N6764P

On October 28, 2004, at 1909 central daylight time, a Piper PA-24, N6764P, piloted by a private pilot, was substantially damaged during a forced landing following a complete loss of engine power near Buffalo Grove, Illinois. The personal flight was being conducted under 14 CFR Part 91 on an instrument flight rules flight plan. Instrument meteorological conditions prevailed at the time. The pilot sustained serious injuries. The flight departed Palwaukee Municipal Airport (PWK), Wheeling, Illinois, at 1850, with an intended destination of Evansville Regional Airport (EVV), Evansville, Indiana.

In his written statement, the pilot reported that approximately 10 minutes after takeoff, when the flight was about 3,000 feet mean sea level, he heard a "loud bang followed by extreme vibrations of the aircraft." He advised air traffic control of the problem and turned toward the nearest airport, which was PWK.

The airplane did not have sufficient altitude to glide back to the airport. The pilot executed a forced landing on a four-lane highway about 4 miles north of the airport. He noted, "While flaring to land a car turned in front of me. I avoided the car, however, the left wing started clipping trees." The airplane came to rest on the highway median.

A post-accident inspection of the engine determined that the crankshaft had failed aft of the number 2 main bearing journal. The crankshaft was retained and sent to the NTSB materials laboratory for further review.

Metallurgical examination of the crankshaft fracture surface revealed crack arrest marking (beach marks) indicative of fatigue cracking. The beach marks indicated that fatigue initiation was at the surface of the main bearing journal slightly forward of the aft radius. The adjacent journal surface was roughened and discolored with multiple longitudinally oriented parallel cracks (ladder cracks) in the surface.

Magnified examination found that the fatigue fracture originated at one of the ladder cracks and grew aft through about 75 percent of the crank cheek before the crankshaft failed.

The other journals showed some circumferential scratches and light wear. However, none showed the high level of surface damage exhibited by the fractured main journal.

The engine was a Lycoming O-360-A1A, serial number L-1661-36. The maintenance logbook showed that the engine was overhauled on October 8, 1998. The engine had accumulated 2,233 hours time in service prior to the overhaul.

The engine was subsequently installed on the accident aircraft on October 17, 1998. The aircraft's recording tachometer read 3,619 hours at that time, according to the logbook endorsement.

The most recent annual inspection was completed on April 14, 2004. The logbook entry noted the aircraft tachometer time as 4,251.2 hours, and engine time since overhaul as 632.2 hours.

The aircraft tachometer read 4,495.8 hours when observed at the accident site.