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-   -   A320 difference in predictions on FMGS/ND (https://www.pprune.org/tech-log/357306-a320-difference-predictions-fmgs-nd.html)

kijangnim 15th January 2009 03:02

Greetings
The point I am taking about is the NEXT WAYPOINT, displayed on the ND versus the active leg.
For the JET case, as long as you are not yet within the jet stream it makes sense, the FMS is blending the wind using an actual wind much weaker therefore the wind average is far less that what it should be, and it affects your predictions, until you are within the jetstream then ...

CONF iture 15th January 2009 08:37


Originally Posted by waren9
FCOM 1.31.45 indicates that current G/S only is used to give the ETA for the next waypoint shown on the ND

Thats it !

Best exemple is to take a first waypoint something like 200 NM after takeoff and look at the difference of ETA between ND and MCDU.
Take that reading early after takeoff when GS is still pretty low and the difference will not be counted in minutes ... but in minutes X 10
As soon as GS increases, difference shrinks.

Aikon 15th January 2009 14:23

kijangnim,


The point I am taking about is the NEXT WAYPOINT, displayed on the ND versus the active leg.
For the JET case, as long as you are not yet within the jet stream it makes sense, the FMS is blending the wind using an actual wind much weaker therefore the wind average is far less that what it should be, and it affects your predictions, until you are within the jetstream then ...
I thought you said the difference is because of

and That wind is used to compute the waypoint displayed on the ND, but will use the distance based on the bearing between the aircraft position and the waypoint, whereas on the MCDU it is based on the active leg (which could be great circle, rhumb line, Arc ....)
So which is which now?!

kijangnim 15th January 2009 14:58

Greetings, everyone

The least I can say is that I made you open the books, and kept you very busy :E

scorpilot 16th January 2009 05:40

i still havent opened the fcoms, reading the thread has drained me!

TheGorrilla 18th January 2009 19:09

i agree.... ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ :zzz::zzz::zzz::zzz::zzz:

Time to get a life.


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