Investigation Summary
The accident was initiated by a mechanical failure of the pilot-in-command's seat reclining mechanism, which had been over-tightened during maintenance. This failure occurred at a critical high-speed phase of the takeoff roll (117 knots). The physical collapse of the seat caused the captain to lose his grip on the controls and inadvertently retard the thrust levers. Because the Boeing 737's autothrottle was in 'THR HLD' (Throttle Hold) mode, the levers remained at the reduced 77% setting rather than commanded back to takeoff power. Crew Resource Management (CRM) broke down during the subsequent five seconds. The captain handed over control to the first officer, but the first officer did not follow the standard pilot incapacitation protocol, which would have required verifying thrust and flight instrument parameters. When the captain resumed control, he focused entirely on the remaining runway and rotation, failing to cross-check his engine instruments. The aircraft rotated late and at a high pitch angle (10.7 degrees) to compensate for the lack of speed, causing the aft fuselage to strike the ground and the landing gear to smash through a brick boundary wall. Remarkably, the crew climbed to 36,000 feet and flew for several hours over the Arabian Sea before the airline, alerted by ground reports of debris, insisted on a diversion.
Final Conclusions
The AAIB India concluded the primary cause was the delayed takeoff resulting from the reduction of takeoff thrust from 98% to 77% before V1, and the failure of both crew members to monitor thrust parameters or take corrective action. Contributory factors included the mechanical failure of the PIC seatback recliner, a breakdown in crew coordination during the transfer of control, and a loss of situational awareness. The investigation was completed approximately 2 years and 4 months after the event.
Video Analysis
How A Broken Seat Flew This Jet Into A BRICK Wall | Air India Express Flight 611 — A detailed breakdown of how a mechanical seat failure led to a near-disastrous takeoff in Trichy, including simulator recreations of the crew's options.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Experienced seat failure during takeoff roll. Had 500 hours in command on type.
First Officer
Failed to verify thrust settings during pilot incapacitation event.
Systems & Failure Modes
Autothrottle (THR HLD)
Above 84 knots during takeoff, the autothrottle enters 'Throttle Hold' mode, where the servos are de-energized to allow manual thrust adjustments. This prevented the system from automatically restoring the 98% thrust setting after the captain accidentally pulled the levers back.
Seat Reclining Mechanism
The mechanical failure was traced to over-tightening of the reclining mechanism during maintenance, which led to the sudden collapse of the backrest under the pilot's weight.
Interesting Facts
- 01The aircraft sustained substantial damage including a large hole in the underside, a ripped-off VHF antenna, damage to the horizontal stabilizer, and damage to the cowling of the number two engine.
- 02A motorist passing the airport boundary wall was injured by flying debris during the impact.
- 03Post-flight inspection found wire mesh from the airport fence embedded in the landing gear.
- 04Simulator tests showed that if the crew had restored 98% thrust upon the captain returning to his seat, the aircraft would have cleared the wall safely.
- 05The crew continued the flight to 36,000 feet and pressurized the cabin despite ATC warnings of a possible wall strike, which violated standard tailstrike protocols.
- 06The aircraft was approximately 500nm west of Mumbai over the Arabian Sea when the crew finally initiated the diversion to Mumbai.
- 07The aircraft was a Boeing 737-800 manufactured in 2009 (MSN 36340/3122).
Safety Actions & Advisories
Maintenance Procedure Review
The investigation highlighted the need for precise torque specifications when maintaining cockpit seat reclining mechanisms to prevent over-tightening.