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TSB: Undetected engine defect led to fatal Port McNeill helicopter crash

Avatar for Oliver JohnsonBy Oliver Johnson | November 17, 2023

Estimated reading time 5 minutes, 52 seconds.

The accident aircraft — a Kestrel Helicopters MD 500D. Tim Martin Photo
The accident aircraft — a Kestrel Helicopters MD 500D. Tim Martin Photo

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.

The aircraft crashed in a wooded area shortly after dropping off a load of cedar blocks. TSB Photo
The aircraft crashed in a wooded area shortly after dropping off a load of cedar blocks. TSB Photo

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.

The fractured sixth stage compressor wheel. The drawn circle indicates the circumference of the wheel before it was fractured. TSB Photo
The fractured sixth stage compressor wheel. The drawn circle indicates the circumference of the wheel before it was fractured. TSB Photo

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.

In 2007, Rolls-Royce issued a commercial service letter to inform customers about the release of the new compressor wheels. Following the accident near Port McNeill last year, the manufacturer re-issued the letter, including a recommendation for 250-C20B operators to convert the compressor to the new wheel design during the next overhaul.

The full compressor assembly. TSB Photo
The full compressor assembly. TSB Photo

The crash took place shortly after 9 a.m. local time, during the pilot’s third flight of the morning. The aircraft had not long departed the staging area for the day’s work, where the pilot had prepared the helicopter for slinging by removing the left door and attaching a 180-foot long line.

The pilot was vastly experienced, with 13,000 hours total flying hours, including 11,000 on the type, and 6,000 hours slinging cedar blocks.

The TSB noted that he had completed annual training in April 2021, which covered engine failures while in a hover and various autorotation practises.

However, it said that the aircraft’s low altitude at the time of the engine failure — it had just released a load of blocks — meant it had insufficient height and forward speed to successfully autorotate.

“If single-engine helicopters routinely operate with unsafe height and airspeed combinations, the likelihood of a successful landing after an engine failure is significantly reduced,” the TSB report states.

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