# NTSB ERA17LA194: Avions Mudry Cie CAP 231, N231X, Lebanon, PA, May 27, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: May 27, 2017, 13:30 local (17:30 UTC) - Place: Lebanon, PA - Coordinates: 40.289165, -76.33361 - Nearby events: https://openairdocs.org/map.md?lat=40.2892&lon=-76.3336&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-aerobatics: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report June 25, 2019 - Report: Approved by Office Director - NTSB office: Eastern Region Aviation - Parties: FAA/FSDO - NTSB case key (mKey): 95259 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA17LA194 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95259/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95259 - Page: https://openairdocs.org/ntsb/ERA17LA194 ## Probable cause The partial separation of one counterweight and the subsequent seizure of the engine due to mechanical interference. Contributing to the partial separation of the counterweight was the overstress fracture of a retaining ring and the fatigue fracture of the counterweight washer for reasons that could not be determined based on the available evidence. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip engine power section](https://openairdocs.org/ntsb-findings/01058520): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [All aircraft, 233 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md) - [Engine (reciprocating): recip engine power section](https://openairdocs.org/ntsb-findings/01058520): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [All aircraft, 233 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md) - [Engine (reciprocating): recip engine power section](https://openairdocs.org/ntsb-findings/01058520): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [All aircraft, 233 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md) - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-aerobatics: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Maneuvering-aerobatics: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md) - [Landing-flare/touchdown: Miscellaneous/other](https://openairdocs.org/ntsb-events/900); cases with it: [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Landing-landing roll: Runway excursion](https://openairdocs.org/ntsb-events/300); cases with it: [All aircraft, 3,643 cases](https://openairdocs.org/ntsb-events/300/sequence.md) - [Landing-landing roll: Nose over/nose down](https://openairdocs.org/ntsb-events/096); cases with it: [All aircraft, 2,287 cases](https://openairdocs.org/ntsb-events/096/sequence.md) ## Analysis The private pilot reported that he was practicing aerobatics near the departure airport and that the airplane was in a 45° nose-up maneuver when he heard a "loud knock" from the engine, followed by a significant "shake." He leveled the airplane, reduced the manifold pressure, and then turned the airplane back toward the airport. Subsequently, the engine rattled and began to shake more, followed by a total loss of power. The pilot's attempts to restart the engine were unsuccessful. He planned a high base leg and sideslip onto the final approach leg of the airport traffic pattern to ensure the airplane would reach the runway. During the landing flare, the airplane floated, touched down beyond the midpoint of the grass runway, and bounced. The pilot applied hard braking, but the airplane rolled off the end of the runway, down an embankment, and nosed over. Postaccident examination of the engine revealed that it was seized and that one counterweight, which was normally secured to the crankshaft at two places, was separated at one location. The retaining ring for one side of one counterweight, which was properly installed, fractured due to overstress, and its associated washer fractured due to reverse bending fatigue. The fracture of these components allowed the roller to separate and jam between the crankcase and crankshaft, which resulted in mechanical interference. The roller's contact with the counterweight bushings and/or counterweight washers could have been caused by a several things; however, because the fatigue crack initiation sites were destroyed by postfracture damage, the root cause for the overstress fracture of the retaining ring and fatigue fracture of the washer associated with the counterweight could not be determined. ## Factual narrative On May 27, 2017, about 1330 eastern daylight time, a privately operated Avions Mudry CIE CAP 231, N231X, was substantially damaged during a forced landing at the Keller Brothers Airport (08N), Lebanon, Pennsylvania. The private pilot was not injured. The airplane was being operated under the provisions of 14 Code of Federal Regulations Part 91as a personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight which originated about 10 minutes earlier from 08N.The pilot stated that he was over 08N in the active aerobatics box practicing maneuvers, and had completed a hammerhead, a Cuban 8, another hammerhead, and two verticals. He was in a 45° nose-up climb maneuver when he heard a loud knock from the engine followed by a significant "shake." He leveled the airplane, reduced manifold pressure and announced that he was returning to 08N over the common traffic advisory frequency. As he turned towards the runway, the engine rattled and shook more, and then stopped producing power. The pilot attempted to restart the engine but was unsuccessful. He planned a high base leg and side slip onto the final approach leg of the airport traffic pattern to assure that the airplane would reach the runway. While gliding, he determined that the airplane felt unstable under 100 mph, and conducted the approach at a speed of 100 mph. During the subsequent landing flare, the airplane floated, touched down beyond midpoint of the nearly 2,700 ft long grass runway, and bounced. The pilot applied hard braking; however, the airplane rolled off the end of the runway, down an embankment, and nosed over. Examination of the AEIO-540-L1B5D engine following recovery revealed the engine was seized, and there was a hole in the crankcase near the crankcase parting line below the intake and exhaust valve pushrods. The No. 4 cylinder connecting rod cap was fractured, a nut from the No. 4 connecting rod was recovered from inside the crankcase, and the No. 4 exhaust valve cam follower was found inside the lower engine cowling. Considerable force was required to break the crankshaft free. Disassembly