What RNP level is required for an RNP approach if the chart does not specify a value?

Question

RNP (Required Navigational Performance) approaches require the aircraft to monitor the navigation accuracy within a specified limit, called RNP level:

There are several different levels of RNP. Examples of RNP levels used for approach include RNP 0.1, RNP 0.3, and RNP 1.0 (There are also RNP 4.0 and RNP 10.0 levels that apply in the en route environment). "A performance value of RNP 0.3, for example, assures that the aircraft has the capability of remaining within 0.3 of a nautical mile to the right or left side of the centerline 95 percent of the time."

[...]

The minima line will include a performance value, RNP 0.30 for example. GPS with WAAS can support RNP 0.3 and above.

^{(faa.gov on Satellite Navigation)}

Usually the RNP level is given in the minima section of the approach chart (and according to the above FAA quote, this is always the case in the US). There are however approach charts that do not include this. Consider for example the following 3 approaches into Innsbruck (LOWI), Austria. While the first example lists the RNP levels, the other two do not:

• RNP Z RWY 26 (AR)

  

  There are two different minima for the different specified RNP levels.

• RNP E RWY 26 (LPV ONLY)

  

  There is no RNP level specified, also not anywhere else on the chart (as far as I could find). Maybe this is because this approach is LPV only (requires EGNOS¹)?

• RNP Y RWY 08

  

  Again, there is no RNP level specified and this time there are only LNAV minima. So which RNP level would apply here?

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¹ EGNOS is the European SBAS (Satellite Based Augmentation System), equivalent to the North American WAAS.

Answer 1

RNP approaches require a minimum value of 0.30, be it LNAV only, LNAV/ VNAV or RNP AR. Most of the approaches around the globe are RNP approaches. So, they do not put in the value because it remains the same at 0.30.

In RNP AR approaches they put in the value because these are approaches that require specially trained pilots and specially equipped aircraft. That is where the AR comes from. It stands for Authorization required. The RNP AR approaches have RNP values starting from 0.30 down to 0.10. The biggest difference between a typical RNP approach and an RNP AR approach is the lateral obstacle clearance. In an RNP approach, you have a clearance of two times the RNP value (0.30 x 2 = 0.6 miles) and also a buffer of 0.2 miles either side. In an RNP AR approach, the buffer is taken out of the picture and it only offers two times the RNP number left or right. If the RNP value is 0.10, then the lateral obstacle clearance will be 0.20 miles either side. This allows tighter approaches in areas with high obstacles such as mountains (such as Innsbruck). But because such approaches are a bit demanding you need better equipment. So, airplanes that are not designed for it need extra modifications. These modifications will depend on the manufacturer and it will also depend on the actual procedure. The pilots who fly these approaches need extra training as well, so that they are more accustomed to flying it and to teach them the required contingency procedures. Depending on the operator and the aircraft configuration, an RNP AR approach maybe approved with an RNP value between 0.30 and down to 0.10. For example, Airbus offers A320 and A330 with modifications and approvals for either RNP AR approaches with 0.30 or 0.10. In case of the A350, the aircraft comes with RNP AR 0.10 approval as a basic setting.

For LPV approaches, there is not an RNP value as it is basically an ILS type approach flown to category I minima using the GPS and a ground based GPS signal augmentation system such as WAAS (Wide area augmentation system).

Answer 2

All those approaches require RNP APCH capability, i.e. a precision of 0.3 on the final segment (see table 1 under GM1 SPA.PBN.100 of Annex V Specific approvals via easa.europa.eu):

They also have a RNP AR APCH option (which requires additional equipment and a specific authorisation), with a 0.15 precision requirement. I suspect that indicating 0.30 on the "standard" Z approach is to avoid any confusion and clarify that usual RNP APCH equipment is appropriate.