Brazil’s Cenipa accident investigation bureau has issued its report on the September 2006 midair over the Amazon, along with an NTSB dissent. The report makes public some new facts on what led two brand-new aircraft– a Gol Boeing 737-800 airliner with less than a month of service, and an Embraer Legacy 600 on its delivery flight to ExcelAire, in New York–equipped with the most modern safety and navigation systems, to be put on a collision course, and to continue unimpeded for an hour.
According to Cenipa, a botched clearance, an hour-long communications failure and the disabling of the Legacy’s transponder were significant factors in the collision. The lack of a reliable altitude from the transponder conspired with flaws in ATC software and inadequate training and supervision to allow the Legacy pilots to fly at the incorrect altitude for the airway without correction from ATC. Turning off the transponder also disabled the TCAS collision avoidance system. Both report and dissent acknowledge that the Legacy crew most likely inadvertently turned off the transponder.
The Brazilian report says that the Legacy’s crew, Joe Lepore and Jan Paladino, were flying together for the first time as captain and copilot, and each had only five hours piloting a Legacy 600, though Paladino had extensive experience with the regional jet version of the airframe. Only in the air did they read the notam that the Manaus runway was partly interdicted for maintenance, which prevented taking off with a full load of fuel for the flight’s second leg to Fort Lauderdale.
While both pilots were engrossed in fuel calculations, the Legacy’s transponder went into standby–thus disabling the TCAS– and resumed transmitting three minutes after the collision. Cenipa attributed the fact that neither pilot noticed to the crew’s failure to properly divide tasks; it also said that the pilots prepared inadequately for the flight, took a long time to recognize the hour-long communications failure, and did not undertake procedures for communications failure.
NTSB: Pilots Proceeded as Cleared
The NTSB dissent says, “There was no evidence of regulatory violations by the crewmembers,” and calls attention to “the basic investigative question, namely, how the primary mission of ATC to separate aircraft within positive controlled airspace was unsuccessful.” In Brazil, both accident investigations and ATC are under Air Force control.
In addition, the NTSB maintains that the evidence does not support most of the charges against the pilots. In response to the claims that the pilots had inadequate flight plans, it contends, “The crew flew the route precisely as cleared and complied with all ATC instructions.”
The flight plan for Legacy N600XL included three altitudes, initially 37,000 feet, descending to 36,000 at Brasilia and later climbing to 38,000 feet. The airplane was put on a collision course with the Boeing when the São José dos Campos controller cleared it to proceed at 37,000 feet to Eduardo Gomes, the Manaus airport. The crew took the clearance to be a modification of their flight plan, and the NTSB concurred. “We believe that the ground controller’s statement ‘clearance to Eduardo Gomes,’ could not realistically be interpreted as anything other than the ‘clearance limit’ item of the clearance,” wrote the Board. The same week the report was issued, the Brazilian judge examining criminal charges in the case asked prosecutors for an indictment against the ground controller.
The Legacy remained out of contact with ATC for 57 minutes. A frequency for another sector had been assigned, and not corrected before they were out of range. Of the five frequencies on the crew’s Jeppesen chart, one was incorrect, and the controller’s console was not configured with three others. Only one frequency was operational, and it was not the one the crew was tuned to, which was not even on the chart.
Nonetheless, the pilots continued to receive transmissions in Portuguese from other aircraft, masking the ground communications failure. On the length of time without two-way contact, the NTSB noted that regulations “specify procedures to be followed in the event of lost communication but do not specify criteria for determining when this condition is met.”
On Brazilian ATC radar screens, two altitude numbers appear side-by-side for each airplane. On the left, when the secondary radar stopped receiving signals from the Legacy’s transponder, the system substituted the inexact height given by air defense radar, which is “not to be used for civilian ATC separation” and confused the controller about the airplane’s real altitude. At the same time, the software altered the number on the right. As the NTSB put it, the “automatic change of the datablock field from ‘cleared altitude’ to ‘requested altitude’ without any indication to, or action by, the ATCOs led to the misunderstanding by the Sector 7 controller about what altitude clearance was issued to N600XL.”
The Brazilian report finds numerous flaws in ATC procedures. Incomplete clearances were routinely transmitted. Control of the Legacy was transferred incorrectly between sectors. While his screen showed indications of the loss of the transponder, the controller did not note them or do anything about them. Nor was the loss of radio communications properly dealt with. Supervisors were uninvolved in the events involving the control of N600XL.
N600XL remains on the air base in Brazil. According to the Cenipa report, “The recuperation of aircraft N600XL is considered economically viable.” However, the family of one of the 154 accident victims has filed a lien against the aircraft. Sources at Embraer say that although the model is certified to fly without the winglets, due to possible torsion damage a new wing will have to be flown to Cachimbo.