What happened
On a flight path near Sydney, Nova Scotia, two Airbus A340 aircraft operated by Lufthansa German Airlines—D-AIBC and D-AIGO—traveled on nearly opposing tracks at flight level 370. The eastbound flight, DLH411 (D-AIBC), notified the Gander, Newfoundland, air traffic controller after receiving a traffic alert and a TCAS alert indicating another aircraft was 20 miles directly ahead.
In response, the controller directed DLH4 and the westbound aircraft, DLH420 (D-AIGO), to descend to flight level 360, while DLH411 was instructed to turn left 20 degrees. During the maneuver, the pilot of DLH411 climbed in response to a TCAS resolution advisory, and DLH420 received a descending resolution advisory. Despite these maneuvers, the lateral distance between the two aircraft decreased to approximately 3 nautical miles before the required 1000-foot vertical separation was established, violating the minimum required radar separation of 5 nautical miles laterally.
The investigation
The investigation focused on the transition of responsibility between air traffic controllers at the Gander Area Control Centre. It was established that the second controller, who assumed control of the west sector, lacked the necessary information to maintain accurate situational awareness. This was due to an incomplete handover briefing and the failure to use the available position handover checklist.
Investigators found that the second controller incorrectly assumed both Lufthansa flights were traveling eastbound, a conclusion reinforced by his previous experience and the lack of a standardized method for indicating flight direction on the radar display. Furthermore, the first controller had not utilized established strip-marking procedures, such as highlighting potential conflicts or marking altitudes that deviated from standard airspace structures.
Findings
- The handover briefing between controllers was incomplete, and the provided checklist was not utilized.
- The second controller misinterpreted the direction of flight for D-AIGO, failing to recognize the converging courses.
- The failure to use the handover checklist and standard work practices prevented the detection of the conflict.
- The first controller did not use standard procedures to indicate the potential conflict on flight progress strips.
- The second controller did not complete a flight progress board check immediately after assuming the position.
- The use of non-standardized phraseology by the controller meant the pilot of DLH420 did not descend with the necessary urgency, extending the period of risk.
Safety action
Following the occurrence, the Gander Area Control Centre implemented a mandatory requirement for controllers to complete the briefing checklist when assuming sector responsibility. Additionally, the TSB issued an information letter to Nav Canada to encourage nationwide methods for reducing risks associated with memory-dependent handover briefings.