What happened
During a night flight from Pukablewagan to The Pas, Manitoba, a Beaver Air Services Ltd. Piper Navajo PA31-310 experienced a sudden loss of power immediately after becoming airborne. The aircraft, carrying six passengers, was performing a VFR company flight using a short-field takeoff configuration. Shortly after rotation, the left engine surged, causing the left wing to drop sharply.
As the aircraft drifted off the runway centerline, the pilot lost sight of the runway lights. Noticing the engine anomaly, the pilot initiated engine failure procedures by retracting the landing gear. Fearing the rising terrain to the left of the runway, the pilot applied heavy back pressure on the control column. This maneuver, combined with the reduced power, caused the aircraft to descend rapidly into the ground. The aircraft struck the terrain in a nose-high attitude and slid through deep snow, resulting in one injury.
The investigation
Investigators examined the aircraft's airframe, fuel system, and the left engine. While the fuel was found to be clean and uncontaminated, the engine underwent testing in a test cell. During the test, a momentary surge was observed when the engine reached takeoff power, though the exact cause of the surge could not be isolated.
Technicians noted that two clamps on the turbocharger compressor discharge housing duct were loose. These clamps had been disturbed during maintenance performed three weeks prior to the accident. It was determined that a sudden leak at these loose clamps could potentially trigger an engine surge by causing the engine to momentarily revert to a normally aspirated mode, reducing power by up to 25%.
Findings
- The left engine experienced a surge immediately following takeoff for reasons that could not be definitively determined.
- The loose clamps on the turbocharger duct may not have been sufficiently tightened during recent maintenance.
- In response to the engine surge and rising terrain, the pilot maintained full aft pressure on the control yoke.
- The aircraft's airspeed decreased toward the aerodynamic stall speed due to the high pitch attitude and high-drag configuration.
- The aircraft was likely approaching an aerodynamic stall before impacting the ground.