On August 1, 1999, about 2115 Eastern Daylight Time, a Beech A36, N6357Y was substantially damaged while landing at Carroll County Regional Airport (W54), Westminster, Maryland. The certificated airline transport pilot and three passengers were not injured. Visual meteorological conditions prevailed for the flight that originated from Martin State Airport, Baltimore, Maryland. No flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot stated that he flew a straight-in approach to Runway 34 at W54. The touchdown was normal, then the airplane veered to the right. He was unable to control the airplane, and it went off the right side of the runway, into a ditch. The pilot further stated that he was not sure if the loss of control was pilot error or a mechanical problem. During the morning hours, on the day of the accident, air was added to the right tire. Subsequently, the pilot flew with a student before the accident flight. The student pilot reported that the left rudder pedal had to be depressed to taxi the airplane along a straight line. Examination of the wreckage by a Federal Aviation Administration Inspector, and a local mechanic, did not reveal any pre-impact mechanical malfunctions. The inspector observed damage to the propeller, landing gears, and webbing along the longeron. An on-site examination was conducted by the Maryland State Police. According to the trooper, all three landing gears left skid marks on the runway. The trooper stated that the main wheel skid marks were oriented 20 degrees to the right of the runway centerline, before the nose gear touched down. The skid marks continued for approximately 505 feet, off the right side of the runway and onto the grass. The reported winds, at an airport approximately 30 miles from the accident site, at 2054, were from 280 degrees at 8 knots.