[Nox]

The Russian OOB does not have air transports attached to the Airborne Pl -formation so you have to buy them separately from the Misc menu (look for: Air transports).

Heres how the infantry fits in the planes:
Antonov An-2P
1x Squad
Antonov An-32
1x Platoon
Antonov An-72
1,5x Platoon
Antonov An-12BP
2x Platoon

So if you buy 3x Airborne platoons you need to buy 3x An-32's or 2x An-72's, etc...