Descent below the glide path in poor weather and a failure to execute a timely go-around led to the fatal RusAir Tupolev Tu-134A crash on approach to Petrozavodsk, Russia, investigators have concluded.
Russia's Interstate Aviation Committee (MAK) also found that the aircraft's navigator - who was supposed to aid the pilots in aligning the aircraft with the runway - was mildly intoxicated at the time of the 20 June accident.
Only five of the 52 passengers and crew survived the crash. The flight from Moscow's Domodedovo airport was originally scheduled to operate through fellow Russian carrier RusLine, with a Bombardier CRJ regional jet. This flight was cancelled, and the RusAir Tu-134 was chartered to replace the service.
The flight had progressed normally and the aircraft was about 8min from touchdown when the crew took full manual control at an altitude of 2,700m (8,860ft). The aircraft then continued to descend towards a cleared height of 500m.
However, as it made its right-hand base turn to Petrozavodsk's runway 02, the aircraft drifted 4km (2.2nm) to the left of the centreline. MAK said strong south-easterly winds of 17kt (31km/h) probably contributed to the jet being off course.
Discussions between the pilot and navigator led the crew to try correcting the flightpath by bearing right. The drift gradually reduced, but as the flaps were deployed the Tu-134 gained height, rising to 550m, and the crew increased the rate of descent to regain the glide path.
As the height reduced the wind weakened, but the crew did not compensate with a heading correction and the Tu-134 drifted to the right of the approach. MAK said the crew appeared to be referring to a satellite positioning system which was prohibited during approach.
The aircraft descended "well below the desired path", it added, and the co-pilot failed to warn about the steep approach.
Weather conditions in the immediate vicinity were substantially different from those relayed to the crew, with low cloud and fog reducing visibility to 500-700m. Despite failing to make visual contact with the ground, the crew did not execute a missed approach. The aircraft struck trees at a height of 25m, while still 1.2km from the runway. It was 270m to the right of the centreline.
MAK said the aircraft's crew descended below minimum safe altitude while in poor weather and in absence of seeing the approach lights of the airport or other landmarks.
There had been poor communication and a lack of crew resource management. The navigator had a "mild degree of alcoholic intoxication", while the co-pilot appeared to have been left out of the command loop, MAK added.