I'm still reading the 4th edition rule.
I've found a contradiction between rule 11.4 :
Some aircraft have a special Anti-Tank factor (a number printed on a black circle). When attacking, these units fire on hexes using their Direct Fire values normally (15.11). In addition, if any vehicle units are in the hex attacked, the owning player rolls a number of dice equal to the circled Anti-Tank factor on the air unit
And rule 15.13 :
Some aircraft also have a special Anti-Tank attack ability indicated by a printed number on a black circle on the unit (11.4). An aircraft may execute one type of attack OR the other (Anti-Tank or Direct Fire), not both.
During our game session this week end we've played with the old fashionned rule (ie one DF attack + one AT attack).