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What is a RNP AR approach?

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  • What is a RNP AR approach?

    Malaysia Airlines (MAS) is the first airline to introduce Required Navigation Performance (RNP AR) approaches on Boeing 737-800 aircraft in South-East Asia, said its director of operations, Captain Izham Ismail.

    "At remote airports, RNP AR approach can provide a precise approach capability without the need for ground infrastructure, and in nearly all cases, RNP AR approach reduces the miles flown which in turn lowers fuel consumption, emissions, noise, and costs," he said.
    Well, some good news from MAS is great. The article does a horrible job of explaining, though, what a "RNP AP" approach is - and how it differs/improves from current procedures, and so - what better a place to ask...
    Whatever is necessary, is never unwise.

  • #2
    Originally posted by AA 1818 View Post
    what better a place to ask...

    Basically, an NRP is an approach where the airplane is able to follow one specific curved 3D path between waypoints or fixes with a required precision, and that has a performance monitoring and alerting so the pilots become aware if the required precision is not met.

    The AR suffix means "authorization required". It has lower terrain/obstacle clearance minimums but the airport, the plane and the crew must be "rated", like what happens with the CAT II and III ILS approach.

    More details (not good for the laymen, including me) in the wiki-article, more precisely here:

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---


    • #3
      Originally posted by Gabriel View Post
      The AR suffix means "authorization required". It has lower terrain/obstacle clearance minimums but the airport, the plane and the crew must be "rated", like what happens with the CAT II and III ILS approach.
      That's right, also the Airline/operator must be qualified.

      A good way to remember it is the 4 "A" form.

      Juan Felipe Arango Pérez
      FAA Commercial Multi-Engine Pilot
      C172 PA44 JS32 B767F A332F


      • #4
        We've been doing RNP-AR for many years now.

        Its basically the new generation GPS-based approach that is NOT augmented.

        As Gabriel points out, they can be curved, but they're not always. Many are straight in from 10nm.

        Again as Gabriel points out, the key is that they are whats called 'Performance Based Navigation' approaches (PBN). The GPS systems are clever enough to work out their own accuracy, and give a value of 'Actual Navigation Performance'. The approaches are then created giving terrain separation based on a figure of Required Navigation Performance (RNP). If your actual GPS navigation performance is better than what the approach requires, then you can do the approach. There are also tolerances (similar to an ILS) of how close to the computed path you must be. This technique allows significantly smaller areas for which terrain has to be assessed, and so you can get closer to the hills, and therefore lower minima. This comes into play particularly at terrain-rich environments. Queenstown in New Zealand is a famous case where it has basically opened up the airport to a significantly increased number of flights, reducing the minima by a LOT. Its a hell of an approach, including a 360 degree orbit AROUND a hill. But it has made the airport a lot safer.

        The advantage of them really is that they can produce lower landing minima than traditional approaches, will end up with you being aligned with the landing runway (when VOR/NDB approaches may not), and do not require a ground based aid (so can be quickly established at locations that do not have ground based aids). This reduces the cost significantly.

        The concept of them being shorter, and saving fuel, is very much situation dependant and can be a furphy and will remain that way until everyone is using them. But thats where its heading.

        They're good approaches that are another weapon in the arsenal. They are far more stable and controlled than the VOR/NDB approaches they replace.