On October 19, 2003, at 1700 Pacific daylight time, a Cessna 170, N3979V, veered off the runway while landing at Montgomery Field, San Diego, California. Plus One Flyers was operating the rental airplane under the provisions of 14 CFR Part 91. The commercial pilot was not injured, and the airplane was substantially damaged. Visual meteorological conditions prevailed, and a flight plan had not been filed. The personal flight originated at MCAS Miramar, San Diego, about 1645. The pilot told the National Transportation Safety Board investigator that as he flared for landing, the tail wheel touched the runway, and then he heard a "click." At that time the seat slid backwards about 1 foot, restricting his ability to reach the controls. The pilot tried to adjust his seated position to regain access to the airplane's controls, but the airplane entered a ground loop to the left and came to rest left of the runway. A Federal Aviation Administration inspector examined and photographed the pilot's seat. He reported that the seat track locking pin was positioned outside the seat track. Examination of the photographs of the pilot's seat and rail showed that the side floor deck was buckled, the seat was structurally deformed, and the seat locking pin was positioned outside the seat rail and roller.