This flag determines whether a weapon can fire at flying objects or not, by allowing or disallowing its projectile to move towards them.
Note: Although AA is set to "yes" on RA2's and YR's Patriot Missile and Flak Cannon, they do in fact not fire on falling paratroopers. This is due to a special logic involved, classifying paratroopers as ground units. In order to get those defenses to fire on paratroopers as they should, AG=yes must be set on both [AAHeatSeeker] and [FlakProj]. The LandTargeting will prevent these AA defenses from firing on units on the ground.