I had two or three Beverley flights as an ATC cadet, Abingdon being our 'parent' station. On the first occasion, we were seated in the hold area, there being no seats fitted to the tailboom. Soon after takeoff, after we were allowed to unfasten seatbelts, several cadets decided to scale the vertical walls to access the tailboom (no ladder installed - they used the horizontal rungs on the wall) After some time, they came back down looking rather sheepish. One of them told me they'd been sitting on the floor chatting when one of them noticed a lever, and not knowing what it was for, operated it. Inevitably the floor hatch of the tailboom began to open and it took several of them jumping on it to close it again!!