Shooting at Aircraft

When shooting at aircraft, the rules require that you treat the distance as greater than half. -2; hit on 3 or less. Speed of target? Greater than 24. -1; hit on a 2 or less.
Now, if you also treat the aircraft target at Tiny, that’s another -2, and you CANNOT ever hit an aircraft!
So, we leave out any size modifier. 20% chance to hit.

What are the chances of driving off a regular pilot? You need two sixes, which means that you need to roll an average of 12 dice. If you use 40mm or 37mm AA at 4 dice each, you need 3 hits. To get 3 hits you must have 15 guns firing (20% chance of a hit). If anyone believes that this is appropriate, or has a good solution to flak, please respond.