WHILE MANEUVERING FOR ANOTHER SWATH RUN, THE AIRCRAFT STALLED AND COLLIDED WITH THE TERRAIN IN A STEEP NOSE DOWN ATTITUDE. A FIRE ERUPTED AND DESTROYED THE AIRCRAFT. NO EVIDENCE OF A MECHANICAL MALFUNCTION WAS FOUND. ABOUT 8 MI WEST AT AMARILLO, TX, THE 1100 CST WIND WAS REPORTED TO BE FROM 250 DEG AT 19 GUSTING 28 KTS.