WPR23LA196 · Cessna 172H
Cessna 172H · Accident: loss of engine power (partial) en route
From Jefferson County International Airport (0S9) to Auburn Municipal Airport (S50)
Narrative check · The NTSB narrative appears to contradict this record's departure or destination. Values are shown as recorded, not corrected; compare with the narrative.
Event
- NTSB case
- WPR23LA196
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Cessna 172H
- Aircraft type
- Cessna 172
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N2550L
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route Possible conflict
- From Jefferson County International Airport (0S9), Port Townsend, WATo Auburn Municipal Airport (S50), Seattle, WA
- Aircraft age
- About 56 years (built 1967)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Loss of engine power (partial)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft power plant
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
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.
Probable cause
A stuck exhaust valve that resulted in a partial loss of engine power and a forced water ditching.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR23LA196
- Event ID
- 20230522192220
- Case number
- WPR23LA196
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: local date, investigation status, coordinates, cause areas. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2023-05-19.
- API snapshot SHA-256: 137ace315813db629e6baee2f07bf02092300ba76dadde2791854a63bc90c445; retrieved 2026-09-16T17:37:54.161Z.