What happened
On 11 February 1978, Pacific Western Airlines flight 314, a Boeing 737, was conducting a scheduled service from Calgary to Cranbrook. During the approach to runway 16, an error in the estimated time of arrival provided by Calgary Air Traffic Control led to a conflict on the airfield. A snow removal vehicle was still operating on the runway because the expected arrival time was inaccurately communicated to the Aeradio station.
The aircraft performed a touchdown approximately 800 feet before the threshold. Following the landing, the crew engaged reverse thrust but quickly cancelled it to initiate a go-around. As the aircraft accelerated down the runway, it passed over the snow removal vehicle at an altitude of roughly 50 to 70 feet. During this phase, the left engine thrust reverser doors deployed while the aircraft was in flight. Following a period of heavy left rudder application and a steep bank, the aircraft lost altitude and side-slipped into the ground. The impact resulted in 45 fatalities and 7 injuries.
Findings
Investigations into the accident identified several contributing factors:
- An incorrect arrival time calculation by Calgary ATC caused the runway maintenance vehicle to remain on the active runway during the aircraft's approach.
- The flight crew failed to report their position at the Skookum beacon, which prevented the error in the ETA from being corrected.
- The deployment of the left engine thrust reverser doors in flight caused the pilots to lose control of the aircraft while it was in a high-drag configuration.
- Inadequate regulatory requirements regarding mandatory position reporting for instrument approaches contributed to the lack of situational awareness.
- Deficiencies in the coordination between Air Traffic Services, Aeradio, and airport services prevented a reliable safety buffer.
- Design standards for the aircraft did not sufficiently account for the aerodynamic consequences of an aborted landing involving thrust reverser deployment.