Bennett, CO, USA
N707SH
Hall Lancair 4P
While in cruise flight, the oil pressure warning light illuminated, and the oil pressure gauge fluctuated between 0 and 10 psi. The engine made a loud noise and began to vibrate and lose power. A forced landing was made in an open field. After touch down, the left main and nose landing gear buckled, then the right main gear collapsed, shearing off the right wing. During the engine disassembly and inspection, it was discovered that the starter adapter drive shaft had fractured forward of the oil scavenge pump gears at a snap ring groove. This allowed pressurized lubricating oil to be discharged through the turbocharger turbine and compressor oil seals. Metallurgical examination concluded that the fracture was in fatigue and had initiated at multiple origins at the snap ring groove root fillet.
On May 28, 2001, approximately 1430 mountain daylight time, a Hall Lancair 4P, N707SH, registered to and operated by the pilot, was substantially damaged when the landing gear collapsed during a forced landing near Bennett, Colorado. The airline transport certificated pilot-in-command, an airline transport certificated pilot-passenger, and another passenger sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal flight being conducted under Title 14 CFR Part 91. The flight originated from Watkins, Colorado, approximately 1400. According to the pilot's accident report, the oil pressure (red) warning light illuminated and he noticed the oil pressure gauge was fluctuating between 0 and 10 psi (pounds per square inch) while the airplane was in cruise flight. Shortly thereafter, the engine made a loud noise, and began to vibrate and lose power. He retarded the propeller control to the high pitch/low rpm setting. The pilot-rated passenger, who was flying the airplane, made an approach to an open field near U.S. Highway 36, Schumaker Road, and Interstate Highway 70. The landing gear was lowered and full flaps were deployed. "We were both on the controls through the flare and we held it off as long as possible," the pilot wrote. After touching down, the left main and nose landing gear "buckled." The right main gear collapsed shortly thereafter, shearing off the right wing. The airplane was given a preliminary inspection on June 1, 2001, at its hangar at Front Range Airport, Watkins, Colorado. The bottom of the fuselage was covered with oil, and the left exhaust stack was wet with oil. The right exhaust stack was dry. There was a hole in the top left engine case abeam cylinder 5, and a piece of connecting rod and cap, including the butt and nut, was found on top of the case between the magnetos. The parts were discolored black and had a melted appearance. The engine, a Continental IO-550-E1B (s/n 803090) was crated and shipped to Teledyne Continental Motors (TCM) in Mobile, Alabama, where, on July 10, 2001, it was disassembled and inspected under the supervision of an FAA maintenance inspector. According to TCM's report, the engine was factory remanufactured on March 31, 1999, and had accumulated approximately 60 hours. There was metallic debris (bearing material, a piece of connecting rod bolt and nut, and pieces of piston) in the oil sump and oil pressure relief valve cavity. There was "heavy scratching" of the oil pump gears. All cylinder barrel skirts were damaged as a result of the separation of the number 2 connecting rod. Damage to the skirt of the number 2 cylinder precluded removal of the piston. The left half of the crankcase had internal damage at the top of numbers 2 and 6 cylinders. The right half of the crankcase was punctured above numbers 1 and 3 cylinders. Number 5 cylinder was also damaged. Number 2 connecting rod journal was partly melted due to oil starvation. Number 4 connecting rod journal was discolored due to heat, and numbers 5 and 6 connecting rod bearings were extruded. The crankshaft connecting rod journals bore oil starvation signatures. The drive shaft for the scavenge oil pump on the rear of the starter adapter (p/n 649866) was fractured forward of the scavenge pump gears at a snap ring groove. According to TCM's report, pressurized lubricating oil was discharged through the turbocharger turbine and compressor oil seals. Loss of lubricating oil damaged the connecting rod bearings and burned numbers 2 and 4 connecting rod journals The number 2 connecting rod bearing was completely extruded and the rod was thrown from the crankshaft. Metallurgical examination of the starter adapter drive shaft by a TCM metallurgist concluded that the fracture was in fatigue and had initiated at multiple origins at a snap ring groove root fillet. The snap ring groove had not been case hardened as required by the engineering drawing. However, the TCM metallurgist stated this represented "a drawing oversight," and previous gears produced at TCM were without a carburized snap ring groove.
unsuitable terrain on which to make a forced landing. A contributing factor was a fatigue fracture of the starter adapter drive shaft, which resulted in a loss of engine power due to oil starvation.
Source: NTSB Aviation Accident Database
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