Either take off from LLMZ and you'll crash about 500 AGL during climb out or try an approach to the same airport. Set a minimal rate of descent, fully configured, through sea level and about three or four hundred feet below sea level (I forget exactly) you'll "land" on thin air... you can come to a stop and everything. Submitted a bug report about it a couple of weeks ago. Haven't tried it in an aircraft with a radio altimeter so I don't know if whatever is bugged shows up on one's RA.