Accident Overview
An airplane sustained a total loss of engine power when the number 2 cylinder separated from the engine during flight. The pilot, flying at 8,500 feet mean sea level, reported that no airports were within gliding distance. He elected to land in a farmer's field, where the airplane collided with a fence and a guy wire.
Engine Examination
Following the accident, the number 2 cylinder and the left magneto were not located. Components including half of the crankcase, two fractured cylinder through-bolts, two cylinder through-bolt nuts with bolt fragments, four cylinder hold-down nuts with stud fragments, a connecting rod cap with its bolt, and a connecting rod nut were submitted for metallurgical examination.
Metallurgical Findings
The studs and through-bolts were arbitrarily numbered clockwise starting at the upper forward stud. All examined studs and through-bolts exhibited fatigue cracking, with stud 3 showing the largest fatigue region. A lip was observed on the crankcase surface corresponding to the forward edge of the cylinder barrel flange, adjacent to the through-bolts. Linear marks aligned with the cylinder axis were found on the aft side of the cylinder hole, indicating sliding contact with the cylinder barrel skirt.
Sectioning of studs 3 and 4 revealed cracks and/or rolling laps at the thread roots. On stud 4, many cracks extended radially before turning. Two studs were removed from cylinder #4, and one displayed sharp thread radii and cracking; notably, this cylinder did not fail.
Engine History
The engine was overhauled on July 6, 2000, at a tach time of 2,440.33 hours. It had accumulated 194.03 hours since the overhaul at the time of the accident.