On February 4, 1995, at 1330 hours Pacific standard time, a Piper PA-38-112, N9905T, exited the right side of runway 25 at Rosamond Skypark, Rosamond, California, and nosed over onto its back. The pilot was completing a visual flight rules personal flight. The airplane, owned and operated by the pilot, sustained substantial damage. The certificated private pilot sustained minor injuries; his passenger was not injured. Visual meteorological conditions prevailed. The flight originated at Bullhead-Laughlin Airport, Bullhead City, Arizona, at 1155 hours. National Transportation Safety Board investigators conducted a telephone interview with the pilot on February 4, 1995. The pilot said that after passing over Daggett, California, he heard a loud thud. He continued the flight to Rosamond Skypark. The pilot said that he landed the airplane on its main wheels. However, when the nose wheel touched down, the airplane swerved violently to the right and exited the north side of the runway. The airplane nosed over when it entered the soft terrain next to the runway. A Federal Aviation Administration (FAA) inspector from the Van Nuys (California) Flight Standards District Office said that the pilot told him that he has Parkinson's disease. The pilot's last third-class medical certificate was issued on June 14, 1983. The FAA Western-Pacific Region deputy flight surgeon said that Parkinson's disease can, and probably will, affect the pilot's coordination and his ability to fly an airplane. This condition will worsen in the advanced stages. The pilot also told the inspector that his last biennial flight review was 4 or more years overdue. The airplane's current registered owner told the inspector that the pilot purchased the airplane about 1 year before the accident. The pilot did not submit the required Aircraft Accident Report, National Transportation Safety Board Form 6120.1/2. He did provide the Safety Board with a written statement. In his written statement, the pilot generally repeated his telephone statement he gave to Safety Board investigators. He added, however, that ground witnesses said the nose wheel was not aligned with the runway when it touched the runway. The FAA inspector did not report any preexisting airplane malfunctions or failures.