Originally Posted by
Gypsy
If you divert from overhead destination with your normal reserves, you should be able to fly to the alternate and land still with 'final reserve fuel' on board; there is no need to declare an emergency of any sort. If you are go below final reserve fuel, you must declare a Mayday.
If you set off on a diversion and have to declare Mayday straight away, then something has gone wrong. Either the crew held for too long and have started the diversion below the normal reserves or the fuel planning was wrong, by which I mean maybe an unrealistic route from destination to alternate was catered for.
I guess you didn't read the thread. First of all, no, you do not declare mayday only once you are below final reserve fuel, you declare it as soon as you are reasonably sure that you will land with less than final reserve fuel. Which can be at a time where you are still quite a bit above final reserve fuel. Not to mention, at some point the low fuel warning of the aircraft will come on, that is a LAND ASAP amber indication which could be interpreted as reason for a PAN or MAYDAY depending on how you are trained.
And as has been explained in here, you fly to your destination, you do the approach, missed approach, decide straight away you want to divert, and ATC tells you to stand by for 15 to 20 minutes. That is an amount of time that is not included in your alternate fuel. You are straight away in a mayday situation as you will land below final reserve fuel. Of course, there could be contingency fuel, if that hasn't been used before, but that is at minimum only 5 minutes worth of holding. You still have to wait another 10 to 15 minutes until ATC has sorted out the approval, routing and so on. Still a mayday situation.
Of course, we could always take those 15 minutes as extra fuel. And personally i like to take 20 minutes into the london TMA simply because they advise us that "no delay" means up to 20 minutes of holding. But during a low season day to your homebase in benign weather? Probably not.