Garmin GTN750 - VNAV not working?

[mthocker]

I have a GTN 750 / 650 setup in my 2001 C182T with steam gauges. Since getting my instrument rating, I've noticed that I only am offered LNAV on RNAV GPS approaches when the Jepp charts clearly show that VNAV is available. I called Garmin about this and they said to check the SBAS settings to make sure that WAAS/EGNOS was enabled and it is.

Is there something that I'm doing wrong or a setting that I don't have enabled? Or am I missing some equipment that would enable this?

Thanks

[alexbrett]

In the UK, Garmin products are not able to use SBAS in place of barometric VNAV, unlike they can in the US - as such it is expected that you don't get LNAV/VNAV. The exact reasons for this are unclear, it appears at least historically the CAA were unsure about its use, and while there are rumours they may have decided they don't mind any more, the databases as produced are still preventing it.

If the approach has LPV minima, then you should get that, and if it doesn't have VNAV, you are likely to get LNAV+V (unless there is something specific about the approach to prohibit it). Annoyingly if there is LNAV/VNAV minima you will never get +V as far as I'm aware, so unless there is LPV you're stuck with plain LNAV :(

[mthocker]

The weird thing is that I have a friend with a 182 and the same 750/650 setup and his does work. But mine stubbornly refuses to. Same approaches, same database.

There must be a setting somewhere, right?

[alexbrett]

The weird thing is that I have a friend with a 182 and the same 750/650 setup and his does work

It's possible he has a barometric VNAV input, though normally you only see that in full glass panel setups...

As far as I'm aware there's no switch, it's a flag in the database which says must be barometric and not SBAS.

[LastStandards]

At the moment NCO.OP.111 applies, showing that LNAV/VNAV minima may only be used across EASA states if the VNAV profile is generated from Baro-vertical navigation, ie BaroFMS as alexbrett stated. EASA are aware of the anomaly wrt equipment capability vs regulatory permissions, but at the moment it's just not a major priority since all RNP Approaches were planned to include LPV minima. Sadly this hasn't always happened... Fortunately there aren't that many in the UK that are LNAV/VNAV but not LPV, with more recent approach approvals covering all possibilities.

[WTON]

Hi guys,
During my SE/IR PBN test last December in France, on TB20NG, we have been caught by the same issue...

[bookworm]

I've noticed that I only am offered LNAV on RNAV GPS approaches when the Jepp charts clearly show that VNAV is available.

Which approach and airport?