There is a good overview given in BR what a FOC mean to IAF w.r.t to Tejas
imo FOC = IOC + the below
open the full AoA and G envelope
reach the max speed as designed at various levels
all weather ops - night cockpit extensive tests, heavy rainfall (NE), dusty conditions (jamnagar), a good spell in Leh/Thoise
full qualification of litening pod for target spotting and designation
integration to griffon/paveway initially and sudarshan in a couple yrs. litening should aready be able to 'talk' to all of these.
more extensive weapons trials in A2G like guns, rockets, bombs of all types
more realistic R73 trials against manouvering high speed targets like lakshya
full testing of the "mayavi" EW suite & elta SPJ against ground based and airborne threats
testing the chaff and flares pkg against some kinda SAM thing
getting the Tejas tracked by SAM radars and testing how fast and surely it can escape
full qualification of the radar (being EL2032 the front end should be in working shape already)
firing and proving of the BVR weapon against airborne lakshya targets
and finally **this is what we want** - all out DACT against Bison, M2k, Mig29, MKI in A2A role and practising chasing and hunting down strike a/c and UAVs..with a chase a/c recording in Imax or HD and release of footage that same night to salivating br boyz.
airborne tanking in day and night , plus getting the UK go to fit the refueling probe if possible on Mk1 itself
credits to Singha ..