It's a pretty well known event. The copilot locked the captain out and used the purposefully designed system to also disable the cockpit entry code. Of course the primary cause wasn't the security setup, but it did contribute to the event.

"The captain had a code to unlock the door, but the lock's code panel could be disabled from the cockpit controls...The captain then tried to break down the door, but like most cockpit doors made after the September 11 attacks, it had been reinforced to prevent intrusion."

https://en.wikipedia.org/wiki/Germanwings_Flight_9525