I really don't know why I am getting involved in this discussion, but I will. For those of you who have been involved in pprune for some years; I will apologise in advance for I have said most of this before.
I flew DC-10s for Fred Laker. Laker, from an operating crew point of view, was a pretty efficient operator. We always, as a matter of course, carried an extra hour of fuel contingency for New York and Chicago. Those of you who know anything about carrying extra fuel will already know that you will burn 10% of the weight of the extra fuel just getting it to the destination.
So, when JFK went out in severe thunderstorms (such as MAD), it was not unknown to go round in circles at Micke intersection with lots of other fellow travellers burning fuel like there was no tomorrow and then end up diverting to Bradley or Boston.
After Laker went down the tube, I went to work for a Part 121 operator at JFK flying ex-Laker DC-10s on the N-register.
They had a minimum (plog) fuel policy which worried me a little.
So, I found myself in an ex-Laker DC-10 but now under Part 121 arriving at Micke intersection with not a lot of extra fuel but the decision was amazingly simple from a captain's point of view.
As soon as the fuel got to Bradley or Boston minimums, then off you went
and there were absolutely NO GREY AREAS.
I really cannot see the problem with aircraft arriving at VLC on diversion from MAD announcing a "Mayday" on the basis of low-fuel. I would have to go into my attic to dig out the old regulations (CAA and FAA) but I have to say that any aircraft that is likely to land with less than the minimum emergency hold fuel, is absolutely required to declare a Mayday.
(In approximate terms, emergency hold fuel (15-30 minutes) is to cover the situation where you have arrived at your diversion airfield, made an approach and then had to go-around because the runway was blocked and then make a circuit to land with dry tanks.
Have things changed?