# NTSB CEN17LA292: Piper PA 46 350P, N786MD, Tahlequah, OK, July 30, 2017 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: July 30, 2017, 18:59 local (23:59 UTC) - Place: Tahlequah, OK - Coordinates: 35.930278, -95.004447 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.9303&lon=-95.0044&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: Minor injuries - Injuries: 4 minor - Status: Completed, report November 6, 2019 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Lycoming Engines, FAA Oklahoma City FSDO - NTSB case key (mKey): 95701 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN17LA292 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95701/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95701 - Page: https://openairdocs.org/ntsb/CEN17LA292 ## Probable cause The total loss of engine power, which resulted from fatigue failure of two engine through bolts and the No. 2 cylinder attachment studs due to the lack of sufficient clamping force. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Piper PA 46-350P, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=7104620), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Piper PA 46-350P, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=7104620), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Incorrect service/maintenance; cases with it: [Piper PA 46-350P, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=7104620), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) - [Maintenance](https://openairdocs.org/ntsb-findings/02062000): Personnel issues › Task performance · Maintenance personnel; cases with it: [Piper PA 46-350P, 3 cases](https://openairdocs.org/ntsb-findings/02062000/cases.md?model=7104620), [All aircraft, 143 cases](https://openairdocs.org/ntsb-findings/02062000/cases.md) - [Object/animal/substance](https://openairdocs.org/ntsb-findings/03022000): Environmental issues › Physical environment · Contributed to outcome; cases with it: [Piper PA 46-350P, 1 case](https://openairdocs.org/ntsb-findings/03022000/cases.md?model=7104620), [All aircraft, 224 cases](https://openairdocs.org/ntsb-findings/03022000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Piper PA 46-350P, 9 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=7104620), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Piper PA 46-350P, 8 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=7104620), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Piper PA 46-350P, 40 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=7104620), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The private pilot reported that he was in cruise flight when the engine experienced a total loss of power. Oil covered the windshield and smoke filled the cockpit, making it difficult for him to see out of the airplane. He attempted to land at an airport but conducted a forced landing to a field about 300 ft short of the runway. The right wing separated from the fuselage when it hit a hay bale. The examination of the engine revealed a large hole in the engine case near the No. 2 cylinder. The engine maintenance records indicated that when the engine had a major overhaul about 8 years before the accident, the engine crankcase was repaired at a facility specializing in crankcase repairs. The facility typically used glass bead media to clean engine crankcases instead of "mildly abrasive organic substances" as required by the engine manufacturer. About 1 year before the accident, about 825 hours since the major overhaul, all 6 cylinders were replaced. The engine failure occurred about 198 hours after the cylinders were replaced. The metallurgical examination of the eight through bolts revealed that two of the through bolts and the No. 2 cylinder studs had fracture surfaces that were consistent with fatigue. The fatigue in the studs and through bolts likely resulted from insufficient clamping force due to insufficient torque applied to the attachment nuts during installation or could have developed in service as asperities on the clamping surfaces worked down over time, leading to a reduction in clamping force. ## Factual narrative On July 30, 2017, about 1859 central daylight time, a Piper PA-46-350P, N786MD, sustained substantial damage during a forced landing to a field near the Tahlequah Municipal Airport (TQH), Tahlequah Oklahoma, after a complete loss of engine power. The pilot and three passengers received minor injuries. The airplane was owned by ALP Air LLC and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions existed near the accident site at the time of the flight, and a visual flight rules (VFR) flight plan had been filed. The flight departed from the Joplin Regional Airport (JLN), Joplin, Missouri, about 1800, and was en route to Addison Airport (ADS), Addison, Texas. The pilot reported he was receiving VFR flight following at 12,500 ft above mean sea level (msl) when the engine started to lose power. The pilot turned toward TQH since it was the nearest airport, and he flew about 6 to 8 nautical miles before the engine stopped producing power. Oil covered the windshield and smoke filled the cockpit, making it difficult to see out of the airplane. The pilot maintained communications with the Fort Worth Center as he glided toward TQH. Once over the airport, he made about 1 1/2 left circles as he prepared to land on the runway 35. However, the landing gear indicator lights indicated that the nose landing gear was not in the fully extended position during the landing approach. He attempted to manually lower the landing gear but without success. While attempting to lower the nose landing gear, he determined that there was insufficient altitude to make it to the runway, so he executed a forced landing to a field about 300 ft short of the runway. During the landing, the right wing struck a hay bale which separated the wing from the fuselage. The engine was sent to an engine overhaul facility for an engine teardown and examination. The examination revealed that there was a large hole in the engine case near the No. 2 cylinder. The examination of the pistons, piston connecting rods and bearings, and main bearings revealed heat distress signatures consistent with a lack of lubrication. The cylinder attachment flange of the No. 2 cylinder to the engine case exhibited fretting and a metal ridge buildup on the surface of the flange. All 