Data from investigators suggests Embraer corporate jet was at the wrong flight level and was out of radio contact
The ExcelAire Embraer Legacy 600 corporate jet that collided with a Gol Linhas Aéreas Boeing 737-800 on 29 September was at the wrong flight level, say sources close to the Brazilian investigators. After the collision, the 737 spiralled out of control and broke up in mid-air well before it hit the ground, killing all 148 passengers and six crew on board. The Legacy, although damaged, was able to land safely.
The collision took place about 17:30 at flight level 370 (37,000ft/11,300m) in clear weather on airway UZ6 with the two aircraft on reciprocal headings (see diagram below). Before the collision, the Legacy went out of radio communication soon after passing over Brasilia heading for Manaus, according to air traffic control.
The location of the collision, near the remote, rainforested area of the Serro do Chachimbo mountains, is the point at which the two airspace sectors controlled by the Manaus and the Brasilia en-route ATC centres meet. It is also at the limits of radar coverage from both Manaus and Brasilia. Radio communications are notoriously unreliable there, according to local pilots, and the Legacy crew say that they had tried and failed to make ATC contact with Brasilia in the 10min before the collision. At the time of the accident, the 737 (a new-build aircraft, registration PR-GTD) bound for Brasilia was still in contact with Manaus, and the Legacy was technically under Brasilia’s control (but with no contact). A journalist travelling on the Legacy quotes the pilots as saying that they did not see the 737 at any time, and did not know of its proximity.
According to its flightplan, the Legacy (N600XL) was to cruise at FL370 on airway UW2 as far as Brasilia, and then descend to FL360 when it joined UZ6 there. Early statements from the investigators, however, indicate it is not clear whether the Embraer changed level. Aircraft on UZ6 are supposed to fly in a north-westerly direction at even flight levels, and the south-easterly heading at odd flight levels, but soon after the Legacy passed Brasilia, the authorities say they not only lost radio communication with it, but also with the aircraft’s transponder “squawk”, which would have provided its height readout.
Immediately after the collision, say the investigators, the Legacy’s emergency squawk  was visible on radar, but the crew’s mayday call on the emergency frequency had to be relayed to ATC by a Polar Air Cargo flight. The Legacy diverted safely to Cachimbo Brazilian air force base with damage to its left winglet and left horizontal stabiliser, but no injury to the two crew and five passengers. Investigators found the wreckage of the 737 widely spread, indicating structural break-up well before impact with the ground.
Read more on the Gol Boeing 737-800 fatal crash and the unknown factors still being investigated in the incident.