I had such a hang while fighting enemy air craft myself for the first time right now. I was fighting an alien harvester with a stiletto 1 while having my sam site shoot at it, maybe that was the reason. I'll confirm by loading my savegame and see what happens if I fight without sam support, and also I'll try the same scenario again to see if this was caused by long runtime of the game.
EDIT: Interestingly enough, I had the same problem again without SAM support, so that was not the cause, neither was runtime. Do you want me to upload my savegame, and if yes, where? Playing on a windows 7/64 bit PC, 2.4 version of the game.
Detailed problem decription: while the crafts are fighting, the framerate goes down to zero and here and there cracked sounds of the ongoing fight appear. Even though there is no visual or auditive feedback, the fight seems to continue, and once it is over, the game is 100% responsive again. Reloading the savegame wields the same results over and over again.