RNP is revolutionizing the instrument approach

[photofly]

Here's the plate for the RNAV(RNP) RWY 16 at CYLW, for interest.

[55+]

Well.......... if you look at the RCAP ILS/DME 2 RW 16 Category A-C 1660(251) 1/2 CAT D 1910(501) 1 better than RNP 0.1/RNP 0.15 are others non-RNP certified at any disadvantage. I assume AC/ JAZZ go in there so is there any comparison on arrivals/departures that couldn't happen because of non-RNP........ just asking that is all.

[ea306]

Is there an RNP Approach to RWY 34 in CYLW?

[photofly]

Is there an RNP Approach to RWY 34 in CYLW?

There are two. RNAV (RNP) Y RWY 34 and RNAV (RNP) Z RWY 34.

[ea306]

Cool.

Now there is an operational advantage as there is no conventional approach other than a circling for RWY34 CYLW.

Anyone have a copy of the RNP approaches to RWY34 CYLW that could be posted for viewing?

[photofly]

Here. Thank me later.

[ea306]

Will thank you now...

[MCB]

Just an FYI, all RCAP procedures are on fltplan.com now. Just log in, charts and maps for your desired airport, and there is a link at the bottom for restricted charts. It appears as if all the Westjet approaches are on there.

[cj555]

What does 2 X RNP mean? Is that in relation to the speed & altitude on the approach? So the closer you get, the more strict it gets with respect to allowable "deviations"?

If you were shooting an approach to RNP 0.3 minima, the airplane is guaranteeing it's lateral accuracy to 0.3NM 95% of the time, and 2X (two times, not 2 'the letter X') RNP, also known as the containment area, the airplane has to guarantee accuracy within 2X RNP (0.6nm) 99.999% of the time. This strictness remains the same from the moment we select the RNP value on the FMC (usually 100NM back ish from the top of descent when we're loading and setting up the approach and doing briefings).

so 2X RNP is another tube around the airplane that's twice the radius.

Ahh very interesting. So essentially 2X RNP is a selected setting that dictates the amount of deviation the aircraft can fly with more certainty. For example: RNP 0.3 is certain 95% of the time, whereas 2X RNP 0.3 is certain 99.99% of the time. The reason 2X RNP is more certain is because it refers to a radius twice as large (0.6nm vs 0.3nm).

What is the benefit of enlarging the "tube" that the aircraft must fly in (2X RNP)? Is it just the fact that it can be "guaranteed" with 99% accuracy that the aircraft will fly within that radius when flying close to obstacles? Versus RNP 0.3 being less "certain" and therefore more dangerous when flying near obstacles?

[Go Guns]

So essentially 2X RNP is a selected setting that dictates the amount of deviation the aircraft can fly with more certainty.

Nope, it's just the standard. We select the RNP, for instance 0.3, and FMC must be certain of it's position within 0.3NM 95% of the time, and 0.6NM 99.999% of the time. We see the FMC calculated certainty displayed to us as actual navigation performance, or ANP, at the 95% level. So long as ANP is equal to or less than RNP, we're good to go.

We use this not only in approaches but in other airspace as well, including WATRS and ETOPS where we set RNP to 10.0

The 2X RNP thing is really just part of the theory, or working knowledge of the way the system works. Similar to learning about RAIM on IFR certified GPS systems. On a practical level, the only thing we have to concern ourselves with is RNP and ANP.

[complexintentions]

Thought I'd share the Seychelles approach for some variety. Someone was asking what operational difference you might have. Nothing on the displays really, you're just flying in LNAV/VNAV as you would be in other phases of flight. The difference is really just in how closely things are checked and monitored, and ensuring certain requirements are met, as mentioned, verifying ANP meets or exceeds RNP. As the plates show, having higher actual performance (a lower ANP value) allows lower minima. In the SEZ case, the minima for an ANP of .15 is 410 feet, while .30 only lets you down to 690. The VOR approach is only a letdown maneuver and only allows descent to circling minima!

Coupla other operational notes.

-The chart is not allowed to be temperature corrected. Instead the temperature range within which the procedure can be flown is published (in this case, 5C to 46C - obviously YLW wouldn't work most of the year with this range!).

-Speed management and thought to how a terrain warning would be handled have to be given some serious thought. There is a note on the SEZ plate saying "Fully configured and at APCH speed is mandatory" at waypoint FREDY. If you don't, you WILL get a GPWS warning as you descend in the turn. What if you're night/IMC? No choice but to fly the escape maneuver, which normally would have one climbing straight ahead. Not a great option with terrain directly ahead. So in this case, you would actually have to make an immediate left turn. Better to control the speed.

-Except, being fully configured that early would burn another 1-2 tons of fuel. So have to plan for that too.

So for the extra capability that they give, RNP approaches do require some extra thought and planning.

FSIA RNAV (RNP) Z 13.pdf

(117.3 KiB) Downloaded 138 times

[cj555]

Thanks for all the great responses!

@ Go Guns - So when you say that the 2X RNP stuff is really more just the background theory, and that you more need to concern yourself with RNP and ANP: If I understand that means that you are given a certain requirement (Required Navigation Performance) with respect to how big the diameter of the "tube" around the aircraft must be on an RNP approach. Then you select the appropriate RNP setting that will give you an ANP (Actual Navigation Performance) that meets or exceeds these requirements?
I think I am just a bit confused as to why you would need to have different RNP settings. Couldn't every approach bet set up to use RNP 0.3 and everyone just uses that? I don't see why it needs to be complicated by having 2X RNP settings etc. Sorry for all the questions, I'm just really curious to understand how this system works.

