Accident Overview
A pilot reported that while turning left to base leg, the engine began to lose power. The pilot immediately checked the throttle and mixture controls, which were in the 'Full' position. Subsequently, the engine started to accelerate and decelerate without any input to the throttle or mixture controls. The pilot stated that the engine sounded as if it would recover but then abruptly stopped.
Pilot Actions
During the accident flight, on the downwind leg of the traffic pattern for Runway 01, the pilot reported switching fuel tanks and checking for carburetor icing. In an interview with Federal Aviation Administration (FAA) inspectors, the pilot provided these details.
Post-Accident Examination
An examination of the aircraft at the accident site revealed the following positions of controls: the fuel selector was in the 'Off' position; the throttle and mixture were in the 'Full' positions; carburetor heat was set to 'Cold'; the magneto switch was on 'Both'; the boost pump was 'On'; and the master switch was found 'Off'. However, it was reported that crash/rescue personnel had selected the master switch from 'On' to 'Off'. No other flight controls or instruments were reported to have been changed.
Examination of the engine revealed no anomalies that would prevent operation. A functional test run was conducted with the engine installed on a test stand; the engine ran without any anomalous behavior.
Approximately eight gallons of Aviation grade 100 Low Lead fuel were found in the right fuel tank. The left fuel tank was compromised during the accident sequence.