>'it is within the flight crew limitations, it is legal <
opsjockey, not necessarily and that is the essence of what is being said on this thread.
You can operate a duty in the strict sense that it is within the FTL rules but if before doing so an individual crewmember feels too fatigued to operate safely he/she is LEGALLY obliged not to do so.
However, many companies frown on an individual crewmember declining a duty because of fatigue and many take the easy option (no pun intended) by simply going sick.
The FTL scheme can never cover every situation because pilots are human beings and not machines and it always amuses me that there is an assumption that you can automatically "switch off" during a minimum rest period and sleep. In most other walks of life there is time for some recreation as well as sleep in order that one can return for work in a refreshed state.
My view is that it is just a matter of time before we see a fatigue induced accident. Accidents are always caused by a combination of factors and that is part of the challenge in the context of fatigue. If, in the case of the B777 with the fuel leak, the a/c had speared in because the crew had fouled things up as a result of fatigue that might have made a more impressive headline. (This comment is not to imply that the crew where fatigued but just to paint the picture of what might have happened if they were!)