APU FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -APU FIRE EXTINGUISHING CIRCUIT
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APU FIRE EXTINGUISHING -OPERATION -FLIGHT DECK
General
The APU operates in the unattended mode when the airplane is on the ground with the engines not running. If there is an APU fire in the unattended mode, the fire extinguisher discharges automatically.
If there is a fire during attended mode operation, the fire extinguisher does not discharge automatically. Fire warnings are the same in attended and unattended modes.
APU Fire Warning
If there is an APU fire, the APU fire detection system gives fire warnings and automatically stops the APU. The APU fire warning light comes on to identify the correct fire switch to use to extinguish the fire. The fire switch solenoid releases the switch so you can pull it.
Fire Switch Out
If the APU is on, it stops when you pull the fire switch. The fire switch isolates the APU from the airplane systems.
Fire Bottle Discharge
If the fire warnings do not go away with the switch out, put the switch to the left or right DISCH position. Hold the switch against the discharge stop for one second. This fires the bottle squib and releases the fire extinguishing agent into the APU compartment. Make sure the APU bottle discharge light comes on.
Discharge Indications
The APU bottle discharge light comes on when halon goes out of the bottle. Advisory and status messages also show.
Training Information Point
The fire override switch lets you pull the switch when the solenoid is not energized.
The switch releases during a fire and while you do a fire/ overheat test.
The APU fire switch connects to the hot battery bus. You can discharge the APU fire bottle with the battery switch off and without ground power on the airplane.
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APU FIRE EXTINGUISHING -OPERATION -FLIGHT DECK
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APU FIRE EXTINGUISHING -OPERATION -P40 SERVICE AND APU SHUTDOWN PANEL
General
If the APU has a fire during ground operation, the APU fire detection system gives a fire warning at the P40 service and APU shutdown panel. The APU fire warning light comes on and the APU fire warning horn operates intermittently.
APU Fire Extinguishing
When you push the APU fire shutdown switch, these things happen:
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The fire extinguishing system arms
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The fire warning horn stops
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If the APU is still running it stops
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The APU fuel shutoff valve closes.
Make sure the fire bottle armed light comes on.
If the fire warning light stays on after you push the fire shutdown switch, push the bottle discharge switch to discharge the fire extinguisher bottle. Make sure the bottle discharged light comes on.
Training Information Point
When you push the APU fire shutdown switch, the circuit latches through the fire/overheat test switch in the flight deck. A status message shows a remote APU shutdown. You cannot start the APU with the circuit latched. Do a fire/overheat test to release the circuit and remove the status message. Also make sure the circuit is released before you replace the fire extinguishing bottle.
NOTE: The APU fire switches connect to the hot battery bus. If you push the APU fire shutdown switch and the bottle discharge switch, the APU fire bottle discharges. This happens with the battery switch ON or OFF, and with or without ground power on the airplane.
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APU FIRE EXTINGUISHING -OPERATION -P40 SERVICE AND APU SHUTDOWN PANEL
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777 AIRCRAFT MAINTENANCE MANUAL
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LOWER CARGO FIRE EXTINGUISHING -INTRODUCTION
Purpose
The lower cargo fire extinguishing system extinguishes fires in the forward or aft lower cargo compartments.
General Description
The lower cargo fire extinguishing system has these components:
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Three fire extinguishing metered bottles
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A filter regulator
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Fwd and aft in-line pressure switches
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Two flow valves
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Two fire extinguishing dump bottles
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Eight discharge nozzles.
The fire extinguishing bottles contain halon 1301 fire extinguishing agent pressurized with nitrogen. Tubing connects the bottles to discharge nozzles in the cargo compartment ceilings. Flow valves send the halon to the forward or aft compartment.
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