What happened
In the early morning hours, two aircraft were operating under instrument flight rules (IFR) near Vancouver, British Columbia. The first, a Cessna 208B Caravan with registration C-GRXZ, was traveling from Victoria to Vancouver. Simultaneously, a Piper PA-31 Navajo, registered C-GRXX, was also en route from Nanaimo to Vancouver. Both aircraft were flying at 3000 feet on a heading of 340°.
While being managed by Victoria Terminal controllers, the pilot of the C-GRXX was instructed to switch to the Vancouver Arrival frequency. Although the pilot acknowledged the instruction, they remained on the Victoria frequency briefly to adjust navigation equipment. During this interval, the pilot of the C-GTXZ intercepted the instruction and switched to the Vancouver frequency without an initial acknowledgment.
When the C-GRXZ contacted the Vancouver Arrival controller, the controller mistakenly identified the aircraft as the C-GRXX. The controller issued an instruction for a 270° left turn to join the localizer for the ILS approach to runway 08L. The pilot of the C-GRXZ accepted this instruction. This maneuver caused the C-GRXZ to descend into a 3500-foot minimum radar vectoring area (MVA) while at 3000 feet. While there was no immediate risk of collision with the other aircraft, terrain clearance for the C-GRXZ was not guaranteed. Both flights eventually completed their journeys without further incident.
The investigation
The investigation focused on the breakdown in the readback/hearback process between the pilot and the air traffic controller. Investigators examined why the discrepancy in flight numbers was not challenged by either party. The investigation also looked into the pilot's decision to switch frequencies without acknowledgment and the controller's assumption that the incorrect call sign was simply a speech error. Additionally, the investigation reviewed the risks associated with using multi-digit flight numbers that change frequently throughout the day.
Findings
- The pilot of the C-GRXZ responded to a frequency change instruction intended for another aircraft without providing an acknowledgment, which would have alerted the Victoria controller to the error.
- A failure by both the pilot and the Vancouver Arrival controller to question the discrepancy in flight numbers led to the misidentification.
- The controller assumed the incorrect call sign was a pilot error, while the pilot assumed the controller's use of the wrong flight number was a verbal slip.
- The pilot of the C-GRXZ intercepted and executed a turn instruction intended for the C-GRXX, resulting in the aircraft entering a restricted MVA altitude.