@ complexintentions - Very cool approach chart. If you reach waypoint FREDY and are not fully configured for landing, you must abort the landing? So that means you cannot continue on the approach and start putting flaps and gear down after FREDY? How much time (in minutes) are we talking between FREDY and touchdown?
Can that approach in the chart be flown with an ILS approach? Or is the fact that it "curves" around the obstacle make it a strickly RNP approach?

[Rockie]

For detailed information on how PBN Instrument procedures are designed (RNAV, RNP AR, Departures etc.) download this manual from the FAA website.

http://www.faa.gov/documentLibrary/medi ... 260.58.pdf

It's the latest manual on design criteria as of September 2012, and in it you will find the answer to all of your questions.

[55+]

Orders 8260.58 hasn't been adopted in Canada yet, TC is in the process of "consultations" amongst us all, TP 308(5.3) hasn't been settled either due issues with FAA 8260.54A criteria that FAA themselves acknowledged.. Lots ups and downs in the IAP world that a good percentage don't understand - let alone us......

[Rockie]

That's true. But the whole thing is gradually evolving toward the ICAO standard of Performance Based Navigation with the United States leading the way, and it's not like Transport Canada is going to adopt their own standards. This manual like all the others will be revised but it's the most current I've seen.

If anybody wonders things like why the accuracy requirement is 2X the RNP value or how the temperature limits on a LNAV/VNAV approach are derived this will answer it for them.

[55+]

Yes, PBN is the essence of 8260.58 and the Standards folks over at TC have been caught with their collective "nickers" down. TC will adopt the FAA criteria as it always has, eventually. Big issue is required training.........for those IAP designers. Nav Can has contracted out much if not all of their IAP design(new and cyclical review) to IDS - North America(makers of design software FPDAM) and as of late Jeppesen.........(who will use FPDAM as well). Be interesting to see how the modules will conform to new criteria....

I could ramble on and on with 10 paragraphs but I won't

Have fun with the criteria

[WJ700]

When RNP first came out there was more of a difference between RNP .3 to a higher limit. Our guy at the time who was helping to build the program actually left to work for Naverus on a LOA but something was done around that time he left to work within the 'theory' to allow the lower minima at the higher RNP limits.
The RNP really just sets the flight technical error message and that can be more of an issue as the approach truncates, or nears the runway. The biggest benefit to RNP (that I see) is that it doesn't follow TERPS (in the traditional way). As you increase your distance from a ground based nav aid, you have to account for splay. So that hill way out from the airport must be accounted for on a traditional approach or missed approach track. When building the approach for RNP you just 'bend the straw' around the obstacle.

I'm interested to see if Encore comes out of the box with RNP installed. I suspect it may because of the YCD route.

[complexintentions]

@cj555,

As far as being fully configured, well, "mandatory" would imply you have to be. Usually that would be about the point you'd be calling for landing gear and Flaps 20, so it's not THAT early, you just have to be fully configured (Flaps 30) at that point. So really, only a couple miles earlier. The difference in fuel burn with the drag of the gear is quite large though. I think about 16 tons/hour in the B777? (Not usually watching it at that phase of flight!) I would estimate you're about 2-3 minutes from landing at FREDY. Depends on groundspeed.

Would you actually go around if you WEREN'T fully configured at that point? Well, it depends I guess. I'd prefer to just take it easy and get configured early and drag it in slow so I don't have to make that decision. (I'm lazy! ) But if someone was a little late, then I'd consider if I was daylight VMC or night IMC and take it from there. As with all approaches, preparation will take all the stress out.

And you are correct, no ILS is possible on 13 due to the terrain. There is an ILS on 31, but prevailing winds will often render it unusable. Because SEY is out in the middle of nowhere, the RNAV RNP for 13 was a logical approach to make a priority to develop. Seychelles is a long way from anywhere to go if you don't have a good chance of landing.

[Go Guns]

@ Go Guns - So when you say that the 2X RNP stuff is really more just the background theory, and that you more need to concern yourself with RNP and ANP: If I understand that means that you are given a certain requirement (Required Navigation Performance) with respect to how big the diameter of the "tube" around the aircraft must be on an RNP approach. Then you select the appropriate RNP setting that will give you an ANP (Actual Navigation Performance) that meets or exceeds these requirements?
I think I am just a bit confused as to why you would need to have different RNP settings. Couldn't every approach bet set up to use RNP 0.3 and everyone just uses that? I don't see why it needs to be complicated by having 2X RNP settings etc. Sorry for all the questions, I'm just really curious to understand how this system works.

@cj555

Don't get hung up on the 2X RNP, it isn't a setting, it's just one standard the FMC looks at when computing it's accuracy vs the accuracy required. It's part of the magic taking place in the FMC.

ANP is being calculated all the time and a reading on the navigation display is constantly there for us to look at. It's not a setting either, but a reading of the FMCs actual navigation accuracy in real time. It's continuously being calculated by the FMC.

The only setting is RNP. It changes not only for approaches but certain airspace as well. In ETOPS and WATRS airspace RNP is changed to 10NM. This allows for reduced separation with other aircraft in the airspace.

For approaches, we usually fly at RNP 0.3, but have the option of flying to 0.1 accuracy. This sometimes allows lower minimums for the approach. If you look at that RNAV RNP Z RWY34 approach in Kelowna posted earlier, RNP 0.1 gets us 166' lower than RNP 0.3. You may ask why not do 0.1 all the time then? Much like RAIM, satellite coverage may effect the availability of the required accuracy. So 0.1 may not be an option, in fact, there are usually a few times in the day when it's not. 0.3 is almost always available however.

Finally, If ANP is ever equal to or greater than the RNP we've got set, we get FMC caution lights and messages to advise us.

[NB Wings]

I just stumbled upon this today. It's a quick but interesting look at the RNP in Kelowna.

http://youtu.be/Ta-Cqusg4lU?t=19m54s