In my days it was a requirement to have enough fuel to get to destination, hold for 30 minutes, then fly to a diversion airfield and be able to hold there for 30 minutes there as well.
Wetfeet,
Those good ol days of carrying 30 minutes extra at destination has gone, like Concorde, never to be seen again.
Fuel is calculated from A to B (no extra) then to Alternate C and 30 minutes. This last thirty minutes is what must be remaining in the tanks upon landing and is not considered to hold for 30 minutes at alternate at all. Landing anywhere with less than this in tanks is an emergency in itself.
There is a 3% contingency between A and B and can be considered used for weather and inefficient levels, so it does not mean you may have it on arrival at B, as much as you try to protect it.
At times, on arrival at an airport with two independent runways, the alternate may be dropped completely and the alternate is now the 2nd runway at destination airport. This allows a little extra time at destination, but certain parameters must prevail with weather, delays and conditions. The theory is, why divert away to a single runway alternate from a massive airport, with many runways, only to be on final approach once again with 30 minutes in the tanks remaining, and a low cost carriers busy airport. It would be better to remain at JFK, LHR, and have a second or third attempt and land with more fuel at times than a diversion flight.
I say again, this requires certain conditions and is not fully reliable until within one hour of destination or top descent, due delays, WIP, weather types of approach in use.... etc... and ATC informed.
Consider this, someone else diverting from La Guardia to JFK and landing with 30 minutes in tanks, is in the same scenario as this B767. Min fuel and wind that now exceeds his limitations even by a knot. No go-around fuel at alternate is planned. This was the plan instigated by this captain, which would make it legal for him to land, within limits of wind and fuel at such short notice.