Fls is not a procedure is guidance for the approach calculated by FMS , you select an Rnav procedure and if the GLS is available for that procedure you will see the info displayed like an ILS with pesudo Loc and Glide so you will fly it like an ILS .
Also in case of ILS with inoperative glide slope , the GLS is able to calculate a glide and present the info in the PFD like an ILS with glide , you will flight it arming APP with Loc and ( pseudo ) Glide. There is even no need to take into account temperature below the maximum shown on chart , because the FMS with the temperature inserted will make the correction in presenting the calculated glide , so it is a simplified and safer mode to fly all non precision approach.