As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ACCIDENT INVESTIGATION, FOUND RIVNUTS WERE SUBSTITUTED FOR 3 NAS684A3 NUTPLATES FOR REAR SEAT ATTACH HARDWARE. THE RIVNUTS EXTRUDED THROUGH THE HOLES IN THE STRUCTURE AND ALLOWED THE REAR SEAT TO PARTIALLY BREAK LOOSE. PARTS MANUAL FIG 20, ITEM NR 12.