SEA97LA195 · Cessna 170
Cessna 170 · Accident: total loss of engine power (mechanical failure) en route
From Helena Regional Airport (HLN) to Norman Grier Field (S36)
Event
- NTSB case
- SEA97LA195
- 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 170
- 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
- N3964V
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Helena Regional Airport (HLN), Helena, MTTo Norman Grier Field (S36), Kent, WA
- 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
- Destroyed
Cause areas
- Engine assembly, bearing › Seized
- Engine assembly, connecting rod › Separation
- Fluid, oil › Starvation
- Reason for occurrence undetermined
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
While in cruise over mountainous terrain, the pilot noticed a drop in oil pressure followed immediately by engine seizure. The pilot initiated a force landing into rugged terrain and the airplane was destroyed. Exam of the engine revealed that the no. 6 connecting rod had separated due to lack of lubrication and bearing seizure. No evidence of leaking oil was found on the underside of the airplane. The pilot stated that she checked the oil level prior to the flight and that it was adequate. The oil was last changed about one month prior to the accident. According to a maintenance log entry and the accident tachometer time, the airplane had flown about 23 hours since the oil change. The pilot stated that the airplane could not have been flown for more than about 8 hours since the inspection. The rubber seal around the no. 6 push rod tube was found detached after it was salvaged, but it could not be determined if this was a preimpact condition. The published useable oil quantity for the engine is 5.6 qts. in a 5-degree nose down attitude. Conclusive evidence for the loss of engine oil could not be determined.
Probable cause
Oil starvation of the engine due to undetermined reasons, which led to the failure and separation of a main bearing and a connecting rod. A factor contributing to the accident was the lack of suitable terrain for a successful forced landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record SEA97LA195
- Event ID
- 20001208X08754
- Case number
- SEA97LA195
- 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: 93368630108a18ebf0b52d281b490887a54987f90c18da8562d04869ec834ddc; retrieved 2026-09-21T11:52:02.043Z.