CDU At/Above bug?

[speed330]

Hi all,

First of all apologies if this has been mentioned before.

I've noticed that when loading a SID with an AT/ABOVE altitude or FL restriction (e.g FL200A) at a waypoint that the CDU is estimating will already be at the altitude/FL that is currently set in the VNAV Cruise page, all subsequent waypoints are estimated at that same AT/ABOVE altitude/level, which results in insufficient fuel or unable crz alt CDU message (since it is predicting you are flying at that level for the rest of the flight). So it's like the CDU is treating it as an AT restriction instead of AT/ABOVE.

The same situation happens if I was to manually put an AT/ABOVE restriction at any waypoint that the CDU estimates will be at the altitude/FL set in the VNAV Cruise page.

Example;
- CDU VNAV Cruise page is set at FL280
- a SID is loaded that contains a waypoint far from the airport with an AT/ABOVE restriction of FL200. All waypoints after this are estimated at FL200 instead of a higher level up to and including FL280.
 
I have tried this in different default situation files, both classic FMC and the NG versions, using the latest Aerowinx version 10.181. Any ideas what is causing this?

Cheers,
Dave

[Hardy Heinlin]

Hi Dave,

I guess this may happen if you didn't enter a destination airport or an altitude constraint near the destination. In that case the FMC cannot detect whether your distant FL200 constraint belongs to the origin or destination.

Please note that this forum will be moved to a new server soon and that this thread won't be copied to the new server.


Regards,

|-|ardy

[speed330]

Hi Hardy,

Many thanks for your reply and help, I can confirm that I did not have an arrival selected for the destination. Once I entered one this issue was fixed.

Kind Regards,
Dave