Black Box of the Airbus indicates pilot error
Computer registered imperfections in the operation of the thrust levers of the turbines; hypothesis of mechanical error is not discarded
Without control, the pilot tried to stop the airplane pressing the two pedals in its front, braking the tires of the landing gear
FERNANDO RODRIGUES OF THE BRANCH OF BRASILIA
The black box of the TAM Airbus-A320 that crashed in Săo Paulo on the 17th indicates that it had error from the pilot in the operation of the thrust levers, besides catching the desperation of the pilots in trying to brake the airplane on the ground. Although less probable, one pane in the computer of the airplane also cannot be discarded, separately or in set with the probable human error.
A Folha had access to the data, that had arrived yesterday at the Congress in a CD-ROM with about 60 archives of data and audio. The first failure, whose hypothesis had been anticipated by A Folha last week, occurred little before the landing, when the thrust lever of the right engine was kept in an acceleration position. It would have to be in idle, as the other lever.
When landing, the electronic systems had interpreted this procedure as a desire of the pilot to speed up. The two turbines had started to speed up automatically. The air brakes had not been set in motion. The automatic brakes from the landing gear also did not function.
A second mistake may have contributed for the abnormal acceleration: only the left turbine thrust lever was placed in the position of maximum reverse. This turbine had the reverser functioning, equipment that assists the braking when inverting the air flow in the turbine, - the other one not.
Even with the inoperative reverser in the right turbine, the correct procedure must have been to place both thrust levers in reverse. But the right remained speeding up, according to register. Airbus divulged a message last week alerting operators of its airplanes exactly on the necessity to fulfill these two operations, established already in preliminary data of the black box. It had other similar accidents with the A320 attributed the pilot error. The airplane of TAM had the right reverser deactivated for four days, because of a hydraulic problem.
Losing the control, the pilot then tried manual braking to stop the airplane. At the same time, with the hands, he held hard the internal mechanism could that controls the direction the front wheel. But the turbines had continued to speed up.
Last week, the responsible Brigadier General for the inquiry, Jorge Kersul, said that the hypothesis of failure in the computers is not excluded. “The data of the parameter can indicate that lever was in such position, but who can say that the problem was not electronic? Thrust lever can be in another position and the problem could be the electronic signal that the computer is emitting. People can hear something [in the voice recorder] that “thrust lever does not leave the place, its locked”, said to the CPI of the Aerial Apagăo. The audio archive that A Folha had access discloses that the pilot and the copilot emit laconic but important phrases. When touching the ground in the main runway of Congonhas, a voice in the cabin says: “Reverse one only”. That is, the pilot and the copilot knew that only a reverser was operative. After that, another phrase: “Spoiler nothing…”. That is, spoilers (air brakes in from above part of the wings), that they open automatically in the landing, had not functioned. The tone is dramatic: “slow down, slow down, slow down”. It increases the panic: “It does not, it does not, it does not”. Finally, the known phrase already: “turn, turn, turn”. Who heard the complete recordings and passed the content to A Folha did not want to disclose the final words caught at the flight deck, seconds before the airplane blowing up, killing 199 people.
The data will be analyzed today by the members of the house of representatives with aid of technician of the BAF. Beyond the human error and eventually of computers, a third hypothesis has derived from the previous ones. The pilot would have really pulled the two levers to the correct position at the time of the landing - the known position of “idle”, or “dead spot”, in Portuguese. For some defect, the right lever would not have been pulled back enough to emit the electronic signal for the computer. When an airplane as the Airbus-A320 approaches the runway to make a landing, the pilot and the copilot must introduce the data regarding to the landing. At this moment, levers can still be in the so called “climb” position, which means “to go up”. The computer knows that the flight is in the end and decelerates the turbines. However, when touching the ground, it’s important that the two levers are then in the “idle” position. The black box indicates that the right lever was still in the “climb” position, or “near idle” (almost decelerated) when the Airbus touched down. At this time, when the weight of the aircraft sets in motion the hydraulic systems of the landing gear, the computer is programmed to set in motion the air brakes (flaps and spoiler) and the wheel brakes. Nothing of this happened. As soon as the Airbus touched the ground, the two turbines spooled up. One of them had the reverser out (of the left side) and the air flow started to be inverted, helping the airplane to brake a little. On the right side, however, the turbine continued to increase the force, as if the airplane was making a new take-off.
For the attempt of the pilot in “holding” the airplane, it is possible that it has careened to the left at the start of the landing. Regarding Congonhas airport, black boxes have not yet ended up the controversy.
But the fact that the pilot managed to keep the airplane on the track indicates that the track couldn’t be that much below standard.