examination of the engine with FAA oversight revealed that one counterweight, which was normally secured to the crankshaft at two places, was separated at one location. The retaining ring, washer, and roller associated with the separated side of the counterweight were separated. The separated washer and retaining ring were fractured and were found in the oil sump, while the roller was jammed between the crankshaft and engine crankcase. The separated roller and pieces of the fractured retaining ring and washer were retained. The remaining counterweight roller retaining rings were properly installed in the counterweights. Additional retained components consisted of the other counterweight, a remnant of a connecting rod bearing, a fractured connecting rod cap with fractured section of connecting rod bolt, mating section of fracturedconnecting rod bolt without a nut, a nut associated with a connecting rod that was found from the top of the engine, and a nut associated with a connecting rod that was found inside the engine. The fractured components were forwarded to the NTSB Materials Laboratory for detailed examination.. Examination of the fractured pieces of the retaining ring associated with the counterweight revealed the fracture surfaces were consistent with overstress fracture, and the surfaces were consistent with the fractured retaining ring still present in the counterweight assembly. The general circular fracture features were consistent with rotational loading. The fracture surface of one piece of the fractured washer exhibited progressive features (such as crack arrest marks and radial patterns), consistent with reverse bending fatigue, with crack initiation on the outside faces of the washer. However, the fatigue crack initiation sites were destroyed by post-fracture damage. The outer surface of the roller exhibited both axial and radial sliding wear. No other pre-existing fracture was noted on any of the other submitted components. Examination of all circlips revealed evidence they were properly installed. Review of the maintenance records revealed the engine was last overhauled on November 5, 2009. As part of the overhaul, new counterweight bushings, washers, and retaining rings were installed. The engine had accumulated about 242 hours since overhaul at the time of the accident. According to a representative of the engine manufacturer, when operational conditions or non-standard movement cause the rollers to slam against the counterweight washers, impact bending forces on the counterweight washers can and does occur, sometimes causing fatigue cracks to initiate on the outer face of the washers (typically at the corners). The representative indicated that operational considerations for non-standard movement and impact loading by the rollers against the counterweight bushings and/or counterweight washers include: 1. Sudden stoppage, such as prop strike etc.; 2) Sudden accelerations and decelerations as in rapid throttling; 3) Counterweight Detuning; 4) Operating at excessive power/overloading; 5) Operating under detonation conditions; 6) Abnormally high torsional vibrations, and; 7) Improper installation/assembly (wrong part numbers of rollers, or miss-matched rollers in the counterweights). ## Aircraft - Registration: N231X (not matched to a registry record) - Reported make and model: AVIONS MUDRY CIE CAP 231 (UNDESIGNAT) - Category: Airplane - Serial number: 12 - Year built: 1990 - Airframe hours: 1081 - Engines: LYCOMING AEIO-540-L1B5 300 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, March 15, 2017, 3 hours before - Departed: 08N, Lebanon, PA - Destination: 08N, Lebanon, PA - Airport: 08N, Keller Brothers Airport, runway 25, 2,692 × 120 ft, grass/turf - Equipment: Electronic primary flight display, ADS-B, Onboard weather ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 57; injuries: none; private, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review July 11, 2015; seat: single; restraint: 5-point; flight hours: 2,308 total, 57 in this make and model, 2,232 as pilot in command, 3 in the last 90 days, 0.2 in the last 30 days, 0.2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 230° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: 4,700 ft overcast - Temperature: 70 °F, dew point 57 °F - Altimeter: 29.90 inHg - Observed at: LNS, 10 nm away ## 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 20170527007089A](https://openairdocs.org/incident/20170527007089A), May 27, 2017: Avions Mudry Cie CAP 231, Lebanon, PA, Substantial damage. At approximately 1330 on may 27, 2017 the commercial pilot took off from 08N and climbed into the active aerobatic box for aerobatic maneuver practice. The… ## Docket (8 files) The files NTSB released with the investigation on April 17, 2019, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95259. 19.2 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471950&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - FAA Record of Conversation with Pilot-In-Command (item 2, .PDF, 303 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471951&FileExtension=.PDF&FileName=FAA%20Record%20of%20Conversation%20with%20Pilot-In-Command-Master.PDF - FAA Inspector Statement (item 3, .PDF, 1 photo, 346 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471952&FileExtension=.PDF&FileName=FAA%20Inspector%20Statement-Master.PDF - Maintenance Log Excerpt (item 4, .PDF, 277 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471953&FileExtension=.PDF&FileName=Maintenance%20Log%20Excerpt-Master.PDF - Investigative Photographs (item 5, .PDF, 7 photos, 2.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471954&FileExtension=.PDF&FileName=Investigative%20Photographs-Master.PDF - Materials Laboratory Factual Report (item 6, .PDF, 10.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471955&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Materials Laboratory Addendum Report (item 7, .PDF, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471956&FileExtension=.PDF&FileName=Materials%20Laboratory%20Addendum%20Report-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15, and NTSB Evidence Control Form with Separate Parts Listing (item 8, .PDF, 196 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471957&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15,%20and%20NTSB%20Evidence%20Control%20Form%20with%20Separate%20Parts%20Listing-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.