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;
Possible absence of cabin crew to help occupants escape;
Possible insufficient knowledge of occupants to perform actions that enable survival.
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.
On 4 July 2011, a Eurocopter AS 350 making a passenger charter flight to a mountain cabin in day VMC appeared to suddenly depart controlled flight whilst making a tight right turn during positioning to land at the destination landing site and impacted terrain soon afterwards. The helicopter was destroyed by the impact and ensuing fire and all five occupants were fatally injured. The subsequent investigation came to the conclusion that the apparently abrupt manoeuvring may have led to an encounter with servo transparency at a height from which the pilot was unable to recover before impact occurred.
On 27 October 2018, a single pilot Leonardo AW169 helicopter lifted off from within the Leicester City football stadium but after an almost immediate failure of the tail rotor control system, control was lost and ground impact and a post crash fire resulted in fatal injuries to all five occupants. Seizure of the tail rotor duplex bearing was found to have initiated failures which culminated in the unrecoverable loss of control of the tail rotor blade pitch angle. This failure was a direct consequence of gross failures in risk assessment at the aircraft manufacturer and an inadequate type certification process.
On 13 October 2016, a Cessna 500 crashed and was destroyed after an apparent loss of control shortly after taking off from Kelowna at night. In the absence of recorded flight data the Investigation was unable to explain the circumstances which led to loss of control but did identify significant safety concerns about both lack of progress in mandating the carriage of lightweight flight data recorders on small aircraft and a significant lack of effectiveness in the regulatory oversight of the business aviation sector in Canada.
On 4 August 2008, a Cessna 500 on a business charter flight encountered a flock of very large birds shortly after take off from a small Oklahoma City airport. Wing damage from at least one bird collision with a force significantly greater than covered by the applicable certification requirements made it impossible for the pilot to retain control of the aircraft. Terrain impact followed. Both engines also ingested a bird. The Investigation noted that neither pilot nor aircraft operator were approved to operate commercial charter flights but concluded that this was not directly connected to the loss of the aircraft.
On 19 November 2010, a Cessna 501 being operated by The Frandley Aviation Partnership on a domestic cargo flight from Belfast Aldergrove to Birmingham continued descent on an initially visual day ILS approach to Runway 15 into IMC and until collision with the ILS GS aerial adjacent to the intended landing runway occurred. The aircraft caught fire and was destroyed. Both pilots were injured, one seriously.
On 26 May 1993, a Cessna Citation II being operated by a UK Air Taxi Company on a positioning flight from Oxford to Southampton to collect passengers with just the flight crew on board overran the very wet landing runway at the destination in normal daylight visibility and ended up on an adjacent motorway where it collided with traffic, caught fire and was destroyed. The aircraft occupants and three people in cars received minor injuries.
On 3rd September 1999, shortly after take-off from Glasgow UK, a Cessna 404 experienced an engine failure which was mishandled, leading to loss of control, and the aircraft was destroyed by a post-crash fire.