Prior to JAA and EASA , sim instructors were often ex military aircrew who who did not hold any civilian qualifications. Instructing in a sim can be part of a Flight Crew Licence qualification in which case it would be as a TRI. The SFI is to allow aircrew who may have lost their medical to continue in the sim only situation as a SFI or STI. It is a separate qualification to an FI or TRI and does not require a current medical certificate or valid flight crew licence.