CEN11FA347 · Beech F33A

The pilot obtained two abbreviated weather briefings prior to departure and initially planned to fly a familiar route over mountainous terrain. The pilot later changed his proposed route of flight to one that would take him further north over the mountains on an unfamiliar path. The pilot did not obtain any additional weather briefings. Had he obtained a weather briefing for his revised flight path, he could have received an AIRMET for mountain obscuration along his route of flight. A review of ground positioning system (GPS) track data revealed that the flight was uneventful until the pilot began to cross over the mountains on a northwesterly heading at 12,500 feet and into instrument meteorological conditions, which witnesses described as a fast, west-to-east moving front that involved mountain obscuration, turbulence, snow, and icing conditions. During the last 4 1/2 minutes of the flight, the pilot began a series of climbing and descending turns that involved increasing and decreasing airspeeds, which was consistent with a loss of situational awareness or disorientation. The last recorded data by an onboard GPS indicated the airplane was at an altitude of 11,279 feet on a heading of 84 degrees at a groundspeed of 81 knots. The airplane impacted heavily wooded, mountainous terrain at an elevation of about 10,700 feet. A postaccident examination of the airplane revealed no mechanical deficiencies with the airplane or the engine. Results of postmortem toxicology testing were consistent with the relatively recent use of an impairing antihistamine, which is often used to treat allergies. It is possible that the pilot was impaired by his recent use of the antihistamine, although the role of any such impairment in the accident sequence could not be established.

Verbatim NTSB analysis and probable cause from the NTSB dataset