Why do some approaches say Rnp APCH and others do not?

[Mjg2011]

I have two rnav gps approach plates attached. I cannot figure out what would make one an rnp apch and one not? I really don’t fully understand what an rnp apch is. I tried reading through ac 90-105.

 

[dtuuri]

Allow me to try: Introduction to GPS (avclicks.com)

EDIT: I think you're referring to the Note Box. From the Chart User's Guide:

"For procedures with PBN elements, the PBN box will contain the procedure’s navigation specification(s); and, if required: specific sensors or infrastructure needed for the navigation solution; any additional or advanced functional requirements; the minimum Required Navigation Performance (RNP) value and any amplifying remarks. Items listed in this PBN box are REQUIRED. The separate Equipment Requirements Box will list ground-based equipment requirements."
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So, the RNP APCH note is the PBN "navigation specification". @RussR is in the business of charting these notes, maybe he can amplify for you?

 

[MauleSkinner]

Of course, just to confuse the issue, terminology is in the process of changing. At some time in the future, RNAV(GPS) in the title will be replaced by RNP, and the notes will address the equipment/pilot requirements.

 

[RussR]

Allow me to try: Introduction to GPS (avclicks.com)

EDIT: I think you're referring to the Note Box. From the Chart User's Guide:

"For procedures with PBN elements, the PBN box will contain the procedure’s navigation specification(s); and, if required: specific sensors or infrastructure needed for the navigation solution; any additional or advanced functional requirements; the minimum Required Navigation Performance (RNP) value and any amplifying remarks. Items listed in this PBN box are REQUIRED. The separate Equipment Requirements Box will list ground-based equipment requirements."
​

So, the RNP APCH note is the PBN "navigation specification". @RussR is in the business of charting these notes, maybe he can amplify for you?

Thanks @dturri.

This is something that is gradually being changed as procedures are amended to the new standard.

See my blog post for more detail, this topic starts about 2/3 of the way down.

http://cfiruss.blogspot.com/2018/05/goodbye-dme-hello-equipment.html

 

[NoHeat]

That blog post is very helpful. I learned a lot from it.

 

[Craigd31]

The nomenclature is changing, but here’s some more info
https://bruceair.wordpress.com/tag/rnp/

 

[AlphaPilotFlyer]

Simply put, RNP is required navigation performance. RNP is the required accuracy of your GPS equipment at time of approach and expresses as a decimal such as .3, or accuracy must me within .3 miles of actual position to commence approach. Picture your aircraft in a .3 mile wide circle.....you are somewhere in that circle, but not likely in the center of it.

RNAV approaches typically only require standard 1 mi accuracy, below that (such as airports with close high terrain or obstacles) is may be titled RNAV RNP, meaning that IAP requires higher accuracy to avoid hitting something. Also different approach categories may require lower RNP values because of their wider turn radius or shallower climb gradients.

from a practical stand point as a pilot, you will enter the RNP value, say .3, into your FMS or GPS in the RNP field, and you would get a warning/alarm if the actual navigation performance (ANP, the real time accuracy of your depicted position which is based on such things as number of satellites you are receiving and their signal quality) exceeds RNP, letting you know you are now below the .3m accuracy and thus can not continue approach because you may hit something.

lower RNP IAPs may also add “AR” to the requirements, meaning authorization required..... this refers to mostly airlines that have FAA or relative CAA authorization to use lower minimums due to their onboard equipment and crew training.

RNP is simply a way to be sure you remain in the required RNAV defined route where it’s safe. If your ANP increases in radius beyond the RNP you entered and alarm sounds, you would stop your approach and climb via missed approach procedure.

 

[John Collins]

RNP APCH is the name of the PBN navigation specification for approaches that are titled in the US as RNAV (GPS). With the latest chart standards, these approaches will include the name of the PBN specification that applies to the approach. In the rest of the world, they are changing their naming conventions to use RNP for what we call RNAV (GPS). US agreed to add the name of the PBN specification, but not to change the name of the procedure. It is all intended to confuse you.

 

[NoHeat]

It is all intended to confuse you.

That seems to happen a lot for instrument flying. Instead of IFR, maybe it should be called OFR, obfuscation flight rules.

 

[somorris]

Your blog post was very informative, Russ. Thank you for taking your time to do the writeup.