Preliminary analysis of flight-recorder information from a crashed Let Aircraft Industries L-410 indicates the turboprop entered a near-vertical descent after its right-hand engine effectively began developing reverse thrust.
The Khabarovsk Airlines aircraft (RA-67047) had been conducting a daylight approach, in good visibility, to runway 04 at Nelkan in eastern Russia on 15 November.
Investigators have detailed preliminary findings from the aircraft's flight recorders which show that, at a height of 150m above ground, the right engine entered the "beta range" – the power setting below flight-idle which is normally used to slow the aircraft after landing.
"This mode was maintained until the aircraft collided with the ground," the inquiry says, adding that the left engine continued to operate normally.
The L-410 was fitted with two General Electric H80-200 engines.
Its crew, the inquiry adds, recognised that the engine had entered the beta range and their subsequent actions resulted in the aircraft decelerating and rolling to the right.
The aircraft descended with a high vertical speed but with little horizontal speed, with less than 3m separating the first point of terrain contact from the final resting place, 1,480m from the runway threshold.
Just one survivor, among the seven occupants, was rescued from the wreckage.
Investigators have disclosed that the aircraft – a UVP-E20 variant with serial number 3010, owned by state lessor GTLK – was relatively new, having been manufactured in 2015.
The captain had accumulated over 12,000h with 1,243h on type, while the first officer had 837h on type from a total of 1,220h.
An initial recommendation from the inquiry advises a one-time check on the H80-200's beta mode and propeller control system, and that L-410 crews should ensure they are familiar with engine control procedures and actions after engine failure.
Along with the flight recorders investigators retrieved a Garmin GPS system from the wreckage for analysis. The aircraft had been operating from Khabarovsk to Nelkan via Chumikan.