I experience the same sort of erratic behaviour when trying to get choppers to land in a given area and I have been trying just about everything to correct it. One thing I have found that seems to work nicely insofar as making the birds land on the intended spot on the LZ is by using either the invisible H, or the regular H if you chose, and in the activation box of the trigger use :
heli domove getpos pad; heli Land "LAND"
where heli is the name of the helicopter, and pad is the name of the H.
So far it seems to work fairly well.
