On September 18, 2016, about 0950 Pacific daylight time (PDT), a Cessna 120 airplane, N76284, veered off the runway during the landing roll, and nosed over at Yolo County Airport (DWA) in Davis, California. The empennage sustained substantial damage. The pilot sustained minor injuries and the sole passenger sustained serious injuries. The airplane was registered to a private individual, and was operated by the pilot as a visual flight rules (VFR), local, personal flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the flight; no flight plan was filed. The flight originated from DWA, about 0840 PDT. The pilot of the tailwheel-equipped airplane reported that, during the landing roll, the airplane "began suddenly swerving with increasingly tremendous centrifugal force to the left" and would not respond to opposite rudder inputs. The airplane veered off the runway to the left and into a freshly plowed field. During the runway excursion, the airplane crossed over a dirt trench, and then nosed over. During the nose over, the center safety belt bracket, which secures the pilot and front seat passenger's seatbelts to the cabin floor failed, and the pilot was released from his seatbelt. An examination of the restraint system revealed that the aluminum center safety belt bracket, which was likely installed when the airplane was manufactured in 1946, had failed in shearing overstress during the nose over, which resulted in the pilot being released from the restraint system. Examination of the airplane manufacturer's records revealed that shortly after the airplane was manufactured, the manufacturer began installing a steel center safety belt bracket in new production airplanes. (See Materials Laboratory Factual Report in public docket for additional information.) Following a similar accident (ERA14FA327), the manufacturer issued a service bulletin on February 17, 2015 that called for inspection of the center safety belt bracket on all Cessna 120 and 140 airplanes to determine if the latest type (steel) bracket was installed and replacement of any older type (aluminum) brackets found with the latest type. (See SEB-25-03 in public docket for additional information.) During a telephone conversation with the mechanic that completed the airplane's annual inspection, he stated that he was unaware of the service bulletin related to the center safety belt bracket. A review of the FAA aircraft registry database found that approximately 2,145 airplanes, which were manufactured with this center safety belt bracket, were currently registered in the United States. Of these, about 2,099 (98%) were manufactured before the effectivity of the material change.