The shocking revelation, scooped by the New York Times , that the cockpit voice recorder from the crashed Germanwings flight reveals one pilot locked out, raised all sorts of uncomfortable questions. As the Times reports:

French authorities have just identified the co-pilot who was at the controls of the crashed Germanwings flight as Andreas Lubitz, 28 years old, and claimed he made a “deliberate” attempt to destroy the aircraft.

“The guy outside is knocking lightly on the door, and there is no answer,” the investigator said. “And then he hits the door stronger, and no answer. There is never an answer.” He said, “You can hear he is trying to smash the door down.” While the audio seemed to give some insight into the circumstances leading to the Germanwings crash on Tuesday morning, it also left many questions unanswered. “We don’t know yet the reason why one of the guys went out,” said the official, who requested anonymity because the investigation was continuing. “But what is sure is that at the very end of the flight, the other pilot is alone and does not open the door.”

It could be something as comparatively innocent as one pilot using the bathroom and the other pilot having a heart attack and becoming disabled, unable to open the door. But that seems to have been rejected by the French authorities. As the Washington Post reports:

An Airbus training video shows that the cockpit door of the doomed A320 plane has safeguards in case one pilot becomes incapacitated inside, while the other remains outside, or if both pilots inside were to lose consciousness. To get into the cockpit, one normally needs to request access and aross a camera feed or through a peephole, the pilot decides whether to let the person in. If there is no response, a member of the flight crew can tap in an emergency code, however, again requesting access. If there is still no response, the door opens automatically.

However, there is a way for the pilot in the cockpit to delay entry:

If a person has been denied access, the door remains locked for five minutes, according to the training video.

Moreover, if the sole pilot in the cockpit became disabled, the plane would not descend and crash into a mountain. The automation of an A 320 flight is such that the plane would have continued on course for Dusseldorf.

Lubitz being blamed for a deliberate crash raises the specter of Egypt Air Flight 990:

The cockpit voice recorder (CVR) recorded the captain excusing himself to go to the lavatory, followed thirty seconds later by the first officer saying in Egyptian Arabic "Tawkalt ala Allah," which translates to "I rely on God." A minute later, the autopilot was disengaged, immediately followed by the first officer again saying, "I rely on God." Three seconds later, the throttles for both engines were reduced to idle, and both elevators were moved three degrees nose down. The first officer repeated "I rely on God" seven more times before the captain suddenly asked repeatedly, "What's happening, what's happening?" The flight data recorder reflected that the elevators then moved into a split condition, with the left elevator up and the right elevator down, a condition which is expected to result when the two control columns are subjected to at least 50 pounds (23 kgf) of opposing force.[1] At this point, both engines were shut down by moving the start levers from run to cutoff. The captain asked, "What is this? What is this? Did you shut the engines?" The captain is then recorded as saying "get away in the engines" (this is the literal translation that appears in the NTSB transcript), followed by "shut the engines". The first officer replies "It's shut". The final recorded words are the captain repeatedly stating, "Pull with me" but the FDR data indicated that the elevator surfaces remained in a split condition (with the left surface commanding nose up and the right surface commanding nose down) until the FDR and CVR stopped recording. There were no other aircraft in the area. There was no indication that an explosion occurred on board. The engines operated normally for the entire flight until they were shut down. From the presence of a western debris field about 1,200 feet (370 m) from the eastern debris field, the NTSB concluded that the left engine and some small pieces of wreckage separated from the aircraft at some point before water impact.

Note: This item was rewritten, as a press conference in France took place as it was being posted.