# NTSB WPR23LA196: Cessna 172H, N2550L, Seattle, WA, May 19, 2023 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: May 18, 2023, 18:17 local (May 19, 2023, 01:17 UTC) - Place: Seattle, WA - Coordinates: 47.613142, -122.35534 - Nearby events: https://openairdocs.org/map.md?lat=47.6131&lon=-122.3553&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: FAA Seattle FSDO - NTSB case key (mKey): 192220 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR23LA196 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192220/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=192220 - Page: https://openairdocs.org/ntsb/WPR23LA196 ## Probable cause A stuck exhaust valve that resulted in a partial loss of engine power and a forced water ditching. ## 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 · Damaged/degraded (probable cause); cases with it: [Cessna 172H, 2 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=2072424), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Power plant](https://openairdocs.org/ntsb-findings/01057100): Aircraft › Aircraft power plant · Related maintenance info; cases with it: [Cessna 172H, 2 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md?model=2072424), [All aircraft, 198 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Cessna 172H, 3 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=2072424), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Landing: Ditching](https://openairdocs.org/ntsb-events/441); cases with it: [Cessna 172H, 1 case](https://openairdocs.org/ntsb-events/441/sequence.md?model=2072424), [All aircraft, 186 cases](https://openairdocs.org/ntsb-events/441/sequence.md) ## Analysis The pilot reported that, as the airplane descended to 1,000 ft mean sea level (msl) crossing over a bay, the engine sustained a partial loss of power. The pilot declared an emergency and performed a forced water ditching. Examination of the engine revealed a stuck exhaust valve on the No. 4 cylinder. The No. 4 cylinder was removed for further examination. The exhaust valve guide exhibited evidence of oil coking along with an area of polishing on one side of the guide. A slight amount of discoloration consistent with corrosion was observed adjacent to the polished area. The exhaust valve stem was intact with some coking near the valve fillet and the intake valve exhibited moderate coking. It is likely that the coking resulted in the valve getting stuck. The Nos. 2 and 4 cylinder cooling fins exhibited thermal discoloration. A visual inspection of the internal area of the crankcase showed the crankshaft and camshaft did not reveal any anomalies or mechanical damage. The No. 4 cylinder had been serviced and reinstalled with a new cylinder kit 143 flight hours before the accident and the most recent annual inspection was about 11 months before the accident. ## Factual narrative On May 18, 2023, about 1817 Pacific daylight time, a Cessna 172H airplane, N2550L was substantially damaged when it was involved in an accident near Seattle, Washington. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, while in cruise flight at 1,000 ft msl nearing the destination airport, he heard an audible change in engine rpm. The engine tachometer indicated 1,400 rpm instead of the expected 2,000 rpm. There were no other abnormal engine sounds or indications on the instrument panel. The pilot attempted to troubleshoot; however, the engine rpm continued to decrease. No longer able to maintain altitude, the pilot declared an emergency and ditched the airplane into a bay, avoiding populated areas. A postaccident examination of the engine revealed the No. 4 cylinder exhaust valve was stuck in the partially open position. The intake valve was removed with little effort; however, the exhaust valve was removed with a punch and hammer along with significant force. The exhaust valve guide exhibited evidence of oil coking along with an area of polishing on one side of the guide. A slight amount of discoloration consistent with corrosion was observed adjacent to the polished area. The exhaust valve stem was intact with some coking near the valve fillet. The intake valve had moderate coking. The cooling fins on cylinder Nos. 2 and 4 exhibited thermal discoloration. All intake and exhaust valve springs were found intact and undamaged. The intake and exhaust pushrods were intact and undamaged. The No. 4 piston exhibited evidence of corrosion and combustion deposits were observed on the piston face. All piston rings were intact and had various degrees of corrosion and contamination throughout. The internal area of the crankcase, the camshaft, and crankshaft were found to be unremarkable. The aircraft maintenance logbook revealed that the engine had a major overhaul September 8, 1995. On March 16, 2022, the No. 4 cylinder was serviced and reinstalled with a new cylinder kit. The exhaust and intake valve guides were reamed, and the valves were reinstalled. At that time, the engine had accumulated 1,021.8 hours since major overhaul. The airplane had 143.2 total flight hours from the time of the No. 4 cylinder servicing until the accident and the engine had 1,165 total hours since new at the time of the accident. The airplane’s most recent annual inspection was completed on June 8, 2022. The annual inspection included replacement of the No. 4 cylinder exhaust stack. The engine manufacturer recommended overhaul time for the engine was 1,800 hours or 12 years, whichever occurred first. ## Aircraft - Registration: [N2550L](https://openairdocs.org/aircraft/N2550L), registered now, S/N 17255750 (OpenAirDocs) - Reported make and model: CESSNA 172H - Registry model: [Cessna 172H](https://openairdocs.org/model/cessna-172h) (registry code 2072424) (OpenAirDocs) - Registry engine: [Continental 0-300 series](https://openairdocs.org/engine/continental-0-300-series) (registry code 17022, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17255750 - Year built: 1967 - Airframe hours: 4030 - Engines: Continental O-300 180 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 9, 2022, 1,280 hours before - Departed: 0S9, Port Townsend, WA - Destination: S50, Seattle, WA - Equipment: ADS-B, Electronic flight bag or handheld device, Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 42; injuries: none; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review May 25, 2021; seat: left; restraint: 4-point; flight hours: 1,489 total, 513 in this make and model, 1,143 as pilot in command, 63 in the last 90 days, 23 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 240° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 75 °F, dew point 61 °F - Altimeter: 29.95 inHg - Observed at: KBFI, 4 nm away - METAR: KBFI 190053Z 24005KT 10SM FU CLR 24/16 A2995 RMK AO2 SLP143 T02440156 ## 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 20230518006459A](https://openairdocs.org/incident/20230518006459A), May 18, 2023: Cessna 172H, Seattle, WA, Substantial damage. On may 18, 2023, @ 1810 hrs, [privacy data omitted] inbound to bfi, pilot in command (PIC) reported to lcw that he had lost engine power over north elliot bay,… ## Docket (4 files) The files NTSB released with the investigation on June 20, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=192220. 10.0 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15690021&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Airframe and engine examination report (item 2, PDF, 11 pages, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15877172&FileExtension=pdf&FileName=Airframe%20and%20Engine%20Exam%20Notes-Rel.pdf - Maintenance records (item 3, PDF, 14 pages, 6.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15725724&FileExtension=pdf&FileName=Maintenance%20Logbook%20Photos_Redacted-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 4, PDF, 1 page, 218 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15728137&FileExtension=pdf&FileName=N2550L%20NTSB%20Wreckage%20Release%20Form_Redacted-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.