🔵✈️ 307. Boeing 777 Aircraft Fire Detection and Extinguishing System 🚁🎞️

Source: FAA-H-8083-32A, Aviation Maintenance Technician Handbook Powerplant, Volume 2, Pag: 9-13

The following section discusses the fire detection and extinguishing system of the B777 aircraft. The information is included only for familiarization purposes. 

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.

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 the right sidewall lining of the forward cargo compartment, aft of the cargo door.

The two engine fire extinguishing bottles are identical. Each bottle has these following components: • A safety relief and fill port • A handle for removal and installation • A pressure switch • Two discharge assemblies • An identification plate • Four mounting lugs.

The bottles contain 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. 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 flight deck indications when bottle pressure decreases. The switch monitors the pressure inside the bottle and is normally open. When the pressure decreases because of a leak or bottle discharge, the switch closes an indicating circuit.

Squib 

The squib is installed in the discharge assembly at the bottom of the fire container. A fire container has two squibs, one for each engine. The squib is an electrically operated explosive device. 

When the squib is activated, it fires a slug through the breakable disk, and nitrogen pressure inside the bottle pushes the Halon through the discharge port. The squib fires when the fire switch is pulled and turned to the DISCH 1 or DISCH 2 position.

Engine Fire Switches 

The engine fire panel is in the flight deck on the P8 aisle stand. The engine fire panel has a fire switch for each engine and a discharge light for each fire bottle. The engine fire switch has four functions: • Gives an indication of an engine fire • Stops the engine • Isolates the engine from the airplane systems • Controls the engine fire extinguishing system.

The fire switch assembly incorporates a solenoid that locks the fire switch so that the flight crew cannot pull it accidently. If an engine has a fire, the fire warning light comes on and the solenoid energizes to release the switch. When the solenoid is energized, the fire switch can be pulled.

When the fire detection system malfunctions or the solenoid is defective, and the flight crew wants to extinguish an engine fire, someone must push the fire override switch. The fire override switch allows the fire switch to be pulled when the solenoid is not energized. 

When the fire switch is pulled, the push-pull switch contacts operate electrical circuits that stop the engine and isolate it from the airplane systems. With the switch pulled, it can be rotated to left or right to a mechanical stop at the discharge position. The rotary switch contacts close and operate the fire extinguishing system.

When the fire switch is pulled, the switch isolates the following aircraft systems from the engine: • Closes the fuel spar valve • Deenergizes the engine fuel metering unit (FMU) cutoff solenoid • Closes the engine hydraulic pump shutoff valve • Depressurizes the engine driven hydraulic pump valve • Closes the pressure regulator and shutoff valve • Removes power from thrust reverser isolation valve • Trips the generator field • Trips the backup generator field.

Engine Fire Operation 

If an engine has a fire, the engine fire detection system gives a fire warning in the flight deck. The engine fire warning lights come on to identify which fire switch to use to extinguish the fire. The solenoid in the fire switch energizes and releases the switch so that the fire switch can be pulled. 

If the solenoid does not energize, push the fire override switch to release the fire switch manually. When the fire switch is pulled, it stops the engine, and the fire switch isolates the engine from the airplane systems. 

If the fire warnings do not go away when the switch is pulled, position the switch to the DISCH 1 or DISCH 2 position, and hold the switch against the stop for one second. This fires the squib in the fire extinguisher container and releases the fire extinguishing agent into the engine nacelle. 

Ensure that the engine bottle discharge light comes on. If the first bottle does not extinguish the fire, the switch must be placed to the other DISCH position. This fires the squib for the other bottle.

System Component	Function	Monitoring and Logic	Flight Deck Indications	Activation Method	Isolation Actions
Engine Fire Switches	Stops the engine, isolates engine systems, and controls the extinguishing system.	Solenoid-locked; released upon fire detection or via manual fire override switch.	Fire warning light illuminates on the switch to identify the affected engine.	Manual pulling and rotating to DISCH 1 or DISCH 2 positions.	Closes fuel spar valve, de-energizes FMU cutoff solenoid, closes hydraulic shutoff valve, depressurizes engine-driven pump, closes pressure regulator/shutoff valve, removes power from thrust reverser isolation valve, and trips generator/backup generator fields.
Fire Detection Loops	Monitors engines for fire and overheat conditions by measuring average temperature.	Dual loop operation: both loops must detect condition. Single loop operation: activates if one loop fails and the other detects condition.	Master warning/caution lights, aural alerts, engine fire/overheat messages, and fuel control switch fire light.	Automatic sensing of temperature changes across loop wiring.
Fire Extinguisher Containers (Bottles)	Stores Halon pressurized with nitrogen for engine fire suppression.	Pressure switch monitors for leaks or discharge; includes safety relief port for overpressure.	EICAS messages, status messages, and bottle discharge indicator lights for low pressure.	Activation of explosive squibs via electric current when the fire switch is rotated.
Fire Detection Card	Monitors detection loops and wiring for defects; sends signals to AIMS and Warning Electronics Unit.	Continuous Fault Monitoring and BITE (performed at power-up, after interrupt, and every 5 minutes).	Status message (one loop failure); Advisory and status messages (both loops failure).	Electrical monitoring of loop resistance and temperature.
Squib	Electrically operated explosive device that releases the extinguishing agent.	One squib per engine per container (four total across two bottles).		Fires a slug through a breakable disk when the fire switch is pulled and rotated to the DISCH position.