This popped up today. Avinor will start implementing RNP AR on their airports. This year 3 airports including ENGM will participate in a trial, then if successful (which it of course will be), it will be implemented on most airports within 2020. There are many reason for this, shorter flight by 5-10 min, less fuel, safer, more resistant to weather, the environment etc. The video showing an example of RNP AR is from New Zealand, and is rather cool all by itself.
I have never heard of this stuff before, but from Wikipedia:
When conducting an RNP AR approach using a line of minima less than RNP 0.3, no single-point-of-failure can cause the loss of guidance compliant with the RNP value associated with the approach. Typically, the aircraft must have at least dual GNSS sensors. dual flight management systems, dual air data systems, dual autopilots, and a single inertial reference unit.
Does even a dual autopilot system exist for a light GA aircraft? Most Avinor airports also have either GLS and GNSS or ILS and GNSS, but surely this RNP AR will eventually make ILS obsolete ? Probably also GLS and GNSS ? Seems to me this is a thing that is good for airliners, but how much will this RNP AR equipment cost?
LeSving wrote:
Most Avinor airports also have either GLS and GNSS or ILS and GNSS, but surely this RNP AR will eventually make ILS obsolete ? Probably also GLS and GNSS ?
That’s not the intent. RNP AR are more flexible, you can design an approach which is more demanding, extreme (e.g. terrain can be closer AFAIK), but which requires special training and equipment. E.g. an approach with an RF FAS (radius to fix final approach segment) would be AR (authorization required). AFAIK it doesn’t have to require all that much equipment, it depends on the approach and what they did. Aside from terrain challenged airports, it can be used to create a more efficient approach (less time and fuel consumed), improve noise abatement, etc.
RNP AR and GBAS are solving different problems.
The demand on GLS (based on GBAS) is integrity. It needs to put you within a very narrow vertical window on the glideslope at 100 ft, 50 ft or lower, and tell you if it can’t achieve that level of precision. That’s why LPV 200 (based on SBAS) is hard — the vertical protection level required is very demanding, as it has to have a very high probability of warning you if you if it can’t guarantee that you’re within 100 ft of where it thinks you are. Only GBAS can achieve the integrity required for Cat II and below.
The demand on RNP AR is continuity. It’s all very well for the “navigation integrity warning” to light up, but if you’re flying down a winding canyon in IMC at the time, that’s somewhat unfortunate. Hence all the requirements for duplication and redundancy.
The operational and crew training aspects of RNP AR are now in the AMC to Part-SPA. The airworthiness aspects are still in AMC 20-26.
The challenge for GA is to make sure that RNP AR APCH is not used, e.g. for noise abatement, where RNP APCH would suffice — otherwise we get shut out.
Ok, does this mean RNP is no substitute for other approaches, but only an addition ?
LeSving wrote:
Ok, does this mean RNP is no substitute for other approaches, but only an addition ?
RNP is not the same thing as RNP AR!
An “RNP” approach is basically an RNAV approach — be it based on GPS or some other system. The terminology has shifted over the years, but all new approaches of this kind should be called “RNP” approaches. The “RNP” — “Required Navigational Performance” — approaches are called that because they are independent of the particular navigation system used as long as that navigation system has the necessary performance.
An “RNP AR” approach is not a separate kind of approach, but an RNP approach that requires special authorisation. In principle, there’s nothing new with that. There are ILS approaches that require special authorisation because they are particularly challenging in some way.
(Yes, I know that RNP and RNAV are not the same thing and that both are part of PBN — but I don’t want to go into details as LeSving is unfamiliar with the concepts.)
(PS. Sorry for all the edits, my writing is sloppy tonight.)
As far as RNP AR is concerned, yes.
RNP AR is a special case (Authorisation Required) of RNP. RNP and GNSS approaches are generally the same. For example, some authorities are renaming GNSS approaches to RNP approaches without changing anything else. RNP AR is another kettle of fish. Using the latter requires not only the approved equipment but also operator approval. Use of RNP approaches (without AR) just needs approved equipment and I believe most IFR WAAS GPS’s have this approval. This approval should be listed in the corresponding AFM.
As reference, there are 2 good FAA docs that cover this (granted it is a USA-slant, but the info is still correct). AC 90-105A covers RNP and AC 90-101 covers RNP AR. You can find these docs here:
bq. http://www.faa.gov/regulations_policies/advisory_circulars/
Sorry Airborne_Again, we were both replying at the same time. Fortunately, we agree!
chflyer wrote:
For example, some authorities are renaming GNSS approaches to RNP approaches without changing anything else.
IIRC ICAO just changed the terminology. That is RNAV(GNSS) are becoming RNP APCH and eventually RNAV(GNSS) should disappear. RNP APCH is a broader term.
Martin wrote:
IIRC ICAO just changed the terminology. That is RNAV(GNSS) are becoming RNP APCH and eventually RNAV(GNSS) should disappear. RNP APCH is a broader term.
Correct, there is a presentation from ICAO (http://www.icao.int/MID/Documents/2016/PBN%20SG2/2.PBN%20Charting%20-%20ICAO.pdf) that shows this transition and the intentions behind.
Martin wrote:
IIRC ICAO just changed the terminology. That is RNAV(GNSS) are becoming RNP APCH and eventually RNAV(GNSS) should disappear. RNP APCH is a broader term.
Fortunately, the US will not comply with the annual ICAO renaming of approach procedures, it will remain as RNAV (GPS).
