Under the normal rules, fighters from each unit are treated as separate squadrons ("combat unit"). With this tech, once gained, allows all the FTRs carried by one or more true carrier(s) ("V" designation in its "Notes" section in module G3 or the like) and any number of casual CVs in a SQ, to form up into a single unit during combat. The maximum number of fighters allowed in this combat unit is 24xFTR (any over this limit form a separate combat unit). All of the fighters must be the same size (treat size 1+ such as F14s as 1).
This works with fighters and heavy fighters (subject to the size constraints) but not bombers.
This doesn't work with fighters in different squadrons (i.e., if you had two squadrons, each with 12 fighters, they'd stay as two 12xFTR units).
This does not work with systems or bases but does with R1 ships such as AuxCVs.
This tech is only available after a successful R&D program (D1.0), and has a YIS 185.
Example: CV(12xFTR),DD(2xFTR) are in a SQ (assume relevant escorts are present). If a battle happened without FCF then the 12xFTR from the CV and the 2xFTR from the DD would be separate units in the battle. If FCF tech was available then all 14xFTR would be one combat unit for the battle.
Example: A SQ consisting of LB, 5xRN with 48 Stingers (3 on the LB, 9 per RN; the RN is a "true carrier") engages the Lyrans. Instead of the fighters being treated as six separate units, they'd be treated as two, each with 24 Stingers.
Example: The Federation uses the "homeworld defense" exception (D17.50) to place two CVA(12xF14,6xA20) into a single squadron defending Sol. They could form the fighters into 24xF14 and 12xA20 combat units.