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An undetected engine defect caused the fatal crash of an MD 500D during logging operations near Port McNeill, British Columbia, accident investigators have concluded.
On April 6, 2022, the aircraft, operated by Kestrel Helicopters Ltd., experienced engine failure shortly after releasing a bundle of cedar blocks. The pilot broadcast a distress call, but the aircraft hit the ground just a few seconds later, fatally injuring the pilot and causing substantial damage to the airframe.
Based on the structural damage to the aircraft, the Transportation Safety Board (TSB) of Canada estimated the pilot would have experienced greater than 53g when the helicopter hit the ground. Studies from the Federal Aviation Administration and NASA have shown that forces beyond 27g will cause serious injury and could be fatal.
In its investigation report on the accident, the TSB said that shrinkage voids developed near the inner circumference of the Rolls-Royce 250-C20B engine’s sixth-stage compressor wheel during the manufacturing process — but these went undetected with the existing detection methods.
The affected compressor wheel eventually failed when two separate fractures occurred — one due to fatigue caused by shrinkage voids, and the other due to overstress, the TSB stated in its report. These fractures resulted in a catastrophic engine failure.
According to the TSB report, Rolls-Royce is aware of two other failures of sixth-stage compressor wheels from the same supplier — one of which had the same part number as in the accident aircraft. However, changes have been made to the design of the sixth-stage compressor wheel since the manufacture of those three wheels, most recently through the use of a stainless steel alloy that provides improved mechanical strength and fatigue properties.