The investigation into why an Embraer Legacy and Gol Airlines Boeing 737 collided over the Amazon jungle last September 29 isn’t expected to conclude for several months, but that hasn’t stopped Brazil’s Federal Police from recommending criminal prosecutions for ExcelAire pilots Joseph Lepore and Jan Paladino.

Police officials leading the investigation told Brazilian media that the Legacy pilots and Brazilian controllers share equal blame for Brazil’s worst ever air disaster, in which all 154 people aboard the airliner died. At least three of the controllers on duty at the time of the accident bear some responsibility for the collision, police officials said, adding that they could face charges brought by the Brazilian military.

The business jet landed safely at a Brazilian military base after the collision. The airliner went out of control and crashed in a remote part of the jungle about 460 nm northwest of Brasilia.

NBAA, the Flight Safety Foundation (FSF) and the International Federation of Air Line Pilots’ Associations last month heavily criticized the decision by Brazilian police investigators to seek indictments against the U.S. pilots, arguing that the move could hurt investigators’ ability to gather information after future air accidents. “We are disappointed that Brazilian police officials continue down the road of emphasizing criminalization in the wake of last year’s tragic accident,” NBAA president and CEO Ed Bolen said in a statement issued on May 11.

NBAA and the Flight Safety Foundation blasted the Brazilian Federal Police for launching the criminal probe before the accident investigation is completed.

ATC Concerns Raised
In their report, police investigators say that the controllers and ExcelAire pilots all made mistakes on the day of the collision. Federal Police Chief Renato Sayao has recommended a charge of “endangering an aircraft without intention” for the pilots. If convicted, they would each face a maximum of four years in prison. Brazil and the U.S. have an extradition treaty with each other, but it covers only a narrow list of crimes and not the offense alleged by police investigators. Brazilian prosecutors were expected to respond to the Federal Police recommendation soon.

The rush to judgment on all sides of the criminal and accident investigations has been punctuated by finger pointing, controller unrest and accusations of biased and nationalistic reporting by Brazil’s media. Still, investigators appear to be edging closer to providing answers to a number of key questions about the collision.

Although the exact cause of the accident remains under investigation, the facts that have emerged so far leave little doubt that Brazilian controllers made serious errors on the afternoon of September 29. The Legacy pilots, at the very least, missed clues that their transponders were no longer transmitting data to ATC, experts say.

The International Federation of Air Traffic Controllers’ Associations, which assisted in the initial accident investigation, has pointed to serious flaws in Brazil’s ATC system, the loss of transponder signals from Legacy N600XL and controller errors as the likely culprits in the chain of events leading to the collision.

In its preliminary accident report, the NTSB wrote that after departing São Jose dos Campos the Legacy pilots climbed to FL370 as instructed by ATC. About an hour before the collision, at 3:51 local time, N600XL was instructed to “squawk ident.” Recordings show the transponder ident was observed. This was the last successful radio communication between the pilots and controllers before the collision.

About 11 minutes later, at 4:02, ATC radar was no longer receiving the Legacy’s transponder signal. For more than 20 minutes, however, controllers made no attempt to contact the Legacy crew or to remove the airplane from active RVSM status as was required by Brazil’s ATC rules.

At about the time N600XL’s transponder signal disappeared, the airplane crossed the Brasilia (BRS) VOR on airway UZ6 headed toward Manaus, where the crew and passengers planned to stop for the night before leaving for Fort Lauderdale, Fla., the next day. The Legacy’s filed cruise altitude was FL370, with a planned change to FL360 at BRS and FL380 at teres intersection 280 nm farther ahead.

After the Legacy crossed the BRS VOR, ATC software automatically updated to show the airplane’s current cruising altitude of FL370 and, on a new data tag, the so-called “cleared flight level” of FL360.

Because ATC was no longer receiving the Legacy’s transponder signal, a military primary radar was automatically activated at this time. This radar can’t show geographical position of a target blip, but it calculates altitude based on an angle-height measurement. However, this is an imprecise calculation that experts say can produce errors of 4,000 feet or more when the target is 200 nm from the radar site.

