What happened
At approximately 1900 CDT, an Expedition Helicopters Inc. Eurocopter AS 350 B-2, registration C-GSSS, was performing a routine transport of drilling and seismic personnel between two sites in Ontario. After departing the Butler Lake site and performing a steep climb, the aircraft leveled off at 800 feet above ground level.
Immediately following the level-off, the pilot experienced two distinct yawing motions accompanied by a rotor overspeed warning. This was followed by a complete loss of engine power and a low rotor RPM warning. The pilot initiated an autorotation, but was unable to reach the intended landing zone, instead performing a hard landing in the shallow water near a lake shore. While the tail boom and tail rotor sustained significant damage, all five occupants exited the aircraft safely. The pilot and two passengers escaped without injury, while the remaining two passengers sustained minor injuries.
The investigation
Investigators examined the engine's Honeywell LTS101 700D–2 turbine engine and its power turbine (PT) governor. Laboratory analysis of the removed PT governor revealed that the spool bearing had failed after only 228 hours of operation. Microscopic examination identified diamond particles within the bearing, which likely caused excessive friction and heat, leading to the bearing's destruction.
Testing of the engine in a test cell confirmed that the PT governor failed to maintain the specified speed, allowing the engine to exceed 100% Np. Furthermore, the investigation looked into the engine's fuel pump, specifically the 0.132-inch diameter inducer jet orifice. It was noted that the activation of the engine overspeed protection system (EOS) could cause fuel pressure fluctuations that lead to engine flameouts when using this specific orifice size.
Findings
- Diamond particles found in the PT governor spool bearing caused the bearing to fail, resulting in the failure of the power turbine governor.
- The failure of the governor allowed the engine and rotor to overspeed during the aircraft's level-off, triggering the engine overspeed protection system (EOS) to cycle.
- The cycling of the EOS, combined with fuel pressure changes caused by the 0.132-inch inducer jet, likely resulted in the engine flameout.
- The aircraft's hard landing in shallow water caused substantial damage to the tail section.