[In mourning for six years]

Cockpit doors are always locked! The Flight Attendants were killed because the highjackers were probably looking for the atendant's keys to gain entrance into the cockpit. Flight Attendants would never willing give up those keys. Sadly, these young men and women are an airliners first line of defense against terrorists who are determined to take over an air carrier. Sadly, also, they are usually underprepared to meet such an attack.

[Shooter 2.5]

I understand what you are saying but it's also the definition "always locked" that has to be changed. The cockpit should be secure from the passengers. No one should have access and that was the failure here. I was watching a silly program called "Dead Last" and unbelievably they had the same scenario. There was a problem in the passenger compartment and a pilot came out to see what the problem was. If the pilots need their own washroom facilities, so be it.
"Always locked" should mean just that.