One of the pilots on the German Airbus plane that crashed in the French Alps was apparently locked out of the cockpit just before the plane went down.

That's according to an investigator who's heard the audio on the recovered cockpit voice recorder.

He's told the New York Times that the pilot is heard knocking on the door, but gets no answer from his co-pilot.

Aviation consultant Neil Hansford says since 9-11 aircrew have to follow strict procedures to get back behind the controls.