The planes always fly in the same pattern.
Aim front, left, right, behind.
Shoot in front of the planes paths, it's rare to hit one by chasing it.
Don't shoot while moving the gun aim point (vibration throws the aim off)
WATCH the radar for approaching planes.
Sometimes you can hold the aim for one and get the other 3 in a flight of 4.
Don't go crazy, just watch the approach and aim so that the plane(s) fly into the crosshair.
You can take them out when they are just Dots in the distance. Shoot them down as far away as possible.