On August 21, 1997, at 1435 mountain daylight time, a Rockwell S-2R agricultural airplane, N4893X, owned and operated by Farm and Ranch Aviation Company, Deming, New Mexico, was substantially damaged when it impacted terrain following a loss of engine power, while maneuvering near Columbus, New Mexico. The commercial pilot, sole occupant, received serious injuries. Visual meteorological conditions prevailed for the Title 14 CFR Part 137 aerial application flight. The flight originated from a farm strip in Certzalia, New Mexico, at 1420, and no flight plan was filed. The pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that he had just completed an aerial application order for a farm located 12 miles west Columbus, New Mexico, when the accident occurred. The pilot stated the following; "on the final pass [he] pulled up out of the field and initiated a turn towards Deming, when an object came through the right corner windshield striking [him] in the head." The pilot was rendered unconscious. He regained consciousness as the left wing contacted the ground, and the airplane cartwheeled coming to rest upright in brush covered, desert like terrain. A witness who was approximately 1 mile from the accident site stated that, he saw the airplane "flying straight and then nose into the ground." He added that, he did not hear any engine noises. Several witnesses in a nearby field, reported to the pilot that when he started to pull the airplane out of the field and turn, the engine quit. Examination of the aircraft wreckage by an FAA representative revealed that the wreckage was distributed along a path 75 yards in length. The engine and engine mounts were separated from the airframe. The propeller blades were bent in a "horse shoe" shape. The left wing was twisted, torn and bent upwards. A portion of the left wing was located 20 yards from the main wreckage. The right wing separated from the airplane and remained intact. The right main landing gear and tail wheel separated from the airplane. Control cable continuity was established to the ailerons and elevator. The engine was examined by the owner. The owner reported that it "appears" that the exhaust side rocker box and exhaust valve mechanism broke away from the number 7 cylinder. There was a "deep groove" on the back side of a propeller blade. The owner stated that the rocker box could have been ejected from the engine and contacted a propeller blade, which deflected the rocker box into the cabin. No further examination of the aircraft was conducted.