What happened
On August 4, a Korean Air Boeing 747-200 cargo flight, KAL257, and a Lufthansa German Airlines Boeing 747-200 passenger flight, DLH493, were cruising at flight level 330. The aircraft paths were set to converge approximately two nautical miles east of the JOWIT intersection while under the radar control of the Edmonton Area Control Centre's Bison sector.
At approximately 1854 mountain daylight time, the Bison sector controller issued turning instructions to both aircraft to prevent a collision. During the maneuver, the minimum horizontal distance between the two aircraft dropped to an estimated 1.3 nautical miles. Both flight crews received resolution advisories from their traffic alert and collision avoidance systems (TCAS). The DLH493 crew climbed while the KAL257 crew descended, eventually achieving 900 feet of separation within roughly 10 seconds. This separation fell short of the required 5 nautical mile or 2000 foot standard.
The investigation
The investigation focused on the controller's awareness and the technical capabilities of the Edmonton ACC systems. While the controller was experienced, he had recently been notified of a four-hour shift extension. The investigation examined the use of the Northern Airspace Display System (NADS) and the radar processing system's capabilities.
It was determined that the radar processing system lacked automated collision avoidance notifications. Furthermore, while the controller used the PTL feature of the radar, which showed intersecting track lines, he did not react to the potential conflict because he was preoccupied with other tasks during a period of low traffic. The investigation also looked into the communication between the controller and the aircraft, noting that overlapping radio transmissions made instructions difficult to understand, leading the KAL257 crew to turn right instead of the instructed left.
Findings
- The controller did not recognize the conflict between KAL257 and DLH493 early enough to prevent the loss of separation.
- The controller failed to respond to the potential conflict indicated by the radar's PTL feature.
- The radar processing system utilized at the Edmonton ACC lacked conflict alert software.
- The DLH493 aircraft had not been entered into the NADS system at the time of the incident.
- Training provided by NAV CANADA does not include time-critical conflict resolution.
- The TCAS systems on both aircraft were instrumental in preventing a collision.