On June 14, 1998, about 1145 hours mountain standard time, an experimental Blackmore RV-4, N813R, collided with mountainous terrain south of Sedona, Arizona. The aircraft was destroyed and the private pilot, the sole occupant, sustained fatal injuries. The aircraft, owned and operated by the pilot, was on a local flight conducted under 14 CFR Part 91 of the Federal Aviation Regulations. The flight originated from the Sedona airport about 1120. Visual meteorological conditions prevailed at the time and no flight plan was filed. A Federal Aviation Administration inspector performed an on-site inspection of the aircraft wreckage. He observed that the accident site was located on the northeast side of Cathedral Rock, a tall, rock formation that stands 1,000 feet above the surrounding terrain. Cathedral Rock is formed by two main spires with a 200-foot-wide gap between them. The wreckage was located about 200 yards from the northeast side of this gap, about 100 feet below the steep terrain that angles downward about 45 to 60 degrees. According to the inspector, the aircraft was resting on a southeasterly heading. The inspector judged that, from the frontal damage to the aircraft and lack of disturbance to the surrounding vegetation, the aircraft impacted the ground on a steep angle relative to the terrain. Retrieval of the engine tachometer, altimeter, and turn coordinator indicated the aircraft was developing 2,450 rpm's approximately 4,400 feet msl, while in a slightly banked right turn. An inspection of the engine by the manufacturer representative, under the supervision of the Safety Board investigator, revealed no evidence of abnormalities or malfunctions prior to impact. According to conversations with friends of the pilot, the inspector learned the pilot was planning to attend a high school reunion in the Sedona area that weekend. At the conclusion, the pilot mentioned he wanted to perform some aviation stunts for his friends who would be hiking in the Cathedral Rock area the following Sunday morning. The inspector also spoke with a close friend of the pilot's who had previously flown as a passenger with the pilot during a practice aerobatic flight involving a "roll" maneuver. He recalled that whenever the pilot would come out of the roll, he would "lose his centrifugal force to the outside and drop out of the maneuver." The friend had witnessed the pilot attempting this "roll" maneuver within 15 to 20 feet of the top of the Cathedral Rock cliffs on several previous occasions. People on top of the spires at Cathedral Rock were able to see the pilot smiling and laughing as he flew by. He went on to explain that the aircraft appeared to have needed approximately 75 to 100 feet agl of additional altitude in order to complete the maneuver without contacting the ground. The friend concluded that it was the pilot's intention to "buzz the hell out of them" (the hikers on Cathedral Rock), and that he had continuously tried to persuade him not to do so. Several hikers were on a trail up into the Cathedral Rock area on the morning of the accident. They witnessed the aircraft fly almost one complete loop before it contacted the terrain at the base of the mountain. Hikers stated the aircraft's engine could be heard throughout the loop. One witness encountered a person claiming to be a friend of the pilot's who stated the pilot was "showing off for his party of friends." The kit manufacturer stated that increased density altitude conditions, that occur with higher than standard temperatures, degrade aircraft performance. The accident site was about 4,450 feet msl, with an altimeter setting of 30.24 inches and a current temperature of 72 degrees Fahrenheit. Density altitude was computed by a Safety Board investigator as 5,873 feet. An autopsy was conducted by the Yavapai County Coroners Office with specimens retained for toxicological examination. The toxicological tests results were negative for alcohol and all screened drug substances.