Aviat Aircraft Inc A-1C-200 N43LL accident near Carefree, Arizona

Probable cause

The substandard installation of the airplane’s autopilot system hardware, which resulted in a malfunction of the rudder control system during flight and a loss of directional control during the landing roll.

NTSB analysis

The pilot reported that, during the approach to land, he disconnected the autopilot, and the airplane immediately yawed to the right. The pilot applied left pedal, engaged the yaw damper, and continued the approach. He subsequently disengaged the yaw damper and entered a cross-control slip to descend, and he was unable to make an effective left rudder input. The airplane touched down on the gravel runway surface and veered to the right. The airplane then crossed over to the asphalt runway surface and subsequently ground-looped.

The airplane’s autopilot had been installed in the airplane 7 weeks before the accident. Postaccident examination of the airframe revealed that the autopilot hardware installation was substandard. Specifically, the guard pin, which was designed to prevent the bridle cable from traveling out of the pulley’s groove past the sheaves, was not installed to the yaw servo tray and the right pulley assembly, which allowed the yaw servo bridle cable to separate from the pulley’s phenolic sheave. Additionally, the bridle cable, which was undertensioned, became trapped between the yaw servo pulley and the attachment tray and prohibited the pilot from applying left rudder. As a result, the pilot was unable to maintain directional control during the landing roll. The guard pin is designed to prohibit the bridle cable from being able to travel out of the pulley’s groove past the sheaves.

Text from the NTSB. Open the NTSB docket for WPR21LA135 for the full record.