BOAC,
No criticism intended here and I, of course, agree that
javelin's approach to the problem is a demonstration of how fantastic common-sense can be!
The scenario you share with your FO's supposes you've burnt all your D and on finals, your day gets even worse and you're left with the proposition of diverting on E, correct?
The way I look at it, is, once you're into burning D and commiting yourself to a destination airfield, I think you're in non-normal territory. A PAN at this point might be prudent.
Normally, in the neck-of-the-woods where I fly and on my type, D < E. I could still make my
normal alternate if that happened to me and have some flex...er, vapour left in the tanks.
I hasten to say that I'd be mighty upset if that happened to me, to say the least.
In the above scenario, for your aircraft type, D was only just less than E, correct?
If D is greater than E, and you've burned all your D, you're going to have to think extremely quickly and find another strip of tarmac somewhere, which may or may not exist....
Cognizant of the relative sizes of D and E (the following won't apply if E is greater than D, obviously - see above), it strikes me that if you're staring the "Should I commit or divert?" proposition in the face, what you need to know is where your EAT is in relation to the point at which your fuel onboard (FOB) is equal to D.
Having made the decision to commit, if you get an EAT which means that, if you commit
further, your remaining fuel onboard is going to be less than D (+ whatever "pucker factor fuel" you in particular can handle, call it = D_adjusted),
it is at the point that it is equal to D_adjusted you've got a SECOND decision to make...
You've got three options (at least) as I see it...
You're either absolutely ice-cool, and the possibility of the blocked runway scenario you suppose doesn't bother you, so you're willing to commit anyway and accept the given EAT. The PAN is still active but no MAYDAY? Fair play to you. Professional pilots tend not to like options which leave them no escape bar a PFL in Biggin Hill!
You reach D_adjusted (because you're allowed to and you hope your EAT might come forward - not unusual), bottle it, decide to divert, and somewhere along the line, when FOB = E, declare a MAYDAY. Personally, knowing that at some time during my diversion I'm going to reach this point, you might as well declare it at the point you make the decision.
You reach D_adjusted (because you're allowed to and you hope your EAT might come forward - not unusual), bottle it, decide to declare a MAYDAY, in order to accelerate your progress to the destination airfield, although, in this case, you'll probably land with more than E, whereupon strictly, a MAYDAY is not required....well not according to our OM. However, you'll only get the expedited arrival if you DO declare the MAYDAY.
I think that is right anyway....
Makes you think there is more to fuel planning than meets the eye.
I agree that what the regulations permit could potentially lead you down a cul-de-sac, whereupon, the above is a last attempt to ensure you still have more than one option.
