What happened
During the takeoff roll from runway 17R at São Paulo airport, the crew of TAM flight 402 initiated the takeoff sequence. Shortly after advancing the throttles to takeoff power, an autothrottle malfunction warning occurred. While the crew attempted to manage the throttle settings, the thrust reverser on engine number two unexpectedly deployed during the climb phase.
As the aircraft climbed through approximately 136 kts, a significant loss of power was experienced on the right side due to the deployment of the reverser buckets. The sudden asymmetric thrust caused the plane to roll heavily to the right. In an attempt to restore power, the crew manipulated the thrust levers; however, these actions caused the left engine's power to drop as well. As the airspeed declined at a rate of 2 kts per second, the aircraft reached a critical state where the stick shaker activated, signaling an impending stall. The aircraft entered a 39-degree bank angle and, following a ground proximity warning, impacted a building in a populated area.
Findings
Investigations into the accident identified several contributing factors involving design, operational, and organizational elements:
- Design deficiencies: The thrust reverser system was found to have a design flaw that allowed for an inadvertent opening in flight. Specifically, the secondary lock actuators were performing below acceptable safety standards, and the system inhibited certain unlocking indications at speeds above 80 kts and altitudes below 1,000 feet, depriving the crew of vital information.
- Crew distraction: The crew's attention was diverted from standard takeoff procedures to managing what they initially perceived as an autothrottle failure. This focus on the malfunctioning throttles prevented them from recognizing the actual deployment of the thrust reverser.
- Operational challenges: The sudden reduction of the engine two lever to idle during a critical phase of flight created an unprecedented situation. Furthermore, attempting to manage complex cockpit abnormalities below 400 feet is considered highly risky and contributed to the loss of control.
- Organizational factors: A lack of specific training and written instructions regarding this particular abnormality meant the crew was not prepared for the unexpected sequence of events.