WPR24LA177

The pilot reported that, during takeoff, he felt a shimmy in the tailwheel-equipped airplane. During the subsequent three-point landing, the airplane veered left immediately upon touchdown. The airplane departed the left side of runway and ground looped, which collapsed the right main landing gear and substantially damaged the right wing. An NTSB structures engineer’s review of postaccident photographs of the tailwheel assembly determined that deformation and fracture features on the fitting flanges on the extruded base of the tailwheel assembly were from a twisting motion about the single bolt that secured the tailwheel assembly to the suspension assembly, consistent with that resulting from a tailwheel shimmy event. The accident circumstances and damage evidence are consistent with a failure of the tailwheel assembly due to improper movement or rotation around the tailwheel attachment bolt during the shimmy event during takeoff, which resulted in a subsequent loss of control of the airplane during landing. However, the investigation could not determine if the shimmy event resulted from a loose attachment bolt, or if the movement around the attachment bolt resulted from the shimmy event.

On May 30, 2024, about 1610 mountain daylight time, an amateur-built experimental Kitfox, N506F, was substantially damaged when it was involved in an accident near Parowan, Utah. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot had recently purchased the tailwheel equipped airplane and was conducting a cross-country flight to reposition the airplane. He reported that during takeoff for the accident flight he felt a shimmy in the airplane. He subsequently performed a three-point landing on runway 22 at Parowan Airport (1L9), Parowan, Utah. He reported that, immediately on touchdown, the airplane “unexplainably and severely turned left, and departed the runway” and ground looped. The right main landing gear collapsed, resulting in substantial damage to the right wing. The pilot reported the wind was light and variable at the time of landing and there were no gusts. The airplane was equipped with a Matco, 11-inch, dual fork tailwheel assembly. Postaccident photographs of the airplane provided by the pilot showed that, at the accident scene, the tailwheel assembly was partially displaced to the left side of the airplane and the tailwheel was deflected to the right. The pilot also provided photographs taken of the tailwheel assembly after it was removed from the airplane, including several showing that the fitting flanges on the extruded base of the tailwheel assembly were damaged and fractured on both sides. The pilot reported that he examined the airplane’s brakes and no anomalies were found. A full examination of the tailwheel assembly was not conducted. An NTSB structures engineer’s review of the pilot-provided photographs determined that the damaged and fracture features on the extruded base fitting flanges resulted from a twisting motion about the single bolt that secured the tailwheel assembly to the suspension assembly (see figure). Figure. Damaged tailwheel assembly. (Source: Pilot.) The mode of fracture could not be determined from the photographs, but the deformation suggests shear overload on the flanges consistent with that resulting from a tailwheel shimmy event. Under normal operations, the tailwheel is designed caster about the vertical tailwheel axle such that there should be no rotation of the tailwheel about the attachment bolt that secures the tailwheel assembly to the suspension assembly. The investigation could not determine if the shimmy event resulted from a loose attachment bolt, or if the movement around the attachment bolt resulted from the shimmy event. The pilot reported that the airplane’s most recent condition inspection was performed on October 28, 2023. No detail about any specific pre-accident maintenance or inspection of the tailwheel was provided.