The only ways to avoid a GTAM is to either immediately bail out, dodge a couple buildings, or have an artillery strike fall on top of you.

There are several ways to dodge a GTAM. If you are an inexperienced pilot, just bail from the helicopter. You can also fly in between buildings in order to get the GTAM to slam into one of them. Finally, if you realize that it is a GTAM, start flying fast and slightly sideways. Then, get as low to the ground as possible without hitting anything (within inches). Note: This requires some experience. Hopefully you will get the GTAM to hit the ground and free you from harm. Warning: You may have more than one GTAM on you; make sure you enter third person view. Also, watch out for tanks as they can easily hit you if you are flying low.