Winds (and temp) on TAKEOFF REF page?

[Will]

Hi all,

Line ops question here. As we know, we can enter wind components into the FMS TAKEOFF REF page (and also temperature, with the NG variant). I believe this is to improve accuracy in the FMS's calculation of takeoff speeds.

What if the takeoff speeds are calculated elsewhere, such as by the dispatch office, or dispatch software? In that case, are wind/temp values put in the FMS for redundancy and verification, or are the fields simply ignored?

Thanks everyone.

[jawomba]

Hi Will,

if the takeoff speeds were uploaded, they will not change by wind and/or oat entry unless you accept them.

Once the takoff speeds are uploaded and accepted, entered manually or selected via the prompts (displayed in big fonts) they will be deleted by new wind/oat entries.

As long as they are "reference" speeds they change by wind and/or oat entries.

This is the behavior in PSX.

Cheers Jan

[Hardy Heinlin]

Hi Will.

In that case, are wind/temp values put in the FMS ...

Do you mean ...
"put in the FMS" by the uplink?
"put in the FMS" by the pilot after the uplink?
"put in the FMS" by the pilot before the uplink?


Regards,

|-|ardy

[Will]

Hypothetical: Assume the dispatch office calculates the V-speeds, and the V-speeds are then communicated to the pilots, who then manually enter them into the FMS.

In that scenario, would the pilot also enter wind and temperature into the FMS on TAKEOFF REF, or would this now be a meaningless step?

[Hardy Heinlin]

The weather entry will delete the existing V speeds. The dispatchers took the weather already into account in the calculation of their V speeds. When you enter weather data in the FMC you use the FMC as a calculator (it will suggest V speeds in small font). You don't need to use the FMC as a calculator if you've got V speeds calculated by the dispatcher. So you just enter the V speeds and no weather. In that case you just use the FMC to set the V speed bugs on the PFD.


|-|ardy

[DougSnow]

The thing you need to keep in mind is the speeds in the box are based on a balanced field length, level runway at sea level, normal CG, dry and so on; perfect conditions.  We dont dispatch that way; for example at work we use Optimum V1, which unbalances the field to allow us lift a little more weight.  Our procedures are, since we uplink is for the crew to just use the uplink.  We don't use Alternate Forward C.G., but if we did, one of the elements of that program is an awareness of how the box computes v-speeds, and designing your procedures to not use the FMS for speeds if you're using Alternate Forward C.G.

I dont think the 744 was ever certified for Alternate Forward CG.