turned onto the wrong runway in 2006 for takeoff, the air traffic controller failed to notice. the plane crashed killing 49 on board. the government blamed pilot error but noted that the controller had worked all night with only two hours of sleep before his shift. that devastating accident led to a study of controller fatigue done three years ago but not released until today. two out of ten said they made significant mistakes on the job and over half blamed them on fatigue. most said they were getting less than 6 hours of sleep a night. some less than three. safety experts warned that changing work schedules can also be a big factor. >> the backwards rotating shifts where beam apeople are having t up earlier and earlier each day makes it hard or for them to get the sleep they need. >> it's been a chronic problem for controllers. a huge embarrass at washington's