Russian investigators have determined that both pilots of an Antonov An-28 were intoxicated by alcohol before the aircraft crashed on a domestic service in the country's far east.
Ten of the 14 occupants were killed when the Petropavlovsk-Kamchatsky Aviation Enterprise turboprop came down outside Palana on 12 September.
Russia's Interstate Aviation Committee had already discovered that the aircraft had been off course before striking terrain southwest of the airport.
But the transport division of the country's federal investigative committee states that forensic examination of the pilots has revealed the presence of alcohol.
The captain's blood-alcohol level was 0.92%, corresponding to "mild intoxication", says the committee, while the first officer's higher measure of 2.03%, an "average level of drunkenness".
Medical tests also showed the captain and first officer had respective alcohol concentrations of 4.42% and 2.98% in their urine.
The committee says that, because of the "serious violations" of safety regulations, it will look at the actions of those responsible for releasing the crew to flight duty as part of a criminal inquiry.
Flight 251 had been attempting an approach to Palana's runway 11 after a service from Yelizovo in the south of the Kamchatsky peninsula.
Accident investigators had recovered a GPS satellite-navigation receiver at the An-28's crash site which indicated that the pilots had informed about crossing an airport beacon when the aircraft had actually been 22km (12nm) distant from it.