What happened
On August 9, 2013, at approximately 02:01 local time, an Antonov An-12 BK cargo aircraft was undergoing engine start-up procedures at Leipzig/Halle Airport. The aircraft had arrived from Stockholm, Sweden, the previous evening and was parked at apron 207. The crew was preparing for a scheduled departure to Mineralnye Vody, Russia.
During the start sequence, after the auxiliary power unit (APU) had been running and the first engine was successfully started, the crew began starting the fourth engine. During this process, the crew experienced a loud bang and a physical jolt through the airframe. The copilot noted fluctuations in APU RPM and a rise in temperature, followed immediately by an APU fire warning. The crew promptly shut down the running engines and activated the APU fire extinguishing system.
Despite the crew's efforts, the fire spread rapidly. The fire moved from the APU compartment into the cargo hold and outward toward the aircraft's exterior. The crew evacuated the aircraft via the cockpit floor emergency exit. While the crew attempted to use handheld extinguishers from the outside, the fire intensified, eventually consuming the aircraft. The fire also caused fuel to leak from the underfloor tanks, creating burning puddles on the apron.
The investigation
The BFU investigation focused on the origin and spread of the fire. Investigators examined the wreckage, which showed extensive destruction, including melted magnesium components from the APU gearbox and compressor unit. The investigation established that the fire reached temperatures high enough to melt magnesium, which can burn at up to 3,000 °C.
Investigators also analyzed the aircraft's configuration, noting that the cargo door was open to facilitate the transport of live animals (approximately 48,960 chicks), which provided a continuous supply of oxygen that fueled the fire. The investigation also reviewed the airport's emergency response, noting that while the fire service arrived within minutes, the fire had already achieved a state of full involvement by the time they reached the scene.
Findings
- The fire originated in the APU compartment.
- The fire spread rapidly because the APU compartment was not sufficiently isolated from the rest of the aircraft, allowing flames to reach the cargo hold.
- The intensity of the fire was significantly increased by the combustion of magnesium components within the APU.
- The spread of the fire was further exacerbated by leaking fuel from the underfloor tanks.
- The open cargo door, required for the transport of live animals, provided an abundant oxygen source that promoted rapid combustion.