Accident Summary
On July 30, 2017, about 1859 central daylight time, a Piper PA-46-350P, registration N786MD, sustained substantial damage during a forced landing in a field near Tahlequah Municipal Airport (TQH), Tahlequah, Oklahoma. The airplane experienced a complete loss of engine power while en route from Joplin Regional Airport (JLN), Joplin, Missouri, to Addison Airport (ADS), Addison, Texas. The pilot and three passengers received minor injuries. The flight was operated under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed.
The pilot reported that while receiving VFR flight following at 12,500 feet above mean sea level, the engine began to lose power. He turned toward TQH, the nearest airport, and flew about 6 to 8 nautical miles before the engine stopped producing power. Oil covered the windshield and smoke filled the cockpit, impairing visibility. The pilot maintained communication with Fort Worth Center as he glided toward the airport. After reaching the airport, he made about 1.5 left circles to prepare for landing on runway 35. However, the landing gear indicator lights showed that the nose landing gear was not fully extended. Attempts to manually lower the gear were unsuccessful. Determining insufficient altitude to reach the runway, the pilot executed a forced landing to a field about 300 feet short of the runway. During the landing, the right wing struck a hay bale, separating the wing from the fuselage.
Engine Examination
The engine was sent to an overhaul facility for teardown and examination. Investigators found a large hole in the engine case near the No. 2 cylinder. The pistons, connecting rods, bearings, and main bearings exhibited heat distress consistent with a lack of lubrication. The No. 2 cylinder attachment flange showed fretting and a metal ridge buildup. Eight through bolts, including two fractured bolts, and two pieces of the No. 2 cylinder attachment flange with two fractured cylinder attachment studs were examined by the National Transportation Safety Board's Materials Laboratory.
The NTSB examination revealed crack arrest lines and ratchet marks on the cylinder attachment stud fracture surfaces, features consistent with fatigue. The fatigue regions had a relatively rough appearance, indicating relatively high cyclic stress. The through-bolt fracture surfaces showed relatively smooth areas transverse to the bolt axis on one side of the thread, consistent with fatigue, transitioning to overstress fracture across most of the cross section. The crankcase machined surfaces had a gritty or frosted visual appearance; under stereoscope, they were rough with generally semispherical pits or craters. Similar crater-like features were observed on the cylinder flange stud threads but not on the through-bolt threads.
The Lycoming Engines Overhaul Manual (Revision 14, July 2011) specifies that when grit-blasting parts, sand or metallic abrasives must not be used; instead, mildly abrasive organic substances such as rice, baked wheat, plastic pellets, or crushed walnut shells are recommended, with all machined surfaces adequately masked.
Maintenance History
Engine maintenance records indicated that the engine was overhauled on June 5, 2009, with total engine time 627.2 hours and 0.0 hours since major overhaul (SMOH). The overhaul was performed by a company that sent the crankcase to another company for repair. The repair company's work order was unavailable, but shipping documents indicated billing for inspection and dimension checks only, and the crankcase was shipped back to the customer in 2007. The facility reported using glass bead media to grit blast engine cases.
On July 1, 2016, maintenance was performed that included removal of all six cylinders and installation of six new Lycoming cylinder kit assemblies. At that time, engine total time was 1,452.2 hours with 825 hours SMOH. The engine failure occurred about 198 hours after the cylinder replacement.