TAD in calculating FCF to firm

hi sir!

in exam questions i have noticed two types of treatments for calculating FCF to firm wrt TAD/depreciation
1) when TAD is given, they usually reduce it from the after tax profit assuming the replacement per yr is at the same rate

2) when depreciation is given, they assume the same thing.

So is it always a rule to deduct depreciation from after tax profits to arrive at FCF’s on the assumption that these are the asset replacement costs? or is it only when it has specifically been told?