Russian investigators have disclosed that the fatal fire on the Kolavia Tupolev Tu-154 in Surgut did not originate in either the engines or the auxiliary power unit.
The fire, which broke out as the jet prepared to taxi for a flight to Moscow, killed three occupants of the aircraft.
Although the aircraft had started its engines, and smoke appeared to emanate from the rear of the tri-jet, the Interstate Aviation Committee (MAK) says that the powerplants and APU "were not the source of the fire".
It states that the fire started in the vicinity of fuselage structural frames 62 to 65, which are located at the rear of the passenger cabin.
MAK says its inspectors are examining the remnants of electrical installations stationed in this section of the Tu-154.
It adds that it is conducting an analysis of the power circuitry of the jet.
Kolavia's aircraft was completely destroyed in the 1 January blaze. Russia's transport supervisory authority subsequently recommended the grounding of all Tu-154B variants.