B787 required RNAV Equipment for RNAV (GNSS) apchs?

[AlphaFloor27]

Hello guys, please take the following scenario, flying a commercial jetliner (A320, B787, etc):

While on IMC conditions, you are cleared for an RNAV GNSS APCH, and you lose one of the two GPS receivers; are you allowed to initiate the approach? What if the failure comes after crossing the IAF? And what if it happens after the FAP? Same initial scenario, but this time the Pilot Monitoring loses his PFD or ND, can you begin and continue the approach no matter what? Should I fly a conventional approach?

From my perspective, losing one part of a redundant system for an operation like this is no reason to discontinue the approach, but some fellow pilots tend to think that you need two of everything to begin and continue this kind of approach, so it has me wondering...

Back when I used to fly the A320, there was a very clear list on the FCOM of what onboard equipment must be functional depending of the type of RNAV operation (RNAV 10, RNAV 5, RNP 1, RNAV GNSS, etc). So, in case you were doing an RNAV GNSS apch in IMC and there was some kind of system failure, you knew exactly if that would lead to a go-around or you could just continue using the rest of the equipment.

I fly the B787 now, and I haven't been able to find anything in its manuals that states what is the minimun equipment depending on the type of RNAV/RNP operation. The only thing that I have found that relates to this is the "Instrument Approach - RNAV (RNP) AR" Supplementary Procedure that clearly states the required equipment to begin an RNAV (RNP) AR approach, but again, I haven't found anything on RNAV GNSS, RNP 1, RNAV 5, etc.

I know that for all aircraft types this requirements must come from a "higher" document, so far I have been reading the ICAO DOC 9613 PBN Manual, but haven't found anything as clear cut as that A320 FCOM list. I know I may be asking too much from an ICAO document.

The question is this, does anyone know where to find the required onboard equipment for an RNAV GNSS apch on a B787?

Cheers.

[Cough]

FCTM - Section 5 - Non ILS approaches - Non ILS Approaches (General) - Approach requirements relating to RNP...

There is not a lot there though! But that's (for me!) the beauty of Boeing vs the Bus...

[CaptainSouth]

787 QRH
RNP APCH LNAV VNAV Approaches
Required Airplane Equipment
2 PFD/MFD Displays

[Hofmeister]

Many airlines have asked Boeing to provide details of equipment required to operate in the various specifications of PBN. The latest edition of the 777 DDG includes an appendix detailing the equipment required for each specification. My understanding is that the equipment requirements only apply prior to commencing the approach - I expect it can be surged whether commencement is at the IAF or FAF. Once the approach is started the critical factor is whether or not the aircraft can maintain the RNP. Even on an RNP AR Approach it is permissible to continue IMC even after the loss of both GPS, until the aircraft can no longer be assured to be within the 1 x RNP containment. On Boeing aircraft this is annunciated by the UNABLE RNP EICAS message, and if still IMC would require a go around.

[AlphaFloor27]

787 QRH
RNP APCH LNAV VNAV Approaches
Required Airplane Equipment
2 PFD/MFD Displays

My company's 787 QRH does not have that chapter.

Thank you all for your responses.

[Long Haul]

RNAV (GNSS) or RNP pre-approach reqmts are in the Normal Procedures - amplified procedures section of the FCOM (21.47 in mine) and you can find RNP 1 and 4 reqmts in the Limitations section.

[Smythe]

Depends on the level of RNP.

Here is a Boeing doc on the equipage. https://www.boeing.com/commercial/aeromagazine/articles/2011_q4/5/

Within the design parameters, some losses are accounted for, such as GPS signal where the IRS can handle the drift until you get to the respective containment level.

ICAO doc ref pages 21 for equipage req for RNP 0.3 and below (I believe it is the same req for RNP 0.5)
https://www.icao.int/SAM/eDocuments/11PBN%20AC%2091-009%20RNP%20AR%20APCH%20eng.pdf

Single point of failure.- No single point of failure can cause the loss of guidance compatible with the RNP value of the approach.
Typically, the aircraft must have at least the following equipment:
1) two GNSS sensors;
2) two FMS;
3) two air information systems;
4) two AP; and
5) one inertial reference unit (IRU).

b) Design assurance.- The system design assurance must be consistent with at least a severe or major failure condition due to loss of lateral or vertical guidance during an RNP AR APCH where an RNP value of less than 0.3 is required to avoid obstacles and terrain while executing an approach. Note.- The loss of lateral guidance display during RNP AR APCH operations that require an RNP value of less than 0.3 to avoid obstacles or terrain is considered as a hazardous (severe or major) failure condition.
The AFM shall document designated systems that are consistent with this effect. This documentation shall describe the specific configuration of the aircraft or the mode of operation to obtain RNP values of less than 0.3. Compliance with this requirement may replace the general requirement for the two pieces of equipment described above.


Page 29: Failure on approach.- The operator contingency procedures must cover at least the following conditions: (a) RNP system components failures, including those affecting lateral and vertical deviation performance (e.g., failures of GPS sensors, AP or FD). (b) Loss of navigation signal-in-space (loss or degradation of external signal).

Your airline would have had to apply for operational approval to fly RNP procedures, so they should be describing how to handle equipage failures.

