# NTSB CEN24LA121: Piper PA-28-181, N38696, Watertown, SD, February 25, 2024 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: February 25, 2024, 16:10 local (22:10 UTC) - Place: Watertown, SD - Coordinates: 44.916092, -97.154862 - Nearby events: https://openairdocs.org/map.md?lat=44.9161&lon=-97.1549&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report March 18, 2026 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA-FSDO, Lycoming Engines - NTSB case key (mKey): 193836 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN24LA121 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193836/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193836 - Page: https://openairdocs.org/ntsb/CEN24LA121 ## Probable cause The stuck No. 2 cylinder exhaust valve, which resulted in a partial loss of engine power and a forced landing due to an undersized exhaust valve guide. Contributing to the accident were the improper manufacture of the engine cylinders, and the operation of the engine in an overly rich fuel condition. ## 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 · Malfunction (probable cause); cases with it: [Piper PA-28-181, 6 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=7102807), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Performance/control parameters: powerplant parameters](https://openairdocs.org/ntsb-findings/01062050): Aircraft › Aircraft oper/perf/capability · Attain/maintain not possible (probable cause); cases with it: [Piper PA-28-181, 1 case](https://openairdocs.org/ntsb-findings/01062050/cases.md?model=7102807), [All aircraft, 81 cases](https://openairdocs.org/ntsb-findings/01062050/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01050000): Aircraft › Aircraft power plant · Related maintenance info (probable cause); cases with it: [Piper PA-28-181, 1 case](https://openairdocs.org/ntsb-findings/01050000/cases.md?model=7102807), [All aircraft, 151 cases](https://openairdocs.org/ntsb-findings/01050000/cases.md) - [Manufacture/production: equipment manufacture](https://openairdocs.org/ntsb-findings/04013010): Organizational issues › Development · Manufacturer (probable cause); cases with it: [Piper PA-28-181, 1 case](https://openairdocs.org/ntsb-findings/04013010/cases.md?model=7102807), [All aircraft, 36 cases](https://openairdocs.org/ntsb-findings/04013010/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01050000): Aircraft › Aircraft power plant · Inadequate inspection (probable cause); cases with it: [Piper PA-28-181, 1 case](https://openairdocs.org/ntsb-findings/01050000/cases.md?model=7102807), [All aircraft, 151 cases](https://openairdocs.org/ntsb-findings/01050000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Piper PA-28-181, 9 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=7102807), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Initial climb: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Piper PA-28-181, 23 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=7102807), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing-landing roll: Runway excursion](https://openairdocs.org/ntsb-events/300); cases with it: [Piper PA-28-181, 35 cases](https://openairdocs.org/ntsb-events/300/sequence.md?model=7102807), [All aircraft, 3,643 cases](https://openairdocs.org/ntsb-events/300/sequence.md) ## Analysis During an instructional flight, the airplane had just taken off when the engine lost partial power. The flight instructor took control of the airplane and conducted a forced landing on the remaining runway. During the forced landing, the airplane departed the runway surface and struck a fence and trees, which resulted in substantial damage to both wings. Engine monitoring data showed that during the takeoff, engine power increased to a maximum of 2,505 rpm. About five seconds after rotation, engine power decreased to 1,446 rpm. Postaccident examination of the engine revealed a partially open, stuck exhaust valve on the No. 2 cylinder. The valve stem had a metallic debris smeared at mid span of the stem, and the valve guide had numerous metallic deposits present. The metallic debris and deposits contained lead, carbon, and bromine, consistent with combustion products, and the valve guide was below the manufacturer-specified minimum guide-to-stem clearance from the interior through mid-span of the guide. Relatively thick deposits were also noted on the piston crown and exhaust port. Based on the composition of the deposits, the No. 2 cylinder exhaust valve likely became stuck due to cumulative engine operations at an overly rich fuel condition, leading to incomplete fuel burn and an accumulation of combustion deposits on the valve stem and guide. The presence of the deposits