ERA23LA132 · Stilp Tanner E SAVANNAH S

The pilot/builder in the right seat was on the fifth test flight in his amateur-built airplane with another pilot on board who was assisting. While turning from left base to the final leg of the traffic pattern for landing, with the left-seat pilot at the controls, the Y-stick that controlled both pitch and roll jammed. Both pilots attempted to free the Y-stick with force, but it remained jammed with no control of the flaperons and elevator. The airplane remained in a left, descending turn until it collided with trees and terrain about one mile short of the runway. The airplane sustained substantial damage; the right-seat pilot was seriously injured and the left-seat pilot had minor injuries.

An examination of the wreckage, including the flight control system, was conducted after the accident. Flight control continuity was confirmed from the flaperons, elevator, and rudder to the cockpit controls, except for the impact-related overload fractures. No areas of flight control binding or improper installation were found that would have prevented normal operation. An examination of the Y-stick revealed that the lower portion of the stick had minimal clearance with the cockpit floor and surrounding structure by design. The stick-to-floor clearance was smallest when the stick was near neutral (straight up). The clearance increased as bank was increased left or right. According to the kit manufacturer, the smallest Y-stick-to-structure clearance was 4.83mm (roll input neutral with full forward stick).

The actual Y-stick pre-accident clearance dimensions of the accident airplane could not be determined because of cockpit floor deformation from impact damage. There was no device installed on the floor that would have prevented a foreign object, such as a note pad, mobile phone, logbook, etc., from rolling or sliding under the Y-stick. Both pilots believed that a note pad used by the right-seat pilot to record flight test data fell to the floor during flight and jammed the control. Examination of photos of the 8.5 inch by 11-inch note pad revealed damage consistent with lower Y-stick impingement. It is likely that the note pad fell to the floor during flight and slid under the Y-stick during to the turn to final; when the stick was moved toward neutral, the jam occurred.

The kit manufacturer offered, as an option, a soft boot to cover the lower portion of the Y-stick; however, it is not known if this boot would have prevented the accident scenario.

Verbatim NTSB analysis and probable cause from the NTSB dataset