Just thinking about their flight duty.
This was a BIG day, even as rostered. Two long 4 hour sectors and a report, one turnaround and a check out.
Pretty much every single short/medium hall UK based pilot has done this sort of duty multiple times in a week at some point. 5 canary return flights in a row from the UK is around a 4:30-5:00 block each time round. Wake up 4am, land at 5pm straight into rush hour traffic on the way home, freshened up and ready for dinner by 6:30. Bed straight after that and attempt to get some decent sleep before the alarm goes again around 8 hours later at 4am. Thats if your neighbours or young kids play ball. Repeat this 4 times over. Done on multiple occasions myself and whilst all within limits absolutely draining.
If it is found that fatigue did play a part then remember these guys were on their first sector! Consider the crew that is up at 4am, 5 hours down to Tenerife and picks up a 2 hours slot and goes into discretion. 5 hours after that approaching home base where the weather is gusting 50 knots, you're both tired and theres a distinct possibility of diversion. This happens and it happens all the time.