Rnp and Ils, Vor approaches
 

i recently went for an interview where i was asked a question:
i fly the airbus A-320 and this question confused me a bit and i stated that there is no relation between RNP and an ILS approach.

however, i was told that this is not the case and apparently there are RNP values of .3, .5 and .6 for the approaches respectively. i have not been able to find these values in any airbus specific or general literature on RNP.

However, on consultation with a few friends flying the Boeing 777, i found that these values are mentioned in their SOP. (the person asking the questions was a 777 Examiner).

can someone please clarify with source. the interview was a navigation interview for ATPL and feel it was not fair to be asked a 777 specific question. (my friends on the 737 say there is no such thing in their SOP).

however i wouldnt mind being contradicted.

thank you.

Hm, for our 737s the RNP for all approaches is 0.3... Beats me where that comes from though!

For Boeing, RNP Requirements are detailed in FCTM, and for Airbus in Instructor support section on GPS Primary description, although again mentioned in the training materials on approaches and NAV ACCURACY.
The whole RNP subject is also detailed in Operations Manual B for most companies, covers en-route, terminal and approach RNP requirements.
General rule is " Unable Reqd Nav Perf" or " Nav Accuracy Low" you are stuffed.

Speed Freak:

RNP = Required Navigation Performance. ILS, VOR, or NDB are not predicated on performance-based navigation.

Having said that, I can see the value of expressing an RNP value for VOR or NDB approaches if they are authorized for RNAV overlay flight of the final approach segment; i.e., "VOR or GPS Runway36," for example.

But, for ILS it makes no sense at all because ILS, per se, must be used to fly the ILS final approach segment and, in the U.S. at least, the ILS intermediate segment as well.

RNP values for non precision approaches is of course something kinda old as many airlines use LNAV/VNAV to fly them for quite a long time (we use LNAV for more than 15 years now, VNAV for 10+ years and only recently, 5 years ago, switched to IAN), of course with full approval by the relevant authority. But same as others i fail to see the relevance for an ILS as long as only the ILS is meant. I can understand a RNP value for initial approach and missed approach, but not the final or intermediate approach.

VOR, NDB and ILS are 'conventional' approaches. There is no associated RNP value. The RNP values only apply to RNP APCH (charted as RNAV(GNSS)), where the final approach segment is always 0.3 and all the other segments are 1.0, and RNP AR APCH (charted as RNAV(RNP)) where any leg can be as low as 0.1.

thats what i said and even went on to explain that suppose my rnp falls below 0.3 does that mean i cant even do an ils approach. how do i land then:confused:

told them of the 320 where if my nav accuracy falls below 1 i just switch to raw data and continue. he wasnt convinced at all.

i hope he was talking about this but i doubt it.

will try to refer to them

1 nm as per 320 sop.

LLLK:

True of initial, intermediate, or final. Feeder cannot be less than 1.0. Missed approach can start out at value of final segment, but must increase incrementally ("telescope" expansion) to RNP 1.0. Incremental increases are predicated on presumed IRU performance assuming failure of GPS in the final segment.

For aircraft without at least one IRU minimum leg performance is 0.3, and missed approach must be RNP 1.0 or greater.

Speed Freak,

The simple (and most correct) answer to this RNP thingo is that, for the approaches listed, there is no such thing because they do not depend on GPS or any form of RNav.

AFAIK most RNav approaches have a limit of 0.2 for the final approach segment just for interest.

Spead Freak,

I would be very cautious of some of the advice here!

Approach Requirements Relating to RNP:

" With appropriate operational approval, approaches requiring RNP alerting may be conducted in accordance withe the following provisions:"

The source of information I suggested then expands the subject:ok:

Aterpster:

Agreed - the RNP(AR) was really a brief aside comment to the main question - where the answer is simple - ILS, VOR and NDB (in fact all conventional NPAs) have nothing to do with RNP!:ugh:

Speed freak

Your understanding is exactly right. RNP values have absolutely nothing to do with any conventional navaid based procedures. Although we use managed nav to fly non-precision approaches, the primary reference is still the navaid itself which must be tuned, identified and displayed. In the case of an ILS you are actively tracking the radio beam itself.

Think of it this way, if an RNP were required how is it that a steam aircraft that has no RNAV capability whatsoever is able to fly the approach? In the case of the Airbus, both FMGC's could completely fail and you are still perfectly able (and legal) to fly any conventional navaid based procedure.

Whoever interviewed you does not know their stuff as well as you do.

The way you explain the question, I would give similar answer. EPE is relevant for NAV use, when out of limits use raw data if it helps. When on raw data mode such as GS/LOC, both actual EPE and database coded accuracy limit are irrelevant.

FD (the un-real)

mustafagander:

Most have 0.3 as the performance value for the final approach segment. LPV is quite different, as is RNP AR.

Not applicable.

The guy asking the question was talking *6576çç???

As long as you use raw data as primary source of navigation there is no RNP, agreed. However, if you have the approval to fly non precision approaches without the need to tune and use the real nav source at all and without the need for an existing RNAV overlay approach, would you still fly it without any RNP?

With respect to the contributions, the interviewer asked a question for which there is a published answer in both Airbus and Boeing manuals, they are simply probing your understanding of the systems as installed and operations of advanced naviagtion systems. I would not tell the Chief Pilot he was talking S,,,t, I would conceed I didn't know... simple as that. The concept using raw data as the primary source is not normal in airline transport operations.

There is nothing in any Boeing or Airbus manual I've ever seen that says you must meet an RNP criteria for conventional navaid based approaches, nor is there a regulatory requirement. And there's a very good reason for that. The two have absolutely nothing to do with each other.

Only if you are conducting an RNAV procedure (SID, STAR or Approach) are you required to comply with the RNP value for that procedure. Non-RNAV procedures have no RNP value to maintain because the procedure is done in reference to a navaid.

The two are mutually exclusive.

One is done with reference to the navaid only. And the other is done referencing the RNAV capability of the aircraft independent of ground based navigation aids.

Apple and oranges.


"The concept using raw data as the primary source is not normal in airline transport operations."

Are you suggesting airline transport operators never conduct ILS, VOR or NDB approaches then? Because raw data on all of those procedures is the primary source?

With respect to Avenger could you give references please?

The question specificly asks for ILS, VOR and NDB for which there are no RNP values required, anywhere in the world.

FE Hoppy:

It's a matter of FMS "overlay" authorization for VOR or NDB, not a RNP specification for the procedures in general.