411A
My company's CAA approved fuel policy under JAROPS allows a flight to continue to destination with calculations showing less than reserve + diversion fuel remaining at destination, for example, so long as max delay known or EAT (expected approach time) received as long as landing assured (*) and possible to land with at least reserve fuel remaining.
At any time, if it becomes apparent that you MAY land with less than reserve fuel, then a PAN is called, and if you WILL land with less than reserve then a MAYDAY call is required.
(*) Landing assured means taking into account any forecast weather changes and aircraft system degradation plausible.
Imagine a scenario, you are holding with 1 hour of fuel on board close to an airfield with 2 runways (say LHR) with a received EAT in 15 minutes + 10 minutes for the approach, so can reasonably predict landing with 35 minutes fuel, the weather is stable with a 400ft cloudbase and 1000 metres vis, is it not better to continue to hold than to divert to somewhere with just one runway, which may be a 15 minute flight away where the weather is the same, where you would then land with 45 minutes fuel at best?
Food for thought?