CEN15LA228

The commercial pilot reported that, during cruise flight on a night training flight, he heard "two knocks" coming from the engine, followed by a total loss of power. After attempting to restart the engine without success, the pilot executed a forced landing onto a field, during which the airplane impacted a tree. Teardown of the engine revealed that the No. 4 piston crown and connecting rod were fractured. Laboratory examination revealed two thumbnail-shaped fatigue cracks on the piston crown's underside near an oil drain hole along the top oil groove on the piston circumference. The fatigue cracks had propagated from initiation sites along the circumferential oil groove at or near the oil drain hole. The cause of the initiation of the fatigue cracks could not be determined due to postfracture smearing damage.

On May 11, 2015, about 2241 central daylight time, a Piper PA-28-161 airplane, N3024S, was substantially damaged during a forced landing near Ranger, Texas. The pilot was seriously injured and the passenger was not injured. The airplane was registered to a private individual and operated by Delta Qualiflight Academy under the provisions of 14 Code of Federal Regulations Part 91 as a training flight. Night visual meteorological conditions prevailed for the flight, with no flight plan filed. The flight departed from Abilene Regional Airport (ABI), Abilene, Texas about 2210 and was destined for Cleburn Regional Airport (CBN), Cleburn, Texas. While in cruise at 5,500 above mean sea level, the pilot reported that he heard "two knocks" from the engine, followed by propeller stoppage and a total loss of power. After attempting without success to regain engine power, the pilot executed a forced landing onto a field, during which the left wing was damaged due to impact with a tree. On-site inspection of the engine revealed two holes on the top of the engine case. The airplane was recovered to the facilities of Air Salvage of Dallas and the engine was subsequently removed for examination. The crank shaft would only rotate 270 degrees before a hard lock was observed. The cylinders were removed except for the number 3 cylinder, which had damage to its skirt area. Teardown revealed the number 4 piston crown and connecting rod were fractured, with metallic debris throughout the engine case and oil filter. Although the number 4 connecting rod displayed substantial impact damage, there was no discoloration or signs of high heat. The number 4 piston crown, pieces of the connecting rod, piston wrist pin, and piston pin plug remnants were shipped to the National Transportation Safety Board Materials Laboratory for further examination. Laboratory examination revealed two thumbnail-shaped fatigue cracks on the piston crown underside, each located near an oil drain hole along the top oil groove on the piston circumference. Closer examination of the crack features found that they 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 initiation of the fatigue cracks. The engine was a Lycoming O-320-D3G, with serial number L-10238-39A. The airframe had 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 the pistons and rings. During the last engine inspection, which occurred about 11 hours prior to the accident, the engine oil and filter were changed. An oil analysis was not performed during this or previous inspections since the last overhaul. Lycoming Engines Service Instruction 1009AW, dated February 24, 2014, which was current at the time of the accident, stated "if an engine is being used in 'frequent' typeservice and accumulates 40 hours or more per month, and has been so operated consistently since being placed in service, add 200 hours to time between overhaul (TBO) time". The engine usage pattern did not meet the requirement for a 200-hour extension past the normally recommended 2,000 hour TBO. The director of maintenance at Delta Qualiflight Academy stated that his organization typically overhauled engines at about 3,000 hours. Engine overhaul times are not mandated in 14 Code of Federal Regulations Part 91.