What happened
A Canadian Pacific McDonnell Douglas DC-10 (Flight 3), registered as CG-CPJ, and a Reeve Aleutian Boeing 727 (Flight 724), registered as N832, were cleared to fly at Flight Level 290 on two different airways. These airways crossed at the Picum intersection, located over the Bering Sea. While traveling in nearly opposite directions at the same altitude, the two aircraft passed within approximately half a mile of each other at the point where the airways intersected.
The crew of the DC-10 visually identified the Boeing 727, but the crew of the Boeing 727 did not see the DC-10. The Picum intersection was situated in an area beyond the normal radio and radar range of Air Traffic Control (ATC) controllers. Two controllers were on duty and had combined sectors 10 and 11, then divided the two sectors in a north/south configuration, which was contrary to standard operating procedures. The incident occurred during a busy period. A supervisor was assisting one of the two controllers.
The controller handling Flight 3 cleared it to descend from Flight Level 330 to Flight Level 290 and stated that he had told the other controller to stop Flight 724 at Flight Level 280 while it was climbing from a lower altitude. However, the controller handling Flight 724 stated that he did not know there was an aircraft at Flight Level 290 when he cleared Flight 724 to that level.
The investigation
The investigation examined the air traffic control procedures and communication protocols in place during the incident. It was found that the two on-duty controllers had combined sectors 10 and 11 and then divided them in a north/south configuration, which was contrary to standard operating procedures. The Picum intersection was located in an area beyond the normal radio and radar range of the ATC controllers. A supervisor was assisting one of the two controllers during the incident, which occurred during a busy time.
Findings
The primary contributing factor was the failure to maintain vertical separation between the two aircraft due to miscommunication between air traffic controllers. The controller handling Flight 3 believed he had instructed the other controller to stop Flight 724 at Flight Level 280, but the controller handling Flight 724 did not receive or acknowledge this instruction and cleared Flight 724 to Flight Level 290. The north/south sector configuration was contrary to standard operating procedures, and the incident occurred during a busy period with supervisor assistance.