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APU fire extinguishing bottle squib
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Cargo fire/engine control module
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APU fire switches
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Service and APU shutdown panel.
The APU operates in the unattended mode when the airplane is on the ground and the engines are not running. In the this mode, a signal from the APU fire detection system discharges the fire bottle automatically.
The APU operates in the attended mode when at least one engine is running. If there is an APU fire in this mode, the crew discharges the bottle manually. Fire switches are on the cargo fire/engine control panel and the service and APU shutdown panel.
EICAS messages and indicator lights show when the bottle pressure is low.
Operation
The APU fire extinguishing bottle contains halon fire extinguishing agent pressurized with nitrogen. A discharge assembly connects the bottle to a discharge tube. The tube goes to a discharge nozzle in the APU compartment.
An explosive squib inside the discharge assembly releases the halon from the bottle. The squib connects to the fire switches and to the APU fire detection card.
A pressure switch monitors the pressure in the bottle. When the bottle discharges, the switch turns on the discharge indicator lights. The switch also causes EICAS advisory and status messages to show.
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APU FIRE EXTINGUISHING -GENERAL DESCRIPTION
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APU FIRE EXTINGUISHING -COMPONENT LOCATIONS -CONTROL PANELS
Cargo Fire/Engine Control Panel
The cargo fire/engine control panel is in the flight deck on the P5 overhead panel.
P40 Service and APU Shutdown Panel
APU fire controls are on the P40 service and APU shutdown panel. That panel is on the nose landing gear.
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APU FIRE EXTINGUISHING -COMPONENT LOCATIONS -CONTROL PANELS
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APU FIRE EXTINGUISHING -COMPONENT LOCATIONS -FUSELAGE Fuselage Component Location
The APU fire extinguishing bottle is on the left side of the stabilizer compartment.
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APU FIRE EXTINGUISHING -COMPONENT LOCATIONS -FUSELAGE
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APU FIRE EXTINGUISHING -APU FIRE EXTINGUISHING BOTTLE
Purpose
The APU fire extinguishing bottle contains the halon fire extinguishing agent.
Location
The fire extinguishing bottle is on the forward side of the APU firewall, inside the control bay access door.
Physical Description
The fire extinguishing bottle has these components:
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A safety relief and fill port
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An identification plate
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A pressure switch
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A handle
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Two squibs
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Two discharge assemblies
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Four mounting brackets.
The APU fire extinguishing bottle is interchangeable with the engine fire extinguishing bottles. Caps cover one squib and discharge port.
Functional Description
The bottle contains halon fire extinguishing agent pressurized with nitrogen. If the pressure in the bottle becomes too high, the safety relief and fill port opens so the bottle does not explode.
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The discharge assembly has an explosive squib. An electric current from the fire extinguishing circuit fires the squib. This releases the halon through the discharge port.
The pressure switch gives control panel indications when bottle pressure decreases. The switch monitors the pressure inside the bottle and is normally open. When the bottle pressure decreases because of a leak or because of bottle discharge, the switch closes an indicating circuit.
Training Information Point
A special service platform is available to use during bottle replacement.
When you replace the bottle, compare the weight of the new bottle with the weight on the bottle identification plate. This prevents installation of a bottle which is not full.
The fire extinguishing bottle must have a hydrostatic test every 5 years. The date of the last test is on one of the mounting brackets and on an inspection tag. The tag is attached to one of the discharge assemblies.
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