There is a way with waypoints easy to extract with an helo:
I have my heli:
- Put a waypoint called LOAD near the extraction AREA.
- Put a empty called H (Invisible) where you want your coppter LANDS.
On your land group:
- Put a waypoint called GET IN near the extraction AREA.
Synchronize the TWO WAYPOINTS (LOAD sync with GET IN).
Your copter will now move to the LOAD position and wait's that your soldiers are over the get in waypoint, once your soldiers are over, the heli lands on the H and thats all... when anyone were inside your copter can go now to a move waypoint or whatever.
If you want that your chopper waits on base until you activate a trigger you can sync the first move waypoint (Should be near the chopper) with that trigger, and when you use the Alpha radio command the chopper will start its flight.
Sorry for my english (But this become me crazy until I know about sync shit)