TAM Flight 402 Accident Investigation (PT-MRK)

TAM Flight 402 crashed into a populated neighborhood after an in-flight deployment of the number 2 engine's thrust reverser during takeoff from São Paulo.

Probable cause

The official findings reported contributing factors including organizational and individual psychological aspects, material design deficiencies, and operational factors. The lack of information, instructions, and practice contributed to the non-recognition of the abnormality. The unusual occurrence of the quick reduction of the lever, the nonoccurrence of failure discriminating warnings, and the lack of cognizance and specific training brought on surprise and distraction. The release of the restriction of the lever of engine 2 at the idle detent without the occurrence of abnormality warnings strengthened the tendency to try to recover the power on the engine. The lack of warnings and the difficulties characteristic of such abnormality diverted the crew members' concentration from the procedures provided for. The occurrence of auto-throttle failure warnings and the lack of specific reverse opening warnings strengthened the belief that they were experiencing an autothrottle failure. Design deficiencies included the reverser fault tree chart indicating a probability of inadvertent opening of the reversers of the order of 10^-6, and the Post-Mod version not meeting airworthiness requirements of FAR/RBHA 25.1309. On two phases of the complete reversers cycle, it is possible to apply power higher than IDLE with the shells partially open, which does not meet RBHA/FAR 25.933. The reverser unlocked indication system is inhibited at speeds higher than 80 Kt and up to the height of 1000 feet. The SECONDARY LOCK ACTUATORS presented a performance much below the minimum acceptable. The applicable FAR 25.993(a)(3) requirements determine that each reverse system is to be provided with means to prevent the engine from producing power higher than idle power upon a failure on the reverse system, which has not been complied with. The TURNBUCKLE is installed on the side to which the connection moves when the reverser is commanded to open. The THRUST SELECTOR VALVE may be moved with less than 2% of the normal functioning pressure. The inductive loads as those of SEC. LCK. ACTUATOR are detrimental to the contacts that command them. The THRUST REVERSER ACTUATOR, in the Post-Mod configuration, remains de-energized during the periods in which there is no commanding by the pilot, and this way it stays in an unstable and dangerous situation. Design faults, an insufficient assessment of the fault tree diagram, and the guidance to the operator not to train the abnormality that occurred on that phase indirectly contributed to the sequence of events that led to place the crew facing an unprecedented situation. Operational factors included little experience on the aircraft and deficient application of control. For three times, the thrust lever of engine 2 has been reduced and advanced. Such interventions on that lever brought on the reduction of the thrust lever of the left hand engine, impairing the aircraft's performance. The non-return of the left hand lever to take-off thrust immediately, and another four seconds delay in attaining such thrust, contributed to deteriorate even more the aircraft's climbing capability.