Russian investigators have concluded that spatial disorientation of an Aeroflot-Nord Boeing 737-500 crew, primarily that of the commander, led to the fatal loss of the aircraft during attempts to land at Perm last year.
Flight SU821, operating Moscow-Perm on 14 September, crashed while performing final manoeuvres in preparation for landing.
Russia's Interstate Aviation Committee (MAK) says the pilots' disorientation occurred in night conditions, in cloud, with the autopilot and autothrottle disconnected.
Among the findings released by MAK is the discovery of unspecified quantities of alcohol in the commander's body. MAK has also determined that rest and work periods before the accident "did not conform" to current regulations, and contributed to a build-up of fatigue.
It attributes the crash partly to difficulties interpreting the attitude of the aircraft from specific instruments, whose indicators differed from other aircraft - such as the Tupolev Tu-134 - previously flown by the pilots.
All 88 passengers and crew on board were killed when, says MAK, the aircraft experienced an upset of its left wing, and entered a rapid descent from which it failed to recover.
The inquiry found a lack of training in flight techniques and crew resource management, and MAK adds that it revealed an "inadequate level of airworthiness and maintenance" of 737s at the airline.
MAK points out that aircraft had been allowed to operate with a 'fork' condition in the throttle levers - meaning that they did not produce equal thrust when moved in alignment, but only when set in separate positions. "This increased the workload of the crew in the approach," it states.