On October 15, 2000, at 1007 Eastern Daylight Time, a Piper PA-28-181, N4381S, was substantially damaged during a forced landing in Southborough, Massachusetts. The certificated private pilot and his passenger were not injured. Visual meteorological conditions prevailed at the time of the accident. No flight plan had been filed for the flight, between Lawence G. Hanscom Field (BED), Bedford, Massachusetts, and Martha's Vineyard Airport (MVY), Vineyard Haven, Massachusetts. The personal flight was conducted under 14 CFR Part 91.

According to the pilot, the airplane was in a climb, passing 3,500 feet, when he heard a "bang". The engine then lost power, and oil began leaking out of the engine compartment. The pilot contacted air traffic control, and was advised that Marlboro Airport (9B1), Marlboro, Massachusetts, was 5 miles to the northeast. The pilot then advised the controller that the airplane would not be able to make it to the airport, and that he would attempt to land on the Massachusetts Turnpike.

The pilot made "one pattern circuit," about 1,000 feet of altitude, and landed westward, with the traffic. During the flare, the airplane struck highway reflectors, a sign and car, and after landing, veered off the road.

According to an inspector from the Federal Aviation Administration (FAA), there was a hole in the engine casing in the vicinity of the number 1 piston, and the number 1 piston connecting rod cap had separated from the rod.

According to maintenance records, the Lycoming O-360-A4M engine was overhauled at Penn Yan Aero Service, Inc., Penn Yan, New York. The overhaul was completed on January 30, 1999, when total engine time was 1,259 hours.

On March 1, 1999, the engine was reinstalled on the accident airplane and serviced with mineral oil. On May 13, 1999, at 11 hours since overhaul, the engine was re-serviced with mineral oil. On October 1, 1999, at 31 hours since overhaul, the oil was changed again, to Aeroshell 80W. On April 7, 2000, at 37 hours since overhaul, during an annual/100-hour inspection, the engine oil was changed again, also with Aeroshell 80W. At the time of the accident, the engine's time since overhaul was 50 hours.

On December 11, 2000, the engine underwent a teardown examination under Safety Board supervision at the Textron Lycoming facility, Williamsport, Pennsylvania. Representatives from Penn Yan Aero Service were also in attendance.

During the examination, it was discovered that "74502" connecting rods were used in the overhaul of the engine. Of those, the number 1 connecting rod was found dislodged from the crankshaft. In addition, the number 1 connecting rod cap was missing from the engine, along with one complete rod bolt, and the manufactured head of the other rod bolt. The connecting rod was broken at the yoke end. One of the forks of the yoke was broken completely, and the other was bent inboard. The ends of both forks were smoothed, and the fracture surfaces were obliterated.

According to a Textron Lycoming air safety investigator, all O-360-A4M engines since engine certification in November 1974 were manufactured using LW-11750 connecting rods. Other engines had previously been manufactured using 74502 connecting rods; however, those rods and their immediate successors were superceded by LW-11750 connecting rods in May 1970.

The LW-11750 connecting rod had a larger grip area than the 74502 connecting rod, and utilized a longer rod bolt to secure the connecting rod cap to the connecting rod yoke.

No information was available to indicate that the use of a 74502 connecting rod instead of the LW-11750 rod would result in a rod or rod bolt failure.

The number 1 connecting rod with bolt/cap remnants, along with undamaged number 4 connecting rod, rod cap, and rod bolts and nuts were submitted to the Safety Board Materials Laboratory for examination. Missing from the number 1 connecting rod assembly were the connecting rod cap, one connecting rod bolt and nut, and the fractured head portion of the other connecting rod bolt.

According to the metallurgist's factual report, the connecting rod arm was observed to be fractured approximately 1.1 inches along the inside circumference from its tip. The connecting rod bolt piece recovered was fractured approximately inches from the threaded end. With an exemplar bolt measuring 2.1 inches in length, approximately 1.0 inch of this bolt was not recovered.

The mating fracture surface on the main portion of the connecting rod was damaged after the fracture, as the fracture marks were smeared out; the piece did not provide any clues to the fracture mode. The relatively undamaged fracture surface on the separated arm had a cupped appearance with the center portion of the fracture being slightly depressed compared to the edges. When observed under the scanning electron microscope (SEM), ductile dimples, indicative of an overstress fracture, were found throughout the entire fracture surface.

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