What happened
On September 18, 2018, a Robinson R44 N632NV was conducting a commercial air tour flight from Daniel K Inouye International Airport (HNL) in Honolulu, Hawaii. During cruise flight at approximately 2,200 feet above ground level, the engine oil light illuminated red. The pilot noted that while the oil pressure light was on, the engine did not lose power, and the pilot began an immediate descent to land.
As the helicopter descended, the pilot observed minor fluctuations in engine RPM. Shortly after, the main rotor began to overspeed. As the aircraft neared the ground, the pilot raised the collective, which triggered a low rotor RPM warning and horn. The helicopter impacted the terrain at approximately 40 knots and slid about 40 feet. The impact caused the left skid to separate and the aircraft to rotate 90 degrees. The pilot and two passengers were not injured.
The investigation
Post-flight inspections revealed oil on the exterior of the lower engine inspection panels, extending down the tailboom, vertical stabilizer, and tail rotor. The engine oil dipstick indicated the oil level was at the 1/8-inch mark.
An onboard camera review confirmed the oil pressure gauge dropped to zero when the warning light illuminated. The footage also showed that during the flare sequence, engine RPM dropped to approximately 80%.
Subsequent maintenance examination found fresh oil in a pan placed under the engine oil filter area. Mechanics discovered that the oil filter required significantly less resistance to rotate than normal. Upon removal, it was found that the threaded fitting for the filter was only two threads into the adapter, and the filter cavity contained no oil.