cctv correspondent jim stillman has been out to find out what the black boxes and about their secrets. the key to finding out what happened to legionnaires three seventy me like people in the indian ocean. how important is that investigators to find black box. it's absolutely critical to locate these boxes. roger owners of kylie aviation expert with the smithsonian institution's air and space museum. a black boxes and they're not black that they've always been one of their assigned report critical flight data as well as cockpit conversations and sounds and the data is then used to analyze aircraft accidents. the black boxes record details late information including altitude air speed rudder pedal position and record cockpit conversations but for me the last two hours of audio a lot of people are wondering how come everybody has a phone that can store hours of video. thousands of songs etc but the black boxes the voice recorders can only hold two hours of audio. well one reason it has to do with the labor units of the airlines that they don't want the tape for long periods of time beca