Russian investigators have discovered that both right-hand engines on an Atran Antonov An-12 simultaneously failed just after take-off from Moscow, before the freighter crashed in woodland.
The An-12 was on a domestic cargo service from Moscow Domodedovo on 29 July and had been airborne for 1min when the outboard right-hand engine stopped operating.
Russia's Interstate Aviation Committee (MAK) says that, within about 1s, the inboard engine on the same wing also failed. It says that the propellers of both engines were feathered.
"Subsequently the aircraft continued flying for about 1min, after which it struck the ground, leading to a fire of high intensity," says MAK. All seven occupants were killed.
The investigation agency has yet to determine the reason for the powerplants' failure. The An-12 was powered by four Ivchenko AI-20 engines.
While overloading of freighters has been a particular concern in Russia, MAK has confirmed that the aircraft was within weight and balance limits.
It was carrying just over 9,000kg (19,800lb) of cargo and MAK says the payload was not dangerous. The An-12 had 15,500kg of fuel on board giving it an overall take-off weight of 60,500kg, far below the maximum of 64,000kg.
The aircraft's centre of gravity was at 25.7% of mean aerodynamic chord and lay within the acceptable range of 16-32%. No evidence of maintenance problems has been discovered and, although the aircraft was 43 years old, MAK says it was still serviceable.
MAK has been forced to investigate the accident using only cockpit voice recorder information because the flight data recorder was badly damaged by the post-crash fire.