JIAAC Investigation
The Junta de Investigaciones de Accidentes de Aviación Civil investigation report was only one of the documents taken into account in the judicial investigation, though it was criticized for focusing solely on blaming the pilots directly.
During the three days after the accident, the United States National Transportation Safety Board (NTSB) sent a team to assist the JIAAC in their investigation. This team consisted of an NTSB representative and technicians from Boeing, Pratt & Whitney, and the US Federal Aviation Administration (FAA). While in Argentina, these investigators worked with JIAAC personnel, forming teams according to their areas of expertise.
The data from the black box, the flight data recorder (FDR) and the cockpit voice recorder (CVR) were read at the NTSB headquarters in Washington. With this information, a computerized animation of the failed take-off attempt was constructed.
Another aspect that was studied and analyzed was the adherence to the maintenance plan in the available technical documentation. The analysis led investigators to believe that the aircraft, its components and its engines complied with the requirements set out in the maintenance plan and the approved operational specifications of the Dirección Nacional de Aeronavegabilidad (National Board of Aeronavigation).
To complete the detailed investigation, the JIAAC technicians reassembled the main components of the aircraft in a hangar in the Aeroparque. They also cleaned, identified and analyzed the boards, actuators, electronic equipment, the cockpit pedestal, etc. that were recovered from the accident site, and dismantled the engines of the plane as much as possible given the state of destruction they faced. The technicians inspected the hydraulic system on thrust reversers of both engines, and the braking system of the landing gear, all of which were found to be in sufficient working order.
The investigation concluded that the engines almost certainly functioned until the final impact, though their behaviour at that particular moment could not be precisely determined. Nevertheless, from the reading of the FDR it was observed that both engines had equal thrust and were set to provide thrust for take-off before power was reduced and the thrust reversers were applied. In order to determine if there was a bird strike, the National Institute for the Investigation of Natural Sciences (Instituto Nacional de Investigaciones de las Ciencias Naturales) performed a study with negative results.
The thrust reversers—which are located behind the engine and direct the exhaust forward to slow the aircraft down quickly after landing (see image)—were found seriously damaged, but the hydraulic mechanism of the left engine was set for reverse thrust, while the right one was set for forward thrust. The investigation was unable to determinate if the thrust reversers were intentionally activated and later deactivated.
It was important for the investigation to establish the position of the mechanical activators on the flaps, since the fact that they weren't activated was a fundamental cause of the accident. A special investigation was carried out to establish what had happened with the flaps. The extended flaps alter the aerodynamic characteristics of the aircraft, giving the aircraft lift to get off the ground at a lower speed over a shorter distance than would be possible without flaps. Even if it had been possible to reach the take-off speed without flaps before the end of the runway, it would still have been necessary to have enough runway. This is why in practice, there are no runways that would allow the take-off of medium- to large- size aircraft without flaps.
The main finding within the remains of the plane was that all of the examined flaps' worm gear operators were in the unwound position, indicating that the flaps were not deployed. This tallies with the fact that the flap command in the cockpit was also in the no-flaps position, that the readings at the FDR indicate they were retracted, and that the flap lights were off, indicating that they were not activated.
The alarm sound recorded by the CVR indicated that there was a problem with the departure configurations. The recording showed that at the time of departure the flaps were not in the correct position for lift-off.
A study was performed on the electrical circuitry to determine the position of the electrical breakers on the departure configuration warning alarm. Also, a study was performed on the slat indicator lights' filaments.
The indicator lights were found to be off, the only fire alarm was off and the main warning indicators (Master Caution) were found on. The latter could be activated by any one of a long list of possible faults resulting in the destruction of the aircraft.
Read more about this topic: LAPA Flight 3142