I have tested it several times but still no clue how to make it happen.
I got it happend 20% of the time that German stukas crashed all by themselves. In this case they are gone for good (Captain Nemo, you can't reincarnate them from this since they are not killed
). Here's what I did:
Evacuate Kirovgrad and let the German have it. For all cities close to (that is, withing 12 squares of) Kirovgrad put at least 4 AA batteries or a fortified position/fortified battery. If you don't have enough AA batteries use fighters temporarily and rush build AAs. One important thing is that the cities with FP/FB should not have other tough units. It seems that 4 AA batteries are stronger than a FP/FB in AI's point of view so the AI stukas will attack the FP/FB cities and they always lose. Of course they all got reincarnated to Kirovgrad. The stuka trap is set at Poltava and Kharkov. Intentionally give Poltava one less AA battery and put several cheap units in Kharkov without giving the city any air defense. The AI stukas will try to attack Poltava first for its 'weak' defense. But after reaching the city, the stukas will either come back to Kirovgrad without attacking, or try to find some new targets in Kharkov. In the latter case it will crash after killing one unit in Kharkov.
I guess the AI's logic is: find a city within range (in this case, 12) with the weakest air defense, and send all stukas there; then, before attacking (this needs to be done since the planes may encounter other units on the way), double check the odds to see if the plane can either win all the battles or can attack once (regardless odds)and retreat to a base. If none of the above is true they will try to find new targets and repeat the logic.
Poltava is 7 squares away from Kirovgrad and the stukas cannot win all 3 battles against AA batteris so it either come back home or go for Kharkov.
Again, I'm not sure how it works. I'm just too smart to figure out how the stupid AI thinks. (JK)
