I promise this is not an “asking for a friend” thread – it’s just honest curiosity. I’ve never shot a GPS approach of any kind (sadly!).
It’s well known that the UK no longer has access to EGNOS as a consequence of Brexit. However, SBAS is a broadcast system that gives corrections to GPS satellites as a whole – unless they actually re-pointed the satellites to exclude the UK from their footprint, you can’t actually “turn it off” for a given location. Thus – is there any reason you can’t actually use EGNOS in the UK? If I any of you have an SBAS GPS (430W or whatever), does it show signal in the UK? And will it let you shoot an LPV approach?
My only guess is that – presumably – RNP approaches in the UK have had any “this can be an LPV approach” flags turned off, so if you have up-to-date Nav data then your receiver won’t let you shoot it in LPV mode. Is that right?
As I say, I’ve never shot any GPS approaches so don’t really know how they work in practice – I only know how to tune radios ;)
It’s well known that the UK no longer has access to EGNOS
The UK has full access to the EGNOS signal.
What happened is that Brussels cancelled the “safety of life certification” (a bogus concept IMHO) and the UK CAA decided that, to cover its ar*se on “liability”, they had to withdraw LPV approaches from publication. So you can’t fly them anymore because the LPV hex data block has been removed with the Jeppesen GPS databases which all IFR GPS navigators use. Jeppesen just follow the AIP data and once an IAP has been removed from there, Jepp remove it from the databases they sell to GPS makers.
you can’t actually “turn it off” for a given location
Indeed. You could degrade it a bit, and the UK operated some ground stations for UK and N France. I don’t know what happened to those but I am developing a GPS product right now and can tell you there is plenty of SBAS signal here (near Brighton). Maybe somebody knows what UK is planning to do with the ~2 ground stations.
so if you have up-to-date Nav data then your receiver won’t let you shoot it in LPV mode. Is that right?
Yes. And you can’t fly with old data for very long – it varies how long for.
You can still fly +V approaches though, which use the EGNOS signal (but in very recent navigators they don’t actually need it), and these are very nearly as good as LPV. The minima is the same as the underlying nonprecision (LNAV) approach, but in reality +V will, just like LPV, give you L and V guidance all the way to the tarmac.
SteakAndAle wrote:
Thus – is there any reason you can’t actually use EGNOS in the UK? If I any of you have an SBAS GPS (430W or whatever), does it show signal in the UK? And will it let you shoot an LPV approach?
Yes, you could still use SBAS, and yes you could fly LNAV/VNAV (or 3D) approaches – the GNSS ones (UK CAA finally allowed those again in 2019), not just the Baro-VNAVs.
LPV approaches won’t work – they’ve already expired from the DB, and they require some special codes, which had to be deleted as they are no longer allowed.
There is also +V, which does not give you an official vertical guidance, only unofficial, so legally it is still a 2D approach. Functionally, it still works OK and simulates a glideslope (kind of).
Interesting – so after a hasty google, if I have this right:
LNAV+V isn’t using any baro information (that’s LNAV+VNAV), but it is is giving you vertical guidance of where it thinks the approach’s glideslope is – if it has an SBAS signal. And because 1) that’s entirely up to the unit whether to do it, no coding in the nav data to allow/disallow the use of +V 2) EGNOS signal can still be received and 3) all “modes” of a given RNP approach use the same glideslope —> you effectively get LPV precision just without the same guarantees (hence “advisory” glideslope)….have I got that right?
You can get LNAV+V in any -W box, no need for SBAS signal (or LPV or L/VNAV), you still need to enable EGNOS = ON in “auxiliary menu” or “status page” (examiners do this trick, anyone with IR/PBN and flying on -W box would have seen it)
On your original question for UK, not much changes really,
Now what has changed: you won’t get LPV annunciation and you can’t fly LPV OCH minima, well unless you fly on outdated database and outdated plates
PS: waiting for Peter to jump saying he did not understood anything in the above
My only guess is that – presumably – RNP approaches in the UK have had any “this can be an LPV approach” flags turned off
There were not that many LPV with 200ft DH in UK…I don’t ever remember flying one? has anyone here ever flown an LPV in UK in GA aircraft other than Cardiff & Jersey? so not sure what was there to be lost? the closest thing I heard of was Kemble, it’s AFIS and restricted to AOC holders, I think it had an had LPV with OCH > 500ft
First you need an airfield which has an LPV procedure.
2nd you need an aircraft equipped with WAAS/EGNOS. WAAS being mainly for the USA region/area of influence.
3rd the procedure has to be in the database.
I’ll leave out.the qualification etc.
AIUI The LPV airfield supplies certain data to a master ground station which in turn corrects the GPS information coming from the GNSS system to make it more accurate. This corrected info in turn is uploaded to the WAAS or EGNOS or whatever SBAS system area you happen to be in which in turn is communicated to your GPS (W) in your aircraft.
This is how it was explained to me when we looked at the idea of an LPV instead of just an RNAV approach.
The cost of running an LPV system and maitaining its equipment was a little to expensive for our tiny airfield and finding the funding would have been difficult.
Still a lot cheaper than an ILS, which we never would have considered.🙂
First you need an airfield which has an LPV procedure.
There are now none.
3rd the procedure has to be in the database.
No current databases, and probably (I posted a link above to a thread) all the ones with LPV IAPs are now disabled.
The LPV airfield supplies certain data to a master ground station
Not normally. Unless you have DGPS but that is something else entirely, not needed for CAT1 LPV. May be needed for “CAT3 LPV”.
which in turn corrects the GPS information coming from the GNSS system to make it more accurate.
The ground station is at an accurately surveyed location, receives the GPS data, and sends the error to a geostationary SBAS satellite (WAAS or EGNOS).
The cost of running an LPV system and maitaining its equipment was a little to expensive for our tiny airfield and finding the funding would have been difficult.
It depends on who pays for the survey (easier if there is an existing IAP). In the US, the FAA (the general taxpayer) pays it. In Europe, normally the airfield pays it, and it costs in the region of 30k per runway end (some previous threads).
waiting for Peter to jump saying he did not understood anything in the above
Finally, that was clearly set out and written
The only way to have LPV in the UK now is with a DIY built GPS receiver, making use of the hex block retrieved from one of the databases before they got unpublished. It is feasible but anybody doing it isn’t going to be talking about it openly.
Peter wrote:
The ground station is at an accurately surveyed location, receives the GPS data, and sends the error to a geostationary SBAS satellite (WAAS or EGNOS).
That reads very much like the generic definition of DGPS (just using one of the possible means for sending the DGPS correction: a satellite )
Peter wrote:
The only way to have LPV in the UK now is with a DIY built GPS receiver, making use of the hex block retrieved from one of the databases before they got unpublished. It is feasible but anybody doing it isn’t going to be talking about it openly
How would the legality and practicality of using that equipment be any better than the use of an LNAV+V certified installation (on approach down to some 200ft in both cases) ? (Honest Q)
Peter wrote:
You can still fly +V approaches though, which use the EGNOS signal (but in very recent navigators they don’t actually need it)
That is interesting. What changed so that they no longer need the SBAS correction signals?
You don’t need SBAS signal to fly LNAV+V you need “TSO146 GPS” with Space Augmentation = ON in “auxiliary menu”…TSO146 GPS like G530W is what one would call SBAS/WAAS GPS
However,
I get LNAV+V on raw VOR IAP flown with GPS overlay in Africa
