What happened
On June 27, 2017, a Eurocopter EC 130 B4 helicopter, registration N151GC, was performing a commercial air tour flight from Boulder City Municipal Airport, Nevada, to Grand Canyon West Airport, Arizona. While executing an S-turn at approximately 3,000 feet mean sea level, the pilot experienced a rightward yaw accompanied by an audible gong and a yellow engine parameter failure indication.
Following the loss of engine power and the activation of the main rotor RPM warning horn, the pilot initiated an autorotation toward a nearby helicopter pad. During the maneuver, the pilot applied left cyclic input to avoid power lines, which caused the retreating main rotor blade to contact a power line. The pilot then completed an up-slope emergency landing on rising mountainous terrain. The flight involved five occupants; while there were no fatalities, 2 passengers sustained minor injuries.
The investigation
An examination of the engine revealed that the gas generator and power turbine were seized and could not be rotated manually. Investigators found significant heat damage to the turbine blades and thermocouples, and the engine multifunction display recorded temperature exceedances. Metal particles were discovered on the accessory gearbox magnetic plug, and sludge was found on the reduction gearbox magnetic plug and electric chip detectors. Notably, the engine oil filter was not installed in the engine.
Further disassembly of the engine at a facility in France revealed a hole in the centrifugal compressor. The investigation determined that the No. 2 oil jet for the axial compressor rear bearing was obstructed by coke pollution (carbon, oxygen, and phosphorus). This obstruction caused oil starvation of the axial compressor rear bearing, leading to its failure. The bearing failure caused the gas generator rotating assembly to seize, which in turn caused the centrifugal compressor to contact the cover.
Maintenance records showed that 109.6 hours prior to the accident, the engine's accessory gearbox had been sent to a facility for a planned overhaul. During the arrival inspection, the oil filter was removed and discarded. Although the overhaul was ultimately deemed unnecessary and the gearbox was returned to the operator, the manufacturer failed to inform the operator that the oil filter had been removed. Consequently, the engine was operated without an oil filter installed.