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Type rated on A330, B747-400, B747, B757, B767, B737, B727. International Airline Pilot / Author / Speaker. Dedicated to giving the gift of wings to anyone following their dreams. Supporting Aviation Safety through training, writing, and inspiration.

Thursday, February 24, 2011

RNP Verses RNAV


My plane is not certified for RNP—yet. But when it is, I’ll be ready to go.

RNP (Required Navigation Performance) utilizes GPS (Global Positioning System), the aircraft FMS (Flight management system), and procedures that enable pilots to fly to lower minimums in areas of critical terrain or obstacles.

How can RNP do this? RNP, unlike RNAV (Area Navigation/Radar Navigation) takes into consideration “containment” where the airplane proves it can fly tighter tolerances utilizing GPS, FMS and trained pilots, enabling us to use lower landing minimums.

RNP in a quantitative value is .3 NM or less, and defines the accuracy limit of the approach. Containment is the protection limit, and is two times the RNP value. For example, with a .3 RNP value there can be no obstacles within .6NM of the course. Observing Actual Navigation Performance, ANP, is accomplished on the MCDU PROG page where we will monitor the aircraft's accuracy.
A key term in the RNP world is the RF (Radius to Fix) leg. The significance of the RF leg mandates a prescribed ground track to be flown, where wind, true airspeed…etc., have no impact.


RNP Reminders:
  • "Special Aircraft and Aircrew Authorization Required."
    • The aircraft must be certified.
    • Pilots must be trained.
  • High/low temperature restrictions are to be adhered to and found on the Jeppesen briefing strip.
    • See the above information: NA below 6 degrees C and above 59 degrees C.
  • Autopilot use is mandatory from the initial approach fix (RF leg) until visual reference with the landing runway. In the example above the RF leg begins at GLRIA.
  • A maximum of 165 knots is required on the RF leg.
    • Remember the A330 has groundspeed mini and could increase speeds above 165 knots, vigilance is necessary.
  • Do not proceed direct to a fix that begins the RF leg. Excessive approach angles may take the aircraft beyond the containment airspace.
Now the mystery--- I'm told there is not a Maltese cross on the RNP chart, and the FAF (Final Approach Fix) is identified by “GP Intcpt” on the profile view. However, I'm finding just the opposite information. In the example above, there is no Maltese cross but there is also not a "GP Intcpt" note. In the example below, I clearly see the cross over WIDGA. What gives? Does anyone have the answer?


If you're certified for an RNP or have been trained to fly this type of approach, I would love to know the tricks. Or my friends in the tower--- do you have anything you could add to increase our knowledge of this type of approach? Thank you all.

Enjoy the Journey!

~ Karlene

    12 comments:

    1. Good post... We've been RNAV RNP certified on the A330/340/380 for about 24months. Works very well.

      Our A330/340's have 0.3 certification. The aircraft is capable for 0.1 but extra paperwork is needed and extremely expensive.

      The FCOM 3 supp proc NAV explains how the approach is flown. The appproach is largely flown like a normal RNAV, exept that it is flown with the FD's versus the bird for RNAV. Airbus has a great doc called a getting to grips with RNAV RNP
      approaches.

      Some of the RNAV RNP approaches have lower minimas than ILS approaches for the same runway. E.g. seychelles runway 31

      Not sure what your problem/question is with Maltese cross... Haven't used jepessen in years. We use Lido (Lufthansa).

      Bjorn
      CAPT/Examiner A330-A340
      Www.bjornmoerman.com

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    2. The chart question might be a Jepp vs. FAA Aero Nav (formerly NACO) thing. If you look at the FAA chart for the KJAC RNAV/RNP Y RWY 1 it doesn't have the cross on the profile view, but does indicate (FAF) over WIDGA in the plan view. It also does have the ziggy arrow (GS Intercept) in profile.
      http://flightaware.com/resources/airport/JAC/IAP/RNAV+(RNP)+Y+RWY+01/pdf

      For some reason, my Jepp charts don't include the RNP Y 12 at MIA, so I can't compare those.

