they have a extra guy in the back called a crew chief sticks his head out the side , via radio comms guides
the pilot into position and hover, also monitors the load during flight.
also keep in mind theres crews on the ground to hook the sling load up as well.
am hoping we can get this feature added into the huey = crew chief call outs.
http://upload.wikimedia.org/wikipedia/commons/e/ee/US_Navy_051103-M-6538A-004_U.S._Marine_Corps_Staff_Sgt._Michael_Chaloupka,_a_UH-1N_Huey_crew_chief_assigned_to_Marine_Light_Attack_Helicopter_Squadron_One_Six_Seven_(HML-A-167),_scans_the_desert_.jpg
http://media.dma.mil/2008/Aug/28/236032/600/400/0/080828-M-0007C-938.jpg