some thoughts to add:-
Doors can be made stronger with kevlar,
not cheap, but VERY strong,it
wouldnt be beyond the wit of man (or design engineer) to achieve a satisfactory fix
fairly easily (it worked for concordes tanks)
Cabin crew protection:-
issue lightweight 'flak' jackets ??
not too bulky of course, but a lightweight version able to withstand personal attack,
probably not really practical though ?
How about issuing anti-personal sprays too ?
(those 'mace' type sprays that provide
temporary impairment to an attacker)
Its a tough call though, how do you
cope with madmen intent on death &
destruction ?
maybe armed sky marshalls would work ?
hope we find the right answer,
keep safe folks,