Robinson Helicopter Company R44 II N4174P accident near Valley Center, California

Probable cause

The failure of the engine’s camshaft due to fatigue of unknown origin.

NTSB analysis

The pilot was performing a pinnacle landing on a large boulder. As he approached the landing zone at an altitude of between 50 and 75 feet above ground level he heard a popping sound followed by a complete loss of engine power. He performed an autorotation, during which the helicopter sustained substantial damage to the fuselage and tail boom. during the hard landing. The helicopter was manufactured about 11 months prior to the accident, had accumulated about 130 total flight hours, and was equipped with its original engine. Examination of the engine revealed that the camshaft had separated into two sections at the forward relief radius of the number six exhaust cam lobe. The fracture surfaces were damaged by the continued rotation of the engine just after the failure; however, the remaining surfaces exhibited features consistent with fatigue. The origin of the fatigue could not be determined. No other anomalies were noted with the engine or airframe. According to the engine manufacturer, the camshaft supplier had produced 4,870 camshafts of the accident type. All of these camshafts have since been installed in similar engines. A search of the Federal Aviation Administration (FAA) Service Difficulty Report (SDR) database revealed no evidence of a similar camshaft separation. Additionally, the engine manufacturer reported no prior instances of any camshaft which had failed in such a manner.

Text from the NTSB. Open the NTSB docket for WPR09LA460 for the full record.