"It said the co-pilot was a licensed veteran with more than 6,500 hours' flying time, about half on board Boeing 767s, and had recently passed a medical examination.
But it said the pilot noticed immediately that his co-pilot was not in good professional shape on the day of the flight, arriving late to the cockpit after all the safety checks and paperwork had been completed. He reported that the co-pilot's behavior worsened once they were airborne."
Why would the Captain depart with an unfit FO in the first place?