Investigators have determined that an Antonov An-28 which collided with high terrain during a domestic service in eastern Russia should have been fitted with a ground-proximity warning system.
The inquiry into the loss of the Petropavlovsk-Kamchatsky Aviation Enterprise aircraft near Palana found that the An-28 had been among the types required to fit GPWS by 1 July 2012.
While the ministry had intended to postpone the deadline to October, the Interstate Aviation Committee (MAK) says this order was not registered with the justice ministry at the time of the accident on 12 September 2012.
Investigators had previously determined that the pilots had been intoxicated with alcohol, despite passing a pre-flight medical check.
MAK suggests "impaired concentration" of the crew contributed to a "lack of response" to radio altimeter indications that the aircraft was approaching high ground. Fitting of GPWS avionics "could possibly have prevented" the accident, says MAK.
Flight 251 from Yelizovo, transporting 12 passengers and two crew, had been intending to approach Palana's runway 11. This required maintaining flight level 70 (2,150m) until reaching Palana's NDB navigation beacon, then entering a hold to descend to 1,200m before exiting to the final approach.
But the aircraft had been far off course. It had been approaching the NDB from the south but the crew gave an incorrect position report to air traffic control. Despite being 80km from the airport the An-28 prematurely descended to 1,700m and subsequently to 1,200m.
MAK says the crew effectively followed an "arbitrary" approach to the airport. As the aircraft continued to descend, it started turning left, possibly to cross the coast of the Sea of Okhotsk and then turn inbound to the airport.
But this track instead took it towards high terrain, which was shrouded with cloud. Flight-data recorder information revealed a sudden elevator deflection, pitch up, which MAK believes to be a crew reaction to obstacles in the aircraft's path. But this failed to avert a collision with trees at a height of 330m.
The impact occurred at 135kt and the aircraft lost power in both engines. It pitched up but the loss of thrust caused its speed to bleed to 70kt and the An-28 stalled, hitting the trees again before breaking up. It came to rest 10.7km from the airport.
Both crew members and eight passengers were killed in the accident, although four others survived.