ia1166,
I think what riggypiggy(cool name) was trying to say; is that they have procedures in their airline that are supposed to be kept as secure as possible to prevent folks with notso good intentions from knowing their secure procedures.
Also, quote him properly, he said "they are most likely aircrew".
Anyone can fly a plane once its in the air, but getting it on the ground where its supposed to be takes a bit of skill that only qualified personel can do. I sincerly doubt any of the hijackers on 9-11 were able to land a plane with any amount of accuracy.
I worked for a carrier that had some A300's , that originally belonged to a dunnunda carrier, and they had a super secret switch located down by the flight bag for HI-Jack squawks. Well, as luck would have it, no one at our company knew about these little switchs, and a check airman inadvertantly activated this little switch. well, had this not happened prior to 9-11, things could have been nasty.