Back in the 1970s Iraq Airways used to fly Tridents from Baghdad to London via Paris le Bourget, later changed to Orly. One evening the crew forgot that this change in destination had been made and flew into le Bourget. Once on the ground they realised their mistake, did a 180 on the runway and took off once more for Orly, evidently hoping that no one would notice. I remember it because a few days later I was on the selfsame flight: this time all that happened was a passenger decided to visit the toilet shortly before landing and didn't re-appear until after touchdown.