Accident Overview
On May 29, 2010, at approximately 0825 central daylight time, a Thunderbird Aviation Top Dog weight-shift control airplane, registration N2574V, impacted terrain while attempting to take off from Carter Memorial Airport (T91) in Luling, Texas. The sport pilot, who was the sole occupant, sustained serious injuries. The airplane’s fuselage structure and wing surface were substantially damaged. The aircraft was registered to and operated by a private individual under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was originating at the time of the accident.
Investigation Findings
There were no witnesses to the accident, and the pilot could not recall the sequence of events, providing no statement. A Federal Aviation Administration inspector examined the wreckage and found no preimpact anomalies. The engine, a Rotax 503 twin-cylinder, dual-carbureted, two-stroke engine rated for 50 horsepower at 6,800 rpm, was removed and sent to the manufacturer in Vernon, Canada, for examination under the auspices of the Canadian Transportation Safety Board.
During the engine examination, all spark plugs were found to be finger-tight. Signatures of water intrusion were detected in one carburetor float bowl, and the other carburetor bowl contained fuel tainted with an unknown substance. The engine was mounted on a test stand with clean fuel, the spark plugs tightened, and the air filter replaced. It started on the first pull and operated normally at idle, but when advanced toward maximum rpm, it could only reach 5,730 rpm. Repeated attempts confirmed the engine could not achieve maximum rpm. Further inspection revealed that the spark plugs and carburetor main jets were not per the manufacturer’s specifications. After replacing them with components recommended by the manufacturer, the engine achieved 6,230 rpm, which was the maximum expected under the test conditions.
Probable Cause
According to the manufacturer, the carburetor main fuel jets installed at the time of the accident provided a lean mixture that would not allow the engine to reach its rated power.