S 755-166

 (25)
 Make sure that all the lights on the P8-1 panel are not on.

 K. Put the Airplane back to its usual condition.
 S 865-167
 (1)  
Lockwire the connectors.

 S 865-168

 (2)  
Close the APU access door and access door 3701.

 S 865-169

 (3)  
Remove electrical power if it its no longer neccessary (AMM 24-22-00/201).

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 26-21-51
 ALL  ú ú 04 Page 520 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

2.

3.

A
737-300/400/500MAINTENANCE MANUAL
 APU FIRE EXTINGUISHING SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________________
General
_______
 A.  The APU fire extinguishing system has controls in two locations that release one application of fire extinguishing agent in the APU compartment.
 B.  The APU fire extinguishing system includes the fire extinguisher bottle, the engine and APU fire control panel, and the APU ground control panel.
 C.  The APU fire extinguishing system receives power from the 28-volt dc hot battery bus through APU FIRE EXT BOTTLE circuit breaker on main power distribution panel P6.
APU Fire Extinguisher Bottle (Fig. 1)
____________________________
 A.  The APU fire extinguisher bottle is on the lower right side of empennage section. The extinguisher bottle includes a squib, pressure switch, filling port, and discharge port.
 B.  The squib, when detonated, ruptures a retaining disc in the discharge port releasing the extinguishing agent.
 C.  The fire extingushing agent is non-corrosive and will not damage the APU. There are no special inspection or cleaning procedures required if the agent is discharged in the APU compartment when there is no fire.
 D.  The pressure switch activates bottle discharge lights when the bottle is discharged or pressure drops.
 E.  The filling port plug is a metal plug with a fusible metal core which acts as a safety relief valve. From the safety relief valve on the bottle, a tube leads to the lower fuselage skin near the bottle where it is capped with a red indicator disk. If the bottle temperature rises to approximately 266°F, the fusible core will melt and the bottle pressure will rupture the indicator disk, dumping the extinguishing agent overboard.
Engine and APU Fire Control Panel (Fig. 1)
_________________________________
 A.  APU fire extinguishing system components of the engine and APU fire control panel are the APU fire switch handle, extinguisher test switch, APU bottle discharge light, and APU extinguisher test light. The engine and APU fire control panel is on the aft electronics panel of the pilots' control stand.
 (1)  
When a fire is detected in the APU compartment, the APU fire switch handle light comes on. A solenoid energizes, releasing a mechanical interlock on the fire switch handle shaft. When the interlock is released, the fire switch handle can be operated by pulling the handle out and rotating it. Rotating the handle releases the extinguishing agent. The fire switch handle can be manually unlocked by pressing the button behind the handle.

 (2)  
The extinguisher test switch, when set to either 1 or 2, checks squib continuity. The APU extinguisher test light illuminates if there is continuity.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 26-22-00
 ALL  ú ú 11 Page 1 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
28V DC
HOT BAT
BUS C452

APU FIRE
EXT BOTTLE

P6-2 CIRCUIT BREAKER PANEL
NORMAL L11 APU BOTTLECCWTEST LIGHT
CW 2
2
APU
28V DCSHUTOFF
MASTER
HANDLE RELEASE
1
WARN AND
APU FUEL
VALVE

CONTROL SHUTOFF
NORMAL
MD&T
FIRE

APU GEN SHUTOFF
S16  APU REMOTE
FIRE SW

M1146SQUIB CLOSEAPU FUEL VALVE
S1 TEST SWITCH
FIRE
1
S10  APU FIRE SW
(P8-1)
　
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