The fire started in the cabin, air flow from the emergency exits intensified it, leading to the collapse of the airframe within 17m
Russian investigators believe the presence of a reserve crew on a Kolavia Tupolev Tu-154B destroyed in a ground fire minimised the number of fatalities during a slow and confused evacuation.
The aircraft suffered a generator fault after starting its engines, having been pushed back for taxiing at Surgut, and electrical arcing set the trijet's cabin ablaze.
Of 10 emergency exits, six were equipped with escape slides; the other four were overwing. Eight of these were opened, all except the rearmost door on the left and a forward cabin door on the right.
While the fire was initially smouldering, with a relatively low temperature, the opening of the emergency exits "intensified" the situation by creating an air flow that resulted in the eruption of flames, said Russia's Interstate Aviation Committee (MAK).
Security video images showed four exits on the left opened within about 6s of one another, but for a considerable time passengers left only through the overwing doors. The overwing exits and the forward left door - from which a slide activated - became the main evacuation points.
No slides were deployed at the other equipped doors. MAK said this was probably the result of technical "ignorance" of passengers and the absence of cabin crew at these stations. Passengers had to jump from the aircraft, or climb down a ladder that ground technician had dragged to the wing.
Even with eight exits activated the evacuation took 3min to carry out, compared with the certification requirement of 90s.
MAK said there was "panic, stampede and confusion" in the cabin, which hampered the evacuation. Two flight attendants were forced out of the aircraft by the crowd and were unable to assist further. The flight crew - who abandoned attempts to switch off aircraft systems because they could not see for thick smoke - found the forward cabin obstructed by people trying to escape.
MAK pointed out that the "clear and timely actions" of the reserve crew, who were seated in the rear of the jet and saw the fire break out, ensured that the number of casualties was minimal.
Although fire-fighting vehicles arrived within about 2min of the alarm being raised, the crowd of passengers around the aircraft meant they could not approach it from the front.
MAK said only a small amount of foam reached the combustion zone and the 20-tonne supply was exhausted "without any visible result".
Despite the intensity of the fire and the chaotic evacuation, only three of the 126 passengers - located in seats 16A, 16B and 18G - did not survive. The aircraft had been preparing to fly to Moscow before the 1 January accident.
14:59 Engines start
15:00 Connection of generators, electrical arc sparks fire
15:01 Evacuation of passengers begins
15:02 Airport emergency alarm sounds
15:03 Fire vehicles arrive
15:04 Evacuation completed
15:09 Large explosions
15:10 Fire out of control
15:17 Airframe collapses, blazing fuel spills over
15:20 Order given to remove nearby parked Tu-134s.
The fire on the plane was started by electrical arcing