Casualties unknown

Single-Engine Airplane Crashes in Rocky Mountains After High-Altitude Flight Without Oxygen (N4637M)

Green River, UT, US

On February 26, 2001, a Beech V35B (registration N4637M) was involved in an aviation accident near Green River, UT. Investigators recorded the probable cause as: 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. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-06-10Data APIEditorial standards

A pilot, after a week of skiing at 8,900 feet, departed in a non-pressurized single-engine airplane without supplemental oxygen, climbed to 22,100 feet, then entered a rapid descent and impacted terrain in an uncontrolled spin. No pre-impact discrepancies were found.

Incident Overview

A pilot who had been skiing in the Rocky Mountains (elevation 8,900 feet) for a week departed in a non-pressurized single-engine airplane. The aircraft climbed to 21,600 feet initially. Approximately 1 hour and 45 minutes into the flight, the airplane reached a maximum altitude of 22,100 feet before entering a rapid descent. It subsequently impacted mountainous terrain in an uncontrolled spin.

Flight Details

The pilot had no supplemental oxygen onboard during the high-altitude flight. The airplane was not pressurized. The flight duration from departure to the peak altitude was about 1 hour 45 minutes. The exact location of the crash site within the Rocky Mountains was not specified.

Investigation Findings

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 day following the accident. No weather, ATC, or other external factors were noted in the investigation.

Additional Information

No injuries or fatalities are mentioned in the official source. The report does not specify the aircraft type, registration, operator, date, time of day, or whether the pilot had any medical conditions beyond the lack of supplemental oxygen.

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20010306X00545. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.