What happened
On an unnamed date, two large transport-category aircraft experienced a loss of separation while operating in the Gimli high-level en route sector. Canadian Airlines International Flight 987, a Boeing 767 (registration not provided), was traveling westbound at flight level 390. Simultaneously, Air Canada Flight 118, also a Boeing 767, was traveling eastbound at flight level 370.
While monitoring the sector, the air traffic controller cleared the Air Canada flight to climb to flight level 410. This maneuver placed the two aircraft on a collision course, resulting in a horizontal separation of only 3 nautical miles and vertical spacing of less than 1,000 feet, violating the required 5-mile horizontal or 2,000-foot vertical separation standards. The pilot of the Canadian Airlines flight reported receiving a Traffic Collision Avoidance System (TCAS) Resolution Advisory (RA) and subsequently climbed to avoid the conflict. The crew of the Air Canada flight observed the other aircraft visually and did not follow the RA descent instructions, which prolonged the need for evasive action.
The investigation
The investigation examined the controller's actions, workload, and fatigue levels. It was established that the controller was performing both radar and data controller duties alone. The investigation found that the controller's radar display was partially obscured because the 'auto tag' feature was not engaged, causing the data blocks of a third aircraft, C-GMTR, to overlap with the data block of the Canadian Airlines flight. This overlap obscured critical altitude and call sign information.
Furthermore, the investigation reviewed the controller's recent work history, noting a pattern of significant overtime and minimal consecutive days off. The investigation also looked into the controller's focus during the minutes leading up to the event, noting that a large portion of the controller's time was spent communicating non-critical turbulence reports to pilots.
Findings
- The controller failed to perform an adequate scan of the radar display for conflicting traffic before authorizing the climb.
- The controller's attention was diverted by the transmission of low-priority weather information, which occupied a significant portion of the time immediately preceding the event.
- The controller's recent work-rest cycle, characterized by heavy overtime and frequent short-duration rests, was consistent with fatigue, which likely contributed to the error.
- The lack of an automated conflict prediction tool left the system without a modern electronic defense against human error.
- The absence of a second controller or an active supervisor in the sector meant there was no human redundancy to catch the error.