777 AIRCRAFT MAINTENANCE MANUAL

APU FIRE EXTINGUISHING -APU FIRE SWITCH

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APU FIRE EXTINGUISHING -P40 SERVICE AND APU SHUTDOWN PANEL

Purpose
The P40 service and APU shutdown panel gives warnings outside the airplane of an APU fire. The panel has APU fire extinguishing controls with easy access from outside the airplane. The panel also gives easy access to controls for other service equipment.
Physical Description
The panel has this fire protection equipment:
*
APU fire warning horn

*
APU fire bottle armed light

*
APU fire bottle discharged light

*
APU bottle discharge switch

*
APU fire shutdown switch

*
APU fire warning light.

Training Information Point
With the battery switch on, push these lights to make sure they operate:
*
APU fire bottle armed light

*
APU fire bottle discharged light.

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APU FIRE EXTINGUISHING -P40 SERVICE AND APU SHUTDOWN PANEL

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APU FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -FIRE SWITCH CIRCUIT

Warning Light and Solenoid Operation
The APU fire warning light comes on if there is an APU fire. The solenoid energizes and releases the fire switch so you can pull it.
This also occurs while you do a fire/overheat test.
Out Position
When you pull the fire switch, these functions occur:
*
The generator field trips

*
The APU fuel shutoff valve closes

*
The APU shutoff valve closes

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The APU stops

*
EICAS messages which are not necessary do not show

*
Fire warnings at the P40 panel are canceled.

Discharge Positions
The left or right DISCH position fires the APU fire extinguishing bottle squib.
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APU FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -FIRE SWITCH CIRCUIT

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D633W101-BEJ  Jan 05/2002 

APU FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -APU FIRE EXTINGUISHING CIRCUIT

General
The APU fire extinguishing bottle squib fires for these three conditions:
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Unattended fire alarm

*
Controls on the P40 service and APU shutdown panel are operated

*
Flight deck fire switch is operated.

For each condition, power comes from the 28v dc hot battery bus.
Unattended Fire Alarm
Fire alarm 1 from the APU control card makes a ground for the APU remote warning relay. The relay energizes if the APU fire switch on P5 is not out. The unattended fire alarm makes a ground for the APU auto fire bottle discharge relay. The relay energizes after a 10-second delay. Power from the hot battery bus goes through the relay contacts to the squib.
Service and APU Shutdown Panel
The APU external shutdown relay energizes when you push the APU fire shutdown switch. The relay latches through its own contact and the fire/overheat test switch. With the relay energized, the fire bottle armed light comes on and power goes to the APU bottle discharge switch. When you push the APU bottle discharge switch, the squib fires.
Flight Deck Fire Switch
When the APU fire switch is in the left or right discharge position, power from the hot battery bus fires the squib.
Indications
When pressure inside the bottle decreases, the pressure switch closes and makes a ground for the discharge indicator lights. The ground also causes advisory and status messages.
When you push the APU fire shutdown switch, the APU external shutdown relay latches through its own contact and the fire/ overheat test switch. A ground for the APU fuel system closes the APU fuel shutoff valve. The ground signal to ELMS causes an EICAS status message. The message shows a remote APU shutdown and stays until you do a fire/overheat test to release the relay. You cannot start the APU with the relay latched.
Training Information Point
You can do a check of the pressure switch circuit on the ground. Push and hold the bottle pressure switch test button to close the switch. The bottle discharge lights on the P5 and P40 panels must come on. Bottle discharge advisory and status messages must show.
EFFECTIVITY BEJ ALL  26-22-00 
　
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