HISTORY OF FLIGHT
On September 20, 2009, about 1440 Pacific daylight time, a Robinson R44 II, N4174P, collided with rocky terrain during a forced landing near Valley Center, California. The pilot was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 91. The certificated commercial pilot and private pilot sustained serious injuries. The helicopter sustained substantial damage to the fuselage and tailboom. The local personal flight departed Montgomery Field Airport, San Diego, California, about 1300. Visual meteorological conditions prevailed, and no flight plan had been filed.
The pilots reported departing Montgomery Field about 1 1/2 hours prior to the accident. They flew to Ramona Airport, Ramona, California, where the private pilot performed traffic pattern practice. They then departed to a practice area near Valley Center. After stopping for a break, the commercial pilot took the controls of the helicopter with the intention of performing a pinnacle landing on a large rock. The pilot stated that he was not familiar with the area, so he circled the intended landing zone, and made a slow descent. As they approached the landing zone at an altitude of between 50 and 75 feet agl, the pilot heard a popping sound followed by "silence." The nose of the helicopter then dropped, and the pilot stated that he assumed the engine had failed. He then lowered the collective and performed an autorotation. During the landing sequence, the helicopter sustained substantial damage to the fuselage, and the tailboom separated midspan.
AIRCRAFT INFORMATION
The helicopter was manufactured in October 2008, and was equipped with its original Lycoming IO-540-AE1A5 engine, serial number L-33155-48E. A review of the maintenance logbooks revealed that the helicopter had undergone an annual inspection on May 23, 2009, at a total airframe time of 98.8 hours, 30.7 flight hours prior to the accident. According to the logbooks, the annual inspection was the last maintenance item performed prior to the accident. The engine had previously received an oil and filter change at 29.9 flight hours on January 8, 2009, and at 51.6 hours on January 26, 2009.
TESTS AND RESEARCH
Engine and Airframe
The engine appeared largely intact, had sustained crush damage to the exhaust and inlet manifolds, and a 2-inch-diameter puncture in the fuel servo inlet manifold. Residual quantities of fuel were noted in the gascolator. Examination of the dipstick revealed the presence of about 6.5 quarts of brown-colored, translucent oil. No rotational scratches were observed on the alternator and main drive pulley surfaces. The engine was rotated by hand at the flywheel, and the exhaust valve rocker for cylinder six moved appropriately; the remaining rockers did not move.
No anomalies were noted to the airframe that would have precluded normal operation.
The engine was removed from the helicopter and examined at the Lycoming manufacturing facility in Williamsport, Pennsylvania. The examination was conducted in the presence of the NTSB investigator-in-charge, and representatives from Lycoming Engines.
Disassembly of the engine revealed that the camshaft had separated into two sections at the forward relief radius of the number six exhaust cam lobe, adjacent to the number five/six intake cam lobe. Further examination revealed that the surfaces of all rotating drive train components were oil wetted, and no evidence of binding or oil starvation was present.
Camshaft
The camshaft was subsequently examined by the Lycoming Materials Laboratory division, and the Safety Board Office of Research and Engineering Materials Laboratory.
The fracture surface exhibited shiny mechanical damage consistent with post-fracture rotation of the mating surfaces.
Visual examination of the fracture surface revealed a 0.354-inch-wide granular region just below the shaft surface extending circumferentially at the forward relief radius of the number six exhaust cam lobe. Intergranular fracture features were noted adjacent to the surface. Radiating outward from this region, ‘beach mark’ striations extended to cover about half of the radial fracture surface. The remaining exposed area exhibited numerous microvoid coalescence features. According to Lycoming, the cam lobe and bearing surfaces undergo a carburizing heat treatment process during manufacture. The fracture was not within the intended carburization area, and sectioning of the fracture surface did not reveal the presence of localized carburization. Additionally, the cam shaft surface adjacent to the fracture area was coated with copper as part of a process which, according to Lycoming, prevents unintended carburization. Multiple grinding marks were noted both completely and partially around the circumference of the shaft. All of the machined surfaces were bright and free of tint. The remaining sections of the camshaft were inspected utilizing magnetic particle inspection; no anomalies were found.
Continued examination of the camshaft revealed that it conformed to Lycoming’s engineering requirements for dimension, hardness, soundness, and microstructure. A complete metallurgical exam report is contained within the public docket for this accident.
ADDITIONAL INFORMATION
Lycoming reported that the camshaft was manufactured by a supplier who had ceased operation in April 2009. During the period from January 2005 through to April 2009, this supplier had produced 4,870 camshafts of the accident type. All of these camshafts have since been installed in Lycoming 540 series engines.
A search of the Federal Aviation Administration (FAA) Service Difficulty Report (SDR) database revealed no evidence of a similar camshaft separation. Additionally, Lycoming reported no prior instances of any camshaft which had broken in such a manner.