Why "RNP APCH." listed in required equipment for RNAV (GPS)-A at KDUH.

[Chicago Bearhawk]

I can't understand why the required equipment line has "RNP APCH." listed for the following approach:

https://aeronav.faa.gov/d-tpp/2108/05811RA.PDF

Very specifically, I read:
https://www.faa.gov/about/office_or...nss/library/factsheets/media/RNAV_QFSheet.pdf
Several times and assume that LP or LNAV lines must exist to have the RNP APCH.

This is a similar question to some other questions however, here is the significant difference from other links on POA, in this case there is only 1 line and it is for "Circling".

 

[Matthew Johnson]

Because you want to make sure that you hit the TAINT (FAF)?!?!?

Actually just replying to follow the thread since it makes no sense to me either and is my home field.

 

[MauleSkinner]

What are you thinking RNP APCH means in terms of your ability to fly the approach and/or what equipment is required?

 

[Chicago Bearhawk]

What are you thinking RNP APCH means in terms of your ability to fly the approach and/or what equipment is required?

So that is the first confusing question: and I think the answer is that there is a significant difference between "RNP AR APCH" and "RNP APCH" where the former requires special crew training.

However,
Based on this statement from the FAA factsheets pdf above:

The expansion of Global Positioning System (GPS)-based instrument approach procedures (IAP), a key element of NextGen’s Performance Based Navigation (PBN) initiative, provides benefits for pilots and stakeholders. This fact sheet will focus on the most common navigation specification called “RNP Approach (RNP APCH)” and titled Area Navigation (RNAV), “RNAV (GPS) Rwy XX”. These procedures offer several lines of minima to accommodate varying levels of aircraft equipage and airport environments without requiring additional navigation equipment at the airport. This promotes airport efficiency and access, pilot flexibility and operational safety.
​

I can't understand why the approach above has RNP APCH listed as required equipment when there is no reference to an MDA. There is no LP, or LNAV.
In thinking about it you are only circling, so you only need to stay within 1.3 miles of the runway, not .3 miles of the MAKAF (MAP) as RNP would indicate.
and you will drop to circling mins 2-3 miles before the MAP. (or atleast that is what I would try....) That only requires an IFR certified Altimeter.

 

[RussR]

I can't understand why the approach above has RNP APCH listed as required equipment when there is no reference to an MDA. There is no LP, or LNAV.
In thinking about it you are only circling, so you only need to stay within 1.3 miles of the runway, not .3 miles of the MAKAF (MAP) as RNP would indicate.
and you will drop to circling mins 2-3 miles before the MAP. (or atleast that is what I would try....) That only requires an IFR certified Altimeter.

There most certainly is an MDA, all Circling minimums are MDAs. But that has nothing to do with it being RNP APCH.

Circling or not, you are still using lateral guidance to navigate from WTRVL to TAINT to MAKAF, right? And then conduct the missed approach if necessary. The level of lateral navigation precision required is included in the RNP APCH navigation specification. That's all it means. You must have an IFR GPS capable of flying to the RNP APCH precision (and alerting) requirements, which all modern IFR GPS units (and many obsolete units) can do. There is no issue here. If you're flying IFR using an approved GPS, chances are nearly 100% you can fly this procedure.

 

[midlifeflyer]

So that is the first confusing question: and I think the answer is that there is a significant difference between "RNP AR APCH" and "RNP APCH" where the former requires special crew training.

It's an unfortunate bit of temporary confusion introduced by new language. All "RNP APCH" in the requirements box means is, you must have a nav box with the "Required Navigation Performance" to perform "AProaCHes." IOW, GPS with approach capability.

No need to make it more complicated than that.

 

[RussR]

It's an unfortunate bit of temporary confusion introduced by new language. All "RNP APCH" in the requirements box means is, you must have a nav box with the "Required Navigation Performance" to perform "AProaCHes." IOW, GPS with approach capability.

And RNP APCH is itself just a short-lived term. The most current charts will read "RNP APCH - GPS", to signify that the RNP APCH requirements must be met using GPS and not some other RNAV method. Pretty much a distinction without a difference for most IFR GPS operations, but there you go.

 

[midlifeflyer]

And RNP APCH is itself just a short-lived term. The most current charts will read "RNP APCH - GPS", to signify that the RNP APCH requirements must be met using GPS and not some other RNAV method. Pretty much a distinction without a difference for most IFR GPS operations, but there you go.

No real difference but adding "- GPS" just might help with the confusion.

 

[WDD]

Yes, I seem to remember something where they are in transition with the nomenclature.

The first approaches using RNAV equipment have been developed before the definition of RNP. For this historical reason RNP approaches are commonly charted as RNAV (GPS).​

I think RNP requires that the equipment be self diagnosing, crew alerting, and accurate 95%. Maybe a hold over from pre WASS GPS, where RAIM GPS was used? I think any modern WASS navigation system (like a GTN 650) meets RNP.

