Anti-Air defence is a game mechanic that causes certain buildings in bases to fire at your aircraft- causing damage if they hit. The buildings firing anti-air are grouped in two categories, light Anti Air (represented with a Triangle symbol) and heavy anti air (represented by a five-sided shape, or a triangle with a rectangle underneath it).
Light Anti-Air is mainly a threat to fighters and multi-role fighters that fly at relatively low altitude. This type of anti-air fires pretty fast, but the damage output is limited and the structures can easily be taken out by gunfire, rockets, or bombs. Ground Attack Aircraft typically suffer less trouble from these anti-air mounts, since GAAs are heavily armoured and have a lot of HP. When taking a long time to capture a base, it is still wise to destroy the AA mounts since you'll be spending a lot of time in their range.
Heavy AA mounts shoot to higher ranges, and don't fire at very low altitudes, in a fashion more similar to high-altitude anti-air grenades or FLAK. The Heavy AA mount can be very dangerous to bombers, since heavy AA produces a lot of damage. Fighters and other lightly armoured aircraft can pretty much be destroyed in a single hit from a heavy AA mount, but should generally be able to avoid getting hit directly by the grenades- unless you're very unfortunate. The heavy AA mount is much more armoured, and cannot be easily taken out with guns lighter than 30mm caliber. Instead, the ordanance of choice should be bombs or rockets mostly- while fighters are best off ignoring them altogether.
The characteristics of light and heavy AA are vastly different, and it can be wise to look at which AA mounts can be present in certain base types. Airfields for instance will (strangely) always have ONLY light AA, while mining plants often have a lot of heavy anti-air with very little light anti-air. The light anti-air mount shoots in a semi-spherical pattern, starting at the AA-mount itself. The radius of this sphere increases with battle tier.
Heavy anti-air mounts produce a cylindrical pattern of anti-air. This cylinder is oriented vertically, with them bottom starting at a specific height, the Flak Floor (increasing with battle tier) and the top ending at the Flak Ceiling, and the Flak Radius specifies how far the FLAK area of effect travels horizontally. Heavy AA mounts can be very dangerous weapons, with huge damage output and an enormous range, so knocking these mounts out should be a high priority when capturing heavily defended sectors such as mining plants, especially in high tier battles.
The detailed characteristics of the AA mount properties can be found in the table and blog below.
|Battle Tier||Light AA Radius||Flak Radius||Flak Floor||Flak Ceiling|
Anti-Air fires in salvos rather than continuous fire, much like autocannons (since they overheat their guns pretty quickly after a fierce burst of rounds). These salvos grow longer at higher tiers. Once a salvo is over, you know you'll be clear from anti-air for a short time, so you can focus on your tasks and enemies again instead of on dodging AA-fire.
It should be noted that Anti-Air, both light and heavy, prioritizes the first aircraft of any aircraft type (fighter, multirole, heavy fighter, Ground Attack or Bomber) that enters a sector. Any aircraft of the same type that enters after this aircraft will receive less AA fire, even if the first aircraft that entered was an enemy aircraft.