Accident Description
On May 11, 2015, at approximately 2241 central daylight time, a Piper PA-28-161 airplane, registration N3024S, was substantially damaged during a forced landing near Ranger, Texas. The flight was operated by Delta Qualiflight Academy under 14 Code of Federal Regulations Part 91 as a training flight. Night visual meteorological conditions prevailed, and no flight plan was filed. The flight departed from Abilene Regional Airport (ABI), Abilene, Texas, at about 2210 and was destined for Cleburne Regional Airport (CBN), Cleburne, Texas.
While in cruise at 5,500 feet above mean sea level, the pilot reported hearing two knocks from the engine, followed by propeller stoppage and a total loss of power. After unsuccessful attempts to regain engine power, the pilot executed a forced landing onto a field. During the landing, the left wing was damaged due to impact with a tree.
Engine Examination
On-site inspection revealed two holes on the top of the engine case. The aircraft was recovered to Air Salvage of Dallas, where the engine was removed for examination. The crankshaft could only rotate 270 degrees before encountering a hard lock. All cylinders were removed except for the number 3 cylinder, which had damage to its skirt area. Teardown revealed that the number 4 piston crown and connecting rod were fractured, with metallic debris throughout the engine case and oil filter. The number 4 connecting rod displayed substantial impact damage but no discoloration or signs of high heat. Fragments of the number 4 piston crown, connecting rod, piston wrist pin, and piston pin plug were sent to the NTSB Materials Laboratory for further examination.
Laboratory Findings
Laboratory examination identified two thumbnail-shaped fatigue cracks on the underside of the piston crown, each located near an oil drain hole along the top oil groove. The cracks had propagated from initiation sites along the circumferential oil groove, at or near the oil drain hole. Post-fracture smearing damage prevented determination of the cause of the fatigue crack initiation.
Maintenance History
The engine was a Lycoming O-320-D3G, serial number L-10238-39A. The airframe had accumulated a total time of 10,672 hours at the last inspection on May 4, 2015. The engine had a total time of 9,309 hours and 2,135 hours since the last overhaul, which included replacement of pistons and rings. During the last engine inspection, approximately 11 hours before the accident, the oil and filter were changed. An oil analysis was not performed during this or previous inspections since the last overhaul. According to Lycoming Engines Service Instruction 1009AW, dated February 24, 2014, a 200-hour extension to the recommended 2,000-hour time between overhaul (TBO) was available for engines in frequent use (40+ hours per month). The engine usage pattern did not meet this requirement. The director of maintenance at Delta Qualiflight Academy stated that the organization typically overhauled engines at about 3,000 hours; however, engine overhaul times are not mandated under 14 CFR Part 91.