Earlier quoted context omitted.
> securing access to the pilot's cabin Well, no, actually it was impossible to get into the cabin from outside long before 9/11 (in fact, I think since the 70’s). The hijackers smuggled box-cutters on board and used the box cutters to kill stewardesses until the pilot agreed to open the door - after which they had full access to the plane.
> until the pilot agreed to open the door That's the problem -- that there was a door that could be opened. It seems to me that there shouldn't be. The pilots should have their own separate entrance from the exterior of the aircraft.
I think they have to be able to get in and out to use the bathroom, though. And get some food.