From the CAA FODCOM and as popay quotes -
'
On the day there is no restriction on departing from home base, in the knowledge that the exercise of discretion is likely to be required to extend the FDP, provided the extension is within the specified limitations. '
The wording unplanned and unforeseen are however relevant. The scheduled block time of 11hr 45 mins fits very conveniently with the max FDP 3 crew of 13 hours does it not?
A charter operator may schedule say 10 only of these flights and find this time avoids a crew change stop and all the positioning necessary. By the time six discretion reports have gone in and the CAA takes an interest it is all over.
Unforeseen does not surely mean such things as not planning for the usual seasonal increase in headwinds for example. At check in ' the third pilot missed his positioning flight - will you do it with two ' may work exceptionally but not often. A last minute strike causing a reroute is probably acceptable as unexpected.
If an operator plans poorly at the scheduling stage and then repeatedly presents the crew with the necessity to use discretion then they are risking the fact that the Captain may decline '' in the interests of flight safety " and the resultant bad feeling or worse.
Surely there are two times for planning - the scheduling stage and flight planning stage at say ETA - 7hrs. Unplanned should really apply to both, especially in the charter case where the two may coincide.