How do you neuralize the air threat?

[lyklam]

In the option, assign a key for Pitch Down.
Use Pitch Down to view the sky.
Face the direction where enemy planes are coming from.
Aim and shoot at the planes using a flak gun.
Repeat shooting when the planes come back again.

[4afc]

put flak at autofire and automove. It takes a while, but finaly the planes got shoot down.