I think almost nobody in light GA in Europe has baro-VNAV. If you want vertical guidance (coupled to autopilot or hand flown) it is LPV or +V.
Currently in the UK, +V is the name of the game and it should be available for every runway which has a GPS approach published.
The basic point about airlines is that LPV is of negligible relevance to them, not least because “airline” airports in the UK have ILS. That in turn leads to a lack of government interest in LPV. Some airports installed ILS fairly recently e.g. Gloucester EGBJ, at a cost (posted by the then manager, and including lighting mods etc) of £1M.
France may be different, but it has better wx (well, the lower half has) so CAT1 may well work well enough for the business model, and anyway this is the UK 
Peter wrote:
I think almost nobody in light GA in Europe has baro-VNAV. If you want vertical guidance (coupled to autopilot or hand flown) it is LPV or +V.
Did you mean “it is either GNSS VNAV or +V”? In the end, LPV is a GNSS-VNAV (SBAS) to a lower minima. And UK CAA actually mermitted GNSS VNAV from 2019 (it was prohibited before with only Baro-VNAV approaches in the database, but then added again after Brexit).
lionel wrote:
Airborne_Again wrote:
I guess it is theoretically possible to design an SBAS LNAV/VNAVThere is an EASA general approval to substitute an SBAS-aided GNSS for BaroVNAV in “EASA AMC 20-27 with CM-AS-002”. It must have been inherited into UK regulation on Brexit and unless overridden since then, should still be valid.
Yes. To clarify, what I meant was (in response to the comment that Baro-VNAV is a different thing) that all LNAV/VNAV procedures are designed as Baro-VNAV procedures. I believe you can design an LNAV/VNAV approach procedure specifically for SBAS but it is never done as an LPV procedure would be better. (Of course today it could make sense in the UK as it has EGNOS SBAS but can’t use the EGNOS SoL service required for LPV.)
In the US, WAAS vertical guidance is approved to fly approaches to the LNAV/VNAV line of minima. There are a few RNAV (GPS) approach procedures with LNAV/VNAV lines of minima in Puerto Rico that prohibit using WAAS for the vertical guidance, but this is due to the lack of availability of VPL that meets the vertical guidance criteria (50 meters).
TERPS has two totally different approach specifications for LPV and LNAV/VNAV. The former is solely based on WAAS for vertical guidance. The latter is based on the characteristics of Baro-VNAV vertical guidance. The fact that the TSO in the US permits using WAAS for the vertical guidance has to do with RTCA DO-229 compliance which specifies limitations on how the vertical CDI FSD is constrained. FSD is angular +/- 0.25 GP angle, but is constrained to be no greater than +/- 150 meters. So for a GP angle of 3 degrees, this occurs at roughly 6.2 NM measured from the GPIP (Glide Path Intercept Point) which is where the GP nominally touches the runway pavement. It is also optional that the angular GP FSD be constrained to be no less than +/- 45 meters when close to the runway. So AFAIK, there is no specification for LNAV/VNAV based on SBAS as the vertical, it is only based on the characteristics of Baro-VNAV and SBAS for the vertical is an accommodation after the fact. An SBAS GP is a straight line in space, whereas a Baro-VNAV vertical GP is not.
And UK CAA actually mermitted GNSS VNAV from 2019 (it was prohibited before with only Baro-VNAV approaches in the database, but then added again after Brexit).
The CAA has no power to do that. If an IAP is published you can fly it. In fact you can fly a totally made-up DIY IAP in the UK but that is a whole other topic although that fact undermines any “prohibition” in the private flying context. It sounds like typical CAA BS “guidance” in Safety Sheet 23456" telling you to not use the “glideslope” feature of some Garmin boxes for DIY approaches.
An SBAS GP is a straight line in space, whereas a Baro-VNAV vertical GP is not.
Is that simply due to the latter curving due to the earth’s curvature i.e. a line of constant pressure is a curve whose radius is the distance from the earth’s centre to the aircraft? I could of course work it out but I am surprised it is significant.
Peter wrote:
The CAA has no power to do that. If an IAP is published you can fly it. In fact you can fly a totally made-up DIY IAP in the UK but that is a whole other topic although that fact undermines any “prohibition” in the private flying context.
If you fly a published approach with different navigational aids that it was designed for is basically becomes a DIY approach, which is legal not only in the UK but in EASA-land as well. (We’ve gone over that lots of times already.) However, you are required to take the obstacle situation into account with DIY approaches. The CAA could argue that if you are using a published approach to published minima with different navigational aids then you would need to do an obstacle assessment for the aids you are actually using.
Let’s get back to basics and for the UK.
If you want vertical guidance, it has to be either ILS or +V. Baro-VNAV is almost nonexistent for GA.
And +V is available (from Garmin or Avidyne, which are the only options) only on GPS approaches.
The +V glideslope is designed to clear all SDFs, and is obstacle-safe all the way down to the DH published for that GPS approach.
All such GPS approaches have published SDFs.
Nobody is suggesting that however you actually navigate you disrespect the published SDFs.
Also nobody is suggesting that you disrespect the DH published for that SDF approach (well, except in emergency, or similar, and then you just need to know there is nothing there from the last SDF to the tarmac if the +V glideslope is continued, and I believe that is true for the UK and, if you get it wrong, you die, but that’s ok because you should know that).
So I don’t see a problem with using +V.
What is an SDF?
I understood +V was just a straight descent path without taking any obstacles or obstacle areas into account.
Stepdown fix e.g.
Peter wrote:
And UK CAA actually mermitted GNSS VNAV from 2019 (it was prohibited before with only Baro-VNAV approaches in the database, but then added again after Brexit).The CAA has no power to do that. If an IAP is published you can fly it. In fact you can fly a totally made-up DIY IAP in the UK but that is a whole other topic although that fact undermines any “prohibition” in the private flying context. It sounds like typical CAA BS “guidance” in Safety Sheet 23456" telling you to not use the “glideslope” feature of some Garmin boxes for DIY approaches.
Apparently (allegedly?), CAA insisted that GNSS VNAV was not in Jepp database for the UK.
Peter wrote:
If you want vertical guidance, it has to be either ILS or +V. Baro-VNAV is almost nonexistent for GA.
It could be ILS, +V or LNAV/VNAV(VNAV could be Baro or GNSS VNAV). While the procedure would have to be designed as BaroVNAV, nothing stops you from flying it GNSS VNAV (I’ve seen reports elsewhere).
