HISTORY OF FLIGHT On August 2, 1997, at 1330 central daylight time (cdt), a Briegleb BG-12A glider, N5516V, operated by a commercial pilot, was destroyed during an in-flight breakup near Superior, Wisconsin. The local personal flight was being operated under the provisions of 14 CFR Part 91, and was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot was fatally injured. The flight departed the Richard I. Bong Airport, Superior, Wisconsin at approximately 1300 cdt. Another pilot was towing the glider. In a statement to the Federal Aviation Administration (FAA), the pilot of the tow aircraft said, "Was asked to give a tow and discussed speed. [The pilot] said his check list showed tow speed 80-85. Normally tow at 65. Took off runway 31, going to 2,500', south of the taconite pile, 2,000'...2,200', circling. Suddenly felt straight pull, yaw left, tail up, looking straight at ground - a really strong jerk. After a couple of seconds felt hard jerk down. Pulled tow release. Started left turn, looking for glider, couldn't see him, no response on radio. Returned to field. Police waiting. Took off again with [a police officer] to search...Never had to pull release before. Tow was real smooth until first jerk..." According to a witness, "On August 2nd, I was parked on a road at [work]. I was facing east. I observed what I thought was a metal object flip-flopping in the sky. It was long and thin. Although I was a long ways away, I could tell it was big. It fell mostly vertically, oscillating back and forth. It fell slowly to the ground." "At the same time I noticed other parts reflecting in the sun. One was large and several were smaller. They appeared to be chrome colored and glinted in the sun." An FAA inspector on scene at the accident stated that the wing failed adjacent to the right hand fuselage attach point. The glider impacted the ground inverted and nearly vertically. The right wing was found 2 blocks away, with the wing tip up, in the bank of a creek. The inspector determined that the glider was above maximum allowed gross weight and beyond the center of gravity limits. PERSONNEL INFORMATION The pilot, born March 2, 1938, was the holder of a commercial pilot certificate with airplane single engine land and sea, multiengine land, and glider aero tow privileges, as well as holding an instrument rating. The pilot was an airplane single engine and multiengine flight instructor with instrument and glider ratings. The pilot held an advanced ground instructor and an airframe and powerplant mechanic certificate. The pilot's last aviation medical examination was performed on November 4, 1996. The pilot held a current second class medical with restriction, "must wear corrective lenses" at the time of the accident. The pilot's logbook was not recovered. FAA records indicate he accumulated 4,600 total hours as a pilot at the time of his last aviation medical examination. AIRCRAFT INFORMATION The Briegleb BG-12A, serial number 1026, was a built-by-plans, all wood, low wing, monoplane that can accommodate a single pilot. The aircraft was certified as an experimental amateur built on March 25, 1982. METEOROLOGICAL INFORMATION A weather observation facility, located at the departure airport, listed the weather approximately 15 minutes after the accident as: Observation time: 1345 cdt Wind: 260 degrees magnetic at 7 knots Visibility: 10 statute miles Sky Condition: Clear below 12,000 feet Temperature: Missing Dew Point Temperature: Missing Pressure: 29.98 inches of mercury WRECKAGE AND IMPACT INFORMATION The glider was destroyed when it contacted the ground nearly vertically and inverted. The right wing from the glider came to rest tip up 2 blocks from the main wreckage embedded in the bank of a stream. (See attached photographs of accident scene and spar fracture surfaces). MEDICAL AND PATHOLOGICAL INFORMATION The Office of Anoka County Coroner, Coon Rapids, MN on August 4, 1997, performed an autopsy. A Forensic Toxicology Fatal Accident Report was performed by the FAA Civil Aeromedical Institute, Oklahoma City, Oklahoma. The toxicology report indicated the following results: *21 (mg/Dl, mg/hg) Ethanol detected in Kidney Fluid *46 (mg/Dl, mg/hg) Ethanol detected in Muscle Fluid *12 (mg/Dl, mg/hg) Acetaldehyde detected in Muscle Fluid *1 (mg/Dl, mg/hg) N-Butanol detected in Muscle Fluid *6 (mg/Dl, mg/hg) Acetaldehyde detected in Kidney Fluid According to a statement by a medical representative of the National Transportation Safety Board, "In its investigations, the National Transportation Safety Board routinely requests complete toxicology evaluation on all transportation operators who are fatally injured. In around 10% of such evaluations, ethanol is detected in the blood and/or tissues. In many of these cases, particularly when significant decomposition has taken place, the ethanol present is the result of production of alcohol by microorganisms in the tissues after death, and does not represent the ingestion of alcohol." TESTS AND RESEARCH The pilot of the glider listed the empty weight of the glider as 693 pounds. His weight at the time of autopsy was 235 pounds, giving the glider a weight of 928 pounds. The pilot listed the maximum gross weight of the glider as 850 pounds. The center of gravity (CG) limits for the glider were between 17 and 18 inches for flight over 100 miles an hour, and 17 to 19 inches for flight under 100 miles an hour. . The wing was found 2 blocks from the main wreckage. Weight and balance computations showed the glider was 78 pounds over maximum gross weight, and the center of gravity was 19.7 inches. The limits for center of gravity are 17-18 inches over 100 miles an hour, and 17-19 inches under 100 miles an hour, due to the possibility of oscillations at the higher speeds. At speeds over 100 miles an hour a CG of 19 inches can permit phugiod oscillations. The tow pilot told FAA inspectors that the accident pilot wished to be towed at 80-85 knots. 100 miles an hour is 86.9 knots.