After an uneventful flight from Stockholm (Sweden) an Antonov AN-12BK was being prepared at Leipzig/Halle Airport (Germany) for its next flight. The crew of seven consisted of the Pilot in Command (PIC), co-pilot, flight engineer, navigator, radio operator and two flight mechanics.
The wreckage after the fire was extinguished (© BFU)
The aircraft was loaded with 3061 kilos of cargo and refuelled with 22/809 litres of Jet A kerosine. All preparations were completed well before the scheduled 02.15 lt (local time) departure. Just after 02.00 lt the start-up clearance was issued, and as part of the pre-flight checks, the APU (Auxiliary Power Unit) was started. Subsequently, the #1 engine (lefthand outer) was started. With the #1 engine stabilised at idle speed, the start of the #4 engine (righthand outer) was initiated. With the start of the #4 engine in progress, a dull bang was heard, and the airplane jerked.
As per procedures, the co-pilot had been monitoring the APU indication and had observed speed oscillations and an increase in APU EGT (Exhaust Gas Temperature). A short time later the APU fire warning indication illuminated. Engine #1 and #4 were immediately shut down and the APU Fire Extinguishing System was activated. When the PIC opened the cockpit door (to the cargo compartment), flames were visible in the cargo compartment. There appeared to be an uncontained APU fire. He (the PIC) sent one of the flight mechanics outside for a check through the emergency exit located in the floor of the cockpit. After he had left the airplane, he immediately reported that the APU was burning. Subsequently, the three fire extinguishers located in the cockpit were handed down. In addition, the flight engineer and the second flight mechanic left the airplane; they confirmed the fire. Together the three men tried to extinguish the fire with onboard fire extinguishers.
The open emergency exit in the lower fuselage, below the cockpit (© BFU)
ATC was informed by the radio operator, ATC alerted the fire brigade who were on the scene just over 4 minutes after ATC was informed. All crew evacuated the aircraft via the emergency exit in the cockpit floor and retreated to an area ~50 meters in front of the plane. Although the fire trucks discharged a total of 4,000 l of extinguishing foam and 70,000 l of water. the aircraft was destroyed by the fire. The fire brigade was able to prevent the spreading of the fire to the wing fuel tanks.
The fire was investigated by the German Federal Bureau of Aircraft Accident Investigation (Bundesstelle für Flugunfalluntersuchung - BFU). In their investigation report (available for your reference by clicking on the .pdf file below this blog) they concluded that;
"The fire originated in the APU and propagated rapidly to the cargo compartment. The fire was not contained within the APU chamber. The propagation and severity of the Investigation Report BFU AX002-13 - 13 - fire were aided by the leaking fuel from the fuselage bottom tanks and the burning light metal alloy components of the APU."
The APU in the aircraft wreckage (© BFU)
Several safety recommendations were made in the report.