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Light Aircraft Post-crash Fires
|Category:||Fire Smoke and Fumes|
For aircraft with a maximum certified take-off weight of 5700 kilograms (12 566 pounds) or less, post-impact fire (PIF) contributes significantly to injuries and fatalities in accidents that are otherwise potentially survivable. A potentially survivable accident is one in which the impact forces are within the limits of occupant tolerance, the aircraft structure preserves the required survival space, and the occupant restraint is adequate.
Although the occurrence of PIFs is relatively rare, they account for a significant portion of the fatalities that result from light aircraft accidents. Because small aircraft have a higher accident rate with a correspondingly greater number of PIF accidents, more defenses are required to mitigate this risk.
In most cases where PIFs contribute to serious injuries or fatalities, the aircraft occupants are in close proximity to fire or smoke after the impact. The main reasons for this are:
- an ignition source in proximity to a combustible material, such as fuel;
- combustible material in close proximity to the occupants;
- occupant egress being compromised;
- the fire not being suppressed in time to prevent fire-related injuries or fatalities;
Reasons Why Post-crash Fires Pose Threat to the Occupants of Light Aircraft
While PIFs are generally a threat for the occupants of any aircraft, they are especially dangerous when light aircraft are involved because of the:
- high volatility and low Flash Point of aviation fuel – it is very easy for the fire to start and spread;
- close proximity of fuel to occupants - fuel tanks can be literally centimetres away from passenger compartments;
- limited escape time (less than 20 seconds) - as a consequence of the two points above;
- limited energy-absorption characteristics of small-aircraft airframes in crash conditions;
- high propensity for immobilizing injuries (especially when combined with the limited time for leaving the aircraft);
- inability of airport firefighters and emergency response personnel to suppress PIFs in sufficient time to prevent fire-related injuries and fatalities;
- onboard handheld fire extinguishers being generally useless – they can be difficult to reach due to the damage the aircraft receives on impact and are not likely to contain sufficient quantity of chemical to extinguish an intense fuel-fed PIF.
The most effective defence against PIFs is to prevent a fire from occurring at, or just after, impact. This can be done by:
- containing the fuel (e.g. designing the aircraft in such a way as to prevent the fuel from spilling into the cabin or the cockpit or by using reinforced fuel tanks)
- ignition prevention (e.g. by using cut-off switches to render electrical components inert);
Other defences include design concepts to:
- provide adequate occupant restraint (reducing impact injuries)
- reduce deceleration forces applied to occupants by designing the airframe with more robust energy absorption criteria (reducing impact injuries)
- design passenger compartments to reduce or prevent occupant entrapment (providing easier egress)
- provide mechanisms for rapid egress
Dissemination of information relevant to PIF risks can be helpful to amateur-built aircraft and ultralight communities.
- Fire, Smoke and Fumes
- Post Crash Fires
- Fire Triangle
- Hydraulic Fluid as a Fire Source
- Post-impact fires resulting from small-aircraft accidents, Aviation Safety Issues Investigation Report SII A05-01, TSB Canada, 2006