What happened
On a flight from Rankin Inlet to Winnipeg, a Boeing 737-210, registered as NWT962, was cruising at flight level 310 when it encountered a potential collision course with a Boeing 747-451, registered as NW69. The 747 was en route from Detroit to Japan.
As the two aircraft approached a crossing point approximately 160 nm northeast of Winnipeg, the North radar controller identified a converging target and instructed the crew of NWT9 962 to descend to flight level 290. However, because the crew was not expecting a descent, there was a delay in their response. During this period, the horizontal separation between the two aircraft dropped to approximately 3 nm, well below the required 5 nm minimum for the Class A airspace.
The investigation
The investigation examined the coordination between the Winnipeg East and North sectors. It was established that the East controller had delayed the hand-off of NW69 to the North sector to avoid potential communication issues at remote radio outlets. Additionally, the North sector was experiencing high workloads; an incoming radar controller had assumed duties without receiving a formal status briefing from the data controller.
Investigators also reviewed the technical tools in use. The Northern Airspace Display System (NADS) was providing an inaccurate separation warning because it had not yet been updated with the most recent arrival estimate for NWT962. Furthermore, the North radar controller's display settings were configured to hide data tags for aircraft not under his direct control, which limited his visibility of the approaching NW69.
Findings
- The primary cause of the loss of separation was that controllers in both the North and East sectors failed to identify the conflict after the arrival estimate for NWT962 was updated.
- High workload in the North sector prevented a proper status briefing for the incoming controller.
- The controllers relied heavily on the NADS system, which was displaying outdated information regarding the aircraft's position.
- The East controller's decision to delay the hand-off of NW69 and a preoccupation with data tasks contributed to the lack of oversight.
- The use of non-standard phraseology by the North controller failed to communicate the necessary urgency to the NWT962 crew.
- The lack of a radar conflict advisory system meant there was no automated alert to notify controllers of the impending breach of separation standards.