Russian investigators have determined that lighting and radio systems at Petrozavodsk airport were operating normally before the fatal Tupolev Tu-134 crash last week.
The power loss at the airport "resulted from the crash" rather than any earlier problem, said the Russian Interstate Aviation Committee.
It stated that, at a distance of 425m (1,400ft) from the point at which the RusAir Tu-134 first clipped trees, the twinjet struck a power line.
This resulted in a short circuit and the shutdown of a substation which cut the power supply to the airport.
But the investigators added that the loss of airport lighting was "short lived" because generators began operating within 5s and restored the power.
Before the damage to the electrical transmission lines, said the Interstate Aviation Committee, the airport's radio systems, navigation beacons and approach and runway lights were operational.