distress call or indicate in anyway, shape or form a problem with the aircraft. that s very unusual, given the fact that they were 38,000 feet. they would have been in complete communication with air traffic control. reporter: among the scenarios investigators will have to krks was there an emergency that forced the crew to program a rapid descent, a fire or smoke or sudden loss of cabin pressure. if that was the problem the pilots should have levelled the plane out at 20,000 fee. instead, it kept descending. so were the pilots and passengers incapacitated? captain john kax once flew the a-320. something obviously occurred that said as soon as they got to 38,000 within just a few minutes, they needed to come down and xa exactly that is i don t know. reporter: the airbus a-320 is among the world s most heavily used planes more than 6,000 flying a. computerized plane with a very good safety record. but they re having recent high