According to French and German prosecutors , the crash was deliberately caused by the co-pilot , Andreas Lubitz . Brice Robin said Lubitz was initially courteous to Captain Sondenheimer during the first part of the flight , then became " curt " when the captain began the midflight briefing on the planned landing . Robin said when the captain returned from probably using the toilet and tried to enter the cockpit , Lubitz had locked the door . The captain had a code to unlock the door , but the lock 's code panel can be disabled from the cockpit controls . The captain requested re-entry using the intercom ; he knocked and then banged on the door , but received no response . 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 . During the descent , the co-pilot did not respond to questions from air traffic control , nor transmit a distress call . Robin said contact from the Marseille air traffic control tower , the captain 's attempts to break in , and Lubitz 's steady breathing were audible on the cockpit voice recording . The screams of passengers in the last moments before impact were also heard on the recording
September 11 attacks
September 11 attacks
Germanwings Flight 9525