DEN08LA069

During a normal descent on approach for landing at 8,500 feet mean sea level, the engine "let go/popped into a higher pitch sound, and the power dropped off. [The pilot] checked the fuel flow, tried to get power with the throttle, but no response." During a forced landing, the airplane impacted the side of a gravel road, traveled across the road, struck a ditch, and skidded on the fuselage bottom for approximately 75 feet were it came to rest upright in a residential yard. Examination of the engine exhibited fretting on all six cylinder decks and the main bearing case half sections. The number 2 main bearing support bearing tang lock-slot was found elongated. Various degrees of wear were noted on all crankshaft main bearings, and the number 2 main bearing showed additional wear. The crankshaft number 2 main journal exhibited signatures of thermal discoloration. All oil transfer galleries were free and clear of debris. The camshaft was intact, however, the camshaft gear had a semi-circular section with 7 gear teeth separated, which was found in the gearbox. Metallurgical examination showed the fracture initiated at the surface and progressed in fatigue. The initiation site was damaged; however, the approximate location was identified by crack arrest lines, which encircled the origin. The reason for the fracture initiation could not be determined.

On March 29, 2008, at 1654 mountain daylight time, a Cessna P210N single-engine airplane, N4839P, sustained substantial damage during a forced landing following a loss of engine power near Elizabeth, Colorado. The commercial pilot and two passengers were not injured. The airplane was registered to Cure Trucking LLC, Bethune, Colorado, and operated by the pilot. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The flight departed Lamar, Colorado, at 1600, and was en route to Denver, Colorado.

Approximately 25 nautical miles southeast of Centennial Airport (APA), Englewood, Colorado, the pilot was instructed by APA air traffic control tower to report a 3 mile final. While descending at 8,500 feet mean sea level (msl), the engine "let go/popped into a higher pitch sound, and the power dropped off. [The pilot] checked the fuel flow, tried to get power with the throttle, but no response." He then attempted a forced landing to a gravel road with the landing gear extended. Subsequently, the airplane impacted the side of the gravel road, traveled across the road, struck a ditch, and skidded on the fuselage bottom for approximately 75 feet where it came to rest upright in a residential yard.

Examination of the aircraft showed the fuslage was buckled.

A review of the aircraft records revealed the engine underwent a major overhaul on May 7, 1993, at a total engine time of 1,331.0 hours. On July 20, 2007, the engine underwent its most recent 100 hour inspection, at a total time since major overhaul of 1,203.9 hours, and a tachometer time of 2,534.9 hours. On September 9, 2007, at a tachometer time of 2,538.9, the alternator was removed and replaced. At the time of the accident, the engine had accumulated 1,221 hours since major overhaul, and the tachometer time was 2,562.0 hours.

On June 3 and 4, 2008, at the facilities of Beegles Aircraft Services, Greeley, Colorado, the engine was examined by a NTSB investigator and a representative of Teledyne Continental Motors (TCM), Mobile, Alabama. Visual examination of the engine and accessories showed that the lower pivot bolt on the alternator was missing, the upper bolt was extruded 3/4 inches, and the alternator belt lacked tension. Safety wire was missing and not secured on several fuel system components. The engine was then disassembled for further examination. Disassembly of the engine showed fretting on all six cylinder decks and the main bearing case half sections. The number 2 main bearing support bearing tang lock-slot was found elongated. Various degrees of wear was noted on all crankshaft main bearings and the number 2 main bearing showed additional wear. The crankshaft number 2 main journal exhibited signatures of thermal discoloration. All oil transfer galleries were free and clear of debris. The camshaft was intact, however, the camshaft gear had a semi-circular section with 7 gear teeth separated, which was found in the gearbox. The camshaft gear and separated section were retained for metallurgical examination.

On June 19, 2008, at the TCM metallurgical laboratory, the camshaft gear was examined by a TCM metallurgist and a NTSB investigator. According to TCM, the fracture initiated at the surface and progressed in fatigue from left to right on the gear. The initiation site was damaged; however, the approximate location was identified by crack arrest lines, which encircled the origin. Two gear teeth were removed for additional analysis. The case depth, surface hardness, and core hardness met specifications and no anomalies were noted with the microstructure. The reason for the fracture initiation could not be determined.