What happened
Two Air Canada Boeing 737-20 00 aircraft, ACA3696 and ACA3627, experienced a loss of separation near the Empress VOR. The eastbound ACA3696 was traveling from Calgary to Winnipeg at flight level 330, while the westbound ACA3627 was flying from Winnipeg to Vancouver. Due to weather, ACA3627 had requested a deviation north of its planned track, and air traffic control had assigned it flight level 330 to accommodate its weight limitations.
Following a clearance to fly direct to the Calgary VOR, the crew of ACA3627 inadvertently turned toward the Empress VOR instead. Approximately four minutes later, air traffic control notified ACA3627 of nearby traffic. The crew of ACA3627 reported they were descending in response to a TCAS resolution advisory (RA). Simultaneously, the crew of ACA3696 observed the approaching aircraft and initiated a right turn. Upon receiving a TCAS RA to climb, the pilot of ACA3696 instead increased the bank angle to 45 degrees. The heavy aircraft experienced aerodynamic buffeting, prompting the crew to descend. This maneuver caused one flight attendant and two passengers to suffer minor injuries after striking the cabin interior.
The investigation
The investigation established that the first officer on ACA3627 was unable to monitor radio communications because they were using the second VHF radio to retrieve weather information, which required turning off the squelch and increased background noise. This left the captain as the sole recipient of the ATC clearance. Furthermore, the aircraft lacked an ACARS system, which would have allowed for digital weather updates without occupying the voice frequency.
Investigators found that the captain of ACA3267 failed to verify that the correct navigation frequency was selected before turning. The investigation also noted that the controller's workload was high, as they were performing duties that could have been handled by a data controller, which hindered their ability to notice the deviation immediately. Additionally, the investigation highlighted that the ACA3696 crew's decision to steepen the turn and descend rather than climb as instructed by TCAS increased the risk of a collision.
Findings
- The captain of ACA3627 turned toward the incorrect VOR because they did not ensure the proper navigation facility was selected.
- The controller failed to detect the course deviation in a timely manner due to high workload.
- The assignment of flight level 330 to ACA3627 was inappropriate for the direction of flight, placing it at the same altitude as ACA3696.
- A lack of readback for the ATC clearance and the absence of a requested readback removed a critical communication safeguard.
- The radar situational displays used by Nav Canada lacked conflict-alert software.
- The crew of ACA3696 increased the risk of collision by not following the TCAS RA instruction to climb.