What happened
On October 11, 2018, an Air India Express Boeing 737-800, registration VT-AYD, was performing a scheduled passenger flight from Tiruchirappalli (Trichy) to Dubai. During the takeoff roll on runway 27, the pilot in command experienced a sudden failure of the seat recline mechanism at approximately 117 knots. The seatback collapsed unexpectedly, causing the pilot to lose balance and momentarily relinquish control of the aircraft to the co-pilot.
This mechanical disturbance caused the throttle levers and control column to move inadvertently, resulting in a significant reduction in engine thrust from 98% to 77%. While the pilot was able to readjust the seat and resume control, the loss of thrust meant the aircraft had insufficient speed by the time it reached the rotation point. The crew initiated rotation with limited runway remaining, leading to a high pitch rate. This resulted in a tail strike on the soft ground of the runway end safety area, followed by the aircraft's fuselage and landing gear striking the airport's localizer antenna and the perimeter boundary wall.
Despite being informed by Air Traffic Control that the aircraft had struck the localizer and damaged the boundary wall, the crew performed system checks and continued the flight toward Dubai. However, after being contacted by the airline's operations center and advised by ATC, the flight eventually diverted to Mumbai, where it landed safely with no injuries to the 130 passengers or 6 crew members.
The investigation
AAIB India examined the aircraft's flight data, the mechanical state of the cockpit, and the crew's decision-making process. The investigation focused on why the thrust reduction went unnoticed and why the crew continued the flight despite evidence of structural impact. Technical examinations at the manufacturer's facility revealed that the seat recline mechanism had been adjusted too tightly, allowing the seatback to move without the control lever being operated.
Findings
- The primary cause was a delayed takeoff due to a reduction in engine thrust that the crew failed to monitor or correct.
- The pilot's seatback recline mechanism failed during the high-speed segment of the takeoff roll.
- There was a breakdown in crew coordination and a loss of situational awareness during the transition of controls.
- The crew's decision-making was flawed, as they relied solely on system confidence checks rather than addressing the high probability of structural damage indicated by the impact with the antenna and wall.
Safety action
- The investigation recommended that the seat manufacturer study global defect data regarding uncommanded seat movement.
- Recommendations were made for airlines to provide guidance for handling unforeseen cockpit failures not covered in standard manuals.
- The report emphasized the need for airlines to reassess pilot training regarding decision-making skills in emergency scenarios.