We also have this:

Compared to RNP approaches, where the segment between the FAF and the runway is straight, RNP with Authorization Required approaches might have “curved” final segments. These approaches are therefore colloquially called “curved approaches”. Furthermore, RNP AR approaches allow reduced obstacle clearance compared to RNP approaches (fig. 4) RNP AR* approaches are charted as RNAV (RNP).​

So, RNAV GPS with RNP APCH is OK to be done with a modern GPS, but RNAV (RNP) isn't because it also means Authorization Required.

 

[Larry in TN]

to signify that the RNP APCH requirements must be met using GPS and not some other RNAV method. Pretty much a distinction without a difference for most IFR GPS operations, but there you go.

True for GA airplanes but DME/DME/IRU RNAV systems were the standard for bigger airplanes for many years. There are still a lot of large airplanes flying around with it.

DME/DME/IRU was the basis of the position updating for the FMS for aircraft as recent as the B757/767 when they were new and many of them are still flying around un-upgraded. Even today, if the GPS updating for the FMS fails, or is deferred, DME/DME/IRU becomes the most accurate position updating source for the FMS and can be used for enroute and terminal RNAV though you can't do RNAV procedures.

 

[RussR]

True for GA airplanes but DME/DME/IRU RNAV systems were the standard for bigger airplanes for many years. There are still a lot of large airplanes flying around with it.

DME/DME/IRU was the basis of the position updating for the FMS for aircraft as recent as the B757/767 when they were new and many of them are still flying around un-upgraded. Even today, if the GPS updating for the IRS fails, or is deferred, DME/DME/IRU becomes the most accurate position updating source for the FMS and can be used for enroute and terminal RNAV though you can't do RNAV procedures.

You are correct. I should have said "Pretty much a distinction without a difference for most light GA IFR GPS operations."

 

[aterpster]

True for GA airplanes but DME/DME/IRU RNAV systems were the standard for bigger airplanes for many years. There are still a lot of large airplanes flying around with it.

DME/DME/IRU was the basis of the position updating for the FMS for aircraft as recent as the B757/767 when they were new and many of them are still flying around un-upgraded. Even today, if the GPS updating for the FMS fails, or is deferred, DME/DME/IRU becomes the most accurate position updating source for the FMS and can be used for enroute and terminal RNAV though you can't do RNAV procedures.

I flew the pre-GPS 767 (1984-86) with the "brain dead" FMS, and inflexible IRUs. The database memory was only 500 kb. Once GPS took hold, Boeing changed to the Pegasus FMS. No retrofits, though, except for $1mil in 1995 dollars.

 

[Larry in TN]

I flew the pre-GPS 767 (1984-86) with the "brain dead" FMS, and inflexible IRUs. The database memory was only 500 kb. Once GPS took hold, Boeing changed to the Pegasus FMS. No retrofits, though, except for $1mil in 1995 dollars.

The 767s I flew in 2012 and 2013 still had the non-GPS original FMS. i think a couple of them had the PIP, but still no GPS. Those airplanes are still flying today without GPS.

I ferried one of them from Miami to Bahrain with a stop in Dakar, Senegal. The tiny memory was loaded with the Central/South American database so we left the covered area by San Juan and used Lat/Long fixes for the crossing. When we hit the west coast of Africa, with no database coverage, the FMS couldn't get DME/DME updating as it didn't "know" any of the VORs or DMEs in range. The map-shift was maybe a mile, or two.

Two days later (had problems with the Senegal overflight permit--the next day was Friday) the mechanic had loaded the Middle-East database but we were a long way from there. As we entered the flight plan, we entered the Lat/Long for each fix from our release. The first fix that the database "knew" was over 9 hours into the flight! We did a quick align just before takeoff then had to monitor the raw data for 9 hours to ensure that the map shift wasn't significant.

That was fun.

 

[aterpster]

That was fun.

Sounds awful.

 

[John Collins]

I can't understand why the required equipment line has "RNP APCH." listed for the following approach:

https://aeronav.faa.gov/d-tpp/2108/05811RA.PDF

Very specifically, I read:
https://www.faa.gov/about/office_or...nss/library/factsheets/media/RNAV_QFSheet.pdf
Several times and assume that LP or LNAV lines must exist to have the RNP APCH.

This is a similar question to some other questions however, here is the significant difference from other links on POA, in this case there is only 1 line and it is for "Circling".

With ICAO PBN (Performance Based Navigation), navigation specifications are used to define the criteria for the PBN operation. So there is a PBN specification for RNAV 2, RNAV 1 and so on. One of the specifications defines approaches for what is called GPS or RNAV approaches and its name is RNP APCH. In the rest of the world, what we call RNAV (GPS) approach is being retitled as RNP. The FAA declined to rename all of its RNAV approach procedures but did agree to add a PBN equipment box and include the name of the specification "RNP APCH". Other items that can go in the PBN equipment Box would be requirements such as RF Leg by adding RNP APCH, RF. So all the RNP APCH means in the PBN equipment means is the name of the PBN specification that applies to the procedure. That's all, nothing more.