaged; and,

(ii)  The unreliability of the PoKeys 55 interface card to maintain an accurate connection with the micro-buttons.

Movement of OEM Chain

The chain, which is similar in appearance to a heavy duty bicycle chain, connects between two of the main cogs in the throttle quadrant.  When the aircraft is trimmed and the trim wheels rotate, the chain revolves around the cogs.  When the chain rotates there is considerable vertical and some lateral movement of the chain, and it was this movement that caused three micro-buttons to be damaged; the chain rubbed across the bottom section of the micro-buttons, and with time the affected buttons became unresponsive.

It took some time to notice this problem, as the chain only rotates when the trim buttons are used, and the micro-buttons affected were primarily those that corresponded to Flaps 5, 10 and 15.  The chain would only rub the three micro-buttons in question when the flap lever was being set to Flaps 5, 10 or 15 and only when the trim was simultaneously engaged.

LEFT:  First Officer side of a disassembled throttle quadrant  (prior to cleaning and conversion).  The large notched cog is easily seen and it's around this cog that the OEM chain rotates (the chain has been removed). 

The cog and chain resides immediately beneath the flaps arc (removed, but is attached to where you can see the four screws in the picture). 

Although there appears to be quite a bit of head- space between the cog and the position where the flaps arc is fitted, the space available is minimal.  Micro-buttons are small, but the structure that the button sits is larger, and it was this structure that was damaged by the movement of the chain (click to enlarge).

An obvious solution to this problem would be to move the chain slightly off center by creating an offset, or to fabricate a protective sleeve to protect the micro-buttons from the movement of the chain.     However, the design became complicated and a simpler solution was sought.

The previously used system is documented in more detail here:  B737 Throttle Quadrant - Flaps UP to 40; Conversion and use.

Replacement System

Important criteria when designing a new system is: accuracy, ease of installation, calibration, and maintenance.  Another important criteria is to use the KIS system.  KIS is an acronym used in the Australian military meaning Keep It Simple.

The upgraded system has improved reliability and has made several features used in the earlier system redundant.  These features, such as the QAMP (Quick Access Mounting Plate) in which linear potentiometers were installed, have been removed.

String Potentiometer Replaces Micro-buttons

A Bourne single-string potentiometer replaced the micro-buttons and previously used linear potentiometers.  The string potentiometer is mounted to a custom-designed bracket on the First Officer side of the throttle quadrant.  The bracket has been fabricated from heavy duty plastic.

LEFT:  Single-string potentiometer enables accurate calibration of flaps UP to flaps 40.  The potentiometer is mounted on a customized bracket screwed to the First Officer side of the throttle quadrant superstructure.  The terminal block in the image is part of the stab trim wheel system (click to enlarge).

A string potentiometer was selected ahead of a linear potentiometer because the former is not limited in throw; all the flap détentes can be registered from flaps UP through to flaps 40.  This is not usually possible with a linear potentiometer because the throw of the potentiometer is not large enough to cater to the full movement of the flaps lever along the arc.

A 'string' is also very sensitive to movement, and any movement of the string (in or out) can be accurately registered.

Another advantage, is that it's not overly important where the potentiometer is mounted, as the string can move across a wide arc, whereas a linear potentiometer requires a straight direction of pull-travel.

Finally, the string potentiometer is a closed unit.  This factor is important as calibration issues often result from dust and grime settling on the potentiometer.  A closed unit for the most part is maintenance free.

To read more about string potentiometers and their advantages, navigate to to this article: String Potentiometers: Are They Worthwhile.

The end of the potentiometer string is attached to the lower section of the flaps lever.  As the flaps lever moves along the arc, the string moves in and out of the potentiometer. 

The ProSim737 software has the capability to calibrate the various flap détentes.  Therefore, calibration using FSUPIC is not required.  However, if ProSim737 is not used, then FSUIPC will be needed to calibrate the flap détente positions.


Apart from the ease of calibration, increased accuracy, and repeatability that using a string potentiometer brings, two other advantages in using the new system is not having to use a Pokeys 55 card or micro-buttons.