suggests that the engine was operated at relatively low cylinder head temperatures (CHT). This is consistent with the accident flight data showing that the No. 2 cylinder temperature peaked at 336°F. Additionally, a review of 109 previous flights totaling about 165 hours showed a maximum No. 2 cylinder temperature of 364°F and a median temperature of 293°F. According to the engine manufacturer’s guidance, continued operations at much lower temperatures could be detrimental to engine operation and likely contributed to the build up of combustion products on the valve. The valve guides on all four cylinders were found to be below the minimum inner diameter specification. The cylinders were factory-new when installed on the engine at overhaul by the engine manufacturer on January 11, 2023. Based on the measurements, the exhaust valve guides were not correctly sized during manufacture of the cylinders. It is likely that the undersized valve guide contributed to the valve sticking with the combustion deposits. Given the CHTs values recorded in the accident flight and accumulation of combustion deposits observed in the examined cylinder, it is likely that combustion deposits accumulated in the valve guide and led to valve sticking in addition to the undersizing of the valve guide at factory overhaul. ## Factual narrative On February 25, 2024, about 1610 central standard time, a Piper PA-28-181 airplane, N38696, was substantially damaged when it was involved in an accident near Watertown, South Dakota. The flight instructor and student pilot were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor stated that while the student pilot was performing a touch and go, just after the airplane had taken off, the engine lost partial power. The flight instructor took control of the airplane and conducted a forced landing on the remaining runway. Engine monitoring data showed that during the takeoff, engine power increased from 851 rpm to a maximum of 2,505 rpm. About five seconds after rotation, engine power decreased to 1,446 rpm. During the forced landing, the airplane departed the runway surface and struck a fence and trees, which resulted in substantial damage to both wings. Postaccident examination of the engine revealed a partially open, stuck exhaust valve on the No. 2 cylinder. Removal of the valve from the cylinder assembly required the use of penetrating oil and a mallet. The neck area and adjacent surfaces on the valve head were covered with reddish-brown deposits. Gray-colored, raised deposits were observed on the side of the valve stem. The piston crown was also covered in similar deposits. Energy-dispersive x-ray spectroscopy of the No. 2 cylinder intake valve deposits by the NTSB Materials Laboratory showed evidence of relatively high levels of lead, carbon, and bromine. A sample from the No. 2 cylinder exhaust valve deposits showed evidence of high lead content with relatively smaller levels of bromine and carbon. With the deposits present, the clearance between the No. 2 cylinder exhaust valve guide and valve stem was between 0.0007 and 0.0009 inches at the middle of the valve guide and between 0.0011 and 0.0029 inches at the inboard (piston side) end of the guide; the engine manufacturer, in Lycoming Service Table of Limits and Torque Value Recommendations (SSP-1176-5), specified that the exhaust valve stem-to-guide clearance should be between 0.0040 and 0.0060 inches. After the exhaust valve guides of all 4 cylinders were cleaned of deposits, the inside diameter of the No. 2 cylinder exhaust valve guide was measured to be 0.4975 inches at the outboard (rocker side) end, 0.4977 inches at middle of the guide, and 0.4983 inches at the inboard (piston side) end, which were all less than the minimum of 0.4985 inches specified by the manufacturer in SSP-1176-5. In addition, the inside diameters of the exhaust valve guides of the other 3 cylinders were each less than the manufacturer-specified minimum in at least 2 locations. The cylinders were factory-new when installed on the engine at overhaul by the engine manufacturer on January 11, 2022. Maintenance records indicated that since being installed, no maintenance work had been performed on the cylinders or valves. As of February23, 2024, the engine had 646.6 hours since overhaul. Review of recorded engine monitoring data for the accident flight showed that the No 2. cylinder’s peak temperature was 336°F. Review of 109 previous flights totaling about 165 hours showed a maximum No. 2 cylinder temperature of 364°F and a median temperature of 293°F. The engine manufacturer recommends CHT values during normal operations for normally-aspirated engines should be 400°F or less. Additionally, Lycoming Valve Sticking – Early Warning Signs and Indications (SSP-525) states that the engine should be properly leaned at cruise power settings to promote complete burning of the fuel, and that long periods of ground operation should be avoided; an oil-lead sludge will form without proper leaning and during long periods below normal operating temperature. ## Aircraft - Registration: [N38696](https://openairdocs.org/aircraft/N38696), registered now, S/N 28-7790577, built 1977 (OpenAirDocs) - Reported make and model: PIPER PA-28-181 - Registry model: [Piper PA-28-181](https://openairdocs.org/model/piper-pa-28-181) (registry code 7102807) (OpenAirDocs) - Registry engine: [Lycoming O&VO-360 series](https://openairdocs.org/engine/lycoming-o-vo-360-series) (registry code 41514, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 28-7790577 - Year built: 1977 - Airframe hours: 5179 - Engines: Lycoming O-360-A4M 180 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: Lake Area Technical College - Registered owner: Lake Area Technical College - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, February 1, 2024 - Airport: ATY, Watertown Regional, runway 35, 6,893 × 100 ft, concrete - Equipment: Electronic multifunction display, Electronic primary flight display, Stall warning system, ADS-B, Auto-pilot, Data recorder ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 23; injuries: none; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review November 21, 2023; seat: right; restraint: 3-point; flight hours: 556 total, 98 in this make and model, 529 as pilot in command, 91 in the last 90 days, 35 in the last 30 days, 7 in the last 24 hours - Student pilot; age 19; injuries: none; student; medical: class 2, with waivers/limitations; seat: left; restraint: 3-point; flight hours: 72 total, 62 in this make and model, 26 in the last 90 days, 6 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 10° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: 2,900 ft overcast - Temperature: 37 °F, dew point 27 °F - Altimeter: 29.78 inHg - Observed at: KATY, 1 nm away - METAR: KATY 252153Z AUTO 01006KT 10SM OVC029 03/M03 A2978 RMK AO2 SNB2057E15 SLP098 P0000 T00281033 ## 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 20240225002099A](https://openairdocs.org/incident/20240225002099A), Feb 25, 2024: Piper PA-28-181, Watertown, SD, Substantial damage. On 02/25/2024, aircraft [privacy data omitted] was on katy CTAF conducting flight insrtuction pattern work (multiple touch and goes) when the aircraft… ## Docket (11 files) The files NTSB released with the investigation on March 18, 2026, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193836. 127 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 10 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932531&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Maintenance records - engine logbook (item 2, PDF, 10 pages, 71.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19985218&FileExtension=pdf&FileName=Engine%20Logbook_Redacted-Rel.pdf - Engine overhaul paperwork (item 3, PDF, 69 pages, 27.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932082&FileExtension=pdf&FileName=L-42332-36E%20Overhaul%20Paperwork_Redacted-Rel.pdf - Photo array (item 4, PDF, 3 pages, 803 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932277&FileExtension=pdf&FileName=Photo%20Array-Rel.pdf - Examination summary (item 5, PDF, 10 pages, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19984183&FileExtension=pdf&FileName=Examination%20Summary-Rel.pdf - Materials laboratory factual report 24-086 (item 6, PDF, 9 pages, 11 photos, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18113362&FileExtension=pdf&FileName=24-086-Rel.pdf - Memorandum for record a�� additional examination by latc (item 7, PDF, 2 pages, 78 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932092&FileExtension=pdf&FileName=MOR%20LATC%20Examination-Rel.pdf - Engine data plots (item 8, PDF, 2 pages, 829 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19931788&FileExtension=pdf&FileName=Engine%20Plot-Rel.pdf - Accident flight engine data (item 9, CSV, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932361&FileExtension=csv&FileName=Accident%20Flight%20Engine%20Data-Rel.csv - Combined engine data for cylinder tempature (item 10, XLSX, 18.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932426&FileExtension=xlsx&FileName=CHT%20ALL-Rel.xlsx - Lycoming SSP-525 valve sticking - early warning signs and indications (item 11, PDF, 2 pages, 122 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19932680&FileExtension=pdf&FileName=SSP-525%20Valve%20Sticking%20-%20Early%20Warning%20Signs%20and%20Indications-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.