The airplane cruised into the western face of Mount Si at about 0154 Pacific time. It fragmented upon impacting trees and upsloping mountainous terrain, which resulted in substantial structural damage. The commercial pilot held a flight instructor certificate; the pilot and two passengers were fatally injured. Dark night visual conditions prevailed.
A pilot-rated witness observed the anticollision and navigation lights from a low-flying airplane cruising southeasterly. Subsequently, he lost sight of the airplane for a couple of minutes. When he regained visual contact with the airplane, it had altered course to a northeasterly direction. The witness estimated that the airplane’s altitude was about 1000 feet agl, visibility was at least three miles and there was an overcast ceiling several thousand feet high. When the witness lost visual contact with the airplane, it was flying toward the Mount Si area and was within three miles of the crash site.