Accident Overview
On 02 November 2017, a Perimeter Aviation LP Fairchild SA227-AC Metro III (serial number AC-756B, registration C-FLRY) was operating as flight 959 (PAG959) from Gods River Airport, Manitoba, to Thompson Airport, Manitoba, with two flight crew members on board. Approximately 40 nautical miles southeast of Thompson Airport, the crew informed air traffic control that they had received a low oil pressure indication on the left engine, which might require the engine to be shut down. The crew did not declare an emergency, but aircraft rescue and firefighting services were put on standby.
After touchdown on Runway 24 with both engines operating, the aircraft suddenly veered to the right and exited the runway. It came to rest in snow north of the runway. The captain and first officer exited the aircraft through the left side over-wing emergency exit and were taken to hospital with minor injuries. The aircraft was substantially damaged. The 406-MHz emergency locator transmitter did not activate. The occurrence took place during the hours of darkness, at 1920 Central Daylight Time.
Findings
The investigation determined that the left engine low oil pressure indications during the previous and the occurrence flights were likely the result of a steady oil leak past the rear turbine air-oil seal assembly. The loss of engine oil pressure resulted in a loss of propeller control authority on landing and the upset of the aircraft. After consultation with maintenance, the crew considered the risks associated with landing single-engine and without hydraulic pressure for the nose-wheel steering, and decided to continue the flight with both engines running, even though this was not consistent with the QRH procedures for low oil pressure indications. Carbon deposits that accumulated within the inside diameter of the bellows convolutions interfered with the bellows’ ability to expand and to provide a positive seal against the rotor seal.
Additional findings noted that if operators do not provide crew resource management training, pilots may not be prepared to avoid crew errors. If operators rely solely on emergency procedures in the aircraft flight manual, continued engine operation with low oil pressure may result in loss of control. Lack of cooldown periods may lead to carbon deposits, and unavailability of flight data recordings can preclude identification of safety deficiencies.