WPR17FA117 · Cessna 180 UNDESIGNAT

The private pilot was conducting a local, personal flight over mountainous terrain. Several witnesses near the accident site reported that they heard a loud sound. Two witnesses stated that before hearing the loud sound, it sounded like the engine was powering up. Another witness stated that after hearing the loud sound, he looked up and saw the airplane spinning towards the ground, and that the engine and both wings had separated from the airplane.

During postaccident examination of the airplane, no pre-existing cracks or anomalies with the horizontal stabilizers, elevators, or wing structures were found. Additionally, the airplane was likely operated within the weight and balance limitations. Further, no preaccident anomalies with the flight controls were found that would have precluded normal airplane control. Damage noted at the wing and empennage separation points indicated that all cables were intact before the breakup. However, damage and deformation were observed on the right horizontal stabilizer and elevator that was consistent with a significant download that exceeded the capabilities of the structure. The wings had separated from the airplane, and the fractures and deformations were consistent with a negative overload failure of the wings.

Examination of the left horizontal stabilizer and elevator could not conclusively determine the cause of the damage and deformation but indicated that it was likely caused by a partial downward failure. The loads required to fail the horizontal stabilizers and elevators could not have been generated by normal flight or control movements. Such failures would have required the pilot to abruptly pull back on the yoke and move the elevator to a trailing-edge-up position, at speeds higher than the airplane's maneuvering speed. A review of the radar data returns indicated that before the in-flight breakup, the airplane was accelerating and had reached a speed that was higher than its maneuvering speed.

Given the radar data and wreckage examinations, it is likely that the pilot performed an abrupt and substantial pull up maneuver, while flying the airplane above maneuvering speed, which caused a downward failure of the right horizontal stabilizer and partial downward failure of the left horizontal stabilizer, which resulted in the airplane rapidly pitching nose down. Subsequently, the wings were overloaded in the negative direction and fragmented due to the abnormal aerodynamic loads. It could not be determined why the pilot would suddenly pull up; no radar returns or structural damage indicative of airplanes or birds were detected in the area. Further, a review of the weather information revealed that no significant weather or turbulence was reported or forecast in the accident area around the time of the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset