Aircraft Engine Fire Extinguishing System

According to 14 CFR part 23, commuter aircraft must have at least one shoot fire extinguishing system, and 14 CFR part 25, transport aircraft must have two discharges (Guide. 2022). Extinguishers must produce the correct concentration for each discharge. If the engine is on fire, the fire detection system will detect a fire in the engine and give an alarm. The engine fire warning light will come on, which means there is a fire in one of the engines. When the pilot pulls the T handle, the fire extinguishing system will be activated. At this point the engine will stop, the flow of fuel to the engine will be cut off to prevent ignition, the generator field relay is tripped, hydraulic fluid is shut off to the pump, the engine bleed air is shut off, and the hydraulic pump low-pressure lights are closed, closed the hydraulic pump isolation valve, disarm the engine thrust reverser, and arm the fire extinguishant discharge squib circuit. Two fire extinguishers containing Halon 1301 are included in each engine. When operating, the extinguishing agent is discharged into the engine, and the engine fan assembly. The fire in the engine core will be extinguished by turning off the engine. Turning off the flow of fuel, hydraulic fluid, and other flammable substances to the engine when pulling the fire handle is to quickly reduce the supply of fuel for the fire (Skybary, 2021). When the pilot pulls the fire handle, the signal will send to the squib to allow all extinguisher in the container to go out the piping and go into the engine. When the extinguisher goes to the engine, the pressure inside the container will decrease, and that will send a signal back to the overhead panel that the extinguisher has been discharged. Also, when the extinguisher goes down through the pipe, the yellow disk discharge indicator is ejected. In case it is red it means thermal discharge occurs when the container is pressurized due to temperature rise. This is a signal to the technician that the crew has activated the fire extinguisher system, and the extinguisher needs to be replaced.

Fixed extinguisher systems are used in most aircraft engine combustion systems. This system is designed to dilute the atmosphere with an inert substance that prevents combustion. The system uses open ends to help deliver extinguishing agents to the fire area in the fastest time of about 1-2 seconds (Aviation maintenance technician handbook, pg. 9-8). The most used and FAA-approved fire extinguishing agent today is Halo 1301, which is effective in extinguishing fires and has low toxicity. The engine will not be corroded by Halo 1301, there is no effect when it comes into contact with the engine and does not require cleaning after it is used. However, the limitation of Halon 1301 is that it depletes the ozone layer, so Halon s1301 will be used until a suitable replacement is available and approved by the FAA. Extinguishers used to store extinguishing agents are manufactured from stainless steel, alternative material may be titanium at the discretion of the designer. The tank is installed with the discharge valve. The outlet of the relief valve assembly is installed a squib and fragile disc type valve. On airplanes, most containers have a spherical design because it's the lightest. However, in some cases a cylindrical shape is also used when space is limited. Each container shall be equipped with a pressure and temperature sensitive safety diaphragm intended to prevent the container pressure from exceeding the container test pressure when the temperature is too high. The containers installed in the nose cowling of nacelle, but sometimes they are in the fuselage. To ensure fire suppression, two extinguishers will be used for each engine fire zone, and each extinguisher is capable of extinguishing fires in the area.

 

References

Aeronautic guide. 2022. Aircraft Engine Fire Extinguishing System. Aircraft system.

https://www.aircraftsystemstech.com/p/engine-fire-extinguishing-system.html

 

Crane, D. (2018). Aviation Maintenance Technician: Powerplant (J. Foulk & D. Scroggins,

Eds.). Aviation Supplies & Academics, Inc.

 

Skybary. (n.d). 2021. Engine Fire Protection. https://skybrary.aero/articles/engine-fire-protection

 

Federal Aviation Administration (FAA). (2018). Aviation maintenance technician handbook –

Powerplant (Vol. II) FAA-H-8083-32. Chapter 9: Engine Fire Protection Systems

 

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