Well, *ahem* a halo drop script would have been fine..
You don't need to check it constantly; for just one person it's a simple matter of creating a trigger, with the condition:
getpos
dude select 2 < 250
and the activation:
para="Parachute" CamCreate getpos
dude;
dude moveInCargo para
And he'll magically spawn a parachute and be moved into it. It'll even unfold
Note: OFP uses the metric system, so this would make the parachute open at 250 meters above ground. If you really really want to change that to feet, feel free...
Good luck!
Wolfrug out.