Thanks for your responses, most helpful, sorry if it was a rather trivial question.
I have now been able to enlighten my friend on the subject. I seems that the pilot of the aircraft may have been having him on as they were probably not in level flight.
A friend of mine who has a lot of experience with aircraft tells me the following:-
His premise seems to be that something changes when your feet are off the floor.
I think what he is saying is incorrect and that the distance jumped will be the same in either direction as the whole...