NTSB Factual Report

HISTORY OF FLIGHT

On December 5, 1993, approximately 1040 central standard time, an Upton Mustang M-II, N4YP, was destroyed during an uncontrolled descent approximately 6 miles southwest of Guthrie, Oklahoma. The private pilot was fatally injured. Visual meteorological conditions prevailed for the personal flight.

The pilot's wife said her husband departed Downtown Airpark in Oklahoma City between 0930 and 1000 for a local personal flight. The only known witness to the accident, a farmer in a field, said he heard a loud noise, looked up, and saw the airplane diving towards the ground.

AIRCRAFT INFORMATION

According to the airplane's designer and the kit's manufacturer, Mustang owners and builders were cautioned several years ago to remove the pop rivets from the aileron counterweights and to replace them with a stronger type of rivet. There were no entries in the aircraft records to indicate this modification had been accomplished.

WRECKAGE AND IMPACT INFORMATION

Both wings and the left wing tip, left elevator, and left aileron were located 1, 2, and 3 miles south of the main body of wreckage, respectively. The right wing tip and both aileron counterweights were not recovered. The right side of the wing carry-through spar was bent down and twisted aft at the fracture point. Both control sticks remained attached to the aileron torque tubes, and one of the torque tubes remained attached to the right aileron. Fracture surfaces were examined by a metallurgist from the University of Denver. All failures were found to be overload.

The leading edge of the left aileron was torn at the rivet line and the aluminum skin was spread out and flattened. The outboard portion of the left elevator leading edge was similarly torn at the rivet line, and the hinge attachment was bent to the right.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy (case no. 9305339) was performed on the pilot by the Oklahoma State Medical Examiner's Office in Oklahoma City, Oklahoma. The results of the toxicological examination, performed by the Armed Forces Institute of Pathology, are attached to this report.

ADDITIONAL INFORMATION

According to the pilot's wife and corroborated by his logbook, the pilot had never taken aerobatic instruction nor logged any aerobatic flights.

NTSB Probable Cause

WAS THE IN FLIGHT FAILURE OF THE LEFT AILERON FOR REASONS UNDETERMINED.