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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.

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Journal Archive (Newest First)

Entries in B737-300 Throttle Quadrant (5)


Replacement Genuine 737 Throttle & Center Pedestal - Full Conversion to NG Style

The last few months have seen quite a bit of activity regarding the throttle quadrant and center pedestal, which has culminated in me selling my former 300 series TQ and pedestal and replacing it with an another unit from a late series 500 airframe.

Brief Recap

In an earlier post late in 2012, I decided to convert the 737-300 throttle to full automation.  A dilemma I faced was whether to keep the throttle unit as a 300 series throttle with the attached two-bay pedestal, or do a full conversion to make it similar to the Next Generation (NG) style. 

After careful consideration, a decision was made to convert the throttle quadrant to a full NG style, bringing the throttle units and center pedestal in line with a 737 NG airframe for which the MIP is designed.

Stab Trim Switches

One of the biggest differences, apart from thrust lever handles, between early model throttle units and the NG units is the stab trim cut out switches.  On the earlier 300 series units, the switches are paddle / lever style switches while the NG uses toggles and T-Locks.  T-Locks are a safety feature and sit beneath the toggle switches and are spring loaded; the pilot must push down the T-Lock to activate the toggle.  

LEFT:  737-300 TQ with old style paddle-style stab trim levers.

To convert the trim switches requires cutting out the old switches and fitting new reproduction NG style switches.  This is a major task requiring precision work of a surgical nature.  Although reproduction switches can be made, the reproduction T-Locks don't operate as the real T-Locks should.  I did search for some genuine T-Locks and toggles, however, my search was fruitless as these parts appear to be reused by airlines.

Replacement 500 Series Throttle Quadrant & Three-Bay Center Pedestal

A friend of mine informed me that a late model 737-500 throttle quadrant was for sale.  This unit was in better shape than my existing throttle, included the genuine 'NG style' stab trim switches complete with T-Locks, and also had a three-bay center pedestal.  It appears provenance was shining on me as the new throttle appeared for sale a day before the stab trim switches were about to be removed (with a metal cutter...)

The throttle and center pedestal were purchased (you only live once!) and the 300 series unit sold to an enthusiast in Sweden.

NG Conversion

To bring an earlier style throttle and center pedestal in-line with a NG airframe requires, at a minimum:

  • Attachment of a NG style throttle lever shroud to existing aluminium levers;
  • Removal of TO-GA buttons and relocation to bring design in-line with a NG (the buttons are identical, but the housing is different);
  • Possible replacement of the stab trim switches;
  • Painting of throttle housing and center pedestal from Boeing grey to Boeing white; and,
  • Painting of all throttle knobs from Boeing grey to Boeing white.

The biggest hurdle is usually replacing the trim stab switches, however, as these are already present on the new throttle, and are the NG style, considerable time and expense was saved in not having to replace them.

Main Differences - NG & Classic

The Boeing airframe that most people associate with today begins with the 737-200 and ends with the 737-800 NG.  In between we have the classics which refer to the 737-300, 400 & 500 series airframes and the NG, which stands for Next Generation and incorporates the 737-600, 700, 800 & 900 series airframes.

The main differences between a classics and NG throttle quadrant are:

  • The stab trim switches are slightly different; the classics having two flat levers while the NG has toggle-style buttons with T-locks;
  • The throttle thrust lever handles; the classics are bare aluminium and the NG is white aluminium that is ergonomically-shaped.  The TO/GA buttons are also positioned in a different place on the NG.  The knobs (handles) on the levers are also coloured white rather than off-grey;
  • The method that the throttle thrust levers move during automation.  The classics move both thrust levers together when auto throttle is engaged.  The NG moves each lever individually in what often is termed the throttle dance (this is due to the computerised fuel saving measures incorporated in the NG);
  • The spacing (increments) between each flap lever position is identical in the NG, but is different in the earlier series throttles;
  • The center pedestal in the classics is either a two-bay pedestal (early 300 series and before), but more likely a three-bay pedestal.  The NG always has a three-bay pedestal.  Base materials for the center pedestal are also different - aluminium verses a plastic composite material;
  • The speedbrake knob is very slightly more elongated on the NG unit; and,
  • The telephone, circuit breakers and mike assembly differ in type and location

NG Skirt - Thrust Levers

Boeing when they designed the NG style throttle didn’t design everything from new; they added to existing technology.  All NG throttles utilise thrust levers which are identical to those of earlier units.  

Boeing designed a shroud or skirt that attaches over the existing thrust levers encapsulating the older thrust levers and sandwiching them between two NG style pieces.  The assembly is made from aluminium and is painted white.

