At about 1300 Pacific time, a Mooney M20E and a Beech BE-76 Duchess collided in midair about 1 mile northwest of McClellan-Palomar Field. The Mooney pilot and the instructor and student in the Duchess were killed. The Mooney checked in with controllers 1255 and reported 10 miles north over Oceanside. At 1258, the controller cleared the Beech for a right crosswind departure on runway 24. About 1300, the controller made a continuous transmission that told the Mooney that a Duchess was on a right crosswind departure, and told the Duchess that a Mooney was inbound on the forty-five. There was no reply from either airplane.