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Aviation Accident

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NTSB Identification: WPR17LA133
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Tuesday, June 27, 2017 in Boulder City, NV
Probable Cause Approval Date: 02/26/2019
Aircraft: EUROCOPTER EC 130 B4, registration: N151GC
Injuries: 2 Minor, 5 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The commercial pilot reported that, during an air tour flight, the engine lost total power. He initiated an autorotation to a nearby helicopter pad, during which the helicopter contacted power lines. He subsequently conducted an emergency landing on up-sloping terrain.

Postaccident on-site engine examination revealed that both the gas generator and power turbine were seized and could not be rotated by hand and that there was a significant amount of heat damage to the turbine blades and thermocouples. The vehicle and engine multifunction display recorded multiple engine temperature exceedances during the accident flight. Metal particles were found on the accessory gearbox magnetic plug. Further, no oil filter was found installed in the airplane.

Subsequent engine examination revealed that there was a hole in the centrifugal compressor. Examination further revealed that the No. 2 oil jet for the axial compressor rear bearing was obstructed, which resulted in oil starvation of the bearing and its subsequent failure. The bearing failure subsequently caused the gas generator rotating assembly to seize and resulted in the centrifugal compressor contacting the cover and creating the hole found in the component. Subsequent oil jet examinations revealed that coke pollution had obstructed the No. 2 oil jet. The lack of an oil filter precipitated the No. 2 oil jet obstruction and resulted in the axial compressor rear bearing deterioration.

The resultant engine inefficiency caused by the bearing failure and obstructed oil jet led to the need for higher fuel flow, which eventually resulted in an overtemperature/high pressure turbine failure and seizure of the gas generator and subsequent flameout; this was confirmed by data downloaded from the digital engine control unit, which recorded exceedances in the gas generator and free turbine speeds and an increase in fuel flow.

The manufacturer conducted the last maintenance, which was planned to be an overhaul of the accessory gearbox, 109.6 hours before the accident. During the maintenance, the oil filter was removed and discarded as part of the normal process for arrival inspection. A maintenance document review revealed that the overhaul was not due and that the manufacturer then sent the accessory gearbox back to the operator as is. However, the manufacturer did not inform the operator that it had removed the engine oil filter before returning the module, which is why no filter was found installed on the airplane.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • A loss of engine power due to the failure of the manufacturer to reinstall the oil filter after it was removed for inspection, which led to coke pollution that obstructed the oil jet and resulted in the subsequent oil starvation of the axial compressor rear bearing oil and its subsequent failure.