Did they not do that already on 11/09 ?.
They (the hijackers) did NOT "pose" as
operating crew.
At least one of them, Mohamed Al Atta, had a pilot's licence, and supposedly used this to request - and gain - entry to the flight deck, as an interested observer.
Access to the flight deck ever since - even to children, is now absolutely prohibited by most (if not all) airlines....even to our own family members!
I'm know that there are some people with very imaginative minds (even employed by airlines), who believe that "someone" with a basic knowledge of flying, and a stolen uniform, is somehow going to pass themself off as operating crew, to the others (real) crew operating the flight.
The mentality that has dreamt this up is somewhere around Infant school age, and totally unaware of how crew interact, and expect certain company procedures (wrt format of briefing, delegation of duties, etc, etc) to be followed, when dealing with each other, and with other company personnel.
"Ring-ins" would stand out like dog's b@lls in about the first 5 seconds.
A
nd in the Silk Air, and Egypt Air cases, did either of those 2 (from all knowledge) use a weapon?
No!