LAREDO, TX, USA
N36254
Schweizer HUGHES 269C
The helicopter was at a 50-foot hover over a creek when the pilot heard a loud banging, followed by a loss of engine power. The pilot executed a right pedal turn and set the helicopter down hard in a creek. Examination of the engine revealed that the crankshaft was separated at the number 3 main bearing journal to number 3 connecting rod journal crossover cheek. A magnaflux examination of the crankshaft revealed that the number 3 main bearing journal displayed lateral cracks. Examination of the crankshaft fracture surfaces revealed that the crankshaft had failed in fatigue. The fracture features were damaged near the origin area; however, 'nearby crack arrest positions clearly indicated crack initiation from at least two locations on the journal surface near the crank cheek.' Examination of the number 3 bearing shell halves revealed that 'one shell had shifted relative to the other when the damage occurred.'
On March 10, 1999, at 0910 central standard time, a Schweizer Hughes 269C helicopter, N36254, was substantially damaged during a forced landing following a loss of engine power while hovering near Laredo, Texas. The non-instrument rated commercial pilot and his passenger were not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations (CFR) Part 91 local flight. The helicopter was registered to and operated by Smith Helicopters, Inc., of Laredo, Texas. The aircraft was contracted by a rancher to aid in herding cattle. During a telephone interview conducted by the NTSB investigator-in-charge (IIC), the pilot stated that the helicopter was at a 50-foot hover over a creek when he heard "loud banging," followed by a loss of engine power. The pilot then applied full throttle, but the engine did not respond. The pilot then executed a "right pedal turn and set the helicopter down hard in the creek." Examination of the helicopter by an FAA inspector revealed that both landing skids had separated, the center frame was twisted, the bottom of the cabin nose was bent, and the main and tail rotor blades were damaged. Initial examination of the engine revealed that the crankshaft would not rotate. On July 13, 1999, the NTSB IIC examined the Lycoming HIO-360-D1A engine (serial number L-25763-51A) at the manufacturer's facility. Disassembly of the engine revealed that the crankshaft was separated at the number 3 main bearing journal to number 3 connecting rod journal crossover cheek. A magnaflux inspection of the crankshaft revealed lateral cracks on the number 3 main bearing journal. The crankshaft and the number 3 bearing shell halves were sent to the NTSB Materials Laboratory on July 14, 1999, for further examination. According to the NTSB metallurgist, "detailed visual examination of the fracture surface revealed a flat fracture plane and crack arrest positions typical of fatigue cracking over a major portion of the fracture surface." The fracture features near the origin area were damaged; however, "nearby crack arrest positions clearly indicated crack initiation from at least two locations on the journal surface near the crank cheek." The bearing shell halves were examined and were found to be "mechanically damaged and partially extruded on the one [aft] end. Matching of the damage patterns on the bearing halves indicated that one shell had shifted relative to the other when the damage occurred." According to the airplane's maintenance records the engine was overhauled at the manufacturer's facility and was installed in the helicopter on June 26, 1997. The total time on the engine at the time of overhaul was 1,594.0 hours. A 100-hour inspection was completed on the engine on February 8, 1999 at 582.6 hours since the overhaul. At the time of the accident, the engine had accumulated 631.0 hours since the overhaul.
The loss of engine power due to a bearing shift, which resulted in fatigue cracking of the crankshaft and subsequent failure of the crankshaft. A factor was a lack of suitable terrain for the forced landing.
Source: NTSB Aviation Accident Database
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