Flight 1907 – Commission clarifies on transponder
Because of the release of information, on the part of organs of the domestic and international press, on the accidental interruption of transponder transmissions in the case of the Flight 1907 accident, which provoked the non-functioning of the anti-collision system, the Aeronautic Accident Commission of Investigation informs that:
1) Up to now, there are no indications that there occurred an intentional act on the part of the crew of aircraft prefix NX600L in the sense of interrupting the transponder's transmission (STAND BY mode) ;
2) Ergonometic studies, CVR (Cockpit Voice Recorder) data, and reconstructions demonstrate that:
- The interruption of transponder transmissions occurred during a period of silence in the cabin, lasting 1 minute and 43 seconds, while the pilots of aircraft NX600L performed flight planning calculations for the next stage of the trip, with the pilot on the right using a laptop;
- According to the report of the reenactment flight, there is no way that a laptop resting on the lap of the pilot on the right can touch the button on the RMU (Radio Management Unit) control screen twice, in less than 20 seconds, to put the transponder in STAND BY mode;
- There is no way to utilize the footrest during the flight with the seat in the normal piloting position. It would be necessary to move it back. Seat position movements register on the CVR and there is no register of movement (cabin noise) during the period in which the transponder ceases operation;
- The footrests have a protection which impedes a shoe sole from directly contacting the panel;
- If this occurs by an action by the pilot on the left, flexing and contorting his right foot, the buttons reached would be the first two, from top to bottom and on the left side of the RMU control panel, which have as their function the changing of the radio frequencies, and not the fourth button, which would permit changing the transponder mode (if it were touched twice in succession, in an interval of less than 20 seconds);
- Only the pilot on the left can, observing the description in the previous item, place his foot on the left side of the RMU;
- On the CVR, there is a commentary by the pilot on the left recommending not putting feet up in the cabin during the flight.
From all the evidence presented, the Commission reiterates that the conclusions aired by some organizations and press organs, domestic and international, on the use of the laptop or of the "footrest" on the flight in question, do not have any technical support in the work of the Aeronautic Accident Commission of Investigation, which is responsible for the procedure aimed at prevention.
Source: Aeronautic Accident Commission of Investigation / CENIPA