Google Translate:
According to our source, the credible, the commission has found that the plane began to crackdown on the runway with the parking brake nevyklyuchennym. This device - analog handbrake in a car - used only for parking. Engine power is enough that the aircraft moved from its place, being on the parking brake (as well as some forgetful motorists gets under way on the "hammer") and have driven on a taxiway to the runway. But to accelerate to takeoff speed is already becoming problematic.
In addition, the source said, "MK", which, according to the transcripts of the speech recorder Yak-42, immediately before takeoff the aircraft commander ordered Andrew Solomentsev second pilot Igor Zhevelovu to take it over, citing poor health.
The parking brake was off just a commander. But perhaps the moment of transfer of control of the pilots just forgot it and did not pay attention to the corresponding signal on the dashboard (beep it is not duplicated).
Neisklyucheno that when the Yak-42 began to accelerate for takeoff and could not gain the required speed, the pilots noticed a mistake and turned off the brake.
I wonder if the brakes would have had trouble disengaging after the amount of energy that would of been placed into it.