On September 14, 1999, at 1810 hours Pacific daylight time, a Nye KR-2, N71KN, was destroyed during an off-airport impact with trees and terrain shortly after takeoff from the Mariposa-Yosemite airport, Mariposa, California. The private pilot was fatally injured. Visual meteorological conditions prevailed for the personal flight, which was operated by the owner under 14 CFR Part 91. No flight plan was filed for the local area flight. An inspector from the Federal Aviation Administration (FAA) Fresno Flight Standards District Office responded to the scene. Witnesses told the inspector that the aircraft departed from Mariposa about 1300 and was seen later maneuvering in the mountain valley north of the airport. The engine sound roared and subsided as the aircraft disappeared from view below mountain peaks. Three witnesses were interviewed by personnel from the Mariposa County Sheriff's Office. According to the sheriff's report, the witnesses reported that in the minutes before the accident, the aircraft returned to the airport and approached runway 26 in left-hand traffic. The aircraft made a touch-and-go landing on runway 26 and then climbed to about 200 feet agl over the departure end of the runway and made an abrupt right roll to nearly a 90-degree bank angle. It then turned to a northerly heading, and, as it turned, descended in a wings vertical attitude into terrain near the runway end and disappeared from view. Two of the witnesses, and a third person who did not witness the accident, reported to the deputy that they had seen the pilot perform the steep right turn departure many times before. Two of the witnesses reported that, during the touch-and-go landing and subsequent climb, the engine sounded different from the aircraft engines they were accustomed to. They assumed this was because the aircraft had an automobile (Volkswagen) engine. One witness reported that the engine was operating smoothly the entire flight until impact; the second reported the engine was operating smoothly during the touch-and-go but did not recall the engine sound during the descent to impact; and the third witness reported that the engine "sputtered" during the climb and descent to impact. The deputy reported there was fuel spilling from the aircraft after the accident, and the aircraft appeared to have impacted on a northerly heading, in a steep nose down attitude causing severe damage to the front of the aircraft and less to the empennage. In a telephone conversation with the Safety Board investigator, the third witness said the aircraft made an abrupt right turn with the wings banked nearly vertical. This witness was not a pilot; however, the steep right turn was something that he had seen this pilot do on previous occasions. It was while the aircraft was in the steep right-hand turn about 150 feet agl that he heard the engine sputter, cough, and the power decrease. He said the aircraft descended toward the ground in the steep bank until he lost sight of it about 30 feet agl. He thinks that the pilot was trying to level the wings when it disappeared from view. The FAA inspector reported that the aircraft's flight controls were continuous at the accident site and there was a strong fuel smell. No heavy aircraft were reported to have preceded the aircraft on the departure runway.