# NTSB ERA24LA271: Cessna 172, N734XT, Hernando, FL, June 21, 2024 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 21, 2024, 12:10 local (16:10 UTC) - Place: Hernando, FL - Coordinates: 28.569722, -82.655278 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=28.5697&lon=-82.6553&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Eastern Region Aviation - Parties: Lycoming Engines, FAA/FSDO - NTSB case key (mKey): 194519 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA24LA271 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/194519/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=194519 - Page: https://openairdocs.org/ntsb/ERA24LA271 ## Probable cause The improper installation of a cylinder rocker stud by maintenance personnel, which resulted in a partial loss of engine power and subsequent forced landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Cessna 172N, 5 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=2072434), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Incorrect service/maintenance (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) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Cessna 172N, 23 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=2072434), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Cessna 172N, 31 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=2072434), [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: [Cessna 172N, 134 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2072434), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The flight instructor reported that, during an instructional flight, while maneuvering about 2,000 ft above ground level, the engine began to run rough and lost partial power. The airplane could not maintain altitude and the instructor was unable to restore engine power. He subsequently performed a forced landing on a road, during which the left wing impacted a tree and the airplane came to rest inverted. Subsequent examination of the engine revealed that the No. 3 exhaust valve rocker was loose and did not depress the exhaust valve when the pushrod was fully extended. The rocker and stud were removed and remnants of threads from the cylinder head were observed between the threads of the stud, consistent with over-tightening of the stud during installation. Review of maintenance records revealed that the No. 3 cylinder was replaced due to low compression about 13 months and 564 engine tachometer hours before the accident. Although the maintenance procedures specified that the stud be tightened to 150 ft-lbs of torque, the stud was likely over-tighten during installation, as was evident by cylinder thread material being pulled into the stud threads, which resulted in its looseness and inability of the rocker to open the exhaust valve. ## Factual narrative On June 21, 2024, about 1210 eastern daylight time, a Cessna 172N, N734XT, was substantially damaged when it was involved in an accident near Hernando, Florida. The flight instructor and commercial pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that the airplane departed about 20 minutes prior with 30 gallons of fuel. The commercial pilot and flight instructor were practicing commercial maneuvers at 2,000 ft mean sea level when they experienced extreme engine roughness and a loss of engine power. The flight instructor could not maintain altitude and could not correct the engine anomaly. He subsequently performed a forced landing on a road. During the landing, the left wing struck a tree and the airplane came to rest inverted. Examination of the wreckage by a Federal Aviation Administration inspector revealed substantial damage to the left wing and fuselage. The engine was further examined following wreckage recovery to a storage facility. During the examination, the propeller was rotated by hand and thumb compression was attained on all cylinders. Crankshaft, camshaft, and valvetrain continuity (with the exception of the No. 3 exhaust valve) was confirmed to the rear accessory section of the engine. The rocker covers were removed, and the No. 3 exhaust valve rocker was loose and did not depress the exhaust valve when the pushrod was fully extended. The rocker and stud were removed and remnants of threads from the cylinder head were observed between the threads of the stud, consistent with over-tightening of the stud during installation. All other rockers were secured in place and operated as expected. Review of maintenance records revealed that the No. 3 cylinder was replaced due to low compression on May 12, 2023, about 564 engine tachometer hours before the accident. According to the director of maintenance (DOM) of the repair station that performed the cylinder installation, he endorsed the maintenance logbook entries once the paperwork was complete and reviewed. The DOM added that a torque wrench was used to tighten the rocker stud to 150 ft-lbs per the Lycoming O-320 Operations Manual Maintenance Procedures, and he provided a copy of those procedures and the calibrated torque wrench serial number that was used to tighten the stud. ## Aircraft - Registration: [N734XT](https://openairdocs.org/aircraft/N734XT), registered now, S/N 17269203, built 1977 (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: 17269203 - Year built: 1977 - Airframe hours: 8309 - Engines: LYCOMING O-320-H2AD 160 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: American Aviation Inc - Registered owner: American Aviation Inc - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, April 19, 2024 - Departed: BKV, Brookville, FL - Equipment: ADS-B, Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 28; injuries: none; commercial, flight instructor; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review April 19, 2023; seat: left; restraint: 3-point; flight hours: 1,192 total, 1,000 in this make and model, 1,130 as pilot in command, 174 in the last 90 days, 55 in the last 30 days, 2 in the last 24 hours - Pilot; age 23; injuries: none; commercial; airplane ratings: single-engine sea; instrument ratings: airplane; medical: class 3, without waivers/limitations; last flight review June 14, 2022; seat: right; restraint: 3-point; flight hours: 271 total, 100 in this make and model, 213 as pilot in command, 19 in the last 90 days, 10 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 30° at 4 knots - Visibility: 7 statute miles - Lowest ceiling: 3,400 ft overcast - Temperature: 84 °F, dew point 73 °F - Altimeter: 30.09 inHg - Observed at: INF, 23 nm away - METAR: KINF 211615Z AUTO 03004KT 7SM SCT026 OVC034 29/23 A3009 ## 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 20240621009259A](https://openairdocs.org/incident/20240621009259A), Jun 21, 2024: Cessna 172N, Pine Island, FL, Destroyed. On June 21st at approximately 1210 EST, pilot elected to land aircraft on public road due to intermittent engine power. Aircraft left wing clipped tree upon… ## Other investigations on N734XT (1) 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. - [NTSB NYC80FFJ15](https://openairdocs.org/ntsb/NYC80FFJ15), Aug 26, 1980: Cessna 172N (N734XT), Fulton, NY, substantial damage ## Docket (8 files) The files NTSB released with the investigation on June 24, 2025, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=194519. 5.6 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 446 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753197&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Memorandum for the record (item 2, PDF, 1 page, 66 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17752373&FileExtension=pdf&FileName=MFR-Rel.pdf - Excerpts from engine logbook (item 3, PDF, 2 pages, 326 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753495&FileExtension=pdf&FileName=Mx%20Excerpts_Redacted-Rel.pdf - Cylinder installation work order (item 4, PDF, 7 pages, 2.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753110&FileExtension=pdf&FileName=WO%2010931_Redacted-Rel.pdf - Cylinder repair work order (item 5, PDF, 3 pages, 300 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753207&FileExtension=pdf&FileName=WO%2061065_Redacted-Rel.pdf - Excerpt from Lycoming O-320 operations manual - maintenance procedures (item 6, PDF, 1 page, 490 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753120&FileExtension=pdf&FileName=Mx%20Manual%20Except-Rel.pdf - Engine examination summary (item 7, PDF, 8 pages, 5 photos, 974 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17752383&FileExtension=pdf&FileName=ERA24LA271%20Engine%20Examination%20Summary-Rel.pdf - Investigation photographs (item 8, PDF, 6 pages, 5 photos, 814 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17753505&FileExtension=pdf&FileName=Investigation%20Photographs-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.