FMC Question B777

[Hellenic aviator]

I have noticed on the ALTN page, PG1 gives you the 4 closest alternates at any given time, unless I override this with the ICAO designator that I choose to be as a more suitable alternate.

What are the fuel and ETA predictions when selecting any one of these ALTNs based upon, if I do not change anything on the second page?

Does this page use the same philosophy as the fuel and ETA predictions on the ACT RTE data page, based in actual winds entered and mixing 200 nm ahead between actual and predicated?

When selecting to divert from this page, does it predict fuel and ETA based direct to the aerodrome reference point?

I have noticed that if I choose an ALTN from this page, then type the same ALTN ICAO designator into the 3L (DEST) on PROGRESS page, the fuel and ETA predictions are not the same nor anywhere near. I have noticed discrepancies of up to 2T :confused: and times of about 10 mins :confused:

Having looked through my FCOMs I cannot find enough information on why the differences and to where the ALTN page bases its fuel and ETA predictions.

Any help is greatly appreciated.

[mr ripley]

As far as I remember they are still wind unless you uploaded the alternates as a batch via ACARS, these are winded.

The criteria can be found by selecting the alternate. Then you should see:
Routing
Speed
Altitude
Wind
that are used in the calculation.

[Hellenic aviator]

Whenever I select the ALTN, the option is DIRECT or O/HEAD via a waypoint. The waypoint must be on the LEGS[age if I choose the second option.

On the right side of the page, the options are altitude, speed, wind - these are always blank. Oddly enough, I still am given an ETA and fuel prediction.
It's this discrepancy compared to the PROGRESS page that has me confused.

These ALTNS are not uplinked via ACARS - we don't have this option in our Company.

Thanks for your reply.