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Isolates the engine from the airplane systems

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Controls the engine fire extinguishing system.

Physical Description
The engine fire switch includes these parts:
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Engine fire warning light

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Solenoid

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Engine fire override switch

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Push-pull switch contacts (internal)

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Rotary switch contacts (internal)

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Electrical connector.

Functional Description
The solenoid locks the fire switch so you cannot pull it accidently. If an engine has a fire, the fire warning light comes on and the solenoid energizes to release the switch.
The fire override switch lets you pull the fire switch when the solenoid is not energized.
When you pull the fire switch, the push-pull switch contacts operate electrical circuits which stop the engine and isolate it from the airplane systems.
With the switch pulled, you can rotate it left or right to a mechanical stop at the discharge position. The rotary switch contacts close and operate the fire extinguishing system.
When you release the switch, a spring moves the switch a small distance from the discharge position to open the rotary switch contacts.
You must put the switch back to the center position before you can push the switch in.
Training Information Point
The left and right engine and APU fire switches are not interchangeable. The fire warning light labels and the electrical connectors are different. The engine fire switches have a hole that engages a peg in the control panel. The hole position is different in the left and right switches.
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ENGINE FIRE EXTINGUISHING -ENGINE FIRE SWITCH

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ENGINE FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -BOTTLE DISCHARGE

General
Each bottle has two discharge assemblies. The discharge assemblies connect the bottles to the discharge manifolds. One manifold goes to discharge nozzles in the left engine nacelle. The other manifold goes to discharge nozzles in the right engine nacelle.
Functional Description
Explosive squibs inside the discharge assemblies connect to the fire switches in the flight deck. Squibs for the left engine connect to the left switch; squibs for the right engine connect to the right switch. A squib for bottle 1 fires when you put the related fire switch to DISCH 1. A squib for bottle 2 fires when you put the related switch to DISCH 2. When a squib fires, the bottle releases the halon into the engine nacelle.
A pressure switch monitors the pressure in each bottle. The switch turns on the discharge indicator light when the bottle pressure decreases. The switch also causes advisory and status messages to show.
Training Information Point
Rigid tubing connects the bottles to the check valves. The diameter of the tubing is different for the left and right engines. This prevents incorrect connection.
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ENGINE FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -BOTTLE DISCHARGE

EFFECTIVITY BEJ ALL  26-21-00 
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ENGINE FIRE EXTINGUISHING -ENGINE FIRE SWITCH CIRCUIT -FUNCTIONAL DESCRIPTION

General
The engine fire switch includes a solenoid, fire warning lights, and two sets of electrical contacts. One set of contacts controls engine functions. The other set of contacts controls the engine fire extinguishing system.
Solenoid and Warning Light Operation
The solenoid energizes if an engine has a fire. This releases the fire switch so you can pull it. The engine fire warning lights come on to help you identify the correct switch to use.
The same condition normally occurs in both engine fire switches while you do a fire/overheat test.
The solenoid also energizes when the battery switch is ON and the fuel control switch is in CUTOFF.
You can override the solenoid with the engine fire override switch.
Out Position
When you pull the fire switch, this is how the switch isolates the engine:
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Closes the fuel spar valve

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De-energizes the engine fuel metering unit (FMU) cutoff solenoid

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Closes the engine hydraulic pump shutoff valve

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Depressurizes the engine driven hydraulic pump valve

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Closes the pressure regulator and shutoff valve

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Removes power from thrust reverser isolation valve

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Trips the generator field

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Trips the backup generator field.

A signal to the AIMS cancels messages related to these isolation functions.
　
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