Originally Posted by
KRviator
If, having committed to land at a particular airport (destination or otherwise) and you may have less than your FFR if your current clearance changes, then you must declare MINIMUM FUEL.
That's how I understood the regulation as well.
When discussing this with others, something I always miss is the notion that the minimum fuel situation does not create itself "in an instant". It should be a result of many things that have happened already in which both you and the controller have been in contact and the situation is clear to both of you. The "commited to the airport" is already a pretty strong decision made prior in time, which means ATC gave you some kind of confirmation they should be able to get you in, otherwise you would have already been long gone on diversion.
As long as the controller's plans seems to get you in while you are keeping final reserve fuel in the tanks, that is fine, and you can let him control the situation. From the moment something changes (either longer time in the hold, adapted routing, weather changes,...) and you feel you need to take control over the flight path to protect your final reserve, you declare the mayday to give yourself that priority/"freedom". That doesn't stop you from giving him a signal ahead of course (like "unable STAR", he might give you a direct and the mayday might not be required)