Fire Protection – B737

Engines

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:

  1. Overheat detected
  2. Fire detected
  3. During an OVHT/FIRE test
  4. Pressing manual override buttons

Pulling a fire switch will do the following:

  1. Arm firing circuits
  2. Allow fire switch to be rotated for discharge
  3. Close engine fuel shut-off valve.
  4. Trip the associated GCR (i.e. switches off the generator)
  5. Close hydraulic supply to EDP & disarms its LP light (Not if APU)
  6. Close engine bleed air valve (If APU will also close air inlet door)
  7. Close thrust reverser isolation valve (Not if APU)

The engine fire bottles (NG)

 

Wheel-Well

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).

 

APU

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

Cargo Fire Panel – Alternative version

The cargo holds have dual-loop smoke detectors powered by DC bus 1 & 2. There is only one cargo fire bottle, it is powered by the hot battery bus and can be discharged into either the fwd or aft hold. On later 737NG’s the cargo fire smoke detector sends a signal to the cabin pressure control system. This triggers the cabin pressure to descend at 750 slfpm which helps prevent smoke penetration into the passenger cabin from the lower lobe. (This function is inhibited on the ground.)

Cargo Hold Smoke Detector

Lavatory Smoke Detection (Optional)

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.

 


Engines

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:

  1. Overheat detected
  2. Fire detected
  3. During an OVHT/FIRE test
  4. Pressing manual override buttons

Pulling a fire switch will do the following:

  1. Arm firing circuits
  2. Allow fire switch to be rotated for discharge
  3. Close engine fuel shut-off valve.
  4. Trip the associated GCR (i.e. switches off the generator)
  5. Close hydraulic supply to EDP & disarms its LP light (Not if APU)
  6. Close engine bleed air valve (If APU will also close air inlet door)
  7. Close thrust reverser isolation valve (Not if APU)

The engine fire bottles (NG)

Wheel-Well

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).

APU

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

Cargo Fire Panel – Alternative version

The cargo holds have dual-loop smoke detectors powered by DC bus 1 & 2. There is only one cargo fire bottle, it is powered by the hot battery bus and can be discharged into either the fwd or aft hold. On later 737NG’s the cargo fire smoke detector sends a signal to the cabin pressure control system. This triggers the cabin pressure to descend at 750 slfpm which helps prevent smoke penetration into the passenger cabin from the lower lobe. (This function is inhibited on the ground.)

Cargo Hold Smoke Detector

Lavatory Smoke Detection (Optional)

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.

See also NG engineering notes by M Ferreira

Jet Time Expands MRO With Dublin

Dublin Aerospace announced on Sept. 2 that Jet Time, one the MRO’s first landing gear customers, signed an overhaul contract valued in “the low million” euros range for Honeywell 131-9B and Honeywell 85-sereis auxiliary power units (APU) on the Danish carrier’s Boeing 737s, says Frank Burke, head of sales for the privately held, two-year-old company. This five-year deal also provides Jet Time with a loaner APU if one has a problem on-wing so the aircraft remains operational while Dublin Aerospace refurbishes then returns the APU.

Dublin Aerospace has six 85 series APUs and two 131-9Bs that can serve as loaner units.

Burke estimates 7-10 APUs will fail during the contract with Jet Time and another 10 will require repairs, based on the carrier’s fleet size.

The MRO’s APU shop is about 70% full, “but our capacity can increase easily;” its base maintenance is about 90% full and has been “solid” since last October; and its landing gear shop is about 80% full, says Burke.

This year Dublin Aerospace started overhauling easyJet’s Airbus A319 landing gear as part of a five-year contract, which was a big win for the company founded in 2009 by executive chairman Conor McCarthy, who previously held senior leadership positions at Aer Lingus and Rynair.

Jet Time was one of Dublin Aerospace’s first customers.

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