Hi Popay,
Thanks for the reply. I think we're getting to the nub of the issue, I do understand how Final Reserve Fuel is calculated - I think 212man said "It's simply a means of defining what fuel consumption you should apply to calculate what 30 minutes fuel actually is!" So I'm afraid I have to take issue with your statement "So one can say it's equates to a holding fuel" I really don't think it is, I won't be using it to hold - I'll be using it to get my sorry @rse out of trouble if I was dim enough to get down to Final Reserve.
Telstar - I think MAYDAY comes from the French - Help Me. Entirely appropriate I think if you're down to 30 min (at best!) before your engines stop.
John T - Ta for the clarification on useable fuel.