Unreliability of PoKeys 55 Interface Card

The PoKeys card, for whatever reason, wasn't reliable in the previous system.  There were the odd USB disconnects and the card was unable to maintain (with accuracy and repeatability) the position set by the micro-buttons.

I initially replaced the PoKeys card, believing the card to be damaged, however, the replacement card behaved in a similar manner.  Reading the Internet I learned that several other people, who also use ProSim737 as their avionics suite, have had similar problems.

Micro-buttons can and do fail, and replacing one or more micro-buttons beneath the flaps arc is a time-consuming process.  This is because the upper section of the throttle quadrant must be completely dismantled and the trim wheels removed to enable access to the flaps arc.

Registering the Movement of the Flaps Lever in Windows

The movement of the flaps lever, prior to calibration must be registered by the Windows Operating System.  This was done using a Leo Bodnar 086-A Joystick interface card.  This card is mounted in the Throttle Interface Module (TIM).    The joystick card, in addition to the flaps lever, also registers several other button and lever movements on the throttle quadrant.  

Final Call 

The rebuild has enabled a more reliable and robust system to be installed that has rectified the shortfalls experienced in the earlier system.  The new system works flawlessly.

Acronyms and Glossary

OEM - Original Aircraft Manufacture (real aircraft part).


OEM Brackets to Secure Gauges and Modules to Boeing 737 MIP

Original Equipment Manufacturer (OEM) parts usually attach to the infrastructure of the flight deck by the use of DZUS fasteners.  The easy to use fasteners allow quick and easy removal of panels and modules.  But what about the gauges that are used in the Main Instrument Panel (MIP); for example, the yaw dampener, brake pressure and AFDS module.

LEFT:  Take your pick – brackets for different sized modules and gauges.  The brackets when tightened provide a snug and secure fit for any OEM gauge or module.

These items do not use DZUS fasteners for attachment to the MIP; rather they are inserted into the MIP from the front and secured from behind by a specially designed bracket.  The different sized brackets are made from lightweight aluminum and are designed to fit particular gauges and modules.   Each bracket incorporates, depending on the style, a number of screws.  These screws are used to loosen or tighten the bracket. 

The gauge is inserted into the MIP from the front.  The bracket is then placed over the gauge from behind the MIP and tightened by one or more of the resident screws.  The screws cause the bracket to clamp tightly to the shaft of the gauge and ‘sandwich’ the MIP between the flanges of the gauge and the edge of the bracket.  Once fitted, the Canon plug is then re-attached to the gauge.

LEFT:  Selection of gauges.  Note the flange on the forward part of the yaw dampener and brake pressure gauge (nearest glass) Click image to enlarge.

Of interest is that some brackets have been designed to fit the differing thicknesses between MIPs.  By turning the bracket end on end the appropriate thickness of the MIP is selected.  

As mentioned above, the brackets are designed to fit specifically sized and shaped gauges and modules; therefore, it is important to purchase the bracket that fits the gauge you are using.  There are several different sized brackets on the market that are used in the Boeing 737 classics and NG airframes.  The 'NG' for the most part incorporates identically sized gauges as the classics, so a bracket is not necessarily NG specific.

One of the benefits in using the OEM brackets is that they are designed for the purpose, are very easy to install, and facilitate the quick removal of a gauge or module should it be necessary.

In the next post we look more at flight training and discuss corsswind landings.


B737 Steering Tiller Installed and Operational

The steering tiller is an often overlooked piece of hardware for many virtual flyers.  The steering tiller provides greater control of the aircraft during taxi operations, and if calibrated correctly works very well.

LEFT: B737 OEM tiller on custom plate (OEM 737-400 handle).   Click image for larger view.

OEM B737-400 Steering Tiller

The tiller has been salvaged from a B737-400 series aircraft and is identical to the tiller used in the 800NG series airframe.  The actual OEM part is only the black handle and white arrow.  The remainder of the unit has been custom fabricated to allow easy attachment to the inside wall liners of the flight deck.

