Russian investigators believe an Antonov An-24 crew’s belated recognition of a serious engine problem contributed to the deterioration of the powerplant and the eventual decision to ditch in the Ob river.
The Angara Airlines aircraft (RA-47302) had been carrying 33 passengers and four crew between Tomsk and Surgut on 11 July 2011.
It had been flying at an altitude of 6,000m when a technician on board noticed a warning of fragments present in the left-hand engine.
The crew proceeded for another 8min before – having detected a burning smell in the cabin – opting to reduce power from the engine and divert to Nizhnevartovsk.
It descended to 4,800m but, despite indications that the engine’s condition was deteriorating, the captain did not shut it down, even though the aircraft was still some 23min from landing.
Russia’s Interstate Aviation Committee says the captain was “psychologically unprepared” to turn off the engine, owing to a lack of experience in flying with one powerplant inoperative.
The aircraft was cleared to descend to 1,800m but, at around 3,600m, the captain declared that there were severe vibrations and a fire in the left engine.
Although the crew initiated engine-fire procedures, attempts to extinguish the fire were unsuccessful and – around 18min after the first sign of problems – the captain decided to abort the approach and ditch the aircraft.
It descended and touched down on the surface of the river just under 18km from the small Strezhevoy airport, which lies some 65km east of Nizhnevartovsk.
The An-24 collided with underwater obstacles and broke up. Seven of those on board were killed in the accident.
Investigators state that the crew could not have anticipated the presence of the obstacles or avoided them.
While the engine failure was traced to an internal component fracture, the investigators point out that the late reaction of the crew to the developing problem meant that no timely measures were taken to extinguish the fire.