Leaks from the investigation on the mid-air collision between a Gol Transportes Aéreos Boeing 737-800SPF and an Embraer Legacy over Brazil's Amazon region reveal that an incorrect air traffic clearance put the two aircraft at the same flight level on opposing headings.
Just over a year after the accident, Brazil's investigation board CENIPA is finalising its report for release in early November. Meanwhile much of its content was recently leaked to the São Paulo-based daily newspaper Folha de São Paulo.
According to the newspaper, CENIPA will report that 11 factors - most of them ATC procedural errors - played a part in the accident that led to the loss of 154 occupants aboard the Gol 737. The Legacy and its occupants survived.
The chain of events leading to the 29 September 2006 mid-air collision began when Brasilia's CINDACTA 1 area control centre liaised with São José dos Campos airport from where the Embraer Legacy was due to depart, having filed a flight plan that contained expected flight level changes according to the airway tracks on which it was to fly.
CINDACTA 1 indicated that the flight was cleared all the way to Manaus at FL370 (37,000ft/11,270m) - when in fact there were three planned flight level changes. The erroneous clearance was relayed to the Legacy's crew, which did not question the changes.
After arriving overhead Brasília at FL370, the Legacy joined airway UZ6. It was flight-planned to descend to FL360 at that point, but the crew continued at FL370 as cleared. The CENIPA report is expected to detail a succession of Brasília air traffic controller errors and delays that directly contributed to the failure to instruct the Legacy's crew to change to an even-number flight level, which would be correct for aircraft flying UZ6 in that direction (the opposite direction traffic would fly odd-number flight levels).
The Legacy crew made correction more difficult by selecting the wrong radio frequency when the aircraft exited that the Brasília centre's sector 9 and entered sector 7, where the mid-air collision took place.