(2)  
Squibs are replaced more frequently than the fire extinguisher bottles. A manufacturer's date is on the edge of the squib. See the manufacturer's instructions for the specified life of the squib.

 WARNING: DO NOT TOUCH THE SQUIB BEFORE YOU DO THE PROCEDURES FOR DEVICES
_______ THAT ARE SENSITIVE TO ELECTROSTATIC DISCHARGE. ELECTROSTATIC DISCHARGE CAN CAUSE THE FIRE BOTTLES TO RELEASE ITS CONTENTS SUDDENLY AND CAUSE INJURY TO PERSONS AND DAMAGE TO EQUIPMENT.
 (3)  Before you touch the squib, do the procedure for devices that are sensitive to electrostatic discharge (AMM 20-41-02/201).
 B.  References
 (1)  
AMM 20-41-02/201, Electrostatic Discharge Sensitive Devices

 (2)  
AMM 26-21-04/401, Engine Fire Extinguisher Bottle Discharge Cartridge (Squib)

 (3)  
AIPC 26-21-03 Fig. 1

 (4)  
WDM 26-21-01 thru WDM 26-21-04

 C.  Access
 (1)  Location Zones
 514 Krueger Flap No.1, Left
 614 Krueger Flap No.1, Right

 D.  Procedure
 S 026-006
 WARNING: PUT A PROTECTIVE COVER ON THE SQUIB WHEN YOU DISCONNECT THE
_______ ELECTRICAL CONNECTOR FROM THE SQUIB. THE SQUIB IS AN ELECTRICALLY FIRED EXPLOSIVE DEVICE. IF THE SQUIB FIRES, THE BOTTLE WILL SUDDENLY RELEASE ITS CONTENTS AND CAN CAUSE INJURY TO PERSONS.
 (1)  Remove the squib (AMM 26-21-04/401).
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A
747-400 MAINTENANCE MANUAL
SEE A
EXTINGUISHER BOTTLE, M228 THRU M231
MOUNTING LUG 
GLAND NUT (TIGHTEN TO 55 TO 65 POUND-FEET)  PRESSURE SWITCH ELECTRICAL CONNECTOR 
ASSEMBLY GROUNG LUG  PORT DISCHARGE 
O-RING 
ELECTRICAL CONNECTOR  (SQUIB) CARTRIDGE DISCHARGE 
ENGINE FIRE EXTINGUISHER BOTTLE A 

Engine Fire Extinguisher Bottle Discharge Cartridge (Squib) Check
Figure 601

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L81898
A 747-400 MAINTENANCE MANUAL
 (2)  S 216-003Examine the squib for damage. (a) Examine the soft seal which seals the explosive cartridge. 1) Replace the seal if it is damaged. (b) If the squib has corrosion on the threads between the O-ring and the sealed end, replace the squib.
 (3)  S 216-004Examine the date on the edge of the squib. (a) If the squib has been installed more than the manufacturer's recommended life, replace the squib.
 (4)  S 426-005Install the squib (AMM 26-21-04/401).

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 1.

2.

3.

4.

A
747-400 MAINTENANCE MANUAL
 APU FIRE EXTINGUISHING SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________________General
_______
 A.  The APU fire extinguishing system is a gaseous smothering system designed to flood the auxiliary power unit with an inert gas in case of fire.
 B.  The APU fire extinguishing system includes the APU fire extinguisher bottle, the fire control module, the APU fire shutdown module, and the squib test module.
 C.  The APU fire extinguishing system receives power from the 28 V DC hot
 battery bus.APU Fire Extinguisher Bottle (Fig. 1)
____________________________
 A.  The fire extinguisher bottle and a single discharge line are located on the lower left forward side of the APU firewall. A single discharge nozzle is provided in the APU compartment.
 B.  The bottle contains a squib, a discharge port, a pressure switch, and a fill/safety relief valve. The bottle is hermetically sealed by welding. The bottle capacity is 18.0 +0.25/-0.00 pounds of Halon 1301, and the pressurizing gas is dry nitrogen.
　
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