Journal Archive (Newest First)


Flight Controls - General Information

Second to the yoke, a throttle quadrant (TQ) is probably the next important item in the simulator.  However there is more to a TQ than just thrust levers.

LEFT:  The throttle quadrant installed into the simulator.  Compared to the reproduction units available, the use of a real throttle unit is second to none (click to enlarge).

A throttle quadrant incorporates the following functionality:

(i)        Thrust levers;
(ii)       Reverse thrust;
(iii)      Fuel idle cut-off switches;
(iv)      Stab trim cut-off toggles;
(v)       Speedbrake lever;
(vi)      Park brake lever;
(vii)     Rotation of stab trim wheels;
(viii)    Stab trim tab indicators; and,
(ix)      Horn cut out.

The throttle unit will be used constantly on all flights, both in autopilot and manual mode; therefore, it is best to try and not scrimp with this piece of equipment.

Over the years I have used several different throttle units.  At the 'dawn of time' I used a keyboard (FS1) prior to migrating to a throttle manufactured by CH Products, and then to a more higher-end unit manufactured by Precision Flight Controls (PFC).  

The throttle unit I now use in the simulator is an Original Equipment Manufacturer (OEM) Boeing 737-500 throttle unit which has been converted for use in Flight Simulator.

The B737-800 Project uses the following flight controls:

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

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

For the purpose of this post, a throttle quadrant is the actual quadrant and does not include the attached center pedestal.

Historical Perspective

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

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

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

Classic or NG Style Throttle Quadrant

Obviously, a NG style throttle quadrant is sought after; however, truth be told, NG style units are very expensive and are not easily acquired.  The next contender is a throttle unit from a classic series airframe (200 through 500 series).

LEFT:  A 300 series throttle.  Note the TOGA button square box assembly, lack of shroud, and overall colour in contrast to the NG throttle (click to enlarge).

The 200 and 300 series throttle units are antiquated and include two-bay center pedestals.  The 400 series units, with the exception of interval spacing and the stab trim cut-off switches, are very similar to the NG throttle units.  The 500 series throttle quadrants all use a three-bay center pedestal, have larger internal working space, and have the correct stab trim cut-off toggles.

There are inherent visual differences between the 500 series and NG style throttles; however, the differences are marginal and if engineered correctly, the differences can be rectified.  The main disparity that cannot be altered is the flap gate détentes.  In the NG style throttle the détentes are equally spaced where in the 500 series they are not.

Main differences abetween NG and 500 series throttles are:

(i)      Flap détentes;
(ii)     Speedbrake lever handle/knob (thinner in NG);
(iii)    Throttle lever shrouds (enclosed in NG);
(iv)    Stab trim indicator tabs (defined points on the tabs in NG);
(v)     Square TOGA button assembly (part of shrouds in NG); and,
(vi)    Stab trim cut-out paddles/toggles (T-Lockers in the NG).

To Avoid Confusion - Throttle Conversions

As you peruse this website you will discover several posts that appear to deal with different throttle quadrants.  This is because since the inception of the B737 Project in 2011, two OEM throttle units have been used.  The second throttle was rebuilt in 2015 to rectify several persistent and inconsistent problems.

LEFT:  Throttle detail showing flaps lever and distinctive NG stab trim cut-off toggles (T-Lockers).  Despite the NG units appearing more stylish than earlier series  throttle units, they are still utilitarian (click to enlarge).

The first throttle unit was from a B737-300 with a two-bay center pedestal.  This was converted by Northern Flight Simulations in 2011.  This throttle did not include any automation – it was a manual throttle only.

I was not overly happy with the conversion and the throttle was subsequently sold and replaced, in 2013, by the second throttle unit - from a B737-500 quadrant with a three-bay center pedestal.  This unit was converted to NG style with full automation.

In 2014, this throttle unit was modified with advanced technology to improve the automation, amongst other improvements.  The 'rebuild' was completed in May 2015.

Evolutionary Process

The conversion of the throttle unit has been an 'evolutionary process' and the 2015 advanced conversion has incorporated high-level mechanical and software engineering.  The design and operation duplicates the systems in the real aircraft, and of those used in high-level commercial simulators that are used for pilot training.

LEFT:  The new throttle unit wrapped in bubble wrap (click to enlarge).

The following link will open a page that deals with the conversion of the 300 series and 500 series throttle units.   The current throttle, a rebuild of the second unit is documented below.


Advanced Conversion (rebuild) - B737-500 Throttle Quadrant (current throttle unit as at 2015)

The throttle unit, in its previous revision, worked well, but there were several matters which needed attention, especially concerning the automation and functionality.  There were also 'niggling' issues with how the clutch assembly operated - it was somewhat loose which caused several flow-on problems.  The result was that the throttle unit was completely rebuilt from the ground up. 

Although the outside may appear identical to the earlier quadrant, the rebuild has replaced nearly everything inside the quadrant and the final product is far more reliable than its predecessor.

Dedicated Interface Modules

Of importance, is the replacement of the trial Interface Master Module (IMM) (1) which was responsible for controlling much of the functionality of the earlier used throttle unit, with two dedicated modules.  The modules accommodate the interface cards and wiring that controls the function of the throttle unit.  There are no Interface cards in or mounted to the forward section of the throttle unit.  Likewise, wiring has been kept to a minimum.

The throttle quadrant directly interfaces with two dedicated modules called the:

Both of these modules contain only the interface cards, relays and other components required to operate the throttle and automation.  Additionally, the system incorporates a revised Interface Alert System which evolved from the original concept used in the IMM.

Advances and Improvement

The improvements have primarily been to the automation, the autothrottle and the speedbrake system. 

LEFT:  Throttle quadrant installed into the simulator (click to enlarge).

However, during the rebuild other functionality has also been improved.  The synchronised movement of the thrust levers is now more consistent and reliable,  and an updated system to operate the parking brake has also been devised. 

The parking brake system replicates the system used in the real aircraft in which the toe brakes must be depressed before the parking lever can set or disengaged.

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

In the previous throttle unit, there was an issue with the speedbrake not reliably engaging on landing.  This in part was caused by a motor that was not powerful enough to push the lever to the UP position with consistent reliability. 

LEFT:  I was fortunate that the light plates in the throttle were in very good condition.  All backlighting to the unit is 5 volts (click to enlarge).

This motor has been replaced with a motor more suitable to the power requirement needed.  The speedbrake is mechanical, mimics the real counterpart in functionality, and does not require software to operate.

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

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

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

Flight Testing

Flight testing is a rigorous and time-consuming task.  During the test period, it is anticipated that minor ‘teething issues’ will occur, and these issues will be rectified on the fly.

LEFT:  The clean white colored lines of an NG throttle are unmistakable (click to enlarge).

Journal Posts

The posts that document the conversion of the Boeing 737 throttle to Flight Simulator have generated considerable interest.  To consolidate the posts for retrieval, I have provided links to those posts that deal with the conversion of the throttle quadrant.  These links only relate to the second throttle quadrant (B737-500 conversion) and do not relate to the B737-300 throttle which was sold in early 2012.
Any post after 2013 refers only to the current throttle unit in its original or rebuilt format.

The links below relate only to the conversion of B737-500 throttle quadrant:

The links below relate ONLY to the advanced rebuild of the B737-500 throttle quadrant:

Information concerning the center pedestal is located on a sister page.