[aterpster]

Even on an RNP AR Approach it is permissible to continue IMC even after the loss of both GPS, until the aircraft can no longer be assured to be within the 1 x RNP containment. On Boeing aircraft this is annunciated by the UNABLE RNP EICAS message, and if still IMC would require a go around.
Unless you have at least one IRU, you cannot commence an RNP AR approach if any approach segment has an RNP of less than 0.30, and/or a missed approach of less than RNP 1.0 (i,e, "telescoping" missed approach") If you lose both GPS sources, and don't have at least one IRU, you should receive an "Unable RNP" alert, which requires a missed approach at that time. And, continuing an RNP AR approach to a line of minima less than 0.30, without at least one GPS source should result in "Unable RNP" before you get to DA.

RNP AR approaches in terrain-rich airspace are not to be taken lightly when some of the "belts and suspenders" are inoperative.

Some flight management systems cannot continue an RF leg with loss of GPS and no IRU. That wouldn't be fun time in the final segment of KBIH RNP AR Runway 30.


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/871x1500/kbih_rnp_rwy_30_0ef3cd873bcf4adcfada3be18fe00240cf730f78.jpg

[AlphaFloor27]

RNAV (GNSS) or RNP pre-approach reqmts are in the Normal Procedures - amplified procedures section of the FCOM (21.47 in mine) and you can find RNP 1 and 4 reqmts in the Limitations section.


Our FCOM’s Amplified normal procedures only state that one should verify the RNP as needed, nothing more.

[AlphaFloor27]

Depends on the level of RNP.

Here is a Boeing doc on the equipage. https://www.boeing.com/commercial/aeromagazine/articles/2011_q4/5/

Within the design parameters, some losses are accounted for, such as GPS signal where the IRS can handle the drift until you get to the respective containment level.

ICAO doc ref pages 21 for equipage req for RNP 0.3 and below (I believe it is the same req for RNP 0.5)
https://www.icao.int/SAM/eDocuments/11PBN%20AC%2091-009%20RNP%20AR%20APCH%20eng.pdf

Single point of failure.- No single point of failure can cause the loss of guidance compatible with the RNP value of the approach.
Typically, the aircraft must have at least the following equipment:
1) two GNSS sensors;
2) two FMS;
3) two air information systems;
4) two AP; and
5) one inertial reference unit (IRU).

b) Design assurance.- The system design assurance must be consistent with at least a severe or major failure condition due to loss of lateral or vertical guidance during an RNP AR APCH where an RNP value of less than 0.3 is required to avoid obstacles and terrain while executing an approach. Note.- The loss of lateral guidance display during RNP AR APCH operations that require an RNP value of less than 0.3 to avoid obstacles or terrain is considered as a hazardous (severe or major) failure condition.
The AFM shall document designated systems that are consistent with this effect. This documentation shall describe the specific configuration of the aircraft or the mode of operation to obtain RNP values of less than 0.3. Compliance with this requirement may replace the general requirement for the two pieces of equipment described above.


Page 29: Failure on approach.- The operator contingency procedures must cover at least the following conditions: (a) RNP system components failures, including those affecting lateral and vertical deviation performance (e.g., failures of GPS sensors, AP or FD). (b) Loss of navigation signal-in-space (loss or degradation of external signal).

Your airline would have had to apply for operational approval to fly RNP procedures, so they should be describing how to handle equipage failures.

Thanks you for the links. I’ll start digging through those FAA ACs.

Totally agree with your last sentence, but unfortunately, that piece of information seems to be missing from our Manuals.

[oggers]

I fly the B787 now, and I haven't been able to find anything in its manuals that states what is the minimun equipment depending on the type of RNAV/RNP operation. The only thing that I have found that relates to this is the "Instrument Approach - RNAV (RNP) AR" Supplementary Procedure that clearly states the required equipment to begin an RNAV (RNP) AR approach, but again, I haven't found anything on RNAV GNSS, RNP 1, RNAV 5, etc.....From my perspective, losing one part of a redundant system for an operation like this is no reason to discontinue the approach, but some fellow pilots tend to think that you need two of everything to begin and continue this kind of approach, so it has me wondering...

Ok so first you have to disitnguish between ordinary RNAV, and RNAV (RNP) type appropaches. See this link and its sidebar (https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/factsheets/media/RNAV_QFSheet.pdf)

The original question was: what equipment is required for an RNAV (GNSS) apch, Notwithstanding what is in your company ops manual, the bottom line is you only need ONE receiver for the RNAV (GPS/GNSS) apch (ie the vast majority of RNAV approaches curently out there).

It is for the Authorisation Required (AR) type approaches that you require extra training, redundancy and approval. Confusingly, whilst all RNAV approaches are now technically RNP, if you see (RNP) in the title of the plate that means it is actually an AR type approach. Eg "RNAV (GPS)" is a bog standard RNP approach, whilst "RNAV (RNP)" is an AR type approach. Quite how the authorities made such a pig's ear of the terminology is a mystery to me. If your company is approved for AR approaches you will have done the extra training that spells out what you need when carrying out an "RNAV (RNP)" approach (in other words, an Authorisation Required approach) in your specific aircraft.

[8che]

Oggers is about there.

RNAV (GNSS) only requires one GPS. An RNAV with out the GNSS label can be done without GPS at all as long as ANP is within limits.

Only RNP AR approaches require 2 GPS on commencement of approach. If they fail after the approach has started then you may continue until NAV UNABLE RNP occurs.

To correct Oggers slightly, there are RNAV approaches, RNP approaches and RNP AR approaches. RNAV and RNP approaches are essentially the same but an RNP approach requires an on board monitoring and alert system.

The labelling is really poor.

RNAV RW23
RNAV (GNSS) RW23
RNP RW23
RNAV (RNP). RW23