What do you do when someone yells “Fire!” on an airplane? If a fire detection and extinguishing system is installed, you just read a checklist and follow procedure.
The turbine engine, with all of its associated systems, appears to be a complex machine, but the engine itself actually is pretty simple: a fan that directs air into the core of the engine, followed by a compressor that prepares the air for combustion, and an ignition chamber that sets it all aflame. Finally, a turbine is driven by the exhaust gases that spill out the back. All this action adds up to intake, compression, combustion, and exhaust.
This is a highly controlled environment with little room for excursion. It’s generally a good idea to keep the flames inside the combustion chamber, but sometimes they may escape. For that purpose, almost all turbine engines are designed with an integrated fire and heat detection and extinguishing system.
Detection is accomplished by sensor tubes installed on the engines and the pylons that connect the engine to the fuselage. These tubes are filled with a volume of inert gas as well as gas-impregnated core material. Fire or overheat is detected when the tubes are heated, causing the internal pressure to increase. This increase will activate the alarm switch, which alerts the flight crew to a potential fire.
This is where the fire-extinguishing system comes in. Connected to each engine is a bottle that contains a fire-extinguishing agent under pressure. When activated, the seal is broken and the pressure of the bottle forces the agent out and into the engine compartment. Hopefully only one discharge is required to extinguish the fire. A second shot can be delivered via a cross-connect from the other engine’s bottle.
So when the fire bell rings, you follow the procedural items and checklist workflow. Visually confirm which engine is reporting a fire, and secure that engine. Shutting down the engine might extinguish the fire, and that’s always the first choice. Should the fire warning persist, when directed by the checklist, discharge the engine fire bottle. You should declare an emergency immediately after the engine shuts down. Now it’s time to find a nearby suitable airport at which to land.
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