rog747 Ref that night in 1999 at BCN and GRO - not sure whether emergency was declared but I do recall that the BY a/c had missed an approach to RW 02 at GRO (due no visual contact) and then flew the ILS to RW 20 when it came to grief. BCN was in TS so they couldn't divert there and couldn't go anywhere else due minimal extra fuel loaded although TS forecast.
Funny you should mention this since it was in my mind after the Ch 4 Dispatches programme on Ryanair.
The essential point is extra fuel gives you more options - useful if TS about!
Rather than the cost of fuel (although that is a factor) it's the fact that if you take extra fuel you are heavier and therefore burning more fuel. From an accounting point of view this may only be 50 kgs on an individual flight but over the year on lots of flights that's a lot of dosh!
But what seems to have been lost here is that surely you want to get pax to their chosen destination?' Leave the Commanders to take sensible decisions re carriage of extra fuel.
Flight plan fuel on many flights is totally appropriate but if the TAF is TEMPO big TS surely it makes economic sense to take an extra one hours holding! If the field is socked in with TS when you get there you hold until the TS is passed which if the forecast is correct (since TEMPO is a change of less than one hour) will be within your extra hours holding?!
You then land at your chosen destination! Surely more economic than having to divert with ramifications for landing/handling fees, delays, crew hours etc?