What happened
At approximately 1454 PDT, a sequence of communication failures led to a loss of separation between an Air Canada Boeing 767 (ACA109), an Air Canada Boeing 747 (ACA897), and a Morningstar Cessna 208 (MAL7072) near Vancouver International Airport.
The incident began when the arrival controller issued an instrument landing system (ILS) approach clearance intended for ACA109. However, the crew of ACA897 incorrectly accepted and read back this clearance. Neither the controller nor the crew of ACA109 identified the error in the aircraft call-sign during the exchange.
As ACA109 continued its flight path, it flew through the localizers for runways 08 Left and Right while maintaining an altitude of 3,000 feet, despite having been previously instructed to descend to 2,000 feet. This altitude maintenance placed the Boeing 767 on a course toward the Cessna 208, which was also at 3,000 feet. The controller identified the conflict and issued avoidance vectors, but the aircraft separation had already been reduced to 2.11 nautical miles, violating the required 3 nm lateral or 1,000 feet vertical separation. While the separation was lost, there was no immediate risk of collision.
The investigation
The investigation examined the radio communications and radar data surrounding the event. It established that the controller had prioritized the approach clearance for ACA10 9 and did not immediately acknowledge the initial check-in from ACA897.
Investigators found that the crew of ACA897 accepted an approach clearance that was atypical for their position, 18 nm from the airport, and would have allowed them to descend below the minimum vectoring altitude (MVA) of 3,700 feet. The crew of ACA109 heard the incorrect read-back from ACA897 but assumed the clearance was intended for the other aircraft because the controller had acknowledged it. Furthermore, the captain of ACA109 misheard a subsequent heading instruction and initiated a left turn that directed the aircraft toward the Cessna 208.
Findings
- The loss of separation was caused by ACA109 turning left after crossing the localizers and failing to descend as instructed.
- The pilot of ACA897 accepted and read back a clearance intended for another aircraft.
- The controller failed to detect the incorrect call-sign during the read-back process.
- The crew of ACA109 did not recognize that the approach clearance was intended for them.
- The captain of ACA109 misheard a heading instruction, believing the instruction was 130° instead of 230°.
- The controller did not utilize standard safety alert phraseology to convey urgency.
- The failure of ACA109 to descend to the assigned 2,000 feet directly contributed to the loss of separation.