[QUOTE=TurnAndBurn;1236324]Across the pond, "mayday" is used more loosely than in just the instances you describe. I know that some european carriers train their crews to call "mayday" on single engine out, loss of pressurization, and other 'routine' emergencies.

I cross regularly also. Trained in the US however. If a procedure calls for landing at the nearest suitable airport I would agree that you should indeed declare an emergency but PAN PAN would be the correct call unless disaster (ditching, off airport landing or uncontained fire etc) is imminent.

Wikipedia, for what its worth:
In radiotelephone communications, a call of three repetitions of pan-pan[1] ( /ˈpɑːn ˈpɑːn/)[2][3] is used to signify that there is an urgency on board a boat, ship, aircraft, or other vehicle but that, for the time being at least, there is no immediate danger to anyone's life or to the vessel itself.[4] This is referred to as a state of urgency. This is distinct from a Mayday call, which means that there is imminent danger to life or to the continued viability of the vessel itself.[5] Thus "pan-pan" informs potential rescuers (including emergency services and other craft in the area) that a safety problem exists whereas "Mayday" will call upon them to drop all other activities and immediately initiate a rescue attempt.