16 fighter jets had been scrambled to intercept the aircraft when Athens air traffic control declared it a "renegade plane" after it had failed to make contact with the crew. Post 9/11 regulations give authorities the option of shooting down a plane if they believe it has been taken over by hijackers and could pose a danger. The two fighter pilots reported seeing the pilot's seat empty and the co-pilot slumped over the controls, possibly unconscious. Officials also said an F-16 pilot saw two unidentified people in the cockpit trying to regain control of the plane during the final 23 minutes of flight. According to reports, the unidentified individual was likely 25- year-old flight attendant Andreas Prodromou, who according to his family had a pilot's license. The person took control of the plane as it flew on autopilot and then backed the plane away from Athens, lowering it first to 2,000 feet and then climbing back up to 7,000 feet before the plane apparently ran out of fuel and crashed. Investigators are focusing their investigation on a possible combined fault in the plane's air conditioning and its electric decompression system. --more 2336 Local Time 2036 GMT