Brazil Midair Underscores Value of Thorough Research

 - April 29, 2009, 7:43 AM

Operational threat identification and risk mitigation remain a primary concern for those who operate internationally. NTSB senior air safety inspector Roger Cox, the lead investigator on the Gol Airlines/ExcelAire Legacy midair, used the accident as an example of why international operators should take the time to fully understand what may be asked of them in less than normal situations in another country.

He explained that the state of registry is responsible for the investigation of an accident on foreign soil, in this case Brazil, under ICAO Annex 13, meaning the NTSB can act only as an advisor. In this case, the NTSB filed a Safety Recommendation Letter after the Brazilian report was released. “The U.S. team has no substantial disagreements with the facts gathered,” Cox said. “However, the interpretations, conclusions and understandings differ in a number of respects.” For example, Brazilian investigators were not allowed to interview the individual controllers involved in the accident.

Cox mentioned four substantive areas of concern about the Brazil crash: how effectively the equipment on board the Legacy was functioning; the preparation of the flight crew for a long trip over unfamiliar territory; the ATC rules and procedures these pilots would be expected to adhere to; and finally, how well the Brazilian airspace system functions. While these concerns are specific to this accident, they have implications for all operators.

To the U.S. parties involved in the investigation, the primary question was why the Brazilian ATC system failed to maintain separation between two jets operating under positive control in high-altitude airspace at FL370. The U.S. findings focused essentially on the archaic Brazilian ATC software as the reason the air traffic controller simply misinterpreted the information he was seeing on his screen, mainly that the altitude displayed in the Legacy’s data block was showing what was filed, not the actual cleared altitude. This caused the Brazilian controller to believe separation existed. Obviously, the U.S. pilots and the Boeing pilots were completely unaware of what was going on at the time. No mention was made of any communication between the Boeing and ATC before the accident.

The NTSB report certainly did not absolve the U.S. pilots of all responsibility as some believed, Cox added, because the Legacy’s TCAS was disabled for some as yet unexplained reason. This made it impossible for either crew to detect the other. Adding to the lack of TCAS avoidance information, Cox said, was the Legacy crew’s lack of communication with ATC for nearly an hour before the crash. Neither the Legacy crew nor ATC took any decisive action to reestablish contact with the other before the collision. Another ATC issue focused on the Brazilian center controller’s failing to verify the Legacy’s cruise altitude when the crew initially checked in, again assuming that the FL360 altitude the computer showed was correct.

The Legacy crew flew at FL370, precisely as they would have in a similar situation in the U.S. Cox said that while there was no direct communication between the Legacy and ATC, the CVR clearly picked up other conversations on the frequency, perhaps leading the crew to believe two-way communications still existed.

Most important, Cox said, was that although the interpretation by others is that the Legacy crew should have been operating under lost- communications procedures, the trigger point at which the flight transitioned from normal to lost communication would have been difficult for anyone to determine. The question was also whether or not the lost-communications procedures–had they been observed–would have been the ICAO version or the Brazilian one.

Most IOC attendees did not know that Brazilian lost communications would have required the crew to fly their flight-planned altitude (FL360). But again, what remains unclear is whether the Legacy should have been flying in accordance with any lost-communications procedures at all.

The Embraer/Gol accident highlights the importance of U.S. flight crews’ understanding all the details of ATC procedures that apply to a flight. Understanding U.S. lost communications is not enough. Cox said one of the key recommendations the NTSB made was to look closely at the currently vague procedures that explain what kind of international training is required before a Part 91 flight crew leaves the 12-mile limits. The NTSB is soliciting input from airmen with an opinion on the current system through Cox at roger.cox@ntsb.gov.