Fire Protection in Aviation

Abstract

Fatalities on passenger aircraft have several reasons and occur with different numbers. Fire and smoke on board is not the worst in this comparison, but it deserves attention. Aircraft are designed with multiple redundancies, but undetected manufacturing defects or inadequate maintenance can still be catastrophic. Sorting with respect to flight phase, we have in-flight fires that need to be taken care of by an aircraft system itself. The system is called "Fire Protection" (ATA 26). A fire on the aircraft while it is on the ramp as well as a post-crash fire is taken care of by Aircraft Rescue and Firefighting (ARFF) located at the airport. In-flight fires can be hidden fires (electric circuit), visible fires in the cabin, or from the engine or Auxiliary Power Unit (APU) – a gas turbine in the tail of the aircraft that provides electric power and compressed air. Protection against fire and smoke on board is by prevention, slow growth policy (flame-retardants), detection, and extinguishing. Certification rules on fire protection are in place that regulate the design of the aircraft. Rules are from certification authorities (EASA, FAA, ...) and in addition from aircraft manufacturers (Airbus with its ABD0031). Certification rules on fire protection are revisited regularly and have been written more stringent, but ways to improve safety still exist. As often, a compromise between safety and economics must be found. EASA CS-25.803 "Emergency Evacuation" demands that an aircraft can be evacuated under simulated emergency conditions (doors on one side are closed, ...) within 90 seconds. This is a good but arbitrary standard. Its validity can be challenged, when looking at evacuation with fire and smoke and with other combinations of doors in use. Many emergency landings took place with smoke on board, where it turned out later that the smoke was not from a fire, but from engine oil transported into the cabin and cockpit by means of so-called bleed air from the engines. The problem is a fundamentally wrong design principle applied for the environmental control system (ECS) of all present passenger aircraft (except for the Boeing 787). It is wrong to use (unfiltered) compressed air from the engine (bleed air). Instead outside air must be compressed in dedicated compressors using air from a separate inlet. Smoke and fumes from the engine (or APU) does not require to land As Soon As Possible (LASAP) as in case of a fire. Nevertheless, pyrolyzed engine oil (and hydraulic fluid) is toxic and has caused crew and passengers to get acutely and chronically ill.