Hi everybody!
Andrew should know how to get back by now.
By now, he knows what the general directions are (by where the sun rises and sets).
He should remember which direction he came from.
That should at least give him a direction to travel to get back closer to the rest of the gang. By then he should be seeing something familiar (like Olympus). Unless his compass is totally messed up (didn't they say there are some goofy magnetic areas there?) he should be able to figure out which way to start back.
Another possibility that is kind of scary is "The Groove". Maybe he is someplace totally different.
Nice to be back.
apollo