P-RNAV/RNAV-1

[zonoma]

I'm a slightly confused controller that can do with a little education please!

RNAV-1 routes are beginning to pop up in various places however someone has told me that the aircraft has to be turned into "RNAV-1" mode by pressing a button and doesn't fly it routinely. Is that correct?

Second question, how aware are you as a pilot that you are now on an RNAV-1 portion of a route, and would you fly differently?

Last question, can you be RNAV-1 compliant and manually flying or does the FMS have to be in full control?

Thanks in advance.

[B737900er]

1st question - That person is pulling your chain.

2nd question - The enroute map would tell us if its an Rnav 1 portion, and no we would not fly it any different except monitor the RNP/ANP values.

3rd Question - You can fly it manually but it would be difficult without flight directors. Let the autopilot fly it.

[Denti]

3rd Question - You can fly it manually but it would be difficult without flight directors. Let the autopilot fly it.

Wyh would it be difficult? Especially in a 737NG with its wonderful navigation performance scales?

[zonoma]

Thanks for the replies. Can I assume then that if an aircraft is RNAV-1 able, that it always flies within the parameters required, even when on an RNAV-5 route? If manually flying, are you fully aware of the navigational requirements to be RNAV-1 compliant? Finally, the enroute map, is that what is displayed on the FMS or do you have to physically pull out an enroute chart and have a look? Do you think if a STAR was established that was an RNAV-1 or better requirement that this would be easily identified in the cockpit?

Edited to ask: Is there any specific training required to be an RNAV-1 pilot or is it assumed if you fly an RNAV-1 aircraft that you are capable of flying within the RNAV-1 parameters?

[BleedingAir]

Can I assume then that if an aircraft is RNAV-1 able, that it always flies within the parameters required, even when on an RNAV-5 route?

No, the aircraft will fly as accurately as it can, which most of the time is to around 0.02nm accuracy (which is known as ANP or Actual Navigation Performance). The only thing that changes between RNAV-1 and RNAV-5 is how "happy" the aircraft is to be off-track, or how much its ANP can degrade before you'll get flashing amber stuff.

So if, say, the GPS receivers fall offline and ANP gradually rises to 2.0, the aircraft will still happily navigate in RNAV-5 airspace, but not RNAV-1.

Is there any specific training required to be an RNAV-1 pilot or is it assumed if you fly an RNAV-1 aircraft that you are capable of flying within the RNAV-1 parameters?

It's worth mentioning that RNAV-1 is not particularly accurate. That's the RNP we're used to seeing flying SIDs and STARs - most RNAV approaches default to 0.3, and we fly RNP approaches down to 0.1 (required accuracy 10 times that of RNAV-1), which does require specific training.

Second question, how aware are you as a pilot that you are now on an RNAV-1 portion of a route, and would you fly differently?

The current RNP (required nav performance) is displayed on the bottom of the ND on the aircraft I fly, along with the ANP. Nothing changes from oceanic RNP10 airspace to an RNP0.1 approach, except the tolerances involved.

Last question, can you be RNAV-1 compliant and manually flying or does the FMS have to be in full control?

At most RNP values you do have the option of manual flight. We're allowed to hand fly approaches down to RNP 0.3, below that, autopilot use is mandatory.

[BleedingAir]

P.s. What your friend may be referring to when they said you have to "push a button to get into RNAV-1 mode", is manually altering the RNP if the route isn't correctly coded in the database (which shouldn't be the case). So if you're on an RNAV-1 route and the aircraft is flying at RNAV-5, it's a couple of button pushes in the FMC to change the nav tolerance to 1.0. Which as I stated before, won't actually affect or increase nav performance, only tolerance.

[zonoma]

Thanks everyone, that's really helped and cleared up the confusion.

[Mansfield]

I think we have to be careful in how this is explained.

RNP is not a measure of how accurately the approach is flown. It is a measure of the probability that the FMC will be think it is somewhere that it isn't. As we get closer to the ground, we increasingly prefer that probability to be lower.

Consequently, the performance referred to in the terms "required navigation performance" or "actual navigation performance" does not refer to either the pilot's skill or the autopilot skill. It refers to the "ability to perform" of the complete navigational system. For example, the satellite data accuracy, transmission accuracy, and the receiving component's ability to interpret the data satisfactorily are all part of the system performance. Any breakdowns in the system function will create an alert that the ANP, actual navigational performance, is not acceptable for whatever RNP you are trying to use. Hence, if a satellite is missing, your flight plan may contain a warning of an ANP limitation around your ETA.

In other words, if a given satellite is off line, what is the probability that your FMC will think it is on centerline when it is more than 0.3 miles off centerline? If that probability, the ANP, is within the RNP, then the chances that the FMC is confused are within acceptable limits.

But you could be a half mile off track during the approach and you will not get an ANP alert. The rest of the on-board system may be screaming at you, as well as the other pilot, but the ANP will be just fine...the probability that the FMC is lost has nothing to do with your piloting ability.

The concept of RNP/ANP is totally dependent on average risk. The difficulty is that 99.9% of pilot training is predicated on specific risk. The average risk concept is pretty foreign to us, so the explanation of RNP can get convoluted, particularly after it has been re-written into the manuals six times over by flight ops/flight standards people of varying levels of understanding...

[underfire]

mansfield, I think you need to read up a bit on RNP and the parameters. A design criteria manual may be the best, as all of the variables are explained in detail.

Check the sat level required, what the number of sats available will give you, RAIM, and the error budgets.

Some can hand fly to 0.3 RNP level.

[JammedStab]

Our plane typically changes itself as appropriate to the various RNP levels. For example, we do a lot of RNP-1 departures and it always seems to say RNP-1. Then at some point it will change to RNP-2 or we may be over the ocean and see that it is RNP-4(my last type went to RNP-12 over the ocean).

