I was sitting in the back of a PA-28 while the pilot did the walk round, the door was partly open. A JetRanger hover taxied past at about 50', buffeting the aircraft and banging the door wide open. We then started and taxied to the pumps with the door closed - couldn't open it from inside. Fuel man opened it from outside; an engineer replaced a broken split pin somewhere in the latching mechanism, all dandy again. Glad the previous occupant hadn't topped it up after their bimble...