Supporting material in a new US National Transportation Safety Board recommendation based on investigation into the 29 September mid-air collision over Brazil raises more questions as to why the business jet's Honeywell-built collision avoidance system does not appear to have been operating at the time.

A Legacy 600 business jet and Gol Airlines 737-800 collided over the Amazon basin while flying the airway between Brasilia and Manaus.

Last week the NTSB called on the US Federal Aviation Administration to provide enhanced visual and audio information regarding the functional status of traffic alert and collision avoidance (TCAS) systems. The board wants alerts in the event of "loss of collision avoidance system functionality, for any reason", and for the pilots to be compelled to acknowledge the TCAS status.

All 154 passengers aboard the Gol aircraft perished when it crashed out of control after its left wing struck the Legacy, which was flying a reciprocal track at the same flight level. The Legacy pilots were able to land the damaged twin-engined business jet at a military outpost. Although both aircraft were equipped with TCAS, neither provided warnings.

Currently, TCAS units display a white "TCAS OFF" or an amber "TCAS FAIL" message in "small letters" on the flight displays if there are problems with either the TCAS or the transponder that exchanges relative position data with the corresponding equipment on the other aircraft.

The NTSB notes that about 2min after the collision, the Legacy's first officer questioned whether the TCAS was turned on. The captain confirmed it was not and "immediately afterwards" the transponder data showed up on radar. "Therefore, there is evidence that the flight display warning was available to the crew but not noticed and acted upon until after impact," the board says.

Honeywell says the Legacy's avionics, including the transponders and radio management units, "were functioning properly during the accident flight and did not malfunction in any way", and that the equipment had been "fully certified" by the FAA, European and Brazilian authorities.

The company says the annunciation and alerting philosophy was "consistent with both industry and government certifying authority standards".




Source: Flight International