LAX98LA258 · M. C. Thomas STEWART S-51 STEWART S-
M. C. Thomas STEWART S-51 STEWART S- · Accident: total loss of engine power (mechanical failure) en route
From Reno Tahoe International Airport (RNO) to San Luis County Regional Airport (SBP)
Event
- NTSB case
- LAX98LA258
- 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
M. C. Thomas STEWART S-51 STEWART S-
- Aircraft type
- M C Thomas STEWART S-51
- 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
- N151MT
- Operator
- Michael W. Clipperton · private individual
- Onboard fatalities
- Unknown
- Route
- From Reno Tahoe International Airport (RNO), Reno, NVTo San Luis County Regional Airport (SBP), San Luis Obispo, CA
- 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
- Owner/builder › Maintenance, modification, improper
- Propeller system/accessories, governor › Failure, total
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
While en route to the destination airport, the airplane experienced a loss of engine power. The pilot made a forced landing on a highway and collided with a snow pole. The airplane veered off of the road and came to rest after it collided with a tree. The owner/builder stated that he had modified the drive shaft from the original 'V' belt drive to a dual 'serpentine' belt/pulley system. He further stated that in order to install the new belt/pulley system, he had to weld a retaining pin in the center of the original drive shaft. The propeller governor pulley was found at the bottom of the engine compartment and the shaft was found to have separated at the center point. The drive shaft exhibited a bluing and discoloration at the center where the owner had welded it on the pin. It was noted that the original manufacturer of the propeller governor drive shaft had placed a heat treat stamp on the shaft.
Probable cause
Failure of the propeller governor pulley drive shaft due to a modification made to the system by the owner that included welding a retaining pin to the center of the heat treated drive shaft, which compromised the shaft's design strength margin.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX98LA258
- Event ID
- 20001211X10894
- Case number
- LAX98LA258
- 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: b58d4230d38c733dfda2e41de2bb22ca48ada3e4718c9ae88e312350f54c321a; retrieved 2026-09-22T17:15:11.122Z.