Well, a UFO is any flying object that you've yet to identify, so it could for all reasons be the lower half of a goblin that swooshed past you.
What about the Armok? http://mkv25.net/dfma/map-6201-armok Although it flew for all of 2 seconds or so...
Updating lists of people. I'll re-add everyone to the waiting for recruit list who got slaughtered in Kinshasa because that was just not cool.