Investigators have attributed the fatal blaze on a parked Kolavia Tupolev Tu-154B at Surgut to electrical arcing in a generator panel mounted in the rear of the aircraft.
All eight crew members escaped but three of the 126 passengers were killed as flight 7K348 was preparing to operate to Moscow Domodedovo on 1 January.
Russia's Interstate Aviation Committee said the fire broke out as the three electrical generators were engaged, after the 28-year old Tu-154's (RA-85588) three engines had been started and set to idle thrust.
Excessive electrical currents and arcing occurred in the area of the fuselage between frames 62 and 64. MAK said this probably resulted from components in "unsatisfactory" condition allowing an unintentional parallel connection of the generator circuits, creating electrical overload.
MAK, which assessed similar electric panels on a second Tu-154B (RA-85522) during its inquiry, considered several alternatives for the source of the fire, including engine, hydraulic and air conditioning failure, improper engine-start procedures, and even the spontaneous ignition of fireworks in cabin baggage.
But analysis of the flight-data recorders indicated that the operation of the engines was normal, and there were no traces of thermal damage to the powerplants, while the fireworks theory was ruled "impossible".
Thirty minutes after the outbreak, the fire had engulfed and destroyed the fuselage, leaving only the wings and empennage intact. Kolavia has since opted to withdraw from scheduled services.