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