Or you can use the "land" command:
helo land "getin"
or
helo land "getout"
I think that's correct, but check the com ref to be sure. Those will make the helo hover just above the ground.
However, getting helos to stay on the ground until everybody is aboard can be tricky. Sometimes the helo will fly up into the air for a bit, then come back down for no real reason. SnYper wrote a script to fix this. I can't remember the name, but search for "how to make a helo wait until everybody is aboard".