What happened
On a flight from New York's JFK Airport to Narita, Japan, an American Airlines Boeing 777 was cruising at flight level 3 50 when it entered Canadian radar-controlled airspace. Simultaneously, a United Airlines Boeing 767 traveling from Paris to Chicago was also operating at flight level 350. The two aircraft were on converging tracks within the Montréal Area Control Centre's La Grande sector.
During a shift handover between an outgoing controller and an on-the-job instructor (OJI) and trainee, the potential conflict between the two aircraft went unnoticed. The controllers did not identify that the aircraft were on a collision course, and the flight data strips were positioned far apart on the flight progress board, making the risk difficult to spot.
At 1320 eastern standard time, the ground-based conflict alert program triggered a warning. The OJI attempted to intervene by instructing the American Airlines Boeing 777 to descend and the United Airlines Boeing 767 to climb. However, the instructions were not received by the pilots because the OJI used a foot pedal for transmission instead of the press-to-talk switch, causing the radio signal to be treated as background noise. The aircraft eventually passed each other within 600 feet laterally and 1100 feet vertically. The collision was only avoided because both flight crews responded to TCAS resolution advisories.
The investigation
Investigators examined the handover procedures, the functionality of the radar display, and the communication equipment used during the incident. The investigation looked into why the conflict was not detected during the transition of control and why the controller's emergency instructions failed to reach the flight decks. The probe also reviewed the limitations of the flight data strip organization and the capabilities of the conflict alert program in the Montréal ACC.
Findings
- The potential conflict was not identified when the United Airlines Boeing 767 first entered the sector, and the outgoing controller did not alert the incoming staff to the need for a conflict probe.
- Neither the trainee nor the OJI performed a comprehensive review of all aircraft in the sector following the handover, leaving the converging paths undetected.
- The OJI's use of a foot pedal instead of the press-to-talk switch prevented the transmission of critical altitude instructions to the pilots.
- The organization of the flight progress board, which separated the data strips of the two aircraft by sector exit points, hindered the detection of the conflict.
- The lack of a medium-term conflict probe for radar-controlled airspace left the controllers without a secondary backup to detect the converging tracks.