On May 5, 2001, at 1450 hours Pacific daylight time, an Aero Commander 112A, N1159J, veered off runway 27 after landing and collided with a ditch at the Riverside Municipal Airport, Riverside, California. The airplane was operated by the pilot/owner under the provisions of 14 CFR Part 91, and sustained substantial damage. The pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed for the local area personal flight that originated about 1430. A flight plan had not been filed. The Safety Board Investigator-in-charge (IIC) interviewed the pilot. He had been cleared to land, with no discrepancies noted with the approach or initial touchdown. On the landing rollout the airplane veered to the right. The pilot applied left rudder to correct the movement to the right; however, the airplane continued its movement to the right of the runway. He applied the brakes in an attempt to stop, but the airplane went into a ditch. In the pilot's written statement to the Safety Board, he stated that the purpose of the flight was to conduct three takeoffs and landings for currency. The accident landing was the first landing of the day. He stated that he had been cleared to land and that touchdown was normal. On the landing rollout the airplane went to the left and he corrected the airplane back to runway centerline. He reported that the airplane started to move towards the right. He attempted to correct the turn to the right with left rudder input. When that had no effect, he applied the left brake. The airplane continued to the right and went into a ditch. A Federal Aviation Administration airworthiness inspector inspected the nose wheel assembly. He noted that the nose wheel assembly appeared to show "excessive play wear and could have contributed to [a] loss of control when landing his aircraft." No further discrepancies were noted with the airplane during the inspection.