Airbus aircraft are more likely to have LPV than say Boeing, but how do they plan to fly CAT3 with it??
Back to square one: LPV and who can use it. And why did UK not want to pay 30M for the bit of paper?
Peter wrote:
Airbus aircraft are more likely to have LPV than say Boeing, but how do they plan to fly CAT3 with it??Back to square one: LPV and who can use it. And why did UK not want to pay 30M for the bit of paper?
Why do use LPV & CAT3 in one sentence? RNP does not mean LPV-only.
The latest UK plan for SBAS seems to be Inmarsat based.
This PR from Inmarsat is informative. local copy
They plan to use Goonhilly as the monitoring station.
So the whole thing is piggy-backed onto existing facilities.
They have presumably checked that existing avionics will be able to use this SBAS signal 
Reading between the lines, the UK must see other uses for SBAS apart from GA. It is used in lots of applications. But those (e.g. surveying work) don’t need the “safety of life” bit of paper which is the entire issue here. What about for example positioning crop spraying drones… So it is not clear what the reason is. Can anyone think of any other “SOL” application? Is there something in the marine sphere?
I went to see if the UK based EGNOS monitoring stations are still in use.
I haven’t found anything more recent than 2021. But this makes sense since a number of other (EU) countries rely on the UK based stations.
So really nothing has changed as far as the signal is concerned. The reason the UK removed LPV approaches is just because it signed up to the (purely artificial) “safety of life” concept, and then it had to honour that
Peter wrote:
the (purely artificial) “safety of life” concept
What makes it purely artificial? (and doesn’t WAAS have something similar?)
AFAICT it was a self-generated rule. Meaningless.
I did a dig around WAAS and they refer to the term but it doesn’t sound like they created a “certification” system for it.
So the signal has not changed at all. If you had a homemade LPV GPS it would work perfectly now as it always did. But the UK CAA is very happy to make a rod for its own back, like it did with the artificial “cylinder” in its no-prisoners infringements policy.
With reference to this thread.
The UK still has the same signal, still maintains the two EGNOS monitoring stations (I presume, because these serve N France, the C.I. and Ireland too), and the only reason the UK CAA de-published LPV approaches is because Brussels de-authorised the UK from using the “safety of life” certification (which is itself BS).
The CAA didn’t have to do this; it is obviously some sort of a liability limitation maneuver.
The interesting thing to look at is what, if the LFLP situation was in the UK, what the situation would be with +V instead of LPV. But let’s look at actual numbers:
The minima with +V are the LNAV minima but it is obviously safer because the “glideslope” can be autopilot coupled and thus very accurate.
LFLP RNP Z – 200ft improvement, and RNP Y is the same
I have not been able to find old UK plates from before LPV ended in the UK. Can anyone find one e.g. Lydd EGMD?
For LFAT, which is practically where EGMD is, we have no difference for RWY 31
and just 70ft difference for RWY 13 (can anyone work out why? – maybe obstacles in the missed approach?)
This tells me that +V is practically just as good and perhaps this point was not lost on the CAA when they refused to pay the reported £30M which Brussels asked for to restore the SOL authorisation… they realised nobody would actually care, except a few AOC operations when the wx is right on minima.
The LFAT 31 case above suggests that LPV and +V minima might be identical if there are no obstacles!
LNAV/VNAV minimums are not +V. The LNAV using CDFA could be flown with +V, but the minimums are generally higher. Are there RNP procedures in the UK that have LNAV/VNAV minimums and is EGNOS authorized to provide the vertical guidance? In the US, WAAS may provide the vertical guidance for an RNAV (GPS) procedure to an LNAV/VNAV minima as an option to Baro/VNAV with a few exceptions. +V does not require being in the WAAS SSV for flying the advisory GP to a RNAV (GPS) with a LNAV minima, although this capability is only provided in the latest versions of WAAS capable GPS navigators. I can turn off SBAS/WAAS and still use +V with LNAV minima with my GTN 750Xi.
Are there RNP procedures in the UK that have LNAV/VNAV minimums and is EGNOS authorized to provide the vertical guidance?
Not heard of that.
The LNAV using CDFA could be flown with +V, but the minimums are generally higher.
Where would this be published? I don’t see any +V minima published.
I get your drift, sort of, because the trajectory of a CDFA LNAV approach is not the same as the trajectory of a +V approach. The former offers a better opportunity to be visual at the DH, because once you are past the last SDF, you are obstacle-safe at the DH, so logically after the last SDF you are entitled to descend at 10,000fpm but only to the DH But surely this is splitting hairs. And if you do any kind of fast descent after the last SDF, the acceleration will prevent a landing being achieved. So in effect most people flying a CDFA will be flying something like a +V anyway.
+V does not require being in the WAAS SSV for flying the advisory GP to a RNAV (GPS) with a LNAV minima, although this capability is only provided in the latest versions of WAAS capable GPS navigators. I can turn off SBAS/WAAS and still use +V with LNAV minima with my GTN 750Xi.
Yes this is a nice feature, and might be handy if the UK ever lost the EGNOS signal itself (which I am sure is impossible since the Channel Islands, Ireland and of course N France, Belgium, etc would lose theirs too) but I don’t see how this impacts the earlier question (the difference in DH between LNAV and +V).
