737 Flight Crew Operations Manual
Fire Protection -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 8.20.5
Rotating the APU fire switch in either direction electrically “fires” the squib
discharging the extinguishing agent into the APU. The APU BOTTLE
DISCHARGE light illuminates after a few seconds, indicating the bottle has
discharged.
Main Wheel Well Fire Protection
Main wheel well fire protection consists of fire detection powered by the No. 2 AC
transfer bus.
Note: The main wheel well has no fire extinguishing system. The nose wheel
well does not have a fire detection system.
Main Wheel Well Fire Detection
A single fire detector loop is installed in the main wheel well. As the temperature
of the detector increases to a predetermined limit, the detector senses a fire
condition. The WHEEL WELL fire warning light remains illuminated until the
temperature of the detector has decreased below the onset temperature.
The indications for a main wheel well fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the WHEEL WELL fire warning light illuminates.
Cargo Compartment Fire Protection
Cargo fire protection consists of these systems:
• cargo compartment smoke detection powered by DC bus 1 and DC bus
2
• cargo compartment fire extinguishing powered by the hot battery bus.
Cargo Compartment Smoke Detection
The forward and aft cargo compartments each have smoke detectors in a dual loop
configuration. Normally, both detection loops must sense smoke to cause an alert.
In the event of a detector failure, the system can be manually converted to
single-loop detection through the DETECT SELECT switch on the cargo fire
control panel. In the event of a power failure in one loop the system automatically
converts to single-loop detection.
Cargo Compartment Fire Warning
The indications of a cargo compartment fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the FWD/AFT cargo fire warning light(s) illuminates.
September 24, 2015
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