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.
8.20.2 D6-27370-866-EGP
The indications of an engine fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the related engine fire switch illuminates
YW273, YW274
• the related engine start lever illuminates
• all related engine overheat alert indications illuminate.
Engine Fire Extinguishing
The engine fire extinguisher system consists of two engine fire extinguisher
bottles, two engine fire switches, two BOTTLE DISCHARGE lights, and an EXT
TEST switch. Either or both bottles can be discharged into either engine.
The engine fire switches are normally locked down to prevent inadvertent
shutdown of an engine. Illumination of an engine fire switch or ENG OVERHEAT
light unlocks the engine fire switch. The switches may also be unlocked manually.
Pulling the engine fire switch up:
• closes both the engine fuel shutoff valve and the spar fuel shutoff valve
• closes the engine bleed air valve resulting in loss of wing anti–ice to the
affected wing and closure of bleed air operated pack valve
• trips the generator control relay and breaker
• closes the hydraulic fluid shutoff valve. The engine driven hydraulic
pump LOW PRESSURE light is deactivated
• disables thrust reverser for the related engine.
• allows the engine fire switch to be rotated for discharge
• arms one discharge squib on each engine fire extinguisher bottle.
Rotating the engine fire switch electrically “fires” a squib, discharging the
extinguishing agent into the related engine. Rotating the switch the other way
discharges the remaining bottle.
The L or R BOTTLE DISCHARGE light illuminates a few seconds after the
engine fire switch is rotated, indicating the bottle has discharged.
September 15, 2016
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