|IL-2, S. Tsvetkov|
First up, I think that we can all see big problems with GW's implementation in 6th Edition 40K. So I'm not going to use those rules as a basis for anything. Instead, I'll describe how Flames of War implements aircraft. Which is far from perfect, but serves as a better jumping off point for a discussion and an eventual evolution into our own unique system.
(BTW: You might be able to pick up a 2nd Edition Flames Rulebook for cheap these days on the clearance rack. If so, you'll have something to reference when I talk about their rules. If they're still running the deal, you may even be able to get a 3rd Edition mini-rulebook for free if you take that book to a participating store. Not a bad deal for $20, which is what my FLGS is selling the old book for.)
The Flames Of War Way
So how does Air Support work in Flames? Here's a diagram from the free Tunisian Tigers PDF, which you can download here.
There are 3 levels of Air Support in the game: Sporatic, Limited, and Priority. Which give you 3, 5, and 7 Air Support dice respectively.
At the start of your turn, you roll all of the dice you have in your Air Support pool. If any of them come up a 5+, your planes come on. Either way, you lose one die from the pool after you roll. Though you will always have at least one die to roll no matter what.
If your opponent wants to use their aircraft to shoot down yours before they get to the table, he rolls all of his air support dice and if any of them comes up a 5+, your planes are stopped. Afterwards he loses a die from his pool.
If your Air Support gets through, you see how many planes you get. On a 1-2, it's one plane. On a 3-5, it's two planes. On a 6+, it's 3 planes. You then put your single model down within 4" of it's target and mark how many planes the model represents.
In your shooting phase, you then do a couple of things:
1) You make sure that none of your own troops are within 16" of the target. Otherwise the planes will wave off and abort the attack.
2) Your opponent gets to shoot at your planes. The unit being attacked can fire any self-defense AA weapons (usually .50cal machine guns on American tanks), plus any dedicated AA units. For every hit, you roll a firepower test for the weapon. Every successful firepower test knocks down a plane.
If you have any planes left after all of this, you can lay down the artillery template on your target and roll to hit every enemy tank, vehicle, or infantry stand underneath it. If you have 3 planes, you get to re-roll your misses. If you have 1 plane, you have to re-roll your hits.
If your target is within 2" of a wood or building, you have to roll to range in on the target first. I won't go into the detail of ranging in, but you're likely to wind up either having a penalty to hit, or not being able to hit at all.
Note that even if you lose all of your planes in the attack for one turn, it doesn't affect how many planes come on the next turn. It's assumed that there's a squadron of whatever you bought flying around overhead.
What Works About This System
I really like the Air Support pool. It gives you a gradually decreasing chance of getting your air support in over the course of the game. It also lets you trade your own odds of getting air support in order to stop your opponent from getting his.
I also like that you only ever have one group of planes making one attack. You can't spam aircraft in what is (and should be) primarily a ground-combat game. Air Support thus adds flavor to the game and fills certain roles that artillery can't, but it doesn't overpower the game.
Even if you don't have planes or AA guns to counter Aircraft, you can just spread out your forces to limit the damage that can be done. Just like with artillery. You can also hug tree lines and buildings to make yourself harder to hit. So tactics can make up for your lack of a hard counter.
What Doesn't Work
Even with the changes in 3rd that let planes automatically range in on targets in the open, Air Support is still very random. Every once in a while it pays off and kills a tank or two, but mostly it's just annoying without being all that dangerous. If you take AA weapons, then you hardly have to worry about it at all.
So I think that, ideally, you would get a predetermined number of planes. Or perhaps one for every 5+ you roll when trying to bring them on. That would make them much more effective in the early game when you're still far enough away from the enemy to use aircraft, while in the late game you would only see 1-2 aircraft on average as the squadron circling above was depleted.
I also think that being next to woods/buildings should just give you a straight penalty to hit instead of another random roll that might see you not be able to roll to-hit at all.