At about 1312 mountain time, a Piper J3C-65 airplane and a Schleicher ASK-21 aerobatic glider collided in flight and were destroyed about one-half mile north of the Pleasant Valley Airport, Peoria, Ariz. The pilot and pilot-rated passenger in the Piper and the pilot and passenger in the glider were killed. According to witnesses familiar with operations at the airport, the Piper departed runway 05L and made a climbing left turn to a left downwind at pattern altitude of about 600 feet agl. The Schleicher glider was performing aerobatic maneuvers in a predetermined aerobatic box north of the airport. The glider was performing a loop between 800 and 600 feet agl when the Piper flew into its path. The left wing of the oncoming Piper struck the tail of the Schleicher glider between the empennage and the main fuselage, severing the empennage of the glider. A large portion of the left outboard wing of the Piper separated during the collision. Both aircraft entered uncontrolled descents and crashed in the desert north of the airport.