Incident Overview
During the execution of commercial pilot maneuvers, the airplane experienced a loss of aileron control. The pilot reported moving the control wheel to the right without any corresponding response from the aircraft. Observing the wing while continuing to manipulate the control wheel, the pilot determined that the ailerons were not operating.
Emergency Landing
The pilot executed an emergency landing on a dirt road, using rudder and throttle inputs to maintain directional control. During the landing roll, the right wing impacted a tree, resulting in damage to the aircraft.
Control System Design
The control wheel is attached to the control column via a nut plate installed inside the column. A screw and collar are inserted through the bottom of the control wheel into the nut plate to secure it. According to Federal Aviation Administration (FAA) and Society of Automotive Engineers (SAE) publications, proper clamping action requires at least three threads to be visible above the nut. FAA advisory circular AC 43.12 recommends installing screws and bolts from the top down when possible to reduce the effects of gravity and vibration on fastener loosening.
On-Scene Examination
An FAA inspector conducting an on-scene examination found the attaching screw and collar from the left control wheel on the floor of the airplane. When the left control wheel was moved, the column did not respond. Moving the column by hand confirmed continuity of the aileron control system.
Post-Accident Findings
Post-accident inspection of the control wheel attachment screw, along with several others from the same make and model of aircraft, revealed slight variations in length among them. Some screws also displayed different letter markings on the heads. On average, when fully torqued, between one and one-and-a-half threads were exposed beyond the top of the nut plate, fewer than the recommended three threads.
Fleet Inspection
Torque checks were performed on all 35 aircraft in the operator's fleet, comprising 19 PA-28-181s and 11 PA-44-180s. Ten control wheel screws were found to be loose, requiring an additional one-eighth to one-quarter turn to reach proper torque. Similar inspections at other flight schools also uncovered loose screws that needed the same adjustment.