Investigation Summary
The accident resulted from a breakdown in communication and procedural safeguards at an uncontrolled airport. Calgary ATC provided an ETA of 13:05, which was a conservative estimate rather than a precise prediction. The flight crew, arriving nearly 10 minutes early at 12:55, failed to make a mandatory position report at the Skookum beacon. Consequently, the Aeradio operator did not call the snowplow off the runway. When the pilots touched down and deployed thrust reversers, they suddenly saw the vehicle and attempted a high-risk go-around. The Boeing 737's design at the time included a safety feature that cut hydraulic pressure to the reverser actuators upon liftoff (air/ground sensing) to prevent accidental deployment. However, because the reversers were in transit when the plane became airborne, the left reverser remained unlocked. As airspeed increased, aerodynamic suction pulled the left reverser doors open, creating massive asymmetric drag that the crew could not overcome at low altitude.
Final Conclusions
The investigation concluded that the primary causes were the incorrect ETA provided by ATC, the crew's failure to report their position, and the inherent risks of initiating a go-around after thrust reverser deployment. The Boeing 737's hydraulic system logic was found to be inadequate for handling an aborted landing once reversers were initiated, as it could leave a reverser in an unlocked, partially deployed state without hydraulic power to restow it.
Photographic Evidence (1)
Video Analysis
Impossible Situation Pacific Western Airlines Flight 314 February 11, 1978 — A detailed look at the mechanical and operational factors of PWA 314, focusing on the clamshell thrust reverser design and the 'no go-around' rule after deployment.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Age 30; with PWA since 1967.
First Officer
Age 25; with PWA since 1971.
Systems & Failure Modes
Thrust Reverser Hydraulic Isolation Valve
A safety valve that cuts hydraulic pressure to the reversers when the aircraft is in 'air mode' to prevent accidental deployment, which in this case prevented the doors from restowing.
Clamshell Thrust Reversers
Target-type doors at the rear of the JT8D engine that redirect exhaust flow forward; they created massive drag when deployed in flight.
Skookum NDB
A non-directional beacon used as a final approach fix where pilots were expected to report their position to the Aeradio operator.
Interesting Facts
- 01The snowplow driver, Terry George, only realized the aircraft was behind him when he saw it in his rearview mirror.
- 02Captain Miles pushed the throttles forward with such force during the go-around that he fractured his thumb.
- 03The Boeing 737-200 flight manual at the time cautioned against attempting a go-around after reverse thrust had been selected.
- 04Post-crash evidence showed the left thrust reverser override switch guard had been opened, suggesting an attempt to restow the doors manually.
- 05The aircraft was nearly 8 years old and powered by Pratt & Whitney JT8D-9A engines.
- 06While 42 people died in the initial crash, one survivor succumbed to a severe head injury 11 days later, bringing the total fatalities to 43.
Safety Actions & Advisories
Thrust Reverser Logic Redesign
Boeing modified the thrust reverser control system to ensure that if a reverser is not stowed and locked, hydraulic pressure remains available to the stow actuators even after the aircraft leaves the ground.
Mandatory Position Reporting
Regulations were strengthened regarding mandatory pilot position reporting during instrument approaches at uncontrolled airports to prevent ETA discrepancies.
Known Controversies & Unanswered Questions
Discrepancy in Fatality Counts
Reference ↗While the official Transport Canada report and most detailed accounts confirm 43 fatalities (42 initial and one survivor who died 11 days later), several databases and early reports, including BAAA and some FAA summaries, continue to list 42 fatalities.