Just lock on to the jet/heli, at that moment it will probably already use its flares, then quickly lock on to it again and shoot. Sometimes you don't have enough time to pull this off but most of the time it's pretty easy to do. Also, have they fixed the AT-mines glitch yet? Now you can lay down mines, die and continue to lay down more mines without your previous ones disappearing. At the end of the match entire maps are filled with AT-mines.