you will need to force the heli to land with HELICOPTER land mode "Get out". (correct syntax is in the comref), When i do this i usually set flyinheight to 0, dont know if it helps, but i dont have probs. Then to release from land mode, simply set flyinheight to 50 and it will take off. So you dont need to sync it. (its a mp chopper problem). The load / getin Way points will work with AI teams though. to know when to release the chopper, i use a team in chopper script, which is started when group leader is in said vehicle, then is complete when all team is in vehicle, so can trig the flyinheight 50 trigger.
Hope it makes sense, its late and i need to go to bed.
Cheers
GC