B738 / E135, en-route, Mato Grosso Brazil, 2006
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|Category:||Air Ground Communication|
On 29 September 2006, a B737-800, operated by the Brazilian airline Gol, collided head-on with a US owned and operated EMB135 Legacy at FL370 over the Amazon, Brazil. The aircraft were flying at the same altitude in opposite directions along the same airway.
A loss of two way R/T communications between ATC and the Embraer 135 and an almost simultaneous unintended disabling of the serviceable transponder on the same aicraft created an extremely hazardous situation. During the sequence of events which led to this accident, there were numerous opportunities for human intervention which were either not taken or proved unsuccessful. The CENIPA report makes recomendations to address the institutional and operational weaknesses highlighted by the investigation, which will be of interest to all those involved in aviation safety.
The followed is an extract from the conclusions of the official CENIPA report:
"...The airplanes were considered latest-generation aircraft, equipped with VHF and HF transceptors, Automatic Flight Management Systems (FMS), Global Positioning Navigation System (GPS), Radar Signal Transmitter-Responder (Transponders), Airborne Collision Avoidance Systems (ACAS), VOR and NDB Receivers, and other equipment required by the legislation;
The PR-GTD airplane[B738], which was operating the flight GLO 1907, departed from Manaus, and was cleared to maintain flight level 370 up to Brasilia, according to the active flight plan;
The ACC BS transmitted an incomplete clearance to SJ GND relative to the N600XL[E135];
The crew of the N600XL received from the SJ GND the incomplete clearance, and understood that the flight level FL370 was authorized all the way up to the destination. However, according to the active flight plan, the clearance limit for the flight level FL370 was the vertical of BRS VOR;
While the N600XL [E135] was en route, the controller of sector 5 handed off the N600XL airplane to the ATCO 1 of sector 7, at about 52 nautical miles to the south of BRS VOR, although the limit between sectors 5 and 7 of Brasilia FIR is to the north-West of Brasilia.
The controller of sector 5 did not advise either the controller of sector 7 or the pilots of the N600XL [E135] of the programmed flight level, according to the flight plan filed;
When the N600XL [E135] passed over the vertical of BRS VOR, the ATCO 1 of sector 7 received from his equipment a visual information alerting that there was a flight level change programmed to occur over BRS VOR for the Legacy, and this information remained available for seven minutes;
The ATCO 1 of sector 7 neither took any action for the coordination of the N600XL [E135] flight level change nor tried to contact the aircraft;
Seven minutes after the aircraft had passed over BRS VOR, the N600XL [E135] Transponder stopped transmitting the Mode C aircraft altitude, and, consequently, de-activated the TCAS of the airplane, a fact that was not perceived by the pilots;
The CVR of the N600XL indicated that the attention of the crew was focused on solving issues relative to the performance of the aircraft for the operation in Manaus, after they learned of a NOTAM limiting the length of the runway of that airport.
The ATCO 1 of sector 7 did not notice the information alerts relative to the loss of the mode C and did not take the prescribed corrective actions:
When transferring the responsibility for the aircraft to the relief controller (ATCO 2), the ATCO 1 of sector 7 told him that the aircraft was at flight level FL360;
The ATCO 2 of sector 7 started trying to make contact with the N600XL 34 (thirty-four) minutes after the last two-way radio contact;
The N600XL crew started trying to make contact with the ACC BS, 57 (fifty-seven) minutes after the last two-way radio contact;
During approximately 32 (thirty-two) minutes, nineteen attempts to contact ACC BS were made by the N600XL, and seven attempts to contact the aircraft were made by the ACC BS, all of them unsuccessful, up to the moment of the collision;
Three out of the five frequencies listed in the Jeppesen chart used by the N600XL pilots were not available, due to errors in the selection of the frequencies 123.3 MHz and 133.05 MHz at the consoles, and the fact that the frequency 128.00 MHz was not connected to the audio center of CINDACTA I, according to item 3.6 of this report;
Of the five frequencies for sector 7 that were listed in Jeppesen chart used by the N600XL pilots, only the 135.9 MHz was capable of operating accordingly on the day of the accident, because the frequency 134.7 MHz was incorrect and was not listed in the Brazilian chart.
The Assistant-Controller of sector 7 handed off the N600XL aircraft to the ACC AZ and said that it was at flight level FL360, but did not mention that it was without radar contact, without altitude information and without radio contact;
The PR-GTD and the N600XL airplanes were maintaining the same flight level, along the same airway and were approaching each other in opposite directions.
The PR-GTD was flying with its Transponder and TCAS systems in operation, transmitting the Mode C aircraft altitude, as required for RVSM airspace, during all the flight;
Despite the fully visual conditions at the moment of the collision, there was not either visual perception of the approach or an evasive action attempt on the part of the crews;
The airplanes collided head-on, having touched each other’s left wing, within controlled airspace under RVSM, next to the boundary between the Brasilia and Amazonic Flight Information Regions (FIR);
The airplanes collided, whereas their crews did not receive any warnings from the respective TCAS Systems, due to the fact that the Transponder of one of the airplanes, the N600XL[E135], had stopped transmitting 54 minutes before the collision;
The loss of the transponder reply from N600XL made it impossible for the radars of the ACC AZ to warn the controllers of the imminent collision, due to the lack of altitude information;
The damages caused to the left wing of the PR-GTD [B738] by the collision rendered the airplane uncontrollable by its pilots....The aircraft entered a left spiral dive, at an abnormal attitude known as “spin”...The uncontrolled dive of the PR-GTD made the airplane exceed its flight structural limit, and caused the structural separation of the aircraft in flight (in-flight break-up) during the fall, not allowing any chances of survival of its 148 passengers and 6 crew;
The N600XL airplane sustained damages on the left wingtip, having lost part of the winglet. The left horizontal stabilizer was also damaged. The aircraft, despite the damage, remained controllable by the pilots, who managed to make an emergency landing...
Tests of the N600XL TCAS and Transponder were performed and indicated normal functioning, without detection of any failure;...During the emergency descent, the N600XL CVR recorded a dialog in which the pilots refer to the functioning of the TCAS;...Concomitantly to the dialog mentioned, the DFDR recorded that the TCAS screen started being used. At the same time, the radars of the ACC AZ resumed reception of the Transponder mode C, with the same code previously allocated;...Then, the pilots changed to the international emergency code (7700), which was immediately received by the radars of the ACC AZ;
After the collision, during the descent for the landing at SBCC, the pilots of the N600XL had difficulty establishing radio contact with the air traffic control units;
The landing was successful, and all the passengers and crew members of the N600XL airplane were unhurt;.."
- LOS: Loss of Separation
- Safety Nets: Airborne Collision Avoidance System (ACAS)
- Safety Culture: Just Culture
- Safety Alert - Embraer Aircraft Transponder Safety Alert issued by EUROCONTROL in November 2007.
For further information see the full CENIPA Accident Report. Note that the NTSB (USA) comments on the report (Appendix 1 & 2 to the report) agree broadly with the conlusions but differ on the emphasis placed on the contribution of air traffic control and the conclusions regarding the crew pre-flight preparation.