07/08/2023
Aircraft Fire Extinguishing Systems (Basic)
In the modern and general aviation the fire suppression systems is divided into two subsystems: the Fire Detection System and the Fire Extinguish System.
*Fire detection system
The aircraft systems that have fire detection are:
Engines (Turbines)
APU (Auxiliary Power Unit) is a small engine installed generally in the aircraft tail. It is used to start the big engines (Turbines) and provides electrical power and air conditioning mainly on the ground, Cargo Compartment, Avionic Compartment, IFE (In-flight Entertainment) and Lavatories.
The fire detection installed on engines and APU are sensitive loops like protected wirings. This operates when it detects the temperature increasing and suffers variation in its material composition and sends an electrical signal to the smoke detector computer which informs the pilots.
The Cargo compartment has electronic detector boxes installed in the cargo ceiling. When there is signal of smoke, the detector feels the smoke density and then inform to smoke detector computer that transmit this information to the cockpit.
The Avionic and IFE compartments have similar smoke detector, when smoke is detected an electrical signal is also sent to the cockpit.
*Fire extinguing system
Presentely the main fire-extinguishing agent used in all aviation systems is Halon (Bromotrifluoromethane).
Halon systems are the best for avation, but not for the environment or the ozone layer. Because of that, Halon has not been produced since the Montreal Protocol on ‘Substances that deplete the Ozone Layer’ was signed in September 1987. This is an international agreement banning the production of Halon.
There some alternative agents being studied in world to replace halon totally. At the moment there is only an alternative agent called FE36, but this one is a little heavier than halon gas and has been used in lavatory trash can only.
Generally, depending on the manufacturer, the fire extinguishing bottles installed in engines, APU and cargo compartments must be removed at established intervals for weight and hydrostatic testing. These scheduled maintenance intervals can be controlled in calendar days or in flight hours depending on the aircraft utilization.
*Engine fire extinguishing operation
Considering an aircraft dual-turbine, generally there are two fire extinguisher bottles to support both engines. When the pilots are informed by the fire detection system that there is an engine fire, the pilot operates the fire extinguisher handle, which closes all sources such as electrical power, pneumatic and fuel, and further the pilot shoots the first bottle and waits to see if the fire has been extinguished. If the engine fire continues, then the pilot shoots the second bottle. In the meantime, the co-pilot has declared an emergency and prepares to land the aircraft.
*Portable fire extinguishing operation
The portable fire extinguishers are used by crews (pilot and flight attendants) to extinguish any fire in the cockpit and passenger cabin. Some executive aircraft whom baggage compartment is accessed from passenger cabin also use the portable fire extinguishers for fire suppression.
