# NTSB CEN23LA188: Cessna 172, N5550J, Flower Mound, TX, May 17, 2023 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: May 16, 2023, 19:12 local (May 17, 2023, 00:12 UTC) - Place: Flower Mound, TX - Coordinates: 33.058155, -97.204559 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.0582&lon=-97.2046&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-descent: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 174544 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN23LA188 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/174544/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=174544 - Page: https://openairdocs.org/ntsb/CEN23LA188 ## Probable cause The fatigue failure of the rocker arm which resulted in a partial loss of engine power. Contributing was the airplane operator’s failure to inspect the rocker arm in accordance with the engine manufacturer’s service bulletin. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Cessna 172N, 13 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=2072434), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Inspection: scheduled/routine inspection](https://openairdocs.org/ntsb-findings/02061520): Personnel issues › Task performance · Maintenance personnel; cases with it: [Cessna 172N, 1 case](https://openairdocs.org/ntsb-findings/02061520/cases.md?model=2072434), [All aircraft, 167 cases](https://openairdocs.org/ntsb-findings/02061520/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-descent: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Cessna 172N, 11 cases](https://openairdocs.org/ntsb-events/340/sequence.md?model=2072434), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) ## Analysis The flight instructor reported the engine began to run rough and lose power as they descended from cruise flight. Unable to restore full engine power, the instructor performed a forced landing to a field. During the landing the airplane collided with a barbed wire fence and trees, resulting in substantial damage to the wings and fuselage. A postaccident examination of the engine found that one of the rocker arms (p/n LW-15014) had failed. A metallurgical examination revealed a portion of the rocker arm adjacent to the oil squirt hole was pressed inwards in the direction the pushrod drives the rocker arm. Fatigue cracks emanated from the circumference of the oil squirt hole. Rocker arms with similar damage have been observed previously by the engine manufacturer. Lycoming Service Bulletin No. 639 (dated January 17, 2020) details the damage anticipated to the rocker arm oil squirt hole due to contact with the mating pushrod and provides an inspection methodology. Radial cracks are highlighted as warning signs that damage is occurring and once observed, the rocker arm should be replaced. In the subject rocker arm, the missed and/or unaddressed radial cracks likely led to the circumferential fatigue cracking and subsequent failure of the rocker arm and pushrod assembly. The airplane operator was under the impression that the service bulletin only applied to engines overhauled by Lycoming. The service bulletin states that the models affected are “O-320-H2AD, O, LO, TO, LTO-360-E1A6D new, rebuilt, or overhauled engines shipped from Lycoming since June 2017 with less than 500 hours of operation or engines with less than 500 hours of operation since rocker arm replacement.” The service bulletin should then be complied with “at next scheduled oil change, then every 50 hours until 500 hours of engine operation.” The engine had accrued about 173 hours since the overhaul during which the rocker arms were replaced. ## Factual narrative On May 16, 2023, about 1912 central daylight time, a Cessna 172N, N5550J, was substantially damaged when it was involved in an accident near Flower Mound, Texas. The instructor and student pilot were not injured. The airplane was operated under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. The instructor reported that, while descending from cruise flight, the engine started to run rough. The engine sustained a partial loss of engine power with an associated drop in rpms. Unable to restore engine power, the instructor performed a forced landing to a field. During the landing the airplane collided with a barbed wire fence and trees, resulting in substantial damage to the wings and fuselage. The engine was examined under the auspices of inspectors of the Federal Aviation Administration. The examination found that one of the rocker arms (p/n LW-15014) had failed. The part was examined by the National Transportation Safety Board Materials Laboratory. The pushrod was removed from the rocker arm in the laboratory. A portion of the rocker arm adjacent to the oil squirt hole was pressed inwards in the direction the pushrod drives the rocker arm. A fracture surface was visible on the inner surface of the rocker arm extending circumferentially around the hole. The circumferential fracture surface was relatively flat with visible crack arrest marks consistent with fatigue. The