26-22-02
 ALL  ú ú 04 Page 602 ú Feb 18/01
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A 747-400 MAINTENANCE MANUAL
 (3)  S 216-003Examine the squib for damage.
 (4)  S 216-007Make sure the soft seal on the electrical connector is not damaged. (a) If the seal has a hole, is broken, cut, or corroded, replace it with a new seal. (b) If squib has corrosion on it's threads, past the O-ring toward the sealed end, replace the squib.
 (5)  S 216-004Examine the date on side of squib.
 (6)  S 966-008If service life has exceeded the manufacturer's maximum service life, replace the squib.
 (7)  S 426-005Install the squib (AMM 26-22-02/401), if it is applicable.

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 ALL  ú ú 01 Page 603 ú Oct 10/96
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A
747-400 MAINTENANCE MANUAL
 LOWER CARGO COMPARTMENT FIRE EXTINGUISHING SYSTEM -
_________________________________________________ DESCRIPTION AND OPERATION
_________________________
 1.  General_______
 A.  The lower cargo compartment fire extinguishing system is designed to fill the forward or aft cargo compartment with a fire extinguishing agent when smoke is detected. The system is electrically controlled by switches on the P5 pilot's overhead panel.
 B.  The system includes the following: four lower cargo compartment fire extinguisher bottles, the fire control module, the squib test module, two filter/driers, two regulators, and tubing to carry extinguishing agent to the appropriate compartment.
 C.  The system includes the following: four lower cargo compartment fire extinguisher bottles, the fire control module, the squib test module, two filter/driers, two regulators, and tubing to carry extinguishing agent to the appropriate compartment.
 D.  The lower cargo compartment fire extinguishing system receives power from the 28-volt dc hot battery bus 1 or 2.
 2.  Fire Extinguisher Bottle (Fig. 1)________________________
 A.  Description
 (1)  
Four lower cargo compartment fire extinguisher bottles are located aft of the forward cargo door on the right side of the cargo compartment. The fire extinguisher bottle includes two discharge cartridges (squib), a temperature compensated pressure switch, and a combined safety relief and filler port.

 (2)  
The squib cartridges are on the discharge valves of each extinguisher bottle. When detonated, the cartridge ruptures a retaining disc in the valve releasing the extinguishing agent.

 (3)  
The extinguishing agent is Halon 1301 (CBrF3), and the pressurizing gas is dry nitrogen. The agent leaves no residue when discharged.

 B.  Pressure Switch
 (1)  
The pressure switch on the extinguisher bottle detects a decrease in bottle pressure, and activates bottle discharge lights and sends EICAS messages. The pressure switch is temperature compensated, which nullifies the temperature effects between -65°F and 160°F.

 (2)  
A discharge line pressure switch (S1890) in the forward and aft compartment distribution tubing for extinguisher bottle 1 and 2 is connected in parallel with the pressure switch on extinguisher bottles 1 and 2. The discharge line pressure switch recognizes bottle discharge prior to the temperature compensated pressure switch on the extinguisher bottles. The discharge line pressure switch gives an immediate indication (EICAS message: CARGO BTL DISCH) that extinguishing agent is being released in the forward or aft compartment. A reset switch on the discharge line pressure switch should be pressed after servicing the fire extinguishing system.

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