While details are gradually emerging about the fatal Gol Boeing 737-800 crash in the Amazon jungle, the precise nature of the accident and the circumstances leading to it have yet to become clear.

The widely-accepted theory is that the 737 collided with an Embraer Legacy 600 business aircraft. Although officials from Brazil’s civil aviation administration ANAC are privately referring to the accident as a collision, investigators are keeping an open mind regarding the condition of the 737 immediately before its loss.

Having revised its passenger count owing to an error in the manifest, Gol has confirmed that 154 occupants – comprising 148 passengers and six crew members – were on board the jet when it came down on 29 September.

Both the 737 and the Legacy were apparently travelling along airway UZ6, which connects Brasilia and Manaus; the 737 was heading southeast to Brasilia at flight level 370 (37,000ft, 11,210m) , the Legacy travelling northwest towards Manaus.

Brazil implemented reduced vertical separation minima last year and, under this scheme, FL370 on the UZ6 airway is allocated to eastbound traffic; westbound traffic is normally assigned the adjacent levels FL360 or FL380.

It remains unclear why – if the aircraft did collide – the Legacy was operating at the same altitude as the 737. There are suggestions that it should have been at FL360, although this has not been confirmed officially.

Both aircraft were new; the Legacy was on a delivery flight and the Gol aircraft was barely two weeks old. No details have been released about the status of either’s traffic collision-avoidance systems.

The role of air traffic control is also being investigated, to understand the degree to which controllers were able to track the aircraft, whether they were aware of any altitude discrepancy or the potential for a collision, and whether they were able to communicate with the jets.

Brasilia and Manaus are separate flight information regions, and are overseen by two different parts of the Brazilian air traffic system, Centro Integrado de Defesa Aérea e Controle de Tráfego Aéreo (Cindacta). Brasilia falls under the Cindacta-1 centre while Manaus comes under the Amazonian Cindacta-4.

While airspace surveillance infrastructure, particularly in the Amazonian region, has been extensively modernised in the past five years, Brazilian authorities have yet to clarify whether the aircraft were within primary or secondary radar coverage range, and have yet to address persistent suggestions that controllers were not receiving transmissions from the Legacy’s transponder.

Representatives of the Flight Safety Foundation have urged law-enforcement authorities in Brazil to allow the country’s accident investigation authority, Centro de Investigação e Prevenção de Acidentes Aeronáuticos (CENIPA), to conduct its inquiry without interference, and avoid premature judgment of those involved.

“We call on the Brazilian government to stay strong in the face of public pressure and continue to respect the integrity of the investigation and not rush to judge the various players in this accident,” says the foundation’s president, Bill Voss.

“This allows an efficient investigation to proceed and answers to be found. In the case of clear negligence, appropriate civil and administrative remedies exist to deal with this tragedy after all the facts are in.”

Source: FlightGlobal.com