Accident Overview
On August 4, 2016, at 2004 eastern daylight time, a Cessna 150L, registration N10770, impacted terrain in a soybean field near Russellville, Ohio, following a loss of engine power. The private pilot on board sustained a minor injury, while the pilot-rated passenger was not injured. The airplane, registered to and operated by a private individual under 14 CFR Part 91, sustained substantial damage. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from Brown County Airport (KGEO), Georgetown, Ohio, at about 1945.
Events Leading to the Forced Landing
According to the pilots, while descending for landing, they heard a loud "bang" and the engine began running rough. Unable to maintain altitude, they executed a forced landing in a soybean field. The airplane struck a ditch and nosed over.
Engine Examination
Examination of the engine revealed that the number 2 cylinder had completely separated between the flange and the head. The cylinder was shipped to the National Transportation Safety Board's Materials Laboratory for examination.
Metallurgical Analysis
The Materials Laboratory's Factual Report (16-110) detailed that the cylinder had fractured about the circumference of the seventh cooling fin valley through approximately 40% of the cross section. The fracture was relatively flat, exhibited a reflective luster, and was oriented in the direction of piston movement. The fracture surface showed crack arrest marks consistent with progressive fatigue cracking. Additionally, several cooling fin flange surfaces exhibited small circular features consistent with pitting. An initial thumbnail crack was present adjacent to the crack initiation site, with radial marks and crack arrest marks propagating outward. Fatigue striations were present, consistent with fatigue crack propagation. The crack initiation site on the head side of the fracture surface consisted of three stepped features containing ratchet marks between the steps, consistent with multiple crack initiation sites that had coalesced as the fatigue cracks grew and propagated inward. The mating fracture surface (open piston side) exhibited three ridge shapes, consistent with the previously observed ratchet marks.
Maintenance History
According to engine maintenance records, cylinder number 2 (serial number 0049), manufactured by Superior Air Parts, Coppell, Texas, was overhauled on April 14, 2000. The overhaul included grinding the intake and exhaust valve seats, grinding the intake valve, replacing the intake and exhaust guides, and replacing the exhaust valve. The cylinder was then pressure checked and returned to service.