chairs. you can hear any sounds of crashing, cracks, decompression would be a very loud sound. and if they had smoke or fire in the cockpit, they will say so on the recording. >> reporter: in 1996, black boxes also helping investigators piece together twa flight 800. >> the jet liner that went off of long island -- >> reporter: the plane's pieces gathered and put together, helping investigators determine an electrical short circuit caused the blast. >> i think the national transportation safety board got it right. >> we continue to bring you the latest. >> they found nothing. every lead proved false. >> reporter: then there are the planes that just disappear, like flight 370. not one single piece of debris