Two years after the collision between an Embraer Legacy 600 and a Gol Boeing 737 sent the Brazilian airliner crashing into the Amazon forest with the loss of 154 lives, key questions remain unanswered, but the safety cost of efforts to place blame are clear.

The principal puzzles in the crash are why both aircraft were at the same altitude, why the Legacy’s transponder was not operating, and why the Legacy and ground control remained out of radio contact for close to an hour.

The day before the anniversary, Brazil’s Center for the Investigation and Prevention of Aeronautic Accidents (CENIPA) announced that the final report is under review by American and Canadian members of the investigative commission, and should be released by year-end. The statement recapped some conclusions already reached.

The Honeywell transponder, CENIPA says, was operational although not in use, and “no errors were found in design or integration” of the Embraer’s avionics. The American pilots, Joseph Lepore and Jan Paladino of Long Island-based Excel-Aire, did not turn off the transponder, or notice or remember doing anything that might have turned it off accidentally. CENIPA also declared that ATC radio and radar equipment did not contribute to the accident.

Radio Silence
When the Legacy was over Brasilia, the crew was told to change to the frequency of a sector behind the airplane, rather than that of the sector they were entering. ATC did not attempt to contact them until they had passed out of range of that frequency. The pilots continued to hear transmissions throughout their flight, but only from other aircraft, never from the ground, which was not apparent as the transmissions were in Portuguese. When the pilots attempted to contact Brasilia before entering the airspace of the Manaus control center, minutes before the collision, three out of the five frequencies listed on the aeronautical chart were disabled on the controller’s console.

Still unexplained, however, is why the last transmission picked up by the Legacy from Brasilia was captured more clearly on the recorder of the more distant Gol Boeing, and why after the collision the Legacy was unable to communicate with either Brasilia or Manaus, finally relaying through a nearby cargo airplane a request for clearance to make its emergency landing at an Air Force base.

TCAS equipment on the two brand-new aircraft did not warn of the impending collision because it depends on both aircraft having operating transponders. With the Legacy’s transponder off, the business jet’s exact height also disappeared from ATC displays.

Controllers point to one specific feature of the X-4000 ATC software as having compounded the problem. A review of the software by the Federal Court of Audit (TCU) in August described the issue: “The X-4000 system possesses a functionality that automatically alters the flight level at the point on the route foreseen on the plan, without the controller’s acquiescence, and independent of the true level at which the aircraft is flying.”

When the system loses an aircraft’s exact height, either through failure of the secondary radar or loss of the transponder signal, the automatic height substitution can be misleading, controllers claim, and contributed to the Gol tragedy.

The TCU report highlights the dynamics of Brazil’s military-run ATC system, in which nearly all controllers are military personnel with their careers capped at the rank of sergeant, reporting to Air Force officers for whom ATC is normally a brief detour from flying.

On the issues of automatic altitude change, the TCU sided with the controllers, with the understated conclusion that “the incorrect presentation of the level in the data block increases the risk of traffic conflict.”

The 83-page report candidly gave the Air Force’s position. “In a meeting realized in the editor’s office, the managers alleged that they have not made this change because they fear that doing so could be used in the courts, since the controllers involved in the Gol 1907 accident used, as a line of defense in the trial on the case, the thesis that this functionality had been one of the causes of the accident.” The report says that the Air Force asked that the issue be suppressed from the text altogether.

Criminal and Civil Trials
The two American pilots of the Legacy were detained in Brazil for more than two months. They have been criminally charged with “endangering an aircraft” in Brazil’s federal courts, along with four air traffic controllers. The controllers, along with a fifth, are simultaneously being tried on charges including manslaughter in the independent military court system.

In May the Brazilian court sent questions to the U.S. to be answered by the pilots. However, Brazilian trial procedures changed in August, causing the judge to cancel the questioning until further notice.

After a U.S. judge ruled in July that civil suits in the case should be brought in Brazil, many families rushed to meet the two-year statute of limitations in the Brazilian Code of the Air. Leading indemnity lawyer Luiz Roberto de Arruda Sampaio explained, “Under Brazilian law the airline that carried the victims, Gol, has ‘objective responsibility.’ Objective responsibility means, roughly, ‘I don’t want to know who’s responsible; I want you to pay me.’”

Only one family has sued ExcelAire and Honeywell in Brazil. Gol says it has reached settlements with the families of 76 victims.

While Sampaio’s statement failed to answer some of the mysteries, it did make clear the safety costs of criminalization. The American pilots refused to speak to the Brazilian investigators until January of this year, delaying completion of the report. On their lawyers’ advice, none of the air traffic controllers has yet testified in the safety investigation, CENIPA says.

The newspaper O Estado de S. Paulo in September reported a steep drop-off in the number of Confidential Reports for Flight Safety received by CENIPA. The voluntary reports have fallen from 159 in 2005 to only nine so far this year. Brigadier Jorge Kersul Filho, head of CENIPA, said, “When a crewmember fills out a report and later sees that being used in court, he feels inhibited and stops collaborating.” The reports have been one of CENIPA’s principal safety tools.