FMC-RNP question

[hoschi]

Have you ever had to change the RNP value in the FMC because of an incorrect value set by the FMC for a sector. For example RNP 1.0 is displayed but instead RNP 0.3 or lower is needed, because of the type of approach or within the terminal area. Until now I didn´t pay a lot attention to the RNP, as long the FMC didn´t make me to(Verify position etc). But with the increasing use of RNP/GPS approaches, should I?

[kijangnim]

Greetings
The RNP is either defaulted or as per NavData Base, and like all the data in the NavDB, errors can exist such as the wrong RNP, so if your procedure clearly states that the RNP should be XXX and you have ZZZ change the RNP value to XXX.
BRNAV is RNP 5, PRNAV is RNP 1, procedures < 1 i.e., 0.3 (DME/DME)

RNP< 0.3 should be GPS if your aircaft has such a certification. :)

[divinehover]

RNP value should change by itself as the aircraft moves to differant phases of the approach (0.3 for the final approach seg of an RNAV App). There is however nothing stopping you from changing this during your App Prep. I has seen cases where the RNP did not auto-adjust. This could be a Database coding error and should be taken up with your Database provider (Honeywell, Smiths, Jepp ect).

If you have changed the required RNP to the most restrictive value and you get a Nav Accuracy Downgrade Caution it might not prevent you from continuing that phase of the approach which might have required a less restrictive value (ie 0.5nm for an initial app seg).

PS. I am a Airbus driver so the Boeing (or other) info might be different.

[kijangnim]

You can only set the RNP for which the aircraft is certified, Airbus is not certified < 0.3, Boeing much less, in fact Air Alaska is the first airline in the world which had designed, and certified RNP approaches in JUNEAU Airport, it is worth doing some research.:cool:

[Bitburger]

You are right RNP should be cheked. I try to do the following.
Before RNAV we used to check or nav aids for the approach. Well with RNAV you do the same.
If you use RNAV for arrival or app just check it as you used to do before with the conventional means. With computer technology introduced in navigation we are forced in a more monitoring function and that exactly what we should do.

Before RNAV .....app checklist....nav aid identified

With RNAV .......app checklist.....nav aids...that is in this case RNAV....checked and valid.

Greetings

Curly Mountains

[c100driver]

You can only set the RNP for which the aircraft is certified, Airbus is not certified < 0.3, Boeing much less, in fact Air Alaska is the first airline in the world which had designed, and certified RNP approaches in JUNEAU Airport, it is worth doing some research.


The Air New Zealand Airbus A320 is certified for at least RNP 0.3. Air New Zealand is operating the A320 into and out of Queenstown on RNP AR approaches. Air NZ has had a lot of work done with Airbus to move toward PBN approaches.

Jetstar are using the A320 with whats is known as RNP lite using 0.3 at Brisbane.

The Air NZ B737-300 and Qantas B737-800 have been operating RNP AR into Queenstown for three years. Air NZ are using 0.3 and Qantas are using 0.15 both are planning 0.11 approaches.

[Bitburger]

The planes are capable only to use the nav information if it is valid.

There is no reason to assume that their would be any diff btw Boeing or Airbus.

It is up to the local CAA to make sure this is the case

[reynoldsno1]

Air NZ are using 0.3
without GPS as well....:hmm:

[c100driver]

without GPS as well....:hmm:


Both the Air NZ A320 and B737-300 have dual GPS fitted.

Boeing developed an STC for the B733,4,5 classic to have GPS retrofitted.

[FE Hoppy]

In reply to the original question, Make sure you know when the RNP should change before making manual changes.

On the E-jets when flying NPA using FMS as primary nav source the RNP will change to 0.3 only 2 miles before the FAF. This is by design as before that the approach is RNP 1. If you change early and get a degrade you should go around by the book but if this is because you manually changed the RNP early it's your own mistake that caused the go around.

[kijangnim]

Greetings

RNP 0.3 is the smallest for Airbus regardless of its FMS, now RNP is the budget of all systems involved, and to start with we should begin with the FG (flight Guidance, or Auto-pilot if you will) and until today nothing have been done, I suggest everyone to check the AFM (airplance Flight Manual) and verify what is the smallest RNP the Airbus is certified for, and with what type of sensors, i.e., DME/DME, GPS, ILS.... :}

[LLLK]

If the procedure requires less than 0.3 you need to have special approval (RNP AR APCH being the new term for such approaches AR=approval required) This special approval impacts the operational aspects as much as the airworthiness aspects and in many cases, a formal 'Flight Operational Safety Assessment' has to be carried out - this is done on an operator-by-operator basis.

As I understand it, some Boeing and Airbus models (737, A320..) meet the airworthiness criteria for RNP AR APCH and others are in the approval pipeline but don't expect to fly an RNP 0.15 approach just because that is the lowest figure you can find in the AFM.

[kijangnim]

Greetings
I never said that you can fly what the aircraft is approved for in terms of RNP, indeed airlines have to do their homework, with their respective civil aviation authority, before they can fly using the value in the AFM, which reflects only to what RNP value the aircraft is certified for.

[cfm56dash7]

You may (I should say will) see errors in the coding of your database. When you see this, get after the flight technical group at your carrier to correct it. The RNP value for each leg is an insignificant looking, three-character value buried deep in the ARINC 424 procedure record. I always imagine these values being painstakingly created by engineers with massive computers, detailed obstacle surveys, laser theodolites and pocket protectors inside their pocket protectors. Once created, your database provider has some white-haired grandmother, with absolutely no aviation experience (and no clue as to what she is entering), quietly enter the data via a keyboard. Errors are made by one or both parties.

Generally, you are able to run comparison checks between the last database and the new one and any change requires some scrutiny. Obviously, new procedures deserve a complete top to bottom physical so that no errors go undetected.

All that said, if you see an RNP value on the CDU that does not match the value shown on the chart you need to do something.
Eliminate the obvious. Is the FMC on the correct nav cycle (valid dates on the IDENT screen)? Do you have the correct plate? Be especially careful if you are one of those guys that files your approach plates without looking at the effective date. If all that well and truly matches up, then change the RNP value on the CDU to match the plate. Manually entered RNP values display in a different font and cannot be overwritten by the FMS. This means that if you enter a more restrictive RNP for the approach and then miss, as the speed picks up you may run into GPS latency issues and the dreaded UNABLE NAV PERF message may appear.

The Air NZ B737-300 and Qantas B737-800 have been operating RNP AR into Queenstown for three years. Air NZ are using 0.3 and Qantas are using 0.15 both are planning 0.11 approaches.

We use approaches at RNP values of 0.5 all the way down to 0.15. We have a new approach that specifies RNP 0.11 but the cert test flights are not yet complete, so we aren't yet flying it for score. The 737 NG can be certified down to RNP 0.10 but you must specify the NAV PERFORMANCE SCALES option to get that value.