Anders wrote:
Is it so that I would actually get LNAV+V when flying into EKRK but that I need to be closer to the EKRK airport for the LNAV+V to show?
No that doesn’t matter. It seem you only have a 3D fix, not a 3D Differential fix.
Jesse wrote:
I have asked Garmin about this.They indicate that that this is due to an LPV being an official coded and approved approach, which is always expected to be available, and is only downgraded when the horizontal and/or horizontal limits are not met 60 seconds prior to FAF.
They also indicated that the +V is not part of the official procedure and is only be expected during good GPS reception, hence the removal of it from the menu anytime you don’t have good GPS fix.
This is the same you experiance now. You will see LPV as that is expected to be available, yet the advise +V is not showed now, as you didn’t have a good fix (3D DIFF)
This is what you would get when you have a 2D fix, with or without SBAS enabled. Note you will get a yellow caution annunciator for terrain functionality.
This is what you would get when you a 3D fix, without SBAS enabled, or as indicated by 3D fix without SBAS reception when it is enabled
This is what you would get with you have a 3D DIFF (differntial fix). You have 3D GPS, AND you have SBAS turned on (EGNOS) AND it receives this EGNOS signals.
You can easily check this kind of behavour using the GTN simulators. It is available as GTN trainer in the Apple store or available as GTN Simulator for PC For some strange reason Garmin now asks money for this simulator.
I would only turn on EGNOS for SBAS if flying in Europe. The VFOM and HFOM are adequate for LPV, LNAV/VNAV or LNAV+V, so it does not make any difference if you get closer to EDDE, if the database and software level permitted it, then it should show up with vertical guidance. The final approach segment is 9.2 NM and a bunch of approaches, mainly in Europe that have a final approach segment greater than 7.0 NM don’t provide vertical guidance.
NCYankee wrote:
The VFOM and HFOM are adequate for LPV, LNAV/VNAV or LNAV+V, so it does not make any difference if you get closer to EDDE, if the database and software level permitted it, then it should show up with vertical guidance.
I am not sure, if only a good VFOM and HFOM are enough to get this enabled, It doesn’t seem to be, See images I posted before, and Garmins response on the +V only being available if SBAS (EGNOS in this CASE) signal is received. From Ander’s GTN GPS page it seems it didn’t receive EGNOS signals at that time. It does indicate 3D NAV instead of 3D DIFF NAV
From GTN pilot guide:
When this is checked with the simulator unit, you can see that this behavour is exactly such, and also confirms to Anders findings.
Agreed with the 3D Diff Aspect.
You have to be within the service volume of the SBAS and the VFOM needs to be below about 60 in order to avoid a downgrade. This covers LPV 250+, LNAV/VNAV, and LNAV+V. For LPV 200, the VFOM needs to be below 40 ish.
+V is also affected in Europe by whether there is a (even hidden) LNAV/VNAV approach to the same runway. If the LNAV/VNAV is there it seems like +V won’t appear on an LNAV approach. Given that most of the LNAV./VNAV in Europe are Baro (not SBAS) only so won’t appear on the menu it is quite frustrating.
Is it fair to say that LNAV/VNAV approaches were developed in a time before WAAS/EGNOS (SBAS) came along to allow Baro-assisted precision-like approaches….
LNAV/VNAV can continue to be used with Baro correction by aircraft without SBAS and/or in locations where there is no SBAS reception…..
LNAV/VNAV can now also be (technically) used with SBAS instead of Baro…however to me this would only be an option in cases where there is no LPV approach (yet)…so in other words the use of SBAS corrected LNAV/VNAV approaches is only a fix until an LPV approach is coded implemented at a given location…
Is that a fair assessment?
Finally. At the third attempt. RNAV approaches looks as expected.
At my the first attempt to look at RNAV approaches and what minima I would get, the aircraft was in the hangar with a Loss of Integrity warning that removed LNAV+V and LNAV/VNAV.
At my second attempt someone had disabled WAAS, EGNOS and MSAS. And even though I re-enabled them, I did not wait long enough for the GPS to pick-up EGNOS. (I only got 3D NAV) So, once again – no LNAV+V and no LNAV/VNAV.
At the third try.
I made sure that I had “3D DIFF NAV”.
I get LNAV+V at Roskilde EKRK.
And LNAV/VNAV at EDDE Erfurt.
And LNAV at Ängelholm ESTA. (ESTA has LNAV/VNAV minima but it is not approved for EGNOS glide slope only BARO-VNAV)
One conclusion is that I should have read the manual for the GTN 650.
One consequence of Loss of Integrity, LOI, is that LNAV+V and LNAV/VNAV is removed.
And “3D NAV” means that EGNOS has not been acquired and that LNAV+V and LNAV/VNAV will not show.
But from a user perspective I find the Garmin software implementation inconsistent.
If there is a LOI, why show LPV but not show LNAV+V and LNAV/VNAV. The argument is that LPV has been approved/tested and therefore WAAS and EGNOS is assumed to be working and that for LNAV+V and LNAV/VNAV the criteria are more dynamically checked. But I would find it more logical if LPV, LNAV+V and LNAV/VNAV were handled in the same way. After all, based on where an approach is located geographically, it is known whether it is inside the WAAS or EGNOS service area, so just by looking at a map you know if you can expect “3D DIFF NAV”. The GTN software could do the same.
And then I find the GPS signal names to be badly worded.
One could easily think that “3D NAV” is good enough to provide a glide slope. But it isn’t.
And “3D DIFF NAV” does not say outright that it uses SBAS. Only that the GPS is in “differential” mode.
This is going to be a dumb Q but what exactly does LNAV/VNAV give you, in terms of vertical navigation, autopilot coupling, etc?
It isn’t LPV because no “GS” is shown on the Jepp chart (EDDE)
This is LPV (EGTE) where the converging dashed lines indicate LPV
and I know what +V is.
LNAV/VNAV gives a glideslope. The autopilot shouldn’t see any difference between LPV, LNAV+V and LNAV/VNAV and happily fly all three glideslopes. (Maybe there could be some small difference how the autopilot navigates laterally on LPV vs LNAV+V and LNAV/VNAV. LPV becoming more sensitive as you come close to the threshold.)
