million flights. veteran aviation safety expert john cox. >> what's significant about that is that we're improving by 50% over last year, which was the aviation's safest year previously. >> reporter: why the improvement? pilots have never been better trained. computerized cockpits monitor every aspect of flight. alert systems warn of a potential mid-air crash or mountain ahead. hd simulators for pilots and air traffic controllers train them to handle emergencies before they face a real one. debbie herzman is chairman of ntsb. >> we've learned from accidents, plowed those lessons back, in they've been embraced and we're not seeing repeats of those same accidents. >> reporter: experts say two accidents in which human failure was at least partly to blame underscore that remains the biggest threat to safety. air france 447 crashed into the