"If a crew member locks down the flight deck with the manual doors, nothing will open it," a second Australian pilot said.

It is possible for one pilot of an Airbus A320 to lock the other pilot out of the cockpit to the extent that he cannot regain entry, even if the aircraft is in a fatal dive, says an Australian pilot of an A320.
The New York Times has reported, citing an official involved in the Germanwings crash investigation, that the cockpit voice recorder shows one of the pilots had left the flight deck and could not regain entry.
"You can hear he is trying to smash the [cockpit] door down," the official said.



An Australian A320 pilot, who declined to be named, said the locked flight deck of the aircraft could be entered using an emergency code on a keypad – in the case of the pilot flying the aircraft being incapacitated, the door will automatically open after a set period of time if the correct code is entered. However, in the event the pilot flying the aircraft does not want the other pilot to enter the flight deck, the one in the cockpit has the ability to block entry if he reacts before the door would open automatically.
"If the person on the other side of the door says 'no', you can't get in," the Australian pilot said. 
He added that the doors are bolted and heavily protected and it would likely be impossible to break it down within minutes, even if passengers or flight attendants assisted.


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