AA units

[macbeth]

Is there to the number of AA units you can have at one location.Why no AA fire at enemy planes yet on occasions will open fire at own aircraft coming into land.Thanks in anticipation

[Alfred]

Remember that AA has different ceilings. Enemy air can fly above the AA ceiling (not difficult if you have only small and even medium AA at a site) where as landing aircraft once on their approach path will always come within ceiling limit.

Alfred