What happened
On an instrument flight rules flight from Pukataralwagan, Manitoba, to Winnipeg, a Piper PA-31-350 Chieftain carrying one pilot and seven passengers experienced a critical engine failure during an approach to runway 36 at Winnipeg International Airport. While executing an instrument landing system approach, the aircraft's right engine lost power, causing the plane to yaw sharply to the right.
Following the engine failure, the aircraft's airspeed dropped significantly below the required levels. The pilot attempted to manage the emergency but struggled to maintain control as the aircraft descended through the cloud base at a rate of 800 feet per minute. The aircraft eventually settled into a wooded area approximately two nautical miles south of the airport. The impact resulted in two serious injuries and several minor injuries, though no fatalities occurred. The aircraft sustained substantial damage, but no post-crash fire was reported.
The investigation
Investigators examined the aircraft's fuel system and the pilot's actions during the emergency. Radar data was analyzed to reconstruct the approach profile, revealing that the aircraft's airspeed had decreased to between 70 and 90 knots prior to the engine failure.
Examination of the right inboard fuel tank revealed a rust line, suggesting water had accumulated in the tank. A large piece of ice was recovered from the right surge tank at the crash site. Laboratory tests simulated sub-zero conditions and demonstrated that water could freeze around the one-way flapper valve, effectively blocking fuel from flowing into the surge tank.
Furthermore, the investigation looked into the pilot's response to the engine-out drill. While the pilot performed several necessary steps, such as feathering the propeller and raising the landing gear, the flaps were left in the approach setting, which increased aerodynamic drag and hindered the ability to regain necessary airspeed.
Findings
- Water in the right inboard fuel tank froze, likely obstructing the flapper valve and causing the right engine to stop due to fuel starvation.
- The pilot failed to maintain a safe airspeed and altitude following the engine failure.
- The approach was not stabilized, as the aircraft's speed had fallen below the threshold required for safe flight.
- Task saturation prevented the pilot from executing the emergency checklist effectively.
- The design of the inboard fuel tank lacks a drain valve for the larger segment, allowing water to accumulate and freeze.