Max:
Well said, and hopefully to strengthen your point:
Over a 6 day block it is not uncommon
1. to start at 0615 (to preserve the previous day off?????),
2. followed by 0530
3. lie in and start at 11.00
4/5. followed by further lie in but start at 1800 - 0600
5/6. followed by the coup d'etat, the same night at 22.00 - 10.00
So, do I tell you I'm fatigued at 0700 on day 5 or wait until 2100 on day 5??
Often I've phoned crewing in the morning and said I'm likely to be fatigued. They want a definite answer there and then. Knowing there is only 1. SBY, or more likely none at all, as Max says. you try to keep the show on the road, thus the early warning, but it is rejected.
So now you have to sleep twice in 12 hours. Good game this; except that you can't sleep before the duty: kids, neighbours, dogs, all the normal things in life. So at 2100 you phone in unfit to complete a duty until 10.00 the next morning due lack of sleep. You've had the rest time, but it was useless.
Guess the answer; "there is no-one else". So, do you step into the breach or stand your ground as the ANO says you should. What of the F/O approaching command?
Which stupid idiot rostered it in the first place??? There's the problem, and until a/c eat concrete because of this crassness IT WILL NOT CHANGE!
And if bent metal is the consequence I can guarantee the pilot will be declared fit and legal.