ERA24FA209 · Rockwell International 690A

The airplane was in cruise flight at 20,000 ft on an instrument flight rules (IFR) cross-country flight when the pilot reversed course. When an air traffic controller queried the pilot, he replied, “we have lost…we need to climb.” The controller then asked the pilot, “what is your issue?” and the pilot responded, “we have lost autopilot.” There were no further communications received from the pilot and radar contact with the airplane was lost shortly thereafter. A witness who saw the airplane as it descended toward ground impact described that it was on fire. The wreckage of the airplane was heavily fragmented and scattered amongst a wooded area, with a debris path over 3 miles long. The left wing, left engine, left propeller, and empennage were heavily burnt and found at the main wreckage site. The right wing was separated at the wing root and was found 1/4-mile north of the main wreckage. The right wing was fire damaged, and the right engine and right propeller were not located. The vertical and horizontal stabilizers were found about 3/4-mile north of the main wreckage. All fractures exhibited overstress features consistent with an in-flight breakup. Mapping of the wreckage indicated that the tail components likely separated first, followed by the right wing. This structural failure resulted in the horizontal and vertical stabilizers deforming and subsequently separating from the airplane. The lack of heat damage indicated that this separation occurred before the fire and that the inflight fire observed by the witness was likely a result of the inflight breakup. No evidence of any mechanical malfunctions or failures that would have preceded the inflight breakup was found during the postaccident wreckage examination. Review of data provided by a preflight planning application vendor revealed that before the accident flight, the pilot filed an IFR flight plan and received a weather briefing. The briefing included an AIRMET for moderate icing with the freezing level between 9,000 and 13,000 ft, with tops at 24,000 ft, which included a portion of the intended route of flight. This AIRMET was active at the time of the accident. Satellite imagery of the accident area and upper air sounding model data depicted cloudy, instrument meteorological conditions across the region from the surface to above 30,000 ft. Upper air data and computer modeling also identified the potential for some icing as the airplane climbed above 11,000 ft, and it is possible that some trace icing could have accumulated on the airplane’s structure during this time. Weather radar reflectivity values indicated that along the final portion of the accident flight path, the potential for an encounter with more significant structural airframe icing was greater, though the severity of that icing could not be definitively quantified. The airplane was equipped with de-ice boots on the leading edges of the wings, horizontal stabilizer, and vertical stabilizer. Most of the components of the airplane’s de-ice system were destroyed during the accident sequence and could not be examined. Review of maintenance logbooks did not reveal evidence of any anomalies or preexisting discrepancies that would have precluded normal operation of the de-ice system before the accident flight. The pilot’s statement to air traffic control that he had “lost the autopilot,” shortly before radar contact with the airplane was lost and the airplane broke up in flight, suggest that he may have been experiencing difficulty controlling the airplane, either with or without the aid of the autopilot. The airplane’s pilot’s operating handbook contained an airworthiness directive (AD) that explicitly warned pilots who encountered certain types of structural icing in flight not to utilize the autopilot, as it could mask tactile cues indicative of adverse changes in the airplane’s handling characteristics. Given this information, it is likely that the pilot’s loss of control that ultimately resulted in the airplane’s inflight breakup was preceded by an accumulation of structural ice that altered the airplane’s handling characteristics in a way that the pilot had not anticipated and was unable to recover from.

Verbatim NTSB analysis and probable cause from the NTSB dataset