A320 Constraint Query
 

Hi all, hope everyone is well.

Question regarding constraints on STAR's and airbus logic.


Scenario: VASUX1G into LGW.
Descent initiated at the correct time. ATC issue descend FL130 level by TELTU. Set FL 130 in the FCU manage the descend and that's that.
Further descent issued before TELTU, "descend FL080", keep the TELTU restriction.
Set FL080 in the FCU and keep in manage des.

Now I know the bus will keep the constraint as 130 is still inserted as a constraint by TELTU, however how come I don't get ALT magenta with 130 on the altitude tape? Is it because a level-off hasn't been predicted therefore it will just show ALT blue?
It is still magenta on the ND and in the box.

Where as, is my understanding correct that if I initiated the descent really early (which you wouldn't do anyway) & say for example I was at FL140 20 miles before TELTU, if I selected FL080 and managed the descent, would ALT be magenta in this case because it's predicting I'd need a level segment in order to meet the TELTU restriction?


Whilst I would never take any 'simulator' for the source of this question by providing a bad reference I have seen a few vids online where Alt has been magenta (in a scenario like above) but the aircraft just flies straight through the constraint at say 130 and then would go from alt magenta to alt blue.

Is it potentially a FMS release 2 update or is it as simple as if a level off is predicted to meet the constraint alt would be magenta, or if no level off is needed alt would just be blue.

Appreciate any words of wisdom.

Thanks!

That’s my understanding of the logic.

That is exactly the reason.

Thanks guys...
so if I initiated descent really early in theory I therefore should get alt magenta, correct?

Affirmative. This is described in some detail in the relevant manuals.