Overheat / Fire Protection Panel 3-900 series
Overheat / Fire Protection Panel -200C series. Notice fwd & aft cargo smoke detectors.
Engine & APU fire detection – Battery bus
Engine, APU & Cargo fire extinguishing – Hot battery bus.
There are two fire detection loops in each engine. Failure of both loops in one engine will illuminate the FAULT light. The individual loops can be checked by selecting A or B on the OVHT DET switches.
Fire switches will unlock in the following situations:
- Overheat detected
- Fire detected
- During an OVHT/FIRE test
- Pressing manual override buttons
Pulling a fire switch will do the following:
- Arm firing circuits
- Allow fire switch to be rotated for discharge
- Close engine fuel shut-off valve.
- Trip the associated GCR (i.e. switches off the generator)
- Close hydraulic supply to EDP & disarms its LP light (Not if APU)
- Close engine bleed air valve (If APU will also close air inlet door)
- Close thrust reverser isolation valve (Not if APU)
The engine fire bottles (NG)
There is a wheel-well fire detection system but although the engine fire bottles are located in the wheel-well, there is no extinguishing system for a wheel-well fire. (Suggest extend gear & land ASAP).
The APU only has one bottle. This may be checked externally by looking for the two discharge discs (red for thermal overpressure & yellow for extinguisher discharge) and the pressure sight glass (where fitted) on the aft stbd fuselage.
Cargo Compartment (Optional)
Cargo Fire Panel - Alternative version
Cargo Hold Smoke Detector
Some 737's have a warning light on the flight deck to warn of smoke in the lavatory. If the smoker is in the forward lav you can usually smell it on the flight deck within seconds without a warning light.
Passenger Compartment (Optional)
The cargo 737's had a pressurisation feature which allowed the crew to pressurise or unpressurise the passenger compartment for smoke clearance.