I figured how to kill an AT-AT when you don't have time to do the loops.
Cost: 1 reinforcement.(2 if you're foolish)
Step 1: put 4 mines on the front of a snow speeder
Step 2: fly toward the AT-AT
Step 3: Boost
Step 4: Crash into the neck while boosting
Step 5: you die but the AT-AT will be destroyed
Note: You may miss and not kill the AT-AT, even if it seemed you hit right.
Also, mines may fall off or be destroyed before reaching the target.