Capt blogs
The new descriptions are
2D and 3D approaches;
2D being lateral guidance only (VORs, NDBs, RNP APCH eg RNAV (GNSS) )
3D, being lateral and vertical guidance eg ILS, MLS, GLS, RNP APCH LNAV/VNAV, LPV and RNP-AR.
You are getting confused again, Capt Blogs. The vast majority of GNSS approaches are 3-D approaches, with both lateral and vertical guidance (baro vertical tracking). I presume your RNAV-AR approach has some kind of LAAS/WAAS ground augmentation, and is therefore more accurate, but I presume it is still only a baro vertical tracking system.
The KTM approach is a GNSS with baro vertical guidance (but called here RNAV RNP). As ATC Watcher said, the confusing terminology does not help here - with many different acronyms for the same type of approach, that do not exactly explain the differences between them (RNP-AR, RNAV RNP, GPS RNAV, GNS, GNSS, GLS).
And sorry, but this GNS debate is relevant to this thread. I know several companies whose pilots were all doing GNSS approaches last year, even though the company had no certification, the Part A had no information, and the pilots had no training. Not saying that is what happened here, but there is definitely a regulatory lacuna here.
It could also be a factor if the training that was given did not point out that GNSS is only a non-precision approach. It would appear that many posters even on this thread, thought that GNSS was a precision approach. So the first time the GNSS approach displaces you 0.25 nm left or right of the centerline might come as a bit of a shock. This is why I questioned the 350' decision at KTM, because this seems a bit low for a possible 0.25 nm displacement.
Oh and as an aside WAAS is a GBAS, it is just that the signals are relayed via standard comms satellites, because it is a wide angle system (a large area system) and not a local system. So what I said is correct - the WAAS system itself is a ground based system and NOT a satellite based augmentation system. (How can a geostationary satellite augment a low-earth orbit satellite?
) See the quote below.
Quote:
The Wide Area Augmentation System (WAAS) uses a system of ground stations to provide corrections to the Global Positioning System navigation signal. A network of precisely surveyed ground-based WAAS wide-area reference stations is strategically positioned across the country including Alaska, Hawaii, Puerto Rico, Canada, and Mexico to collect GPS satellite data...
GNSS Frequently Asked Questions - WAAS
GNSS Frequently Asked Questions - GBAS
The links posted previously in this thread are confusing in their terminology - as is most of the terminology used in these systems. The distinction should be between WAAS and LAAS, and not between WAAS and GBLS. Both WAAS and LAAS are GBLS systems (ie: ground based augmentation systems) - it is just the former is a wide area system via satellite and the latter is a local area system via VHF. But it is true that WAAS and LAAS are not compatible, because they receive the ground-based corrections via different antennae.
Oh, and Capt Blogs. Do you now understand that the orbits of the GPS satellites are fixed? The last time you responded by saying: "You can't be serious...". Do you understand how the system works now? You have gone quiet all of a sudden.
And when I said that GNSS is non-precision (because of its low 0.3nm lateral precision, even though it has vertical guidance), you ridiculed that assertion. But now you respond with: "For goodness sake! WAAS gives better accuracy ... That is all!" Hmm, I think you will find that is what I have been saying from day one, but you did not understand the limitations of the system you are using.
GNSS is a non-precision 3-D landing system.
GNSS plus WAAS-LAAS is a precision 3-D landing system.
And GNSS plus a WAAS-LAAS is a GLS (err, usually). But the terminology is very imprecise here. Since the WAAS and the LAAS have different receivers, they should clearly notate the different approaches to reflect this - something like GLS-W and GLS-L. Or even better, just have GNSS, GNSS-W and GNSS-L.
I hope that is clear - sort of.