What aircraft was involved and where did it happen?

The accident on 2002-08-15 involved a Eurocopter SA 315B Lama Helicopter C-GGHG, operated by Western Aerial Applications Ltd., at McBride, British Columbia 20 nm S, CA.

What was the probable cause of the accident?

The engine failure was caused by the progressive failure of the forward coupling sleeve assembly due to premature wear from improper shaft alignment, contaminated lubrication, and a failed washer, which ultimately disrupted the fuel supply.

Engine failure leads to hard landing in Eurocopter Lama

An engine failure during a ferry flight in British Columbia forced a pilot into an autorotation, resulting in a hard landing and minor injuries to two passengers.

What happened

A Eurocopter SA 315B Lama, registration C-GGHG, was performing a visual flight rules ferry flight from Mission, British and Columbia, to McBride via Kamloops. The flight was carrying the pilot and two passengers. During the flight, a passenger reported hearing two distinct banging noises from the rear of the aircraft; the first occurred shortly after takeoff, and the second after a refueling stop in Kamloops. The pilot noted no unusual engine or airframe indications at those times.

While flying near Blue River, the helicopter experienced a sudden rightward yaw, followed by a loud bang and a loud sound. The engine subsequently failed, forcing the pilot to initiate an autorotation. During the descent, the rotor RPM decreased, leading to a high rate of descent. The pilot performed a run-on landing, but the impact was hard enough to break the rear passenger seat. The two passengers sustained minor injuries, though the aircraft remained upright and no fire occurred.

The investigation

Investigators examined the wreckage at a facility in Chilliwack and analyzed engine oil and fuel samples. The engine oil showed signs of fuel contamination and contained metallic particles. Metallurgical analysis of the engine components revealed that the fuel injection tube had broken due to distortion caused by excessive shaft vibration.

Technical reviews focused on the engine's drivetrain, specifically the forward coupling sleeve and stub shaft. The investigation also looked into maintenance records, including spectrometric oil analysis (SOAP) results and vibration check histories. It was noted that a recent oil change had diluted the concentration of metallic particles in the sampled oil, and the engine had not undergone a required vibration check following its initial installation.

Findings

The primary cause of the engine failure was the failure of the splined drive in the forward coupling sleeve due to premature wear.
This wear was driven by improper axial alignment of the stub shaft, which introduced radial motion and shaft wobble.
The failure of a serrated adjusting washer introduced metallic debris into the lubrication grooves, further accelerating the degradation of the splines.
Contamination from an anti-seize compound, applied during overhaul, combined with metallic filings to clog the lubrication system.
The resulting shaft vibration and flexion caused the fuel injection tube to distort and eventually break, interrupting the fuel supply and causing the engine to flame out.
The high rate of descent and subsequent hard landing were caused by the loss of rotor RPM during the autorotation.