Kerosene
There can be no excuse for them to 'overlook' when airlines become creative and invent money-making schemes from junior pilots or create workplace conditions akin to master and serf from times long past.
Do you think it was the airlines that invented this or a creative flight training industry seeing a gap in the market during a financial downturn in the early '90's?
How to know you're fatigued and unfit to fly? When you experience yourself during the end of a flight totally worn out, slow in thinking, lacking in situational awareness to the point that you are not sure you can safely handle a critical situation.
Or when you wake from a rest period feeling exhausted and more fatigued than when you went to bed.
Lubitz was a clinical psychopath who had been identified as suffering from mental health deficiencies that should have prevented him from flying long before he reached an A320 - this is where EASA and all other regulatory bodies should be focussing their attention (as indeed EASA are), as well as greater scrutiny paid to professional pilot selection and training. The suggestion that he was depressed as a result of working conditions, atypical employment or bogus self-employment or any of the other terms bandied about with respect to 'new' employment practices used by some low cost operators or fatigued from FTL's used as targets rather than limits is nothing more than a means for employee associations to promote their interests on the back of a horrible event that could have been prevented if EU (German) privacy laws with respect to those employed in safety sensitive roles worked in favour of those whose ultimate safety should have been assured through the maintenance of an EASA Class 1 Medical.