Why are there no RNAV (ILS) approaches? While studying the PBN (FAA Order 8260.58A) and TERPS (FAA order 8260.3D) documents, I still have some trouble figuring part of the logic behind the naming and definitions of the published IAP Charts. Specifically, I still have not figured out which Lateral Navigation System is combined with which Landing System (if this is how it's done in practice). Take the following examples:


Technically, ILS is a landing system, to the best of my understanding, at least. I expect that it can be combined with any Lateral Navigation System used in-flight, as long as the necessary equipment is available. Therefore, I would expect to find charts using RNAV with ILS. This would mean, to me, that, "RNAV-equipped" flights can still use an ILS Landing System. Is this combination possible?
According to Chapter 3 of the PBN manual, the RNAV(GPS) procedures can also be combined with a GLS Landing System. However, I have not found any published IAP chart mentioning the GLS minima. To my understanding the RNAV(GPS) procedures with GLS Landing System are published separately under the name "GLS". Is this correct?


My confusion can be described, in short, as follows: because I have seen RNAV (GPS) procedures being combined with LPV or LNAV/VNAV, which are Landing Systems, and ILS is also a landing system, I thought that the general idea is that Lateral Navigation Systems are combined with Landing Systems when designing IAP procedures. Is this correct? If yes, where can I find the possible combinations. If no, then what is the logic behind this, what am I missing?
You are confusing some terminology.
RNAV (GPS) approaches can have several different sets of minima.

See the example RNAV (GPS) Y 28L at O'Hare:

It has:
LPV
LNAV/VNAV
LNAV
sets of minima.



LPV is an instrument approach procedure (IAP) with localizer-type precision and with vertical guidance, (hence the name LPV), provides a pilot with a "ILS-style" approach complete with a decision altitude (DA) but using GNSS equipment instead of VHF equipment like that used for an ILS.  Usually the lowest weather minimum of the 3.

LNAV/VNAV is another line of minima with baro-aided (altimeter-based) vertical guidance including a DA but the weather minimum is usually a bit higher than LPV.

LNAV-only is the least precise of the 3 and is a non-precision approach, no vertical guidance, includes a minimum descent altitude (MDA) instead of a DA.  This is a "dive &amp; drive" approach similar to Localizer or VOR approaches.  Normally has the highest weather minimum due to the nature of non-precision approaches.

There are RNAV (GPS) approaches and there are ILS approaches, but there are no RNAV ILS approaches.

Note: There might be a rare exception to this as described in appendix C of FAA Order 8260.58A CHG 2: If the aircraft/aircrew/airline are performance-based-nav (PBN) capable &amp; authorized there could be an IAP constructed with a radius-to-fix intermediate segment leading to an ILS final segment, whereby, the crew would navigate with GNSS equipment on the RF segment and then transition to ILS equipment for the final segment.  I would say in my experience this type of approach construction from the US TERPS is very rare.

I will add that WAAS is to LPV as GBAS is to GLS.  GLS is only available at 2 airports in the US, while RNAV approaches with LPV minimums are available at a great many US airports, adding a "ILS-like" utility to those airports without incurring the infrastructure cost of adding the ground equipment necessary for ILS approaches.

WAAS capable GPS receivers are prevalent; while very few aircraft (the Airbus A350 is one example) have GBAS capable GPS equipment.