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 8.20.7
YK988 - YW274
The lavatory smoke detection system monitors for the presence of smoke. When
smoke is detected:
• an aural warning sounds
• the red status indicator light on the lavatory smoke detector panel
illuminates.
YK981 - YK987
There is no flight deck indication. When smoke is no longer present, ALARM
MODE is reset by pressing the INTERRUPT switch.
YK988 - YW274
There is no flight deck indication. When smoke is no longer present, the system
automatically resets.
Lavatory Fire Extinguisher System
A fire extinguisher system is located beneath the sink area in each lavatory. When
a fire is detected:
• fire extinguisher operation is automatic
• flight deck has no indication of extinguisher discharge.
Fire and Overheat System Tests
The fire and overheat detection systems can be tested by pushing and holding the
FAULT/INOP and OVHT/FIRE TEST switch. Extinguisher continuity can be
tested by pushing and holding the EXT TEST switch. All test indications clear
when switches are released.
FAULT/INOP Test Detection
The fault detection circuits for both the engines and the APU are tested by pushing
and holding the FAULT/INOP and OVHT/FIRE TEST switch in the
FAULT/INOP position.
The indications for the FAULT/INOP test are:
• both MASTER CAUTION lights illuminate
• the OVHT/DET system annunciator light illuminates
• the FAULT light illuminates
• the APU DET INOP light illuminates.
OVERHEAT/FIRE Test Detection
The overheat and fire detection loops on both engines, the APU, and the fire
detector in the wheel well are tested by pushing and holding the FAULT/INOP and
OVHT/FIRE TEST switch in the OVHT/FIRE position.
September 15, 2016
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