That's actually a monumentally stupid password policy, just take a read of the following if you don't believe me:
https://www.schneier.com/blog/archiv...nt_passwo.html (I find it hard to believe people wouldn't write those passwords down...)
Now I've seen pilots and FAs carry books of codes for airport doors, so I wonder if the same applies to cockpit doors. In which case you could just invalidate the codes and send out a new set.