At about 1015 Pacific time, a Cessna Citation 525 ditched in the waters of Penn Cove after losing elevator trim control. The pilot and passenger were not injured. The pilot said they were climbing through 16,000 feet en route to FL 330 when the airplane abruptly nosed over to 45 degrees down. He disconnected the autopilot, throttled back and attempted to re-trim the elevator. He said the cockpit trim indicator was in the full nose-down position and neither the manual trim nor the electric trim would respond to his inputs. After numerous attempts to troubleshoot the problem, the pilot elected to ditch about 300 yards offshore.