K13322 K13262
Cargo Compartment Fire Extinguishing System Location  500 
26-25-0  Figure 1 (Sheet 1)  May 01/01 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

500  Cargo Compartment Fire Extinguishing System Location 
May 01/01  Figure 1 (Sheet 2)  26-25-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(b)  
The Pressure Switch monitors the pressure in the bottle. The switch will be open when the bottle is fully charged. If the pressure in the bottle is below 300 psig (at 70°F), then the switch will close and will send a signal to the flight compartment that the pressure in the bottle is too low. The pressure switch compensates for the temperature of the bottle to maintain an accurate pressure indication.

(c)  
The Filler/Safety Port contains a fusible metal plug that acts as a safety relief valve if excessive temperature causes an over-pressure condition in the bottle.

B.  Cargo Fire Control Panel (P8)
(1)  The Cargo Fire Control Panel is installed in the flight compartment in the P8 panel. The components on the panel that control and monitor the cargo fire extinguishing system are the TEST switch, the ARM switches, The DISCH switch and the EXT lights.
(a)  
The TEST switch is used to initiate a test of the squib circuit and the cargo smoke detection system (AMM 26-26-50/401). When the TEST switch is pushed, a low circuit (1 amp) signal is sent through the FWD and AFT squibs to check for continuity. If the squib circuit is continuous, then the FWD EXT and AFT EXT lights (Green) will illuminate. 

(b)  
When smoke is detected in the forward or aft cargo compartments, then the applicable FWD or AFT ARM light will come on. The appropriate FWD or AFT ARM switch must be pushed to the ARMED position before the bottle can be discharged. When the ARMED switch is pushed and then the DISCH switch is pushed, a signal is sent to the applicable squib to fire the squib and release the halon to the applicable area.

(c)  
When the cargo fire extinguishing bottle is discharged, or the pressure in the bottle is too low, the DISCH light (Amber) will illuminate. The DISCH light can only be tested by the Master Dim and Test switch.

(d)  
The DISCH switch is a guarded, momentary action switch. The ARMED switch is an alternate (latched) action switch.

3.  Operation (Fig. 2)
A.  Functional Description 
(1)  When smoke is detected in the forward or aft cargo compartments, then the applicable FWD or AFT ARM light, on the cargo fire control panel, (P8), will illuminate. The appropriate FWD or AFT ARM switch must be pushed to the ARMED position before the bottles can be discharged. A white ARMED sign will appear on the ARM switch when the system is armed. When the ARM switch is in the ARMED position and then the DISCH switch is pushed, a signal is sent to the applicable squib to fire the squib and release the halon to the applicable area.
500 
26-25-0 Page 4  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/99 

K13353
500  Cargo Compartment Extinguishing Schematic 
May 01/99  Figure 2  26-25-0 
Page 5 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(2)  
When the applicable discharge disc is ruptured by the squib explosion, the halon flows through that discharge port, into the tubing to the nozzles. The nozzles spray the halon throughout the cargo compartment. Flooding the compartment with halon gas decreases the amount of oxygen in the compartment and extinguishes the fire. The halon does not leave any residue and does not require any cleanup afterwards.

(3)  
When the cargo fire extinguishing bottle is discharged, or the pressure in the bottle is too low, the DISCH light (Amber) will illuminate.

(4)  
After a bottle is discharged, you must ensure there are no disc particles in the tubing or nozzles (AMM 26-25-0/701) and the bottle must be replaced.

B.  Testing
(1)  Squib Test
(a)  
The TEST switch on the cargo fire control panel (P8) will initiate a continuity test of the fire extinguishing squib circuits. When you push the TEST switch, a low current signal will be sent through the FWD and AFT squib circuits. If both squib circuits are continuous, then the FWD EXT light (Green) and the AFT EXT light (Green) will illuminate. If one of the squib circuits is not continuous, then the applicable EXT light will not illuminate.
　
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