NTSB Identification: SEA97FA044.
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Accident occurred Monday, January 06, 1997 in WINSTON, MT
Probable Cause Approval Date: 04/10/1998
Aircraft: Piper PA-24-260, registration: N9080P
Injuries: 3 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

An ATC controller observed the night IFR flight with the 68-year old pilot deviating south of course then correcting back a little bit before deviating south again. The deviations were as much as 90 degrees, and altitude varied by about 14,400 feet MSL down to 14,000 feet MSL. Then, approximately 10 southeast of Helena, Montana, radar contact was lost in an area of normally good radar coverage. The airplane sustained an in-flight breakup before impacting in hilly terrain. The flight had been cleared to climb to 12,000 feet at 1936; at 2006 the controlller noted that 'I don't know where he's going...he's all over the place....' During on-scene investigation, it was determined that the portable oxygen bottle being carried in the airplane was not being used by the pilot. The pilot was known to fly at altitudes above 12,500 feet, and as high as 17,000 feet, without using oxygen. An autopsy of the pilot revealed atherosclerosis of coronary arteries with 90% stenosis of left anterior descending coronary artery and 90% stenosis of right coronary artery, as well as multiple blunt force injuries.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Pilot incapacitation due to hypoxia. Failure of the pilot to use available oxygen is a factor.

Full narrative available

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