How can fly's land on the roof upside down?

Can't remember where I found this but it was interesting

Think about this one...When the fly is heading for the ceiling, it's flying right side up. When it lands on the ceiling it is upside down. At some point along the way it has to flip over. But when? And Where? And How?

Scientists dispelled the prevalent theory, that the fly performed a fighter pilot-like barrel roll just prior to landing, by capturing this momentous event on film.
Freeze frames, from the high-speed cameras scientists used, proved that flies do not flip, but flop, as they land upon the ceiling. Prior to impact, the fly extends its forward legs over its head, makes contact, and uses the momentum it has gathered in flight to hoist the remainder of its body to the ceiling. Thus, the fly proves to be more of an acrobat, than of a fighter pilot practicing his manoeuvres.

Once the fly reunites all six feet on the ceiling, it keeps things dizzyingly exciting, by gracefully tiptoeing across the ceiling, securing itself by using sticky pads found under the two claws attached to each of its feet. It is because of these sticky pads and the hairs on the legs that the fly is such a carrier of disease germs.