This is being reported on CNN now.
Oh, I so hope this was not a terrorist event. This is not sounding good.
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They are reporting: Two pilots, one left the cockpit and when went to return to cockpit the door was locked. He knocked lightly on door at first, then began beating on the door and then tried to break it down. He never got back into the cockpit.
1.) Intentional act on part of pilot left in cockpit.
2.) Pilot in cockpit incapacitated by illness?
Commentators are saying it is very unusual that only one person was in cockpit. Normally, even with only one pilot flying, normally a flight attendant would be in the cockpit while the second pilot was out of it.