Fatigue, or the F word as it's known because it's practically a swear word in airlines I've worked at is barely uttered. The last time I heard it was cited by a crew member as a reason for not being fit the company treated him as if he was mismanaging his private life as they didn't accept that their 'legal' rosters could be the cause. Another time the company put the crew member down as sick and demanded a self cert form. It's endemic as far as my experience goes, but we all play our part in covering it up so nothing changes. And just wait til the proposed EASA FTLs come in, apparently we (in the U.K.) have had it too good for too long - according to my local MEP.