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.
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.
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.
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.
Note that as of 2014 this throttle quadrant was revamped to upgrade the clutch assembly and much of the internal wiring.