What happened
On a morning flight near London, Ontario, two commercial aircraft flying at flight level 350 experienced a loss of required separation. The first aircraft, an American Airlines Boeing 767 (registration not provided), was traveling northwest from Boston to San Francisco. The second aircraft, an American Airlines Fokker 100 (registration not provided), was heading south-southwest from Montreal to Chicago.
At approximately 11:04, the crew of the Boeing 767 responded to a Traffic Alert and Collision Avoidance System (TCAS) Resolution Advisory (RA) by climbing. This maneuver was prompted by the proximity of the Fokker 100, which was also flying at the same altitude. The aircraft eventually passed each other with a vertical separation of roughly 1,200 to 1,300 feet, failing to meet the required 2,000-foot vertical or five-mile lateral separation standards. The Toronto Area Control Centre controller subsequently instructed the Fokker 100 to descend.
The investigation
The investigation focused on the workload and operational environment within the Oakville sector of the Toronto Area Control Centre. At the time of the incident, the radar controller was performing the duties of both the radar and data controller positions. This was due to a period of staff breaks, leaving a single supervisor to manage data duties for multiple sectors.
Investigators examined the coordination processes between Toronto and Cleveland. It was found that frequent "estimate-hand-offs"—where aircraft are transferred without prior coordination—required the controller to manually search for and update flight data strips. Additionally, the controller had to manually adjust SSR codes for incoming aircraft because the codes used in United States airspace conflicted with reserved codes in the Toronto database. These tasks required the controller to divert his attention from the radar display to the flight data strips.
Findings
- The Oakville radar controller failed to detect the conflicting flight paths of the Boeing 767 and the Fokker 100 until the crew of the Boeing 767 reported the TCAS RA.
- The controller's attention was diverted by the heavy workload of simultaneously managing radar and data controller duties.
- The necessity of managing uncoordinated "estimate-hand-offs" and performing manual SSR code updates created a significant distraction.
- The lack of certified automated conflict alert software for the Oakville sector at the time of the event contributed to the inability to detect the impending loss of separation.