Planned Optimum Flight Level only considering wind?

[fabristunt]

Hi there! Is it possible to know how exactly does Simbrief chose the optimum FL? I found on this forum that it is looking at a time/fuel ratio, but with the following example something doesn’t work:
Flight from ELLX to LEIB

The first one has the OPT FL310. However, if I force it to FL390, I need less fuel and it’s 7 mins faster!
The AVG W/C for FL390 is P000.
The AVG W/C for FL310 is M004.
I really cannot see why FL310 would be better. How is Simbrief deciding to go with FL310?

[Rodeo314]

This is in eurocontrol airspace. There’s gotta be a city pair level cap or some other restriction that forbids flying higher than FL310 on that particular route.

Regards,

Tim

[fabristunt]

No, the route is CFMU valid up to FL 410.

But if it were due to a cap, I suppose the rmk would be something other than OPTIMUM FLIGHT LEVEL.

[Rodeo314]

Simbrief has a restriction of 32000 between VATIR and PIVUS that might be impacting the altitude selection:

SimBrief - Dispatch

It might be automatically derived from an airport-specific restriction elsewhere.

This can be fixed; I will add verified CFMU-valid routes between ELLX and LEIB shortly.

That won’t necessarily change the cruisd altitude picked by simbrief in your case but at least the incorrect restriction will be lifted if necessary.

Regards,

Tim

[Rodeo314]

This is an interesting route, as there are some vertical restrictions that are passed/ignored/missed by the validator using airliners such as the B737 but triggered by aircraft with a different climb profile:

Regards,

Tim

[Rodeo314]

Regarding your original issue, I couldn’t get FL310 cruise even with the VATSIM route unless I de-select “plan stepclimbs” so I guess it wasn’t related (with the option disabled, all such altitude restrictions are ignored).

With step climbs disabled and altitude AUTO I do get FL310 for a B737 at 46,153 kg of ZFW with a cost index of 10. That is a bit odd, as it’s indeed using more fuel, taking longer and the aircraft should be able to climb higher at this weight.

Edit: that being said, when using the newly-added route and everything else the same (B737, ZFW, CI, step climbs disabled, altitude auto) I get FL410 instead:

I can’t explain it; we should probably just wait for the developers to chime in.

Regards,

Tim

[srcooke]

Try the original route again, submitted as IFPS and tested CI10 ZFW 46135

(FPL-PMDG737-IS
-B737/M-SDE2E3FGHIRWXY/LB1
-ELLX0925
-N0444F410 GTQ1Q GTQ DCT POGOL DCT LASAT DCT MOROK DCT GILIR DCT GVA DCT INCUS DCT BALSI UN852 VATIR DCT PIVUS DCT SULID DCT DIMIB DCT POS POS4N
-LEIB0155 LEVC
-PBN/A1B1C1D1S1S2 DOF/240818 REG/PMDG737 EET/LFEE0003 LSAS0030 LFFF0034 LECB0110 PER/C RMK/TCAS)

[fabristunt]

Is it possible for me as a user to get to the page you show? Seeing the altitude restriction field would be helpful.

[fabristunt]

I do not use the plan stepclimb feature, because it often leads to yoyoing along the route:

I’ve somewhere that the devs are considering to uncouple the Stepclimb and “consider altitude restrictions” feature and give them as separate options. Looking forward to it.