Rnp and Ils, Vor approaches
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An overlay approach shares the plate and minimums with the VOR or NDB procedure, but beyond that it has nothing to do with the VOR or NDB. If you do a GNSS overlay approach you are doing an RNAV approach, which you must be trained, equipped and authorized to do.
The actual VOR or NDB could have been dynamited into oblivion years before and it doesn't matter, because you aren't flying a VOR or NDB approach.
The actual VOR or NDB could have been dynamited into oblivion years before and it doesn't matter, because you aren't flying a VOR or NDB approach.
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Boeing FCTM Page 193 section on Non ILS Approaches and also the section relating to ILS approaches " Approach Requirements Relating To RNP" values are tabulated. Boeing are certified to use the FMS as primary source of naviagtion provided the RNP values are met.. Interesting stuff this..
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Right Avenger. Boeings, Airbus's, Embraers, Bombardier's, Gulfstreams, many aircraft are certified for RNAV operations. That doesn't mean the crews are though.
For commercial operations an operations specification must be obtained from the regulator before conducting any kind of RNAV approach, and that ops spec will not be issued unless the aircraft is certified and the crews are properly trained and checked on RNAV procedures.
What does any of that have to do with ILS, VOR or NDB approaches?
For commercial operations an operations specification must be obtained from the regulator before conducting any kind of RNAV approach, and that ops spec will not be issued unless the aircraft is certified and the crews are properly trained and checked on RNAV procedures.
What does any of that have to do with ILS, VOR or NDB approaches?
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engfireleft, an overlay approach is simply a normal RNAV approach, which uses a specified RNP.
Completely different from that however is the authorization to fly any non precision approach, without the need for any existing RNAV approach being published, by FMC guidance alone. The 737 FCOM even tells us about raw data monitoring during non ILS/GLS approaches "For airplanes with two operational FMC, two IRS and two GPS receivers (or two DME receivers if GPS updating is not available), or if the FMC is RNP/ANP capable, raw data monitoring is not required." Which means only one RNP/ANP capable FMC is enough to fly non precision approaches without using any raw data source related to the procedure. However we do have to keep within certain RNP limits, since we are no longer able to check with raw data if we are within the limits of the procedure.
Of course you need to train the crews for that, same as you train them to fly ILS, GLS or RNAV approaches.
The approach in itself does not have a RNP value, however if you are authorized to fly it without using raw data as primary means of navigation you most probably have to conform to a certain RNP. The values and certification process are of course something to check with both the local regulator and the OEM.
Completely different from that however is the authorization to fly any non precision approach, without the need for any existing RNAV approach being published, by FMC guidance alone. The 737 FCOM even tells us about raw data monitoring during non ILS/GLS approaches "For airplanes with two operational FMC, two IRS and two GPS receivers (or two DME receivers if GPS updating is not available), or if the FMC is RNP/ANP capable, raw data monitoring is not required." Which means only one RNP/ANP capable FMC is enough to fly non precision approaches without using any raw data source related to the procedure. However we do have to keep within certain RNP limits, since we are no longer able to check with raw data if we are within the limits of the procedure.
Of course you need to train the crews for that, same as you train them to fly ILS, GLS or RNAV approaches.
The approach in itself does not have a RNP value, however if you are authorized to fly it without using raw data as primary means of navigation you most probably have to conform to a certain RNP. The values and certification process are of course something to check with both the local regulator and the OEM.
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This is the confusion we have generated in the last 20 years by using the FMGS to fly non-precision approaches.
To reiterate: If you are flying a conventional non-precision approach i.e. LOC, VOR or NDB, then the navaid must be tuned, identified and displayed at all times and it is your primary reference.
We can and do use the FMGS for guidance, meaning using it to steer the airplane, but at all times the primary reference is the navaid stated in the procedure you are flying. That is a regulatory requirement everywhere in the world and there is no relief from that. If the raw data shows you going off track, then you have to do something different to bring it back. Nowhere do you reference RNP because your reference is the navaid.
If your only reference is the FMGC, then you are doing an RNAV approach and they all, without exception, have an RNP attached. Usually it is 0.3 for basic RNAV, but there are RNAV AR and RNP approaches that are more stringent. Conventional navaids are not part of the RNAV picture in any way with the exception of critical DME's in the case of RNAV 1 SID's and STAR's if your aircraft is not GPS equipped.
I can't make it any simpler than that. If you are doing an ILS, VOR or NDB the navaid is your primary reference and has to be there by regulation. The use of FMGC's for guidance in that case is a technique, but doesn't negate the requirement for the navaid.
To reiterate: If you are flying a conventional non-precision approach i.e. LOC, VOR or NDB, then the navaid must be tuned, identified and displayed at all times and it is your primary reference.
We can and do use the FMGS for guidance, meaning using it to steer the airplane, but at all times the primary reference is the navaid stated in the procedure you are flying. That is a regulatory requirement everywhere in the world and there is no relief from that. If the raw data shows you going off track, then you have to do something different to bring it back. Nowhere do you reference RNP because your reference is the navaid.
If your only reference is the FMGC, then you are doing an RNAV approach and they all, without exception, have an RNP attached. Usually it is 0.3 for basic RNAV, but there are RNAV AR and RNP approaches that are more stringent. Conventional navaids are not part of the RNAV picture in any way with the exception of critical DME's in the case of RNAV 1 SID's and STAR's if your aircraft is not GPS equipped.
I can't make it any simpler than that. If you are doing an ILS, VOR or NDB the navaid is your primary reference and has to be there by regulation. The use of FMGC's for guidance in that case is a technique, but doesn't negate the requirement for the navaid.
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enginefireleft:
You, and Denti in the post immediately above your's, are in direct contradiction. My vote goes with Denti.
I can't make it any simpler than that. If you are doing an ILS, VOR or NDB the navaid is your primary reference and has to be there by regulation. The use of FMGC's for guidance in that case is a technique, but doesn't