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Each engine has two fire detection loops: loop 1 and loop 2. A fire detection card in the system card file monitors the loops for fires, overheat conditions, and faults. There is a fire detection card for each engine. 

## Overheat Detection 

If the fire detection loops detect an overheat condition, the fire detection card sends a signal to the AIMS and to the warning electronics unit. The following indications occur in the flight deck: 

• The master caution lights come on. 

• The caution aural operates. 

• An engine overheat caution message shows. 

## Fire Detection 

If an engine fire occurs, the fire detection card sends a signal to the AIMS and to the warning electronics unit, and a warning message illuminates. The following indications occur in the flight deck: 

• The master warning lights come on. 

• The fire warning aural operates. 

• An engine fire warning message shows. 

• The engine fire warning light comes on. 

• The fuel control switch fire warning light comes on. 

## Nacelle Temperature Recording 

The fire detection card measures the average temperature of the loops. This data goes to the AIMS through the system’s ARINC 629 buses and is recorded by the airplane condition monitoring function. 

## Continuous Fault Monitoring 

The fire detection card monitors the two loops and their wiring for defects. In normal (dual loop) operation, both loops must have a fire or overheat condition to cause the flight deck indications. 

If a failure occurs in a loop, the fire detection card sends the data to the AIMS. A status message shows, and the system changes to single-loop operation. In this mode, fire/overheat indications occur when one loop is defective and the other has a fire or overheat condition. 

## Single/Dual Loop Operation 

The fire detection card monitors the loops for faults. In normal (dual loop) operation, both loops must have a fire or overheat condition to cause the flight deck indications. If one detection loop fails, the card sends data about the failure to the AIMS, and a status message shows. The card changes to single-loop operation, if necessary. If both detection loops fail, an advisory message and status messages is displayed, and the fire detection system does not operate. 

## System Test 

Built-in test equipment (BITE) performs a test of the engine fire detection system for these conditions: 

• When the system first gets power 

• After a power interrupt 

• Every 5 minutes of operation [Figures 9-20 and  9-21] 

## Boeing 777 Fire Extinguisher System 

## Fire Extinguisher Containers 

The B777 airplane has two fire extinguishing bottles that contain Halon fire extinguishing agent pressurized with nitrogen. The engine fire switches in the flight deck are pulled and rotated to release the Halon. Halon from each bottle can be discharged to the right or left engine. Engine indicating and crew alerting system (EICAS) messages, status messages, and indicator lights show when the bottle pressure is low. The two engine fire extinguishing bottles are located behind 