crack arrest marks indicated the fatigue emanated from the outboard side of the rocker arm. There were three radial fractures branching from the circumferential fracture (one nearly aligned with the centerline of the outboard curved geometry of the rocker arm, one diametrically opposite the first, and the last about halfway between the other two). The macro fracture surface features were consistent with the fatigue cracking progressing circumferentially from that same location. This is consistent with the radial crack occurring before the circumferential cracking. Rocker arms with similar damage have been observed previously by the manufacturer. Lycoming Service Bulletin No. 639 (dated January 17, 2020) details the damage anticipated to the rocker arm oil squirt hole due to contact with the mating pushrod and methodology to inspect for it. Radial cracks are highlighted as warning signs that damage is occurring and once observed, the rocker arm should be replaced. In a telephone conversation with a representative of the airplane owners, the representative was under the impression that Lycoming Service Bulletin No. 639 only applied to engines overhauled by Lycoming. The service bulletin states that the models affected are “O-320-H2AD, O, LO, TO, LTO-360-E1A6D new, rebuilt, or overhauled engines shipped from Lycoming since June 2017 with less than 500 hours of operation or engines with less than 500 hours of operation since rocker arm replacement.” The service bulletin should then be complied with “at next scheduled oil change, then every 50hours until 500 hours of engine operation.” The engine had accrued about 173 hours since the overhaul during which the rocker arms were replaced. ## Aircraft - Registration: [N5550J](https://openairdocs.org/aircraft/N5550J), registered now, S/N 17273818, built 1980 (OpenAirDocs) - Reported make and model: CESSNA 172 (N) - Registry model: [Cessna 172N](https://openairdocs.org/model/cessna-172n) (registry code 2072434) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17273818 - Year built: 1980 - Engines: Lycoming O-320-H2AD 100 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Registered owner: Optima Aviation LLC DBA - Airworthiness certificate: Standard, Normal - Departed: Denton, TX - Destination: Roanoke, TX - Equipment: ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 28; injuries: none; flight instructor; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; seat: right ## Weather - Conditions: Visual (VMC), Day - Wind: 360° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: 25,000 ft broken - Temperature: 75 °F, dew point 57 °F - Altimeter: 29.93 inHg - Observed at: KAFW, 7 nm away - METAR: KAFW 162353Z 36008KT 10SM FEW045 FEW060 BKN250 24/14 A2993 RMK AO2 SLP124 T02390144 10267 20239 56021 ## 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 20230516012129A](https://openairdocs.org/incident/20230516012129A), May 16, 2023: Cessna 172N, Roanoke, TX, Substantial damage. CFI and student pilot returned to home base from dto. Once over mid-field at Northwest Regional Airport (52F) 1000' AGL, aircraft engine lost power and began… ## Docket (9 files) The files NTSB released with the investigation on October 23, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=174544. 5.2 MB in all. - Record of conversation FAA (item 1, PDF, 1 page, 89 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16849006&FileExtension=pdf&FileName=Record%20of%20Conversation%20FAA-Rel.pdf - Memorandum of record, flight instructor's statement (item 2, PDF, 1 page, 78 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17731169&FileExtension=pdf&FileName=Memorandum%20of%20Record,%20Pilot%20Statement-Rel.pdf - Record of conversation 17 August 2023 (item 3, PDF, 1 page, 64 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17140295&FileExtension=pdf&FileName=ROC%2017%20Aug%2023-Rel.pdf - Photos (item 4, PDF, 4 pages, 3 photos, 916 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16848331&FileExtension=pdf&FileName=CEN23LA188%20Photos%203-Rel.pdf - Material laboratory factual report (item 5, PDF, 9 pages, 5 photos, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16848097&FileExtension=pdf&FileName=23-107%20Materials%20Laboratory%20Factual%20Report-Rel.pdf - Parts ordered (item 6, PDF, 2 pages, 932 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16849016&FileExtension=pdf&FileName=Parts%20Order_Redacted-Rel.pdf - Overhaul log entry (item 7, PDF, 2 pages, 744 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16848646&FileExtension=pdf&FileName=Engine%20Overhaul%20Log%20Entry_Redacted-Rel.pdf - NTSB form 6120 not returned (item 8, PDF, 1 page, 46 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16857987&FileExtension=pdf&FileName=Form%206120%20not%20returned-Rel.pdf - Lycoming service bulletin no. 639 (item 9, PDF, 3 pages, 318 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17139692&FileExtension=pdf&FileName=SB639%20Rocker%20Arm%20Inspection-Rel.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.