What happened
During a flight from Prince George to Vancouver, an Air BC BAE146, registration ABL814, was cleared by an en route air traffic controller to descend to 11,000 feet above sea level. This instruction was issued as the aircraft crossed into a sector where the minimum vectoring altitude (MVA) was actually 14,000 feet. The crew accepted the clearance and descended, inadvertently placing the aircraft below the required altitude for obstacle clearance in that specific airspace.
As the aircraft descended, it entered a zone where ground-based radio coverage was unavailable, preventing the controller from immediately notifying the crew of the error. The controller attempted to contact the aircraft via transmitters in Kamloops and Vancouver but was unsuccessful. The situation was eventually resolved when a pilot from another aircraft in an adjacent sector relayed the instruction to climb. The crew of ABL8 and the BAE146 subsequently ascended to a safe altitude and completed the flight to Vancouver without any risk of terrain collision, as the weather was clear and the mountains were visible.
The investigation
The investigation focused on the controller's actions and the systemic vulnerabilities in the airspace. It was established that the controller had recently returned from a break and was managing a light traffic load. To manage a required flow delay, the controller had intentionally slowed the aircraft and initiated an early descent. Due to the controller's focus on the aircraft's progress and the habit of following standard descent profiles, the controller mistakenly applied a clearance intended for a different MVA boundary.
Investigators also examined the lack of a Minimum Safe Altitude Warning (MSAW) system, which could have alerted the controller to the altitude deviation. Furthermore, the investigation looked into the communication gaps in the area and the fact that the arrival controller was not notified of the communication failure, which prevented a more rapid response to the aircraft's descent.