the longest accident investigations in aviation history to solve the mystery of flight 427. with it investigators are able to bring closure to another cold case, united flight 585, the other boeing 737 that crashed three years earlier. >> the rudder system on the 737 fleet has been completely redesigned. it's a very different system now than it was at that time. there was a lot of changes also to flight crew training. more hands-on flying, being ready to recover from unusual upsets and unusual events. >> history's proven us to be right. there's not been another occurrence of a rudder hardover since, and i think we made a good airplane even better. coming up -- one of the most infamous aviation disaster in history. >> it appeared to be a flare going straight up. >> what really happened to twa flight 800? >> microscopic explosive traces of unknown origin have been