[Rules] 4E Air Support Rules question

[Michael Murphy]

Last night I used an aircraft with an AT value to attack a tank unit and I consulted the 4E rules to see how this works. According to 11.4, "... these [aircraft] 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 ...", making an Anti-Tank attack as well. I jumped to 15.0 Special Unit Types to check out Special Aircraft Anti-Tank attacks. Here, in 15.13, the second paragraph ends with the sentence, "An aircraft may execute one type of attack OR the other (Anti-Tank or Direct Fire), not both."

Rule 11.4 permits aircraft to make both DF and AT Fire attacks at the same time while rule 15.13 prohibits such attacks. Can someone please clarify this puzzle for me?

Thanks.