A lot of the arrivals are RNP-1. The aircraft only seems to change to RNP-1 as we descend through 15000' even though we may be on the arrival earlier than that.

RNAV approaches are usually RNP 0.3 and that has to be manually entered on our aircraft.

Bottom line, we only manually enter for an RNAV approach. The rest is automatic.If there is a problem, there will be a message for us.

[PantLoad]

Our procedure...
For RNP 1 (SIDs/STARs), we have to use flight directors or autopilot or both.
That is, we can hand fly if we choose, but must use flight directors.

For RNP .3, we must use both autopilot and flight directors.


BleedingAir explained it beautifully!

Fly safe,


Pantload

[Capn Bloggs]

mansfield, I think you need to read up a bit on RNP and the parameters.
YOU need to read. Mansfield is correct. I suggest you read up on "Flight Technical Error", Underfire.

the aircraft will fly as accurately as it can, which most of the time is to around 0.02nm accuracy (which is known as ANP or Actual Navigation Performance).
No; read what Mansfield said. "As accurately as it can" is FTE. The ANP can be 0.02, but the aeroplane can be off track for a number of reasons, including hand-flying Bloggs making a hash of his RNP approach when the AP is out of action.

[BleedingAir]

No; read what Mansfield said. "As accurately as it can" is FTE. The ANP can be 0.02, but the aeroplane can be off track for a number of reasons, including hand-flying Bloggs making a hash of his RNP approach when the AP is out of action.

Yes granted, in my attempt to simplify I probably used rubbish terminology. What I meant to say was "to the highest navigation performance it can, regardless of airspace".

[piratepete]

Lets put all this lovely ANP/RNP stuff in to a little perspective instead of arguing who is technically "correct" regarding various levels of accuracy FFS.Do any of you (are you old enough) to recall flying the old NDB or even raw data VOR approaches in really bad CB type weather with NEEDLES wobbling around to and fro? Granted the minima are different for obvious reasons but to be overly concerned about such tiny errors is plain silly by comparison.

[underfire]

Yes granted, in my attempt to simplify I probably used rubbish terminology. What I meant to say was "to the highest navigation performance it can, regardless of airspace".

No worries, bloggs just trolls all of my posts.

[Mansfield]

Ah, I do indeed remember flying raw data VOR and NDB approaches. However, I recommend you look over the approach chart for the RNAV (RNP) Z Rwy 36 at Quito, Ecuador. I don't fly that these days, but I believe you will see more of the point; the only way this can be flown is with an FMC, and you really, really want to be sure the FMC knows where it is... ;)

[underfire]

mansfield,

The systems are set up to keep you within a certain containment area. The HIL is an estimation of the position error of where the aircraft thinks it should be. Where the aircraft thinks it should be is based on several factors, all of which have estimated error built in. As an example. it really is not a waypoint, but a waysphere. The waypoint, just in the coordinates, has a sphere, the waypoint horizontal res is 60 feet. (You can be 60 feet to the left of the coordinate, and it still thinks it is dead on) Vertical res is much different.
In addition, flyby waypoints are used and the resolution value is adjusted, well, it has to be, to get the procedure to connect, especially with S curves and inherent latency in the GPS system.

Here are some variables to consider (this is VEB, but you get some of the horizontal estimates as well such as ANPE, waypoint res, and wingspan. (note they are additive)

http://i65.tinypic.com/2yv1km1.jpg



In regards to GPS sats, I think you will find that at least 5 are required, usually it is 7 I believe. This is so that horizontal and vertical positioning can take place, error trapping, and latency. A GPS signal is about 3 seconds long, so when you are tracking multiple sats, it takes a while for all of the signals to get there and be processed.
Per the US Govt, SPS GPS has the following accuracy
http://i66.tinypic.com/2cr3xbm.jpg

military uses PPS GPS

It is recognized that the ac knows where it was, not where it is, as the kalman filter and inertial systems estimate where the ac is.
As you can see, all of the estimated values start to add up. In short, the RNP value is a based on where the aircraft thinks it should be, but where it thinks it should be has error estimation built in as well. (ie 99.9% of being within 95%)

[Capn Bloggs]

Do any of you (are you old enough) to recall flying the old NDB
You mean rollout of the inbound turn 15° early because you knew the neeldes would swing an extra 10° as you crossed the beach? :ok:

bloggs just trolls all of my posts.
Merely calling you out for unfairly criticising others.

[underfire]

Merely calling you out for unfairly criticising others.

Really? Should you take the time to read and comprehend, there was no criticism on my part, simply stating that there are many parameters to review.

YOU need to read. Mansfield is correct. I suggest you read up on "Flight Technical Error", Underfire.

Did you figure out that FTE is but one of the variables? I can send you a list on suggested reading materials should you have a desire to figure out how an aircraft flies.

And all of the other responses in numerous threads?

[Goldenrivett]

Originally Posted by Piratepete
Do any of you (are you old enough) to recall flying the old NDB
Some of us remember using the Consol station at Plonéis to check our track crossing the Bay of Biscay and remember the Vanguard crash at Basel-Mulhouse when the crew confused the NDB stations during a snow storm.
https://assets.publishing.service.gov.uk/media/5422f54e40f0b613460005c1/11-1975_G-AXOP.pdf

Anything to improve our SA, simplify cross checking and increase NAV accuracy is very welcome.

[FE Hoppy]

https://www.eurocontrol.int/sites/default/files/field_tabs/content/documents/single-sky/mandates/20120705-pbn-manual-advanced-fourth-edition.pdf

suggested reading.
there is a free online course by icao too but it's so boring i will let you find it yourselves.