FTW97FA135

The pilot (plt) departed Cookson, OK, in a homebuilt aircraft (acft) for an approximate 30 minute flight to Stilwell, OK. Witnesses at Stilwell said he made a low pass on a northerly heading (about 50 ft off the ground) at a high rate of speed. One witness estimated the acft was traveling faster than 200 mph, when he saw the acft's right wing skin separate from the acft. The right wing then came off. The acft was observed to roll several times & travel about 1100 ft before it impacted the ground. Postimpact examination of the wreckage revealed a fracture in the wing spar about 18 inches in from the right wing tip. There was a discoloration in the fracture, which had the appearance of a varnish like substance. An FAA inspector reported that 'there were different color glue joints in the wing construction indicating that there were different kinds of glue used.' Also, the failure mode differed; the dark glue joints failed in the wooden structure, where as, the other glue joints failed in the bond. Some of the wing joints that had failed had discoloration between the rib & the wooden skin. The inspector suggested that 'either improper clamping during construction, prevarnishing of the contact surfaces, or bond separation followed by moisture weathering could have caused this.' The plt had purchased the homebuilt acft on 10/1/96. It had been originally certificated for flight on 10/27/72. On 2/11/73, it had been damaged during a takeoff mishap, & 'new wing construction' had been performed.

History

On March 20, 1997, approximately 1735 central standard time, a homebuilt Teschendorf Cassutt Sport airplane, N86T, was destroyed during impact with terrain following an in-flight airframe failure while maneuvering at the Stilwell Airport, near Stilwell, Oklahoma. The commercial pilot, sole occupant in the airplane, was fatally injured. The airplane was owned and operated by the pilot under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country personal flight which originated from Cookson, Oklahoma, approximately 30 minutes before the accident. No flight plan was filed.

According to a witness, "the plane was going north [parallel to the runway], about 50 feet off the ground and at a high rate of speed." Another witness reported "seeing it flying very low and [I] thought it was going to hit the metal building there at the airport but I saw him roll real fast to the right." Another witness estimated that the airplane was traveling faster than 200 mph just before he saw the airplane's right wing skin separate from the airplane and then the right wing came off. The airplane was observed to roll several times and travel approximately 1100 feet before it impacted the ground.

Personnel information

According to the pilot's wife, he had learned to fly helicopters in the Army and fixed winged aircraft in the Air Force. FAA medical records indicate, as of January 13, 1997, that he had a total of 6,527 flight hours with 100 hours in the last 6 months.

Aircraft information

The airplane was a homebuilt experimental aircraft designed for racing and was fully aerobatic. Construction of the airplane was started in the Fall of 1971. Its original registration number was N219, and an airworthiness certificate was issued on October 27, 1972. The airplane was damaged during a takeoff roll on February 11, 1973, and "new wing construction" was installed on June 6, 1974. The airplane's registration was changed to N86T, and a new certificate of airworthiness was issued on June 21, 1974. At the time of the accident, the airplane was flying under an unlimited Special Airworthiness Certificate dated April 30, 1985.

The pilot purchased the airplane on October 1, 1996. A witness reported to the Investigator-In-Charge (IIC) that the pilot, who was a FAA licensed A&P mechanic, performed his own Condition Inspection. There was no documentation of this inspection in the aircraft logbooks.

Aerodrome information

The Stilwell/Cherokee Nation Airport is an uncontrolled airfield with one asphalt runway (17-35) which is 4200 feet by 60 feet.

Wreckage and impact information

The airplane's debris field was distributed over approximately 1,500 feet along a path parallel to runway 35 and approximately 330 feet east to the runway's centerline (see attached wreckage diagram). The IIC did not visit the accident site, but two FAA Inspectors did go to the site to obtain all the facts, conditions, and circumstances surrounding the accident.

Much of the airplane's right wing was brought back to Oklahoma City where the IIC had an opportunity to look at it. The right wing's wooden spar had failed approximately 18 inches in from the wing tip and there was discoloration in the fracture which had the appearance of a varnish like substance. The FAA Airworthiness Inspector reported that "there were different color glue joints in the wing construction indicating that there were different kinds of glue used" (see attached FAA Inspector letters). This observation was further supported in that the failure mode differed, i.e., the dark glue joints failed in the wooden structure where as the other glue joints failed in the bond. Some of the wing joints that had failed had discoloration between the rib and the wooden skin, the FAA Inspector suggested that "either improper clamping during construction, prevarnishing of the contact surfaces, or bond separation followed by moisture weathering could have caused this." The wing was constructed with no access/inspection openings to allow for adequate routine visual inspection of the inner wing structure.

Several cockpit instruments were recovered from the airplane. The engine tachometer indicated 3,000 rpm and the accompanying tach time indicated 179.92 hours. The accelerometer indicated a plus 4.5 g and minus 6.2 g. The vertical speed indicator indicated down 1,400 feet per minute.

Medical and pathological information

An autopsy was not performed per request of the family. The medical examiner from Adair County did perform an examination of the pilot and filed a Report of Investigation by Medical Examiner with the Chief Medical Examiner of the State of Oklahoma. Toxicological tests were performed and were found to be negative.

Additional data

The airplane was released to the pilot's wife.