LAX04LA100 · Cessna 170B
Cessna 170B · Accident: total loss of engine power (mechanical failure) en route
From Charles M. Schulz Sonoma County Airport (STS) to an unrecorded destination
Event
- NTSB case
- LAX04LA100
- 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 170B
- Aircraft type
- Cessna 170
- 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
- N2502C
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Charles M. Schulz Sonoma County Airport (STS), Santa Rosa, CATo not recorded
- 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 · climb to 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, cylinder › Fatigue
- Engine assembly, cylinder › Separation
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The engine lost power and the airplane nosed over during a forced landing in a field. Post accident examination revealed that the number 2 cylinder separated from the engine. The engine had accumulated 900 hours since its last major overhaul 13 years prior to the accident; the cylinder had accumulated 1,212 hours since replacement in 1986. The hours on the cylinder prior to that time could not be determined. A metallurgical examination found that the barrel failed due to a fatigue crack. The barrel fractured circumferentially between the 11th and 13th fin from the head. The fracture initiated approximately 1.8 inches below the head and started from the inner diameter below a plated region. The initiation area was a small, flat, thumbnail-shaped region approximately 0.5-inch wide through the wall thickness, with signatures indicative of fatigue. Multiple crack initiation sites were observed in the origin area. From the initiation point, the fracture continued propagating in the circumferential direction with coarse arrest marks over approximately 45 percent of the barrel circumference. No material, manufacture, or plating defects were found. The metallurgical examination could not determine why the cracking occurred at the given location; however, it occurred below the chrome plating. From this, it is possible that the barrel exhausted the available fatigue life at that location, which was lowered by the presence of plating.
Probable cause
the failure of the number 2 cylinder barrel due to fatigue. The lack of suitable landing terrain was a factor in the accident.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX04LA100
- Event ID
- 20040126X00110
- Case number
- LAX04LA100
- 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: 9f95d1c51e96943eaad3af2c24385cddae128489e8ce0e3d634857996c8f17c3; retrieved 2026-09-22T08:01:19.067Z.