ATL98LA003 · Cessna 150M
Cessna 150M · Accident: total loss of engine power (mechanical failure) en route
From North Perry Airport (HWO) to Florida Keys Marathon International Airport (MTH)
Event
- NTSB case
- ATL98LA003
- 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
- 0
- 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 150M
- Aircraft type
- Cessna 150
- 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
- N7814U
- Operator
- William B. Tinkham · private individual
- Onboard fatalities
- Unknown
- Route
- From North Perry Airport (HWO), FLTo Florida Keys Marathon International Airport (MTH), Marathon, FL
- Aircraft age
- Not recorded
- 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
- First occurrenceThe 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
- Total loss of engine power (mechanical failure)
- 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
- Engine assembly, valve keeper › Worn
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
About 10 minutes into the flight, at a cruise altitude of 1000 feet, the pilot experienced a loss of engine power. He radioed a 'mayday' call and selected a nearby golf course for an emergency landing. The airplane collided with a palm tree during the emergency landing roll. Examination of the engine assembly revealed that number one cylinder lower spark plug was partially separated from the cylinder. During the subsequent engine teardown, the number one exhaust valve head was recovered from inside the cylinder. The examination also of the exhaust valve stem and the and the valve stem keepers showed excessive wear. The valve stem keepers had also separated from their normally installed positions. A review of the aircraft maintenance logs disclosed that the engine had undergone several major engine repairs, involving the valve assemblies, within the last ten years. An engine top overhaul was completed 370 hours before this accident. The engine had accumulated a total of 5,603 hours.
Probable cause
excessive wear to the number one valve stem and valve stem keepers that resulted in the separation of the valve assembly.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ATL98LA003
- Event ID
- 20001208X08952
- Case number
- ATL98LA003
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
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: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 2d33d11e4e2de5d82f6ae3998f569aa842540ab32ce71d234bc0951332fcfae8; retrieved 2026-09-21T21:06:19.050Z.