On Bombers (like the Maurader) AA is purely defensive. The Twin Lascannon have AT attacks, while if it gets close enough, it drops bombs using Barrage templates that can affect both tanks and infantry (check out 1.9.

When fighters attack enemy aircraft, the target aircraft get the chance to defend themselves before the fighters attack. The same principle applies to ground targets that use defensive AA to protect themselves. So in summary the aircraft sequence is:-
1. Bomber flies over the table
2. Enemy fighters on CAP fly to attack the bombers
3. Bombers (and appropriate ground AA**) shoot at the fighters
4. Surviving Fighters (and appropriate ground AA**) shoot at the bombers
5. Surviving bombers complete their mission and shoot at ground target
**Note When flying over the battlefield, any ground units with AA capability that are within range of the flight path may fire, even if the aircraft ends up outside the AA range.