The rank of Flying Officer (Fg Off) is the second ranks in the comminsoned rank structure, above Plt Off and Flt Lt. The rank is gained withn the ACO when the officr has been a Plt Off for 2 years. To advance to Flt Lt, the officer must become an OC or be a Fg Off for 12 years.
Fg off

The rank insignia for a Flying Officer VR(T)