On June 25, 1999, at 2130 central daylight time, a Beech C-23, N9703Q, piloted by a private pilot, was destroyed during a collision with the ground following a loss of control in flight. Witnesses reported instrument meteorological conditions prevailed at the time of the accident. The personal 14 CFR Part 91 flight was not operating on a flight plan. The pilot was fatally injured. The flight departed Aberdeen, South Dakota, exact time unknown. Two witnesses reported seeing the airplane flying about 1 mile northeast of the Mandan Municipal Airport during a heavy rain storm. They said the airplane's landing lights were illuminated and that the sky was black with lightening coming from the clouds. Both witnesses said the rain was very heavy and blowing almost horizontally. One of the witnesses said she saw the airplane pitching up and down and rolling left and right violently before losing sight of it due to very heavy rains. The second witness said the wind was very gusty and strong. He said the wind almost pushed his car off the road. AIRCRAFT INFORMATION The aircraft was a 1970 manufactured Beech C-23 with a Lycoming O-360-A2G 180hp engine. The aircraft and engine had an annual inspection on November 1, 1998 at a total aircraft time of 3791 hours. On July 7, 1997, a gyro horizon, Part Number 5000B-20, Serial Number T36993J was installed in the aircraft. Tachometer time was 3681.6 hours on the FAA Form 8130-3 Airworthiness Approval Tag. METEOROLOGICAL INFORMATION A National Transportation Safety Board Meteorology Factual Report is an attachment to this report. On page 10 of this report, under the category of "Local Storm Reports" at 2127, on the date of the accident, 7 miles southwest of Mandan, ND, there was a 60 mile per hour wind gust report by ham radio skywatch spotter. At 2200 at Mandan, ND flooding of numerous streets and underpasses is reported. Bismarck, North Dakota, about 5 miles east of Mandan, at 2125 was reporting thunderstorm with heavy rain, visibility 1 3/4 miles, thunderstorms all quadrants moving northeast, lightning northwest-south-southeast. COMMUNICATIONS Below is a summary of communications with the Bismarck, ND FAA Air Traffic Control Tower: 2107 - N9703Q checked on with Bismarck approach approximately two five miles southeast of the airport enroute Mandan airport. 2110 - N9703Q reports moderate turbulence. 2112 - Bismarck approach advises N9703Q of an area of weather currently over the Mandan Airport. 0216 - Bismarck approach advises N9703Q that the aircraft is entering an area of weather which extends all the way to the Mandan Airport. 0219 - N9703Q requests vectors to the Mandan Airport. 0223 - N9793Q reports the Mandan Airport in sight. 0223 - Bismarck approach terminates radar and approves frequency change to Mandan Unicom. WRECKAGE AND IMPACT INFORMATION N9703Q's ground impact location was in a field that had a grass and alfalfa mixture that was about 3 feet high. This vegetation was bent almost parallel to the ground about 300 feet around the impact point. N9703Q's wreckage trail went up a hill about 500 feet. The wreckage trail ended about 100 feet before the hill's crest. The trail began again about 75 feet from the hill's crest and continued for about another 550 feet on the downside of the hill (See attached photographs and wreckage diagram). Inspection of the aircraft controls established cable continuity for all 3 flight control axis. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was completed by the State Forensic Medical Examiner, Bismarck, ND on June 28, 1999. A Forensic Toxicology Fatal Accident Report was prepared by the FAA Civil Aeromedical Institute, Oklahoma City, Oklahoma. The toxicology results for the pilot were: No Carbon Monoxide detected in blood. No cyanide detected in blood. No ethanol detected in vitreous. No drugs detected in urine.