Accident Overview
On May 11, 2015, about 2015 central daylight time, a Piper PA-25-235, registration N7279Z, experienced an engine overheating event and subsequent partial power loss. The pilot could not maintain altitude and executed an emergency landing on a dirt road near Omega, Oklahoma. During the landing roll, the left wing contacted a fence, causing damage to the leading edge and spinning the aircraft. The pilot reported no injuries. The airplane was operated under 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions were present, and no flight plan was filed. The flight originated from Watonga Regional Airport (KJWG) around 1930.
Engine Examination
On June 17, 2015, the engine was examined at Air Salvage of Dallas in Lancaster, Texas, under National Transportation Safety Board supervision. The investigator found metal particles in the engine oil, oil pump, and oil sump. On July 31, further partial disassembly revealed a broken number 2 compression piston ring on the number 4 piston. The number 5 cylinder showed chrome peeling from the cylinder wall. The piston rings were also chrome plated. A light oil leak was observed on the top back section of the engine, and the oil was black with a burnt odor.
Maintenance History
According to the maintenance logbook, the engine, a Lycoming O-540-G1A5 (serial number L-23273-40), was manufactured on July 9, 1981. It was initially installed in N8731L on August 1, 1981, and removed on February 13, 1992, with 858.9 hours total time. On September 20, 1993, it was installed in N7279Z; tachometer time was 4,233.0 hours and engine total time 859.9 hours. On August 1, 2006, the engine was overhauled using six ECI nickel carbide cylinders; tachometer time was 5,042.0 hours and total time 1,613.81 hours. On April 28, 2011, six new ECI nickel carbide cylinders were installed; tachometer 5,252.5 hours, total time 1,824.31 hours. On July 5, 2013, cylinders 1 and 2 were removed, honed, re-ringed, and reinstalled; tachometer 5,320.71 hours, total time 1,892.52 hours. Routine annual and 100-hour inspections were conducted between entries. At the accident, tachometer read 5,448.16 hours, with engine total time 2,019.97 hours since new.
Metallurgical Findings
Cylinder and piston number 5 and associated rings were sent to the NTSB Materials Laboratory. A report dated February 22, 2016, indicated the cylinder was manufactured by Engine Components, Inc. (ECi). The coating on the upper cylinder barrel had peeled. Coating thickness was about 0.0058 inch. Energy dispersive spectroscopy (EDS) of the base metal showed major iron and minor nickel, chromium, silicon, and carbon, consistent with a steel alloy. The coating spectrum showed major nickel and minor silicon, carbon, and oxygen, consistent with nickel silicon carbide. A wedge test using a screwdriver tip revealed the inner coating could be peeled from the top half of the barrel with easy to moderate effort, but could not be removed from the bottom half.