Where can you find the UFO crash random encounter in Fallout 3?

There is no definite area where the UFO is. It's called a random encounter for a reason.But if you complete the quest at the temple of the union, where the slaves go to the memorial, just fast travel back to the union save it, then enter as it is now a random encounter area. If the encounter isn't tha UFO one just load it again until you get it (bring dogmeat as a weapon, the firelance, is dropped and kinda hard to find)