Strange VNAV calculations

[crisk73]

Hi, I know that VNAV has remained untouched by the last update, but just to give devs one more case study for a future update, I'd like to report the following behaviour.

Route: LIPZ ROTAR6X.04R ROTAR P11 PUL UN606 ZDA UL607 PETAK PETAK2J.17 LATI
CRZ: FL370
CI: 20
ZFW: 46 t
FOB: 5.2 t
Navdata Aerosoft NavdataPro cycle 1706
Further info in the attached logs.

According to the calculated VNAV profile, TOD should be over PETAK, corresponding to an ALT restriction of FL120A. It seems that past FL370 over PETAK a discontinuity in the vertical profile exists as the next waypoint TRN23 is only 5.2 nm far and calculated at FL100. The first time I trusted this profile and it costed me a very long holding to lose the excess altitude (and a lot of fuel).

Then to adjust the VNAV profile I had to manually delete the ALT restriction over PETAK and force ALT to FL120 (else it would have been less thus violating the restriction). In this way TOD is correctly moved far enough to descend according to the numbers.

It seems that ALT restrictions are the culprits behind VNAV quirks...

Hope this helps and thank you for the good job!

Cris

IXEG_FMS_debug.txt

GizmoLog.txt

Log.txt

[Litjan]

Hi Chris,

thanks for that elaborate report!

You are right, the most obvious stumbling block for VNAV is a complex set of altitude restrictions, and those become more common all the time, with airspace getting more complex and crowded.

We have a pretty substantial rewrite of VNAV in mind to be able to handle that confidently.

Cheers, Jan