What happened
On the evening of December 20, 2005, a Nav Air Charter Inc. Mitsubishi MU-2B-36, registration C-FTWO, departed Terrace Airport for a courier flight to Vancouver. Shortly after takeoff from Runway 1s, the aircraft's left engine lost power. Following the failure, the aircraft entered a moderate left-hand turn and began to descend. The aircraft eventually struck trees approximately 1600 feet east of the runway departure end. The impact and a subsequent fire destroyed the aircraft, and two fatalities occurred as both pilots were killed.
The investigation
Investigators examined the wreckage and the engines, discovering that the left engine's combustion chamber plenum had suffered a fatigue crack. This crack led to a fast fracture that caused the engine to flame out. While the aircraft was equipped with a negative torque sensing system to reduce drag, the left propeller was not manually feathered at the time of impact.
Analysis of the flight parameters revealed that the crew had used a flap setting of 20° for takeoff, which, while following company policy, reduced the available climb performance during an engine-out scenario. The investigation also noted that the crew performed checklist items out of sequence, suggesting confusion in the cockpit. The captain was occupying the right seat, a position he did not normally occupy during emergency drills, which may have contributed to the difficulty in managing the failure.
Findings
- The primary cause of the engine failure was a rupture of the left engine combustion chamber plenum caused by a fatigue crack.
- The aircraft's ability to climb was severely compromised because the crew failed to feather the inoperative engine and did not retract the flaps to 5°.
- The aircraft entered a left-hand turn following the failure, which increased drag and prevented the aircraft from maintaining altitude.
- Uncertainty in the cockpit was indicated by the out-of-sequence execution of the engine failure checklist.
- The use of flap 20° for takeoff, while standard for the operator, hindered the aircraft's climb gradient during the emergency.
Safety action
- The TSB issued several safety advisories regarding the importance of completing engine failure checklists immediately and the impact of flap settings on climb gradients.
- Transport Canada issued a Service Difficulty Advisory recommending that operators replace multi-casting boss plenums with single-casting versions to mitigate cracking risks.