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Old 5th Feb 2013, 05:26
  #114 (permalink)  
Join Date: Nov 2011
Location: Inside their OODA loop
Posts: 243
maggot, the question is how many of these carriers do RNP-AR. It doesn't appear to be a "standard equipment" as is the ILS for all operators.

There are also some subtleties with the RNP-AR. The minima's are quite different with the terrain.
RNP 0.10 285' (264) / 1400m
RNP 0.15 429' (408) / 2200m
RNP 0.30 434' (413) / 2300m

RWY 32
RNP 0.10 263' (250) / 1300m
RNP 0.20 287' (274) / 1400m
RNP 0.30 320' (307) / 1600m

My understanding (open to correction) is that the A320 is only capable of RNP 0.20, however has approval to operate to RNP 0.15 & that current Airbus models won't be able to ever get RNP 0.10.

Recently, the wet xwind was one factor, however the cloud base was 300' and the vis hovering around ~2000m. Two A320's ahead of us missed out for RWY14 (assumed using the RNP 0.15 minima) and we got in visual at the 0.10 minima with the required vis in moderate rain, TWR reported crosswind at 25kts and FMC 23Kts at touchdown.

I might add that both the TAF and TTF indicated conditions above the alternate criteria, forcing diversions for another 4 or 5 aircraft arriving at the same time without ever becoming visual, so the xwind was a moot point.

RNP-AR is better than the a non-precision approach, but not to the same standard as an ILS. It very much depends upon the RNP that you can actually use. Without much terrain around, there isn't much in it. As soon as you get terrain close to the field, the approach minima becomes very sensitive to what your aircraft is capable of, and what you actually have for the ANP (mostly 0.02, but up to 0.08). Cairns RWY 33 is a classic, with a RNP of 0.10 of 333', RNP 0.20 of 494' and RNP 0.30 of 789'. With an ANP of 0.08, I wouldn't start a RNP 0.10 approach.

GLS, now that is a different story...
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