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    3. Great blog and Bjorn provides good info. The only real impact from an ATC perspective is that we wouldn't apply real tight spacing ( 3 nm or 2.5nm) between arrivals because ATC has less control over the path and speeds of the aircraft. Other than that no ATC impact

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    4. My company has been doing the RNP approaches and departures for over five years now (I've only been around for one). I flew five legs today, did four RNP approaches and one RNP departure. In Canada, as we're the only ones doing Performance Based Navigation, we've designed all our RNP approaches specifically for our only type, the 737NG. Generally, if we able to conduct our entire descent uninterrupted by ATC, we're back at idle at TOD, in a constant descent all the way to the runway, and remaining at idle until the gear is down just short of the FAF. Even in visual conditions we're encouraged to fly the RNP because it's more efficient then pilots flying their own visual approach.

      Not much in the way of tricks to fly them. In fact, after a year of flying them I find RNP the easiest of all approach procedures. You're just watching the plane do it's magic and dropping drag as required. If you can think of any specific questions you think I can answer feel free to fire me a message.

      Cheers
      Shawn

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    5. Bjorn, Thank you so much for the great comment. I would love to get a copy of that airbus document. It truly is amazing how far our technology has come. I'll be trained next week. About the Maltese cross... I'm thinking that this, and or the Intcpt could be company specific.

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    6. Thanks for the extra info Steve. I actually have a couple company training examples that has the Intcpt on the final approach fix. Very good point about being Jepp vs. FAA. Thanks for the link.

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    7. Thanks Munawar, That is interesting about the spacing. Makes sense. So... what exactly is tight spacing and what is normal spacing? Does the spacing impact the arrival?

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    8. Hi Shawn, Thank you so much for the info. Glad to hear. So the RNP is actually designed to make a managed NAV approach to landing? This would be easier. I'm sure I'll have questions after the training. I also wonder why it's taking longer to get the A330 certified at my company than the Boeing. Could it be the speed issue and GS mini? I wonder. Maybe I'll have more answers after training too. Thanks for your comment.

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    9. Yep, we can follow the RNP path right to the runway. It will even protect us below the DH/MDA out to missed approach, and degraded performance (engine out) missed approaches. Also, on RNP departures we have an all engine procedure as well as a degraded performance procedure. We verify the waypoints on both proccedures before departing and if we end up loosing performance on one of the engines, the FMC is programmed to notice it and automatically bring up the degraded performance procedure. All we're required to do is "Confirm engine out?" "Execute", stay in LNAV, and the plane will laterally keep on the path, keeping us clear of terrain.


      I think Alaska Airlines is reason the 737NG was first out of the gate with this RNP stuff. They needed a way to improve reliability to airports in Alaska where available approach procedures weren't cutting it. So they made the big push for RNP approaches and with that they probably paved (and paid) the way for the 737 to become certified. For our airline in Canada, we originally pushed RNP for improved reliability in terrain challenging airports (see Kelowna, BC, CYLW) and for a safer, more reliable substitute for the large number of drive and dive, non-precision approaches and circling approaches we were shooting at the airports we served.

      For the A330, I'm just guessing, but I imagine the original benefits of RNP wouldn't have been seen by the big Airbus given the availability of precision ILS approaches at most of the destinations it served.

      After the implementation of RNP in a few airports in our network, we started to realize the fuel savings these approaches were giving us. So we quickly expanded our RNP approach library to include a number of runways already served by ILS. I think it's this fuel saving benefit that is the number one reason behind other operators and types getting on board with RNP.

      A good article here

      http://www.navcanada.ca/ContentDefinitionFiles/Newsroom/InTheNews/2010/itn0827_en.pdf

      and WestJet has a video here

      http://video.google.com/videoplay?docid=-5284773282371819535#

       

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    10. Hi, "Normal" spacing is 3NM (without vortex requirement) and we cut down to 2.5NM in certain wx conditions. This is applied to 4NM from touchdown, after which it is accepting that as the first a/c reduces speed the 2nd one will catch up and there will be a reduction in spacing. Accurate spacing is vital to keep capacity to maximum. All pretty interesting during some wx conditions...

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    11. Thanks Munawar! I know it's a challenge to space correctly. I'll have to tell you about the time I went around in the 744. They weren't spacing very well. But we had some pretty strong tailwinds on final.

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    12. Hi Shawn, thank you for the great information. That makes sense with the 737NG and Alaska. A necessity. I have yet to fly anywhere that I think it will help on the A330... but then I haven't been on the plane that long. I'm sure there is somewhere that we'll need these lower minimums.
      Thanks so much for the great links.

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