I seem to be too stupid to comprehend the term RNP. Though I've read several articles about it in the web, I'm still not able to tell how it is implemented in the MD-11 and how I can use it. So, I ask for "enlightenment", please.From what I understand, RNP is an "advanced" form of RNAV. RNP is "performance based navigation (PBN)" and bound to RNP numbers that define the required performance of the onboard equipment.So far, so good, but from where do the RNP values stem (navigation database?), do I see a difference between pure RNAV and RNP navigation, or better, what tells me either of these modes is used, and is the role of the ANP value the factor that determines when RNP becomes unusable? How is RNP tied to the automatics (I can imagine that RNP is used whenever the ANP value doesn't exceed the RNP value and a switch to RNAV occurs otherwise)?In what situations is RNP required, is that depicted on the approach charts? And what does the RNP value express (a distance, or some kind of a percentage)?Questions, questions...

I'm still not able to tell how it is implemented in the MD-11 and how I can use it.

I don't think it is implemented hence it would be rather difficult to use it.If it was implemented you could select/load and RNP approach through the FMS (say this one at Palm Springs airport - chart) and autopilot should be able to fly it all automatically (with final manual landing). I don't think it is possible. If you select Palm Springs airport in your FMS I don't think you will even see such approach.From pilot's point of view RNP is just another very special type of approach (forget about all these "values"). You have charts for it (I have given you one example above) and the crew MUST undergo special training (in real world) to be able to fly those approaches.

Hi, RNP (Required Navigation Performace)Required Navigation Performance (RNP) is a type of Performance-based Navigation(PBN) that allows an aircraft to fly a specific path between two, 3 dimensionally definedpoints in space. RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board performance monitoring and alerting.RNP also refers to the level of performance required for a specific procedure or a specificblock of airspace. An RNP of 10 means, that a navigation system must be able to calculateits position to within a circle with a radius of 10 nautical miles. An RNP of 0.3 means theaircraft navigation system must be able to calculate its position to within a circle with aradius of 3 tenths of a nautical mile. A related term is ANP which stands for "Actual Navigation Performance". ANP refers to thecurrent performance of a navigation system while "RNP" refers to the accuracy requiredfor a given block of airspace or a specific Instrument Procedure. The performance monitoring and alerting capabilities may be provided in different formsdepending on the system installation, architecture and configurations, including:• display and indication of both the required and the estimated navigation system performance;• monitoring of the system performance and alerting the crew when RNP requirements are not met; and• cross track deviation displays scaled to RNP, in conjunction with separate monitoring and alerting for navigation integrity.The RNP Values for each procedure are stored in the ARINC 424 Navigation Database. As the NGX will support those RNP stuff (see the pinned post at the top) we will be able to fly RNP Procedures.Jan-Paul Schuchna

Yes, RR indeed confirmed implementation of RNP in NGX.

Thank you all for the explanation.So, the MD-11 has RNP/ANP values depicted on the MCDU, but they aren't usable ("dummy values")?

Yes, RR indeed confirmed implementation of RNP in NGX.

Only within the limits of FSX, which is basically that ANP is always perfect, so that whole area of navigation where you only know approximatly where you are does not come into play.

Paul hit the nail on the head. The best that the simulation can do is present the additional systems display requirements for RNP and the ability to follow a flight path definded in the terminal approach procedure navdata, but it cannot simulate the real world paradox that you really never know exactly where you are during a flight.

the MD-11 has RNP/ANP values depicted on the MCDU, but they aren't usable ("dummy values")?

Read again my previous post because I believe you missed the whole thing. What counts here are not the "values" but ability of the autopilot to actually fly such curved and tight approaches (did you even look at the KPSP RNP approach?). This is where most of the software development has to be done, this is far from trivial work. Ability to anticipate turns and concept of "fly-over" versus "fly-by" points and correct handling of altitude without step-downs must be built into the FMS/autopilot.

Only within the limits of FSX, which is basically that ANP is always perfect

Isn't it obvious? Of course and that should more than satisfy sim users. How often in real life the values of ANP are outside of the range and pilots must abandon RNP? Such pedantry in simulation would add little to sim users. Similarly my Garmin G1000 simulator gives me nice implementation of GPS roll steering, LPV approaches, procedure turns, holding patterns, etc - but assumes WAAS is always "good".

You could argue that we are not actually flying down a Localiser and Glideslope "beam", when we are at the controls of our MD11 in FSX. Since the coders have built a "perfect" world

This is a good way looking at it - all our navaids in FSX are perfect navaids and this not only includes GPS but VORs, ILS, NDB. And RNP based on perfect navaids will be ..... well, a perfect RNP :Big Grin:I don't see anyone complaining here that VORs in FSX are so precise - why would they all of a sudden have to complain that RNP is so perfect :(

Only within the limits of FSX, which is basically that ANP is always perfect, so that whole area of navigation where you only know approximatly where you are does not come into play.

Isn't it obvious? Of course and that should more than satisfy sim users. How often in real life the values of ANP are outside of the range and pilots must abandon RNP? Such pedantry in simulation would add little to sim users. Similarly my Garmin G1000 simulator gives me nice implementation of GPS roll steering, LPV approaches, procedure turns, holding patterns, etc - but assumes WAAS is always "good".

No I do not think it is obvious. And I am sorry that you consider this 'pedantry' but 'Required' navigational precision and 'Actual' navigation precision are, as you yourself tried to point out, comparators not absolutes, and so can not be modeled in FSX because it provides an absolute ANP of zero.

and so can not be modeled in FSX because it provides an absolute ANP of zero.

Well, I disagree here because in fact it could be modeled in FSX, yes, with some work and knowledge of typical probability-error distribution (Gaussian, Poisson, etc) could be done but whether it would be worth the effort I doubt therefore IMHO I was fully justified to called it 'pedantry' because even if done correctly it would still deliver very little new noticeable simulation experience (a situation is not totally dissimilar to this "cold soaking").

Simulating a RNAV (GPS) approach is exactly the same as simulating a RNAV (RNP) approach in MSFS, except for the additional displays that the pilot is supposed to have access to; therefore, modelling RNP boils down to providing the error monitoring displays. They can be 'faked' to provide an error value but in fact there will not be an error factor. The big thing I am hoping to test on the NGX is the ability to have crossing altitudes at the approach waypoints that the aircraft descends through rather than attempting to level off a the constraint. This will take us a lot closer to being able to "simulate" the RNP approach. Ryan has advised that features like this and radius-to-fix legs will be included without implementing ARINC424... very exciting.