Accident Summary
On April 25, 2014, at approximately 1742 central daylight time, a Flight Design GMBH CTLS light sport airplane, registration N106SF, was substantially damaged during a forced landing following a loss of engine power near Greenville, Texas. The pilot and passenger sustained minor injuries. The flight was operating under 14 Code of Federal Regulations Part 91 as a personal flight in visual meteorological conditions without a flight plan.
Flight History
The flight originated from Fox Stephens Field – Gilmer Municipal Airport (JXI), Gilmer, Texas, at about 1635, with an intended destination of Denton Enterprise Airport (DTO), Denton, Texas. Earlier that day, a routine maintenance inspection was completed. During the initial flight after inspection, the pilot noted that engine exhaust gas temperatures (EGT) differed by up to 150 degrees, though remaining within operating limits. He diverted to JXI, where a mechanic reported that the EGT difference was not unusual for that engine. Spark plugs were removed and examined; minor debris was removed from one upper right spark plug, but otherwise they exhibited normal wear. Engine oil showed no contamination. After reinstalling the spark plugs, two engine run-ups were normal. A third run-up before takeoff from JXI was also normal, and the takeoff proceeded normally.
About 25 minutes into the flight, EGT indications had equalized. Approximately 5 minutes later, the engine and propeller stopped abruptly. The pilot’s attempts to restore power were unsuccessful. He initially planned to divert to Majors Airport (GVT) in Greenville but lacked sufficient altitude. He executed a forced landing to an athletic field about 3 miles north of the airport. During landing, the nose landing gear separated and the airplane nosed over.
Postaccident Examination
A postaccident engine examination, conducted under FAA supervision, revealed that the No. 4 cylinder exhaust valve had failed near the valve head. Subsequent metallurgical examination determined the failure resulted from bending fatigue. The No. 4 cylinder, piston, and exhaust valve head exhibited extensive gouging, scraping, and deformation consistent with secondary damage from the failed valve. A hole was found in the top of the piston with extensive secondary impact damage. The tappets showed light to moderate spalling, except the No. 4 cylinder exhaust tappet, which exhibited severe wear, reducing its height by more than 5 mm compared to the intake tappet. The No. 4 cylinder exhaust valve cam lobe was severely damaged, with large spalls on both opening and closing sides.
Aircraft and Maintenance Information
The aircraft, a Flight Design CTLS (serial number F-09-10-13), had accumulated 1,613 total hours in service. It was powered by a 100-horsepower Rotax 912 ULS 2, 4-cylinder reciprocating engine (serial number 6775304) with identical service time. Maintenance records indicated compliance with requirements for an extended time-between-overhaul (TBO) of 2,000 hours. The most recent inspection was completed on the accident day at 1,608 hours. Records noted that engine oil was changed; the magnetic plug was described as “dirty, but OK.” Additionally, an exhaust pipe leak on the No. 2 cylinder was repaired, and two exhaust springs were replaced. No maintenance work specific to the No. 4 cylinder was documented.