Why have ILS X / ILS Y / ILS Z ? (and which IAP types are missing in GPSs)

Timothy wrote:

No-one has ever flown the procedural approaches to London City

I have. All of them :)

…and did you notice they were upside down?

Timothy wrote:

Does that mean that the RNAV specification is not technology independent? Presumably an RNAV (GPS) approach cannot be flown using GLONASS, Galileo, DME/DME/DME, DME/DME/INS, or any future technology such as eLoran, because it has GPS in the chart title?

Timothy,

The chart name is RNAV (GPS) if GPS is required. Other GNSS systems are not mentioned. Most RNAV (GPS) charts also have a note DME/DME RNP-0.3 NA which means not authorized. AC 90-105A lists approved RNAV systems that are authorized to fly these RNP Apch procedures and only GPS systems are mentioned TSO C129a, C145/146, etc. The documentation is sloppy with its usage of GPS and GNSS, using the terms almost as synonyms, even though the latter is more general.

Timothy wrote:

…and did you notice they were upside down?

Nope. Who says they are?

ICAO DOC 8168 gives the XYZ answer.

8.5.1.3 Duplicate procedure identification

8.5.1.3.1 A single letter suffix, starting with the letter Z, following the radio navigation aid type shall be used if two or more procedures to the same runway cannot be distinguished by the radio navigation aid type only. For example:

VOR Z Rwy 20
VOR Y Rwy 20

8.5.1.3.2 The single letter suffix shall be used as follows:

a) when two or more navigation aids of the same type are used to support different approaches to the same runway;

b) when two or more missed approaches are associated with a common approach, each approach shall be identified by a single letter suffix;

c) if different approach procedures using the same radio navigation type are provided for different aircraft categories; and

d) if two or more arrivals are used to a common approach and are published on different charts, each approach shall be identified by a single letter suffix. If additional radio navigation aids are required for the arrival, they shall be specified on the chart’s plan view.

Peter wrote:

I could not see others; I don’t think it scrolled down… I hope I am not being thick!

The RNAV (RNP) Z RWY 8 and 26 procedures are authorization required and don’t show in the KLN94 or Garmin GNS/GTN systems.
The RNAV (GNSS) E is an SBAS procedure that only has LPV minimums. If it had LNAV minimums, it would have shown up.
The RNAV (GNSS) Y RWY 8 has LNAV minimums and shows up in your KLN94.

Timothy wrote:

Does that mean that the RNAV specification is not technology independent? Presumably an RNAV (GPS) approach cannot be flown using GLONASS, Galileo, DME/DME/DME, DME/DME/INS, or any future technology such as eLoran, because it has GPS in the chart title?

In the previous edition of PANS-OPS, RNAV specs were not technology independent — i.e. they were not “PBN”. So you’re right that you shouldn’t fly a RNAV (GPS) approach using any other navigation source except GPS. I don’t have access to the most recent edition (if anyone has an electronic version and is willing to share, I’d be most grateful) but my understanding is that it now includes PBN.

Nope. Who says they are?

I do.

Look at the Jepp ILS 09 approach plates. Cat C is 305° outbound and CAT A & B are 288° outbound.

If you go into the GTN, for example, and select the procedure, the upper LCY in the list gives 289°, the lower 306°.

You could have checked this for yourself before challenging.

It would be interesting to know if anyone else has found any other examples….

Peter wrote:

My original Q (today) was triggered by reading a supposedly definitive document on this stuff which states

Only the ‘Z’ variant is coded in the GNSS database, and the procedure identifier does not include the ‘Z’ character

So it looks like there has been a change within the last few years at most.

We have now come to review this page. In context it is clear that the reference was to this particular approach example, not a general statement across all approaches.

But anyway, that page has gone in its entirety and is replaced by a more generalised explanation and example, so it should be clear in Edition 3.0.

A complete root and branch revision of a 200 page book is hard work. Bear with us. We are very close to sending it out for peer review, so you should expect to see it on the PPL/IR website fairly soon and in shops thereafter.