What happened
While climbing through approximately 100 feet above the ground, an aircraft towing a glider experienced an engine roughness that progressed to a complete engine failure. In response to the loss of power, the pilot performed a forced landing into a grassy, rolling field. During the descent and impact, the aircraft struck a small tree and a fence before hitting the ground. The towed glider released from the aircraft and landed without incident. All occupants were not injured.
The investigation
Post-accident examinations of the powerplant, its systems, and accessories showed no evidence of mechanical malfunction or difficulty prior to the impact. During a subsequent run-up, the engine performed satisfactorily.
Investigators examined the fuel supply, draining 7.5 gallons of 80/87 octane aviation fuel from each of the two fuel tanks. The aircraft has a established "no takeoff" value of 6.75 gallons or less. This specific threshold exists because the positioning of the fuel tank outlets creates the possibility of interrupted fuel flow during various flight attitudes.