Background
Two Air Canada Boeing 737-200 aircraft experienced a loss of separation near the Empress VOR (very high frequency omnidirectional radio range) in Canadian airspace. Eastbound Air Canada Flight 3696 (ACA3696) was en route from Calgary, Alberta, to Winnipeg, Manitoba, at flight level (FL) 330. Westbound Air Canada Flight 3627 (ACA3627), en route from Winnipeg to Vancouver, British Columbia, was deviating north of its planned track due to weather and was also at FL330.
Incident
ACA3627 requested deviations north because of weather. Air traffic control (ATC) asked if the crew could climb from FL310 to FL350, but due to aircraft weight, ACA3627 could not accept FL350. ATC then offered FL330, which the crew accepted. This altitude was inappropriate for the direction of flight but was approved by affected sectors, with appropriate markings placed on flight progress strips.
Later, ACA3627 was cleared direct to the Calgary VOR when able. The captain acknowledged the clearance but turned toward the Empress VOR instead. Approximately four minutes later, the Alsask sector controller advised ACA3627 to turn right for traffic. The crew replied and stated they were descending in accordance with a TCAS resolution advisory (RA). Concurrently, the ACA3696 crew, seeing ACA3627 approaching at the same level, commenced a slight right turn. They then received a TCAS RA to climb but instead increased bank angle to 45°, encountered buffeting, and initiated a descent. They arrested the descent after 300 feet, leveled wings, and climbed back to FL330. During this maneuver, one flight attendant and two passengers received minor injuries.
Findings
The Transportation Safety Board (TSB) determined that ACA3627 turned toward the Empress VOR rather than the Calgary VOR as cleared because the captain did not ensure the correct navigation facility was selected. This caused the aircraft to fly directly toward ACA3696 at the same altitude. Additionally, due to momentary high workload, the controller did not detect the deviation in sufficient time.
Contributing factors included the first officer being occupied with retrieving weather via the No. 2 VHF radio, with squelch off, preventing him from hearing ATC communications on the No. 1 radio. The captain did not read back the clearance, nor did the controller request a readback. The radar controller was performing duties that could have been handled by a data controller, increasing workload. The radar situational display lacked conflict-alert software. The ACA3696 captain did not follow the TCAS RA to climb but instead steepened the turn and descended in response to buffeting, increasing risk of midair collision.
Safety Actions
On 19 October 2001, the TSB sent an aviation safety information letter to Air Canada regarding a lack of practical TCAS training for crews training in Toronto. Nav Canada planned operational trials of conflict alert software in Moncton Area Control Centre starting in March 2002.
This report concludes the TSB investigation, authorized for release on 04 March 2002.