Last September 29, over Brazils Amazon jungle, Gol Transportes Areos Flight 1907, a Boeing 737-800, and an Embraer Legacy 600 business jet collided at Flight Level 370. The Boeing tragically crashed shortly thereafter, killing all 154 aboard in the countrys worst-ever aviation accident. The Embraers crew declared an emergency and successfully landed their damaged jet some 30 minutes later at a Brazilian military base. In addition to the two crew, the five passengers aboard were uninjured. What happened,
Because it involved two very modern jets operating under IFR and equipped with the latest in collision avoidance equipment, and because it occurred in controlled airspace, this is an accident that simply should not have happened. Although its cause has not been formally determined, what is known should serve as a wake-up call to operators and ATC alike that all of the automation and safety devices industry can develop still cant prevent this type of accident as long as humans are involved.
Background
Gol Flight 1907 was a scheduled domestic air carrier operation en route from the Eduardo Gomes International Airport, Manaus, Brazil, to the Presidente Juscelino Kubitschek Airport, Brasilia. The Legacy was en route from the Prof. Urbano Ernesto Stumpf airport in San Jose dos Campos (SBSJ) to a stopover in Manaus and eventually to the U.S. The 737s routing was southeast along airway UZ6; the Legacy was routed along airway UW2 to the Brasilia VOR (BRS) and then northwest on UZ6 to Manaus.
The Legacy was on its initial delivery flight. Its U.S.-based operator, Excelaire, had just taken delivery at the Embraer factory. The flight was the first leg of several to Excelaires home base at the Long Island MacArthur Airport Islip, N.Y. (ISP). The Boeing 737-800 also was relatively new, having been delivered less than three weeks earlier. It reportedly had logged just 234 hours before the accident flight.
The 737 was destroyed by in-flight breakup and impact forces; all 154 occupants were fatally injured. According to the NTSB, the most likely scenario is the Legacys left winglet (see image on page 23) contacted the 737s left wing leading edge. “The impact resulted in damage to a major portion of the left wing structure and lower skin, ultimately rendering the 737 uncontrollable. Flight recorder information ceased at an approximate altitude of 7887 feet.”
The 737s wreckage was located in remote jungle terrain with very difficult access. Brazilian personnel recovered the flight recorders and all significant portions of the wreckage except the outer portion of the left wing.
The Legacy sustained damage to its left wing and left horizontal stabilizer. Its crew performed an emergency landing at the Cachimbo Air Base, approximately 60 nm northwest of the collision site. There was no further damage to the airplane, and the two crew members and five passengers were not injured.
There was no indication of any TCAS alert on board either airplane, no evidence of pre-collision visual acquisition by any flight crew member on either aircraft, and no evidence of evasive action by either crew. Visual conditions prevailed.
As this issue of
Aviation Safety was being finalized, the Embraer remained at the base and significant components had been removed from the aircraft for testing.CLEARED AS FILED
As the timeline and details excerpted at left from the NTSBs factual statement demonstrates, the Legacy crew proceeded northwest along airway UZ6, as filed and, presumably, as cleared by ATC. Unfortunately, the NTSB statement is vague on whether the cruise altitudes constituted
filed and requested, cleared or told to expect. These terms and the Legacy crews understanding of them as they applied to Brazilian ATC are at the core of lost communications procedures. And on these details the probable cause of this accident may hinge see the sidebar on page 24.On October 9, 2006, a copy of the Embraers original flight plan was released by Brazilian news media. The plan was for the Legacy to maintain FL370 up to BRS on airway UW2, followed by a descent to FL360. The Legacy was then to fly northwest along airway UZ6 to the TERES intersection 282 nm past BRS. At TERES, a climb to FL380 was planned, which would have been the final cruising altitude.
After the accident, the Legacy crew asserted they were cleared by ATC to FL370 for the entire flight to Manaus. This clearance apparently was confirmed on November 3, 2006, when the Brazilian media obtained ATC transcripts reportedly showing the initial pre-takeoff clearance given to the Legacy was “N600XL, Clear, 370, Manaus.” Any pilot receiving this clearance while still on the ground would have been justified in believing their flight had been cleared to climb and maintain FL370 all the way to its destination.
The transcript reportedly included another opportunity for ATC to verify or modify the Legacys altitude. This occurred when the flight crossed BRS and was handed off to another controller. On its initial call-up, the Legacy crew reportedly said, “N600XL at 370; good afternoon.” The controller responded by requesting the Legacy crew to squawk ident on their transponder and confirmed the flight was in radar contact. At no point did the controller question the Legacys altitude or issue a clearance for it to descend to FL360, the altitude listed in its flight plan after BRS.
What Was ATC Doing?
Shortly thereafter, at 4:02 pm, the Legacys secondary (transponder) radar return ceased, although a primary return apparently was still being observed by ATC. Theres probably no way the Legacys crew knew they were only visible on radar as a primary target, unless ATC told them. Whether the transponder failed, whether ATCs equipment failed, whether the transponder was disabled or whether something else happened has not been established (although there have been accusations). Note that neither aircraft apparently generated a TCAS alert before the collision.
For at least 35 minutes, the Legacy cruised at FL370 without two-way communications, despite repeated, though belated, attempts by ATC and the crew to reestablish contact. Some 31 minutes after it crossed BRS and 24 minutes after losing its secondary target, Brasilia Center called the Legacy but received no reply. At 4:53, Brasilia Center unsuccessfully attempted to effect a handoff of the Legacy to Amazonica Center by calling the Legacy in the blind. Meanwhile and by all accounts operating normally, the 737 was headed down the same airway at the same altitude.
Unanswered Questions
The NTSB statement which was disseminated at Brazils request does not include information on the extent to which, if any, Brazilian ATC attempted internal coordination of the Legacys altitude. For example, it omits discussion of any communication between controllers. Another question is whether anyone at ATC realized the Legacy was, effectively, NORDO and there was no way to ascertain at what altitude it was flying.
Also unanswered is whether ATC implemented lost-comm procedures on the Legacy. Since this information was omitted from the NTSB statement, we can presume ATC a) did not implement lost-comm procedures on the Legacy and, b) did not realize no one had cleared the Legacy to change its altitude from its previously assigned FL370. Its likely no one at ATC ever realized the two aircraft were at the same altitude and closing on each other at around 900 knots.
Based on the information available, it appears ATCs failure to track the Legacys altitude and position will be part of this accidents probable cause. It also appears the Legacy crew performed as expected, especially when considering normal and accepted practices in the U.S.
