Accident Overview
A private certificated pilot was conducting a cruise flight at approximately 800 feet above ground level (AGL) in a ski-equipped airplane. The pilot reported that the airplane initiated an uncommanded left turn. He applied right aileron control to correct the bank, but the left bank continued to steepen. He also applied right rudder to prevent the airplane from becoming inverted. The airplane subsequently entered a left descending spiral. The pilot decided to land as soon as possible and selected an emergency landing area on a small frozen lake. However, he was unable to reach that spot and instead chose a stand of trees for the landing. During the landing, the airplane's wings, landing gear, and fuselage sustained extensive damage. The entire emergency event lasted approximately one minute.
Aircraft and Maintenance History
The airplane had been rebuilt about five months before the accident and had accumulated about two hours of operation since the rebuild. The skis were installed on the airplane just prior to the accident flight. After the accident, the airplane was disassembled and recovered from the site.
Post-Accident Examination
The fuselage and components were examined by personnel from the National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA). No evidence of a flight control system malfunction was found. The ski retention cables and springs exhibited no anomalies.
Probable Cause
The investigation did not determine a probable cause for the uncommanded left turn, as no mechanical or system malfunctions were identified. The source does not state a cause, and therefore, no probable cause is assigned.