System Description by Don Pierce: Nacelle/Pylon Overheat

"Don Pierce is a L-1011 Flight Test Engineer (Ship 3), then in Customer Training, then he had his own business doing maintenance training for L-1011 customers. Don is nothing but amazing in his knowledge of the L-1011. I am going to post several conversations on systems that I have had with Don over the past few weeks"

This is a topic that is part of ATA 36, Pneumatics, but does not appear on the Pneumatics panel. It has its own panel, with is at the top of the FE panel.

It is similar to Area Overheat, but also has many differences. The panel has two loop lights (A and B) per engine - at the top of the panel (not switchlights) . There are also three Loop Selector switches (one per engine) - A/BOTH/B - plus one TEST button on the panel.

Generally explained, there are two loops (A and B) per engine, located near the exhaust of a nacelle cooling vent; these are the nacelle sensors This applies to all three engines.

For the wing engines (#1 and #3), there are two more loops (A and B) near the exhaust vent for the pylon. For the center engine (#2) instead of a pylon, the engine is mounted on a "center engine support structure". This engine has three set of sensors that together qualify as the "pylon sensors". One set of loops (A and B) is located just above the engine and below the horizontal "mounting plate" for the engine. The other two sets are individual sets (A and B) mounted on a bracket to the left and to the right of the engine's pneumatic supply ducting; this is technically considered the pylon for the center engine.

If an overheat condition is sensed, the sensor will send a signal to an Overheat Control, located in the Mid Electrical Service Center (MESC), which in turn will illuminate the A and/or B light(s) on the FE panel - depending on which loop(s) send an overheat signal. At the same time the overheat controller will send a signal to close and lockout the High Pressure (HP) valve. The FE can then use the TEST switch and rotary select switch, as described for the Area Overheat system. If the FE determines it is a faulty signal, and has isolated the faulty loop, or after an overheat signal has cleared itself - the HP valve will not reopen automatically. The HP switchlight must be cycled (unlatched and then latched in) to de-energine a lockout relay, and allow the HP valve to reopen again.

For Area Overheat, no valve closed automatically. For Nacelle/Pylon Overheat, the HP valve does close automatically.

For Area Overheat, there is only one Loop Select switch, which means all nine channels will be monitoring the same loop(s). For Nacelle/Pylon Overheat, there are three loop select switches, so each engine can be set as desired.