As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) THE AIRCRAFT HAD JUST TAKEN OFF WHEN THE PILOTS NOTICED THAT THE LT MAIN FUEL CAP HAD DEPARTED THE AIRCRAFT. THE AIRCRAFT RETURNED TO BASE WITHOUT INCIDENT. IN ORDER TO PREVENT THE AIRCRAFT FROM BEING ACCIDENTALLY FUELED WITH TURBO FUEL, MFG PROVIDES A KIT WITH AN ADAPTER RING TO NARROW THE OPENING TO THE FUEL TANK (SB 797B). IN THIS CASE THE FUEL CAP AND THE ADAPTER RING IT LOCKS INTO WERE MISSING.