History of Flight
On September 20, 2009, at approximately 1440 Pacific daylight time, a Robinson R44 II helicopter, registration N4174P, collided with rocky terrain during a forced landing near Valley Center, California. The helicopter was operated under 14 Code of Federal Regulations Part 91. The certificated commercial pilot and a private pilot were on board and both sustained serious injuries. The helicopter sustained substantial damage to the fuselage and tailboom, which separated midspan. The local personal flight had departed Montgomery Field Airport in San Diego, California, about 1300. Visual meteorological conditions prevailed and no flight plan was filed.
Pilot Account
The pilots reported that after departing Montgomery Field, they flew to Ramona Airport where the private pilot conducted traffic pattern practice. They then proceeded to a practice area near Valley Center. After a break, the commercial pilot assumed control with the intention of performing a pinnacle landing on a large rock. The pilot, unfamiliar with the area, circled the intended landing zone and made a slow descent. At an altitude of between 50 and 75 feet above ground level, a popping sound was heard followed by silence. The nose dropped, and the pilot assumed an engine failure. He lowered the collective and performed an autorotation. During the landing, the helicopter sustained substantial damage and the tailboom separated.
Aircraft Information
The helicopter was manufactured in October 2008 and equipped with a Lycoming IO-540-AE1A5 engine. The most recent annual inspection was completed on May 23, 2009, at 98.8 total airframe hours, 30.7 hours prior to the accident. No other maintenance was performed after that inspection.
Engine Examination
The engine remained largely intact but sustained crush damage to the exhaust and inlet manifolds, and a 2-inch puncture in the fuel servo inlet manifold. Residual fuel was found in the gascolator. Approximately 6.5 quarts of brown, translucent oil were present on the dipstick. No rotational scratches were observed on the alternator and main drive pulley surfaces. Manual rotation of the engine revealed that only the exhaust valve rocker for cylinder six moved appropriately; the other rockers did not move.
The engine was removed and disassembled under NTSB supervision at Lycoming's facility. Disassembly revealed that the camshaft had separated into two sections at the forward relief radius of the number six exhaust cam lobe. All rotating drive train surfaces were oil wetted with no evidence of binding or oil starvation.
Camshaft Metallurgical Examination
The fracture surface exhibited post-fracture damage consistent with rotation of the mating surfaces. Visual examination revealed a 0.354-inch-wide granular region near the shaft surface, with intergranular fracture features. Beach mark striations extended radially covering about half of the fracture surface, and the remaining area showed microvoid coalescence. Lycoming reported that the cam lobe and bearing surfaces undergo a carburizing heat treatment; the fracture was not within the intended carburization area, and sectioning did not show localized carburization. The shaft surface adjacent to the fracture was coated with copper to prevent unintended carburization. Multiple grinding marks were noted around the shaft circumference. The remaining camshaft sections showed no anomalies via magnetic particle inspection. The camshaft met Lycoming's engineering requirements for dimension, hardness, soundness, and microstructure.
Additional Information
Lycoming reported that the camshaft was manufactured by a supplier that ceased operations in April 2009. Between January 2005 and April 2009, the supplier produced 4,870 camshafts of this type, all installed in Lycoming 540 series engines. A search of the FAA Service Difficulty Report database found no similar camshaft separations, and Lycoming reported no prior instances of such a failure.