Investigation Summary
The accident occurred during a night flight in clear weather. While maintaining a cruise speed of approximately 530 km/h, the flaps were extended for reasons that remain officially undetermined. The crew disconnected the autopilot eight seconds after the extension began. They initially attempted to level the aircraft by pulling the control column, but the force on the column was weakened at 00:25:13. Following this, the flaps reached the full 30-degree position, creating massive drag and forcing the aircraft into a steep dive. As the Tu-124 accelerated beyond its maximum safe speed, the aerodynamic loads became unsustainable. At 00:25:13, the right inboard flap tore away, followed by the outboard sections, sending the aircraft into a violent spin. The structural integrity failed completely at 00:26:00 under a 5g load, causing the left wing to detach and the fuselage to disintegrate.
Final Conclusions
The investigation identified the primary cause as the spontaneous extension of the flaps at cruising speed, leading to a loss of control and structural failure. The board proposed two main hypotheses for the initial deployment: an accidental activation of the flap switch by the captain or a latent electrical malfunction in the control circuitry. The crew's inability to recover was likely exacerbated by misleading variometer readings, which indicated a climb while the aircraft was actually descending at a high rate, and the physical difficulty of managing the control column under extreme g-loads.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Flap Control System
The mechanism responsible for extending and retracting the wing flaps; its unexpected activation at high speed caused the loss of control.
Variometer
A vertical speed indicator that provided erroneous data to the crew during the dive, potentially confusing their recovery efforts.
Autopilot
Disengaged by the crew eight seconds after the flap extension began as they attempted to manually level the aircraft.
Interesting Facts
- 01The accident remains the deadliest crash involving the Tupolev Tu-124.
- 02The wreckage was distributed over a vast area measuring approximately 10.7 by 1.6 kilometres.
- 03The aircraft exceeded its maximum safe speed of 590 km/h during the final dive, reaching 860 km/h before breakup.
- 04The variometer provided false readings to the crew, indicating a climb of 15-20 m/s when the actual descent was 40-45 m/s.
Safety Actions & Advisories
Flap Switch Redesign
The design and placement of the flap release switch were modified to prevent accidental activation by the flight crew.
Tu-124 Retirement
Following the accident, the Tupolev Tu-124 was withdrawn from regular passenger service within the USSR.