8 through bolts, including 2 through bolts which were fractured, and 2 pieces of the No. 2 cylinder attachment flange with 2 fractured cylinder attachment studs, were sent to the National Transportation Safety Board's (NTSB) Material Laboratory for examination. The NTSB Materials Laboratory examination of the No. 2 cylinder attachment studs revealed that there were crack arrest lines and ratchet marks on the stud fracture surface, features consistent with fatigue. The fracture features in the fatigue regions had a relatively rough appearance consistent with relatively high cyclic stress. The examination of the fracture surfaces of the through bolts revealed that there wererelatively smooth areas-oriented transverse to the bolt axis observed on one side of the thread consistent with fatigue fracture. The fatigue regions transitioned to rougher matte gray features with a shear lip opposite from the fatigue region, features consistent with overstress fracture across the majority of the cross section. The machined surfaces of the crank case pieces, including the cylinder attachment flange, the crank case split line, and the cam shaft bore surfaces, all had a gritty or frosted visual appearance. When viewed under an optical stereoscope, the surfaces were rough with generally semispherical pits or craters. Crater-like features were also observed on the cylinder flange stud threads. The thread of the through bolts were free of pit or crater-like features. The Lycoming Engines Overhaul Manual – Avco Lycoming Direct Drive Aircraft Engines, Revision 14, (July 2011), in the section relating to the cleaning of the crankcase, states the following: "When grit-blasting parts[,] do not use sand or any metallic abrasives. It is recommended instead that mildly abrasive organic substances such as rice, baked wheat, plastic pellets, or crushed walnut shells be used. All machined surfaces must, of course, be adequately masked…" The engine maintenance records indicated that the engine had been overhauled on June 5, 2009, and the logbook entry stated that the total engine time was 627.2 hours with 000.0 hours since major overhaul (SMOH). (The maintenance records did not indicate the reason why the engine was overhauled) The logbook entry indicated that the company who performed the engine overhaul had sent the crankcase to another company to be repaired. The company that repaired the crankcase indicated that the work order for the repair of the case halves was no longer available, but the receiving and shipping documents indicated that the billing was for inspection and dimension checks only, and that they had shipped the crankcase back to the customer in 2007. The facility indicated that it used glass bead media to grit blast engine cases. The engine maintenance records indicated that following maintenance was performed on July 1, 2016: "Removed all 6 cylinders. Installed 6 new Lycoming cylinder kit assemblies P/N 05K21262. Checked all ring gaps and valve clearances. Reassembled with all new gaskets and seals…" The engine total time was 1,452.2 hours with 825 hours SMOH. The engine failure occurred about 198 hours after the cylinders were replaced. ## Aircraft - Registration: [N786MD](https://openairdocs.org/aircraft/N786MD), registered now, S/N 4636156, built 1998 (OpenAirDocs) - Reported make and model: PIPER PA 46 350P - Registry model: [Piper PA 46-350P](https://openairdocs.org/model/piper-pa-46-350p) (registry code 7104620) (OpenAirDocs) - Registry engine: [Lycoming TI0-540 series](https://openairdocs.org/engine/lycoming-ti0-540-series) (registry code 41533, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 4636156 - Year built: 1998 - Airframe hours: 4103 - Engines: LYCOMING TI0-540-AE2A 350 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, July 1, 2016 - Departed: JLN, Joplin, MO - Destination: ADS, Dallas, TX - Flight plan: VFR - Airport: TQH, Tahlequah Municipal Airport, runway 35, 5,001 × 75 ft, asphalt - Equipment: Electronic primary flight display, Auto-pilot, ADS-B, Satellite tracking device, Onboard weather ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: minor; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, without waivers/limitations; seat: left; restraint: 3-point; flight hours: 559 total, 140 in this make and model ## Weather - Conditions: Visual (VMC), Dusk - Wind: 50° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 86 °F, dew point 59 °F - Altimeter: 30.05 inHg - Observed at: TQH ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20170730015649A](https://openairdocs.org/incident/20170730015649A), Jul 30, 2017: Piper PA 46-350P, Tahlequah, OK, Substantial damage. Pilot and three passengers departed joplin (kjln) at 18:06 central time. Climbed to 12500. About 10 min. After obtaining 12500, pilot noticed a change in the… ## Docket (8 files) The files NTSB released with the investigation on July 15, 2019, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95701. 22.9 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 4.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473550&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Materials Laboratory Factual Report 17-083 (item 2, .PDF, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473551&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2017-083-Master.PDF - Engine Teardown Photographs (item 3, .PDF, 36 photos, 12.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473552&FileExtension=.PDF&FileName=Engine%20Teardown%20Photographs-Master.PDF - Engine Logbook Excerpts (item 4, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473553&FileExtension=.PDF&FileName=Engine%20Logbook%20Excerpts-Master.PDF - Lycoming Overhaul Manual Excerpts (item 5, .PDF, 213 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473554&FileExtension=.PDF&FileName=Lycoming%20Overhaul%20Manual%20Excerpts-Master.PDF - Lycoming SB533C (item 6, .PDF, 600 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473555&FileExtension=.PDF&FileName=Lycoming%20SB533C-Master.PDF - NTSB Party Form (item 7, .PDF, 242 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473556&FileExtension=.PDF&FileName=NTSB%20Party%20Form-Master.PDF - NTSB Wreckage Release (item 8, .PDF, 533 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40473557&FileExtension=.PDF&FileName=NTSB%20Wreckage%20Release-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.