What happened
On a flight path near Sydney, Nova Scotia, a Boeing 767-400 operated by Continental Airlines (registration COA18) and a Boeing 767-300 operated by Iberia Airlines (registration IBE6283) nearly collided while flying at flight level 350. The aircraft were traveling on reciprocal tracks, approximately 23 nautical miles southeast of the airport.
Prior to the encounter, the crew of COA1 and the controller at Moncton ACC had discussed an altitude change to avoid turbulence. The aircraft was cleared to climb to FL350, an altitude that was considered "wrong way" for its direction of flight. As the two aircraft closed to within 10 nm, both flight crews received Traffic Alert and Collision-Avoidance System (TCAS) Resolution Advisories. The Boeing 767-400 climbed to FL354 while the Boeing 767-300 descended to FL335. At their closest point, the aircraft were separated by only 1900 feet vertically and roughly 0.4 nm laterally, failing to meet the required separation of 1000 feet vertically or 5 nm laterally.
The investigation
The investigation focused on the air traffic control handover process at the Gander Area Control Centre (ACC). It was established that the controller being relieved failed to inform the incoming controller that two aircraft were on intersecting paths at the same altitude. Furthermore, the controller being relieved had not used standard markings on the flight progress strips to highlight the potential conflict.
Investigators found that the incoming controller did not adequately scan the flight progress strips or the radar display upon taking control of the combined sector. The investigation also noted that the controller being relieved left the position immediately after the briefing, missing an opportunity to alert the new controller to the impending conflict. Additionally, the flight crews did not immediately notify the controller that they were performing evasive maneuvers due to a TCAS alert, leaving the controller unaware of the situation until after the aircraft had passed one another.
Findings
- The incomplete handover briefing was the primary factor, as the relieving controller was not made aware of the two aircraft on reciprocal tracks.
- The controller being relieved failed to mark flight progress strips according to established procedures.
- The incoming controller did not perform a sufficient scan of the radar or flight progress strips to detect the conflict.
- The altitude change for COA18 to an inappropriate flight level was not communicated between the Moncton and Gander ACCs.
- A lack of standardized radar display markings for potential conflicts made it difficult for the controller to recognize the risk.