The simulator does not have a shell and liner at the moment; therefore, I've attached two pieces of grey-coloured wood to the unit to enable temporary installation to the forward left of the Captain's seat.  

A single potentiometer has been used allow calibration of the tiller mechanism.  A metal strip connects the potentiometer with a metal plate that connects to the the central area of the tiller mechanism.  As the steering tiller is turned left or right, the metal plate moves to and fro with a corresponding movement in the metal strip which registers on the potentiometer (see picture).

To create tension when the steering tiller is moved, several heavy duty springs have been used.  Although rudimentary in design, the tension of the springs provides a reasonable and constant pressure.  The springs also allow the handle to center itself easily when released.  Springs are renowned for creaking when they move and to remove this noise, heavy duty lithium grease has been applied to the upper parts of the spring heads where they join the metal. 

Interface Card and Calibration

The tiller is connected directly to a Leo Bodnar BU086A interface card, although any joystick card such as a PoKeys card can be used.  A USB cable then runs from the interface card to the main computer.  To allow easy connection to the interface card (Leo Bodnar card) a female JR servo wire security clip has been used.  

LEFT:  Tiller mechanism showing springs and potentiometer (click to enlarge image).

The steering tiller requires careful calibration if it's to operate correctly.  Calibration is initially through Windows and then FSUIPC.  Using FSUIPC enables greater accuracy to be achieved.

The steering tiller, when calibrated through FSUIPC does not create an independent tiller axis but piggybacks on the movement of the rudder axis.  The developer has ingeniously written code that enables the tiller to be activated when groundspeed is under 60 kias.  Above this speed the rudder is activated.

How to Calibrate the Steering Tiller 

  1. Connect the interface card to the computer via the USB cable.
  2. Using Windows, calibrate the axis of the interface card (if using Windows 7 type into the search bar joystick and select "Joystick Calibration").
  3. Following the on screen instructions, move the steering tiller handle forward and aft.  Then save the setting.
  4. Open Flight Simulator and then open “Settings/Control” in the FSX menu.
  5. Ensure that any joystick commands relating to the interface card are not registered by FSX.  If so, delete them and save.
  6. Open Flight Simulator and then open FSUIPC settings.
  7. Select the FSUPIC “Axis Assignment Tab”.  Then move the tiller handle to activate the calibration software.  (you will observe the numbers moving).
  8. Select from the left side of the screen the tab that says ”Type of Action Required,  Select "Send Direct to FSUIPC Calibration".  Then open the menu box and scroll down to “Steering Tiller”.
  9. Open the “Joystick Calibration” tab in FSUPIC.  
  10. Scroll through the 11 entries searching for steering tiller (9/11).  When "Steering Tiller" is found, click the SET button which will open three (3) further buttons.  Each button refers to a position on the steering tiller axis.
  11. Turn the steering tiller to the left and click the RIGHT button.  Then turn the tiller to the right and select the LEFT button.  With the tiller in the central position click the MIDDLE button.  Oddly, on some setups the opposite is required.  If calibration fails, try again using the opposite direction.
  12. For more precise and accurate calibration, you may want to use the "Slope" and/or "Null Zone" functionality.

The steering tiller should now be calibrated and ready for use.

Troubleshooting and Suggestions

Some known problems that are easily solveable are:

A:  Only use the steering tiller at very low ground speeds.  If you turn the tiller to the full left or right and the speed is too great, the aircraft may remain stationary or slip; the reason being the nose wheel is locked at a right angle to the direction of travel.  I find the tiller works best turning the handle slowly.

B:  The direction of aircraft travel is opposite that of the tiller handle.  If this occurs, check your FSUIPC settings.  You may have to tick (check) the box that says REV.  REV reverses the direction of the axis (left to right and right to left).

C:  If the tiller exhibits sensitivity issues or if you require a dead zone, open FSUIPC and program the SLOPE function and/or set a NULL ZONE.

D:  If you have issues with the tiller not working correctly, recalibrate in Windows and FSUIPC.  If calibrated correctly, the tiller will change to rudder control at 60 knots.

OEM is an acronym for Original Equipment Manufacturer.