Aircraft Accident/Incident Report

Tranquility, California 93668
Thursday, April 7, 2005 9:03 PDT

About 1 hour into the flight the airplane entered an uncontrolled descent and broke up in flight. The pilot, who did not possess an instrument flight rating, had received a standard weather briefing from a flight service station prior to departure. The briefer advised the pilot that a cold front existed perpendicular to the airplane's route of flight that produced multiple cloud layers to 30,000 feet, overcast conditions, rain, nimbostratus clouds, moderate turbulence, and moderate icing conditions along the frontal boundary. The airplane's radar track depicted the airplane cruising at 13,400 feet mean sea level (msl) on a steady southeasterly course. Analysis of the weather conditions showed that the flight encountered instrument meteorological conditions and ice as it approached the frontal boundary. Weather radar imagery depicted an encounter with the western edge of two bands of radar echoes, which could be associated with strong up- or downdrafts that could result in an upset to the airplane. If the autopilot system were engaged it would have masked the trim and heading changes that usually accompanies ice accumulation, and upon disengagement of the autopilot system, the airplane would be in an unbalanced flight condition. Recorded radar data showed that the last radar return in line with the southeasterly course occurred at 0901:54, with a mode C reported altitude of 13,400 feet msl. The next three radar returns occurred between 0901:59 and 0902:14, and depicted the track in a right-hand turn and a descent to 12,400 feet msl, which was the last identified altitude. This change in altitude corresponded to a 3,000- to 4,000-feet-per-minute rate of descent. Numerous primary targets in patterns indicative of an in-flight breakup were identified in the same vicinity from 0902:14 to 0903:08. Examination of the wreckage revealed permanent set deformation of the structural elements of the wings and horizontal stabilizers that was indicative of positive aerodynamic loading beyond the structures yield point. All fractures were overload in character. The wreckage was widely scattered over a distance in excess of 1,600 yards.

the pilot's in-flight loss of control due to spatial disorientation and a likely accumulation of airframe ice that led to a high speed descent and a structural breakup once the aerodynamic forces exceeded the strength limits of the structure. A factor in the accident was the pilot's lack of experience and training in instrument flight conditions.