Aeroflot Flight 5484

Conclusions

The exact reason for the flaps being released at cruising altitude was not discovered because major portions of the flap control system were not found among the wreckage. The board did speculate several possible causes but produced no definitive cause for the release of the flaps in the first place. Possible causes were as described:

It was possible that the pilot in command accidentally threw the switch to release the flaps without realizing it. Tests of the lock on that switch showed that accidentally activating it was indeed possible.

Electrical malfunction of the signals in the flap control system; investigators speculated if it is possible that a signal from a nearby wire could have activated it, but not quickly, and such issue would not have been detected by mechanics. However, six Tu-124 aircraft with identical flap control systems were examined to test this hypothesis but all the tests showed the flap control system to be in safe working order.

It is also unknown why the crew weakened their grip on the control column at 00:25:13, which led to the aircraft going into a sharp rate of descent. Possible reasons for this include:

The crew could have been misled by the indications of the variometer, which indicated the aircraft was increasing altitude at speeds between 15 and 20 m/s when it was actually decreasing at a rate of 40 - 45 m/s;

The crew could have diverted their attention towards other tasks in the cockpit, ex. changing engine power, attempting to adjust the flaps, checking the position of the spoilers, etc.;

Overload and overspeed on the control column;

The overload from the rate of descent limiting the crew's capability to apply sufficient force;

any combination of the above factors.