What happened
A commercial pilot and one passenger were conducting aerobatic maneuvers in an aerobatic box located near runway 5L at an uncontrolled airport. The maneuver area measured 1 kilometer square, extending from the surface to 6,600 feet MSL. The southern boundary of this box was positioned approximately 1,490 feet north of the centerline of runway 5L.
At the same time, a Piper J3C departed runway 5L. The aircraft was occupied by a commercial pilot/flight instructor in the front seat and a private pilot in the rear seat. The Piper performed a left downwind turn that entered the airspace where the glider was operating. Witnesses observed the glider reach the top of a loop, after which its nose lowered into a vertical descent. As the glider attempted to recover at approximately 600 feet AGL, the left wing of the Piper struck the tail section of the glider between the empennage and the main fuselage. This impact severed the glider's empennage.
The collision caused a large portion of the Piper's left outboard wing to separate. Both the glider and the Piper J3C entered uncontrolled descents, eventually coming to rest near the center of the aerobatic box. There were no fatalities reported in the accident.
The investigation
The investigation noted discrepancies in airport procedures. While the airport facilities directory instructs aircraft departing runway 5L to follow a right-hand traffic pattern, the airport's segmented circle depicts a left-hand departure for that runway. Neither aircraft was equipped with a radio, though a common traffic advisory frequency of 122.9 MHz was available at the field. The pilot of the Piper had been based at the airport for several years and was familiar with local operating procedures.