At a press conference earlier this week, a French prosecutor stated that the co-pilot of Germanwings Flight 9525 most likely deliberately crashed the plane. The co-pilot was alone when the aircraft began its slow descent and the door to the cockpit had "locked automatically." Many questions are being asked about how the cockpit door locking mechanism works and why the captain was unable to get back in.

The co-pilot was identified as 28-year-old German citizen Andreas Lubitz. The press conference revealed that on the cockpit voice recorder, a pilot could be heard knocking to get back into the cockpit, ultimately making sounds like he was trying to smash in the door.


The plane, a 24 year old Airbus A320, was manufactured before the 9/11 terrorist attacks. In the wake of the attacks, measures were taken to reinforce the cockpit doors as a safety precaution to prevent hijackers from gaining access to the cockpit. This hardening typically involved replacing original, light-weight doors with a new designed able to withstand considerable force without failing. This means that the aircraft had to be retrofitted to comply with new security standards. How this particular aircraft was retrofitted has not been revealed. It could have had an Airbus-designed hardened door installed or one designed by another approved third party company, including work done by the airline Lufthansa. In general, the aircraft locking mechanisms are similar no matter what the specific design and entry into the cockpit from the main cabin is also similar.

When the cockpit door is opened in flight and then closed, the door will lock automatically. To re-enter, a pilot would use a code to unlock the door. After the code is entered into the outside keypad there is a small delay before the door actually unlocks. Entering the code sounds an alarm in the cockpit letting the pilot know that someone is trying to get in. This code should be audible on the cockpit voice recorder. During this delay, the pilot in the cockpit can hit a toggle switch that prevents the door from unlocking. There is no way for someone outside the cockpit to override this switch. The switch was installed to prevent potential hijackers from being able to gain unauthorized entry if they were to somehow determine the unlock code.

Video has resurfaced showing the reinforced cockpit doors that regulators mandated Airbus to install following the Sept. 11, 2001 terrorist attacks. An Airbus spokesman confirmed to The New York Times on Thursday that the company had produced the footage. The video from 2002 was posted to YouTube and depicts promotional footage of the reinforced cockpit doors and the locking procedure that crew must undertake when leaving and entering the cockpit. This representation may not match exactly the installation on the crashed aircraft but is a good example on the locking procedure.

Top photo via Matt_Weibo (Flickr / CC Commercial License)