A few minutes after the military radar began tracking the Legacy, a new controller took over at the Brasilia ATC center. On this controller’s radar screen, N600XL was established at FL370, but it was still being shown on its “cleared to” data label at FL360. Brazilian air force officials have said that this controller mistakenly assumed N600XL was flying at FL360 at this time and was therefore no threat to the Gol Airlines 737 traveling on the same airway in the opposite direction at FL370.

At 4:26 the controller tried to contact the Legacy. The pilots reported hearing a garbled instruction at one point to change frequencies, but they couldn’t make out the full message. Subsequent attempts at two-way communication were unsuccessful.

The Legacy and 737 struck each other at FL370 at 4:56:54. There were no TCAS warnings in either cockpit. The prevailing theory holds that the Legacy’s left winglet and horizontal stabilizer clipped the left wing of the 737, causing the airliner to go out of control and crash in the jungle below.

Police investigators claim that the Legacy pilots accidentally switched off their transponders at some point after takeoff. Lawyers for ExcelAire, the Long Island-based owner of N600XL, rejected that theory in written comments supplied to the Federal Police. The company argued that there is “no pilot action that could cause the target position symbol and the aircraft data block to disappear from radar screens.” Independent experts, however, say it is possible to put the Legacy’s transponder into standby mode with just one or two unintentional key strokes on the radio management unit (RMU).

ExcelAire earlier this year submitted what it described as a “minute-by-minute” account of the accident sequence to the Brazilian police. The report “leaves no question that the principal cause of the accident was the breakdown of the air traffic control system,” said Theo Dias, the Brazilian attorney for ExcelAire and the American pilots. The report also alleges that equipment that operates in conjunction with the transponder, TCAS and other avionics in the Legacy has not been properly analyzed or tested, Dias said. “Based upon the open questions identified in the report…it would be premature for the Federal Police to recommend criminal charges.”

Safety Recommendations
The collision has already prompted new safety recommendations. The NTSB last month called for improved cockpit warnings when an airplane’s transponders or TCAS have stopped functioning, saying current cockpit annunciation messages are inadequate. “Regardless of whether the transponder has failed or the TCAS has become inoperative, a flight crew’s ability to mitigate the risk of collision is significantly degraded if the collision avoidance system becomes inoperative and the failure is not quickly and reliably brought to the crew’s attention, as this accident demonstrates,” the NTSB wrote.

From CVR conversations, it is clear the pilots were unaware that the transponders and TCAS stopped working before the airplanes struck each other. In its recommendation, the Safety Board noted that about two minutes after the Legacy and 737 collided, the first officer asked whether the TCAS was on. The captain answered that it was not. Thirty seconds after this exchange the Legacy’s transponder signal reappeared, the NTSB said. ExcelAire lawyers argued that this exchange between the pilots was related merely to the question of whether the TCAS had issued a “pop-up” alert immediately before the collision.

ExcelAire has pointed to equipment problems as the possible reason the transponders stopped functioning, saying that N600XL experienced numerous avionics anomalies in the weeks before delivery and had been fitted at the factory with an RMU that twice had to be sent back to manufacturer Honeywell for repairs. The company said it learned that the RMU had failed in two other aircraft only after the collision.

Honeywell last month went on the record as saying that the transponders and RMUs aboard N600XL were working at the time of the accident. In a statement, it said the Legacy’s “transponders and radio management units were functioning properly during the accident flight and did not malfunction in any way.” Honeywell is facing lawsuits filed by victims’ families, with some lawyers arguing that the Honeywell RMU design contains flaws. ExcelAire is also a target of the lawsuits, but Brazilian OEM Embraer is hardly mentioned in court documents.

ExcelAire noted that any tests performed on N600XL’s avionics were done in a laboratory setting and not in the actual airplane, where wiring faults or other anomalies might show different results. The accident investigation is likely to conclude by year-end, Brazilian officials have said, at which point the reasons why the transponders stopped providing data might be known. The fate of the pilots, meanwhile, remains an open question. ExcelAire declined to divulge their current status with the company or to say whether the pair plans to return to Brazil to face charges.