What happened
On August 15, 2003, at approximately 11:05 PDT, a Bell 204B helicopter, registration C-GEAP, was performing forest fire suppression duties at Bonaparte Lake, British Columbia. Operated by Gemini Helicopters Inc., the aircraft was flying its first mission of the day, transporting an empty water bucket via a 100-foot longline. Shortly after departing a staging site, the aircraft began emitting a high-pitched, oscillating sound. While the flight path initially appeared normal, the aircraft soon experienced a loud main-rotor blade slap, followed by a collision with trees. The helicopter struck the ground roughly a quarter nautical mile southeast of the staging site. A post-impact fire destroyed the cabin and damaged the transmission and pylon. The pilot was fatally injured.
The investigation
The investigation focused on the recent maintenance performed on the engine and transmission, which had been replaced just days prior. While the engine and transmission were recently overhauled, investigators found that a vibration check—required by the manufacturer following engine installation—had not been performed. Furthermore, while the pilot had adjusted the N1 take-off trim to address power issues, there was no record of an N1 topping check to ensure the engine was not operating beyond its specified limits.
Investigators also examined the external load configuration. The remote hook for the water bucket had been intentionally disabled, meaning the bucket could only be released manually or via a secondary system. The investigation also looked into the pilot's ability to react to the emergency, noting that the aircraft's cyclic control switches were configured differently than the pilot's usual fleet, which could impede instinctive emergency actions.
Findings
- An unexplained imbalance developed within the engine compressor rotor assembly, causing the rotor to contact stationary components. This contact led to the destruction of the compressor blades and total engine failure.
- The combination of the aircraft's altitude, the local terrain, and the trailing longline—which had snagged a tree—made a successful emergency autorotation landing impossible.
- The lack of a vibration check following the engine installation and the absence of an N1 topping check after trim adjustments contributed to the risk of operating the engine under unstable or excessive thermal conditions.