Multiple engine failure immediately after take-off caused the fatal crash of a Russian air force Antonov An-124 Ruslan on 6 December in Irkutsk.
The investigation commission says that, based on data from flight recorders, "-between three and 11 seconds after the take-off, engines number three, two and one failed in succession and, at one time engine number four lost its power, but then recovered".
The crew reported simultaneous failure of the left engines, and apparently tried to steer the aircraft away from apartment blocks. The An-124 is powered by four D-18T turbofans designed by the Progress MKB engine design bureau and produced by the Motor-Sich plant, both of Zaporozhye, Ukraine.
The Ruslan crashed into a four-storey apartment block, damaging other buildings in the process. A total of 67 people, including all 23 on board, were killed. The aircraft, air force tail number 08, was first flown in 1985, and had 948 flight hours recorded.
The An-124 was taking off from the Irkutsk Aircraft Production Plant (IAPO) to deliver a pair of Sukhoi Su-27UB two-seat combat-capable trainers to Vietnam. IAPO had insured the two Su-27UBs for $56.2 million and plans to substitute the lost Su-27UBs with two later-model Su-30 two-seaters. The plant has apparently ceased production of the Su-27UB.
The commission is examining the theory that a mix of "summer and winter fuels" played a causal role in the accident. The freighter returned from Vietnam two days before the crash with a substantial amount of fuel left in its tanks.
Temperatures in Irkutsk were below -20íC. Normal operational procedure calls for refuelling the tanks with fuel modified to inhibit crystalisation of ice from particles of water.
The mix of "summer" fuel taken in Vietnam and "winter" fuel added in Irkutsk would not comply with cold-weather requirements. The result may have been that fuel filters were rapidly clogged by ice particles, cutting the fuel flow to the engines.
Another explanation being considered is that an erroneous command from the engine control system caused the shutdown.
The crash has triggered an independent investigation of commercial operations of the air force. It was discovered that IAPO awarded a contract worth $1.7 million to a Russian private company, Cargo Trans, to transport the six Su-27s to Vietnam. Cargo Trans is not registered as a commercial air-transport operator by Russia's Federal Aviation Service.
It is reported that Cargo Trans is headed by a former deputy director of Rosvoorouzheniye, the state-owned arms exporting agency. Cargo Trans transferred $1.4 million to an offshore company called Cargo Lift, which is registered in Cyprus. Eventually, the Russian air force received only $327,000, less than one-fifth of the initial contract sum, to deliver the fighters.