NCYankee wrote:
There are airports in the US where following the +V below the MDA will take you through the obstacle or hill side.
The question is, I guess, that if you have a proper LPV approach which is removed from the database because the EGNOS SoL service is no longer available in the UK, would it be safe to perform an LNAV+V approach down to the old LPV minima?
I reckon you could count the UK LPVs on your fingers (without having to go to binary 
) so it would not be hard to check.
The only one I can think of with any terrain is EGKA 20 and I can tell you for a fact that the +V slope on that will keep you well clear.
I would also be surprised if an approach surveyed for LPV would have a conflict with +V.
Airborne_Again wrote:
The question is, I guess, that if you have a proper LPV approach which is removed from the database because the EGNOS SoL service is no longer available in the UK, would it be safe to perform an LNAV+V approach down to the old LPV minima?
No. The integrity is reduced to the LNAV 0.3 NM values for the lateral (556 meters) and not the 40 meters available on LP/LPV lateral. If it were safe, then there would not be any valid need for LP/LPV.
Seeing those numbers in the context of typical modern GPS accuracy of 2-3m, isn’t that a practically irrelevant limitation?
Bear in mind that EGNOS will still be available, all over the UK unless the UK turns off its monitoring stations and will (normally) be received.
Whether the UK turns off its monitoring stations, which must be costing it millions, is a really interesting Q. Does anybody in the UK use EGNOS based DGPS, non aviation? I know a lot of DGPS work goes on but it uses temporarily erected ground radiators, for centimetre (well, tens of cm) accuracy.
NCYankee wrote:
No. The integrity is reduced to the LNAV 0.3 NM values for the lateral (556 meters) and not the 40 meters available on LP/LPV lateral. If it were safe, then there would not be any valid need for LP/LPV.
@NCYankee, from practical point – what stopping pilot monitoring to switch the GPS to the status page and monitor current uncertainty values? Should work, right?
I don’t mean its legal! :)
arj1 wrote:
from practical point – what stopping pilot monitoring to switch the GPS to the status page and monitor current uncertainty values? Should work, right?
I don’t mean its legal!
Most GPS systems do not provide the integrity values to the user interface. The GNS430W/530W, G1000, GTN6XX/7XX variants, the GPS175 … all do not have the information displayed. There is a TSO requirement to provide HFOM and VFOM, but these are not integrity values of HPL or VPL. Also do you or anyone else know what the requirements are? Most pilots will not know where they are changed, how they are monitored, … so I would say it is impractical.
NCYankee wrote:
No. The integrity is reduced to the LNAV 0.3 NM values for the lateral (556 meters) and not the 40 meters available on LP/LPV lateral.
An SBAS receiver will provide angular resolution on the CDI even with an LNAV approach.
If it were safe, then there would not be any valid need for LP/LPV.
Well, LNAV+V is not an official approach type. It is provided by the avionics manufacturer.
Airborne_Again wrote:
An SBAS receiver will provide angular resolution on the CDI even with an LNAV approach.
Correct, but the maximum FSD indication is not integrity.
Peter wrote:
(whether they are the US Navstar system which practically everybody uses, or the European Galileo system which practically nobody uses).
If they even work.
Last week I was setting up an AIS transponder on the bench. It does GPS (Navstar), Galileo and Glonass.
The only satellites that showed up at all were GPS. To be fair I had no external antenna and it was inside a building (when the thing is on the boat, I’ll have to check again) – but I had half a dozen GPS satellites and zero of the other two systems.
Yeah; I never managed to find more than 1 or 2 Galileo sats on the Aera 660. Right now I am running a UBLOX GPS (in an indoor test rig) which picks up more sats than anything in aviation and it is showing only a couple of them. The rest are the American ones. Could it be the whole multi-BN thing is really useless? Anyway no avionics uses Galileo.
The “drift” here is that we may end up using +V instead of LPV, and +V will continue to be available regardless of database issues (so long as the airport has the LNAV approach; these get removed if say it loses ATC) and it is practically as safe in the cases in question so long as the +V DH is respected.
