Accident Overview
A Tupolev Tu-124 aircraft, operating a multi-leg flight from Odessa to Kazan, crashed near Kirsanov after an uncommanded flap extension during cruise. The aircraft was destroyed, and none of the 63 occupants survived.
Sequence of Events
The flight departed Kiev-Borispol Airport at 2321 local time on the second leg of the route. While cruising at an altitude of 9,000 meters and a speed of 530 km/h, the flaps extended to an angle of 30°. The airplane entered a spin and partially disintegrated at an altitude of 4,000 meters before impacting a field near Kirsanov. The wreckage was scattered over a wide area, and the aircraft was completely destroyed.
Investigation and Probable Cause
The investigation determined that it was not possible to identify the exact cause of the flap extension. Analysis could not definitively attribute the event to an electrical failure or a human action, whether intentional or unintentional. The most likely scenario was that the left pilot's flap control switch handle was moved to the 'down' position by an angle sufficient to trigger the switch. The design of the locking device of the ZPPM-45 switch, including its geographical situation, did not exclude the possibility of an unintentional flap release. This potential issue was revealed by a one-time check of similar devices on 16 other Tupolev Tu-124 aircraft.