How do we test fatigue?
What is always missing in these debates are facts. What is needed is hard data.
The only way to set safe limits to flight and duty times is to have crews fly various rosters/trips and test them at the end of each shift. A set of cognitive, decision making and fine motor skills should do it. A framework of both short and long term testing would be required.
This would ensure they are capable of making good decisions about diversions, handling any expected emergency and otherwsie be at a level of alertness and capability so that the people who are entrusted to our care have every right to expect.
Cheers,
Brad