What happened
On a scheduled flight from St. John's to Goose Bay, a Pilatus PC-12 experienced a series of mechanical issues that led to a forced landing. While climbing to 22,000 feet, the pilot noticed a low oil pressure indication and received notification from maintenance to return to St. John's. During the return flight, a severe engine vibration developed, eventually necessitating a full engine shutdown.
Unable to reach St. John's due to the aircraft's glide range, the pilot attempted to reach Clarenville Airport. During the descent, the pilot's vision was obscured by a combination of engine oil on the windscreen and internal condensation. Unable to locate the airfield, the pilot performed a forced landing in a bog approximately 1.5 nautical miles from the Clareville Airport. The impact destroyed the aircraft and resulted in 3 serious injuries among the crew and passengers.
The investigation
Investigators examined the engine, a Pratt & Whitney PT6A-67B, and the aircraft's maintenance history. The investigation looked into the pilot's response to the initial oil pressure warning and the technical state of the aircraft's monitoring systems. The Board also reviewed the electrical system's ability to support essential instruments during an engine-out scenario and the visibility conditions during the final approach.
Findings
- The engine failed due to an interruption of oil flow to the first-stage planet gear assembly, though the specific cause of this interruption remains undetermined.
- The pilot failed to follow established emergency procedures for low oil pressure.
- The pilot's decision-making was compromised by a mistaken belief that the low oil pressure indications were invalid.
- The aircraft's chip detector system was configured such that indications were disabled when the landing gear was retracted, which did not meet certain passenger transport standards.
- Visibility during the landing was significantly hindered by oil and condensation on the windscreen.