Accident Overview
A Cessna 208B Caravan, registration C-GRXZ and serial number 208B0469, was operating a flight from Tofino, British Columbia, to Vancouver International Airport, British Columbia. While cruising at 9,000 feet above sea level, the engine failed. The pilot initiated a glide toward Port Alberni Regional Airport but subsequently attempted an emergency landing on a logging road. During a steep right-hand turn, the aircraft struck trees and crashed at approximately 1420 Pacific standard time, about 11 nautical miles south-southeast of Port Alberni Regional Airport.
Injuries
Five passengers survived the accident with serious injuries. The pilot and the two other passengers were fatally injured.
Probable Cause Findings
The investigation identified the following causes and contributing factors: 1. The engine lost power when a compressor turbine blade failed as a result of the overstress extension of a fatigue-generated crack. The fracture initiated at a metallurgical anomaly in the parent blade material and progressed, eventually resulting in blade failure due to overstress rupture. 2. The combination of aircraft position at the time of the engine failure, the lack of equipment enabling the pilot to locate and identify high terrain, and the resultant manoeuvring required to avoid entering instrument flight conditions likely prevented the pilot from attempting to glide to the nearest airfield.
Risk Findings
The investigation also noted several risks: 1. Single-engine instrument flight rules (SEIFR) operations in designated mountainous regions have unique obstacle risks in the event of an engine failure. Canadian equipment requirements for such operations do not currently include independent terrain mapping, such as terrain awareness and warning systems (TAWS). 2. Airline operators are not currently required to conduct any additional route evaluation or structuring to ensure that the risk of an off-field landing is minimized during SEIFR operations. 3. Pilots involved in commercial SEIFR operations do not receive training in how to conduct a forced landing under instrument flight conditions; such training would likely improve a pilot's ability to respond to an engine failure when operating in instrument meteorological conditions (IMC). 4. Mean time between failure (MTBF) calculations do not take into account In Flight Shut Downs (IFSDs) not directly attributable to the engine itself; it may be more appropriate to monitor all IFSD events. 5. The design of the Cessna 208B Caravan fuel shutoff valves increases the risk that the valves will open on impact, allowing fuel spillage and increasing the potential for fire.
Additionally, Sonicblue Airways was not providing downloaded engine parameter data for engine condition trend monitoring (ECTM) evaluation at appropriate intervals.