DEN01FA056 · Beech V35B
Beech V35B · Accident: loss of control in flight en route
From Gunnison Crested Butte Regional Airport (GUC) to Fresno Yosemite International Airport (FAT)
Event
- NTSB case
- DEN01FA056
- 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
- 1 · 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
Beech V35B
- Aircraft type
- Beechcraft 35
- 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
- N4637M
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Gunnison Crested Butte Regional Airport (GUC), Gunnison, COTo Fresno Yosemite International Airport (FAT), Fresno, 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
- Loss of control in flight
- Also codedOther events the NTSB coded in the sequence, such as a wire strike after a loss of power. Flight Findings uses them for its kinds of event. Glossary
- Stall/spin
- 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
- Pilot in command › Aircraft control, not maintained
- Pilot in command › In-flight planning/decision, improper
- Pilot in command › Incapacitation(anoxia/hypoxia)
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 had been skiing in the Rocky Mountains (elevation 8,900 feet) for a week. He departed in his non-pressurized single-engine airplane and climbed up to 21,600 feet; he had no supplemental oxygen onboard. Approximately 1 hour 45 minutes into the flight, the airplane reached a maximum altitude of 22,100 feet before entering a rapid descent. The airplane impacted mountainous terrain in an uncontrolled spin. Examination of the airplane and engine revealed no evidence of any pre-impact discrepancies. The Emergency Locator Transmitter (ELT) functioned properly, and the airplane was located by the Civil Air Patrol the following day.
Probable cause
the pilot's failure to maintain aircraft control as a result of incapacitation (from hypoxia) due to the in-flight decision to fly at altitudes where oxygen is required, without oxygen available.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DEN01FA056
- Event ID
- 20010306X00545
- Case number
- DEN01FA056
- 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, coordinates. 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: 51f970c7dee7fcd0bc2543226b523e12d144427ae59de62aebdd7701b0980bc1; retrieved 2026-09-20T20:38:40.324Z.