The TO-GA buttons are located in a different position on the Next Generation units, although the buttons used are identical.

To alter the position of the TO-GA buttons you must detach  the small aluminium box from the 300 series thrust levers, remove the TO/GA buttons, and then re-solder the buttons in the appropriate location on the new unit.

I did not make the NG skirt for the thrust levers, but rather had fabricated, from design specifications, a reproduction skirt.  The skirt is produced from aluminium and replicates the dimensions of the Boeing part.

Time-line, Functionality and Conversion

The TQ is initially being converted in the United States.  The advanced work will be done by a good friend in California, and then by myself after delivery.

The replacement unit will feature several imrovements which will allow: full motorized functionality, full speed brake capability, accurate trim tab movement, alternate trim wheel spin speeds, correct park brake release, trim wheel braking and several other features. 

I want the functionality of the TQ to be as close as possible to that found in the real aircraft; therefore, the methods used to ensure this functionality will be slightly different from the norm.

When the TQ is fully functional and tested, I'll publish a post providing further information and detailed photographs of the various functions.

It is hoped everything will be completed, and the TQ and pedestal installed by late May 2013.  The next month or so will be quite exciting.

Two-bay Pedestal Will Be Missed

I know I will miss the narrower two-bay center pedestal.  A major advantage that will be lost is the ease in climbing into and out of the flight deck; the two-bay provided more room between the pedestal and the seats.  At some stage, I probably will need to install J-Rails because the seats I'm using are fixed-claw feet Weber pilot seats; J-Rails will be needed to allow lateral seat movement.

BELOW:  Montage of several images showing main visual differences between 737-300 classic series throttles and the 737 NG style throttle units. The 300 series TQ is my old throttle unit but, the NG TQ belongs to a mate of mine.


B737-300 Throttle "Full Automation" Upgrade

The throttle quadrant installed in the simulator is from a B737-300.  When I initially  converted the throttle for flight simulator use, I choose to not have full automation included; automation being at the time fraught with issues in relation to correct and accurate operation.  

Technology rarely remains stationary and after one year of operation I’ve been reliably informed that automation can now be implemented without the problems previously experienced.  Therefore, I’ve crated the TQ and it’s now on its way to the US via DHL courier for conversion to full automation.  A process I am told that will take a few weeks.

LEFT:  B737-300 throttle (formally used by South West Airlines).

Automation will include, at the minimum, the following:

  • 4 speed trim wheels dependent upon aircraft status (as in the real aircraft)
  • Accurate trim tab movement
  • 9 point speed brake (speed brake operation as in the real aircraft)
  • Full automation of throttle thrust handles as per MCP speed window and/or CDU
  • Hand brake release by depressing brake pedals (as in the real aircraft)

I don’t mind admitting that that my building abilities don't include complete knowledge on how to convert a B737 throttle correctly - especially in relation to automation; therefore, this task has been outsourced.

The method in which automation will be achieved is slightly different from the usual way throttles are converted, and includes some "magic" programming of chip sets and machining of parts to allow compatibly with ProSim 737.  Taking into account Christmas and New Year, I'm hoping that the machining, installation, configuration and testing will be completed by January (2013) and the throttle will be re-installed into the simulator by February.

In a future post I'll explain the process of conversion, and how automation has been achieved with minimal use of add-on software.

Idle Time

Although the throttle quadrant and pedestal will be absent from the simulator for a short time, work will not be idle.  The conversion of the twin real B737 yokes and columns has been completed and I'm finalising installation of the second platform which incorporates linked B737 rudder pedals.  I am hoping this will be completed by mid-November.  I have discussed the new platform in a previous post.


Throttle Thrust Problem - Loosing Thrust at N1 - The Solution

The throttle installed into the simulator is a converted genuine B737-300 throttle.  Lately, I have observed inconsistent power thrust issues during the take off roll and climb out. 

As I begin the take off roll, engage TO/GA and rotate, but before acceleration altitude or acceleration height is reached, one of the throttles looses or gains power.  Moving the throttle handle reinstates throttle power, but the power is dependent on where the actual throttle lever is physically positioned. 

When the aircraft is above thrust reduction altitude (1500 radio altitude) the problem rectifies itself.  The problem cannot be replicated when flying above 1500 feet.  I also noted, and this may also be part of the issue, that the power indicators located on the EICAS display fluctuate (twitch) a little as I moved the throttle levers.

This problem only began to occur after I transferred the avionics software to ProSim737.

Process of Elimination

Problems like this are not uncommon when interfacing real aircraft parts and the challenge is finding the cause of the problem.  The only method to determine solutions to problems such as this is to systematically, through the process of elimination, identify the problem area.

My first thought was that one of the potentiometers in the throttle quadrant maybe damaged, although I considered this to be unlikely as the units are still relatively new.  The throttle has four potentiometers: throttle 1, throttle 2, flaps and spoilers. Flight testing indicated that the power loss alternated between engine 1 and engine 2; therefore, the likelihood of two potentiometers failing at the same time was minimal. 

The next step involved checking the wiring within the throttle quadrant, to ensure there wasn’t damage to the outer coating of the wires.  A damaged or loose wire can easily short on the throttle frame and generate a spike.  However, if the wiring was loose or damaged, the problem would also occur when flying at altitude, and I had clearly demonstrated that the problem only occurred during the take off roll and climb out to thrust reduction altitude. 

The next step was to ensure that calibration of the throttle unit was correct.

Re-Calibration Using FSUPIC

I decided to re-calibrate the throttles using FSUPIC rather than FSX.  This process isn’t difficult and FSUPIC allows you to fine tune each throttle with greater accuracy than is possible with FSX. 

After re-calibration, the “twitching” of the power indicators ceased, but the initial problem remained.

The Cause of the Problem

The only culprit I could think of to cause this problem was ProSim737.

To check whether ProSim737 was actually the cause of the problem, it is necessary to remove any input from the ProSim737 software.  This is straightforward.  Either use another avionics software package or use FSX itself.  I did twenty trial flights using both Sim Avionics and FSX and the problem did not replicate. 

ProSim737 Excellent Support and Advice

I contacted the developers at ProSim737 explaining my problem in detail, and I received a response to my questions within a few hours.  Marty was especially helpful and we discussed several potential reasons for this issue and possible workarounds.  I must stress that the response I received from ProSim737 was absolutely 100% top notch. 

Marty genuinely wanted to help resolve the issue – whether it be with ProSim737 or otherwise.

Real B737 Throttle Operation

Now this where the comment “as real as it gets” does have meaning…. 

The developers of ProSim737 have designed their software to replicate the logic used by the real B737 auto throttle.  The software (ProSim737) is doing exactly what it’s supposed to do in relation to power thrust, and the issue I was experienced is caused by using a real aircraft throttle without automation.  Let me explain.

In the real aircraft, when TO/GA is enabled, the auto throttle logic has control of the aircraft.  The throttles are off-line and power thrust cannot be manipulated by the pilot.  The flight mode annunciator (FMA) illuminates N1. 

As 84 knots is passed the FMA changes from N1 to THR HOLD.  At this time, the actual throttles come back on-line, meaning that you can manually alter throttle power by moving the levers.  After rotation and at 800 radio altitude the auto throttle system is ready to change from take off power to climb power and the FMA changes from THR to ARM.  When in ARM mode the throttles are still on-line. 

When the aircraft reaches 1500 RA which is the thrust reduction altitude, the throttles go off-line and the AT logic is controlling the power thrust of the throttles.  The FMA changes from ARM to N1.

Throttle Anomaly

The B737 does not have a manual throttle, but an automated throttle.  The software is programmed to move the throttle levers to the correct position mimicking the actual power thrust called for by the auto throttle logic.

If you use a manual throttle (genuine or otherwise) the connection to the automated physical movement of the throttle levers is missing; you must counter this by moving the levers yourself.  This issue should not occur with a correctly calibrated automated throttle.

Using an Auto-throttle

If you have an auto throttle, the levers will automatically and physically move to the indicated thrust position as determined by the auto throttle logic (90%N1 at TO/GA).  When the FMA illuminates THR HOLD at 84 knots, and the throttles come back on-line for possible pilot intervention, the auto throttle logic will not sense any change in the throttle lever position, and power thrust (90%N1) will be maintained.   This is because the automated system placed the throttle levers in the correct position when TO/GA was initiated.

Using as Manual Throttle

However, if you’re using a manual throttle, the throttle levers MUST be physically positioned at the correct location on the throttle quadrant, otherwise the auto throttle logic will sense a change in position of the levers and alter the power thrust accordingly to this new level. 

This is what was occurring in my situation.  I was resting my hand on the throttle and only advancing the levers 3/4 of the way forward.  TO/GA indicated 90%N1, but when the throttles came on-line at 84 knots, the auto throttle logic noted that the position of the throttle levers was not at 90%N1 and subsequently altered the power thrust accordingly.

The reason the issue was inconsistent is that I didn’t always advance the throttle levers to the same position, and if I did the problem did not occur.

LEFT:  B737-300 throttle quadrant converted to Flight Simulator use.  The TQ is a manual throttle meaning that the thrust levers are not automated and must be moved manually.  I have used a pencil to lightly mark the metal adjacent to the most commonly used N1 settings.  This ensures the levers are moved the correct location during take off.  Lever position is set to 90%N1 and flaps 5.

Solution – Change in Procedures

The solution to this anomaly of using a real “manual” throttle is relatively simple.

You must determine where on the throttle quadrant the various N1 power settings are and then ensure, after engaged TO/GA that you move the throttle levers to the correct position (90%N1).  In my situation, the procedure is to advance the throttle to 40%N1, engage TO/GA, and then manually push the throttle levers to 90%N1.

Thank you

I’d like to thank Marty at ProSim737.  Marty worked with me to solve the issue, which ultimately was not really a problem with either ProSim737 or my set-up, but is an anomaly of using a genuine throttle unit without automation.

Possible Update

I may at some stage update the throttle quadrant to allow automation of the thottle levers and speed brake, however, for the time being the TQ will remain manual.


Genuine B-737 Throttle Quadrant - Purchased!

I was very surprised to have found a real 737 throttle quadrant at more or less the same time I was debating which throttle to use in my simulator.  Negotiations have been successful and I've been told my new TQ has just arrived in Florida (from Arizona) where the TQ will be refurbished.

The TQ belonged to a scraped South West Boeing 737-300 series aircraft. 

Attached to the TQ is a two-tier avionics bay.  I was going to replicate a 737NG bay from MDF wood, so the addition of the bay is a added bonus. 

The bay still has workable DZUS rails so adding avionics is just a matter of drop and screw!  Although the NG has a three-tier bay, I was never intending to add all the instrumentation that a NG would have.  I cannot see the benefit in duplicating avionic modules which will never be used.  

Therefore, the two-tier bay will work very well for me.  As I've mentioned in the static section of this blog (tabs) everything with a simulator is about compromise, and the level and detail and realism that you want.  For me, a real avionics bay (even if not a NG bay) is a bigger plus than a wooden bay full of fake instrumentation.

The TQ will be completely dismantled, cleaned and serviced.  Parts that are not required for simulation will be removed.  The lower section of the TQ and bay will be cut off  as this section of the quadrant is not necessary.

The unit will then be retrofitted with appropriate SYS hardware which is to be mounted in the avionics bay out of sight, but easily serviced by removing a few avionics modules.   USB cabling will be routed along the inside bottom of the TQ to come out at the front of the throttles.  This will allow easier connection to a computer.  FD to Phodgets will be used to configure the Throttle to flight simulator.

The unit will be a non motorized unit, however, with the use a a DC motor (run from electrical power) the trim wheels will spin and manual trim will be able to be changed.

Finally, a new coat of paint will be applied along with repaired or replaced labels.  A trim stab will also be attached to the unit.

One of best things in my opinion with using a genuine throttle is the realsism involved.  But another positive aspect is the fact that the chance of breaking a real throttle quadrant is next to impossibel!

I've seen a few TQ's now and it shocks me the condtion they are in - I wonder what pilots do in the flight deck.  Often the throttles are scratched, stained and even chipped by continuous use.

The images here are the throttle straight from the aircraft.  Over time I'll be attaching devlopment photographs as the throttle is converted.


Genuine B-737 Throttle Quadrant - Found One!

After extensive research on the Internet, I discovered that there are only a few quadrants available that strive to replicate a genuine 737 throttle quadrant.

Revolution-Sim, a company in France appears to produce an exceptionally well designed quadrant, however, not with an inexpensive price tag. ThrottleTec also produce a very good intermediate throttle quadrant that is reasonable priced, however, doesn't really replicate a genuine throttle.

After more research and considerably thinking, I have found a real 737 series throttle quadrant from an aircraft scrapped in a tear down yard.

If I manage to aquire this TQ, I will have the internal mechanisms refurbished and retrofitted to work with flight simulator using a SYS board and phidgets.

The throttle will not be motorized as this level of functionality I have been lead to believe involves a level of functionality that can cause issues. Further, many of the issues that people have with throttles revolve around their use in motorized / automation mode.  I like to fly manually, so non motorised suits me.

I must confess that the feel of a real throttle in your hand leads no limit to the imagination!

It's early days yet, but I'm very hopeful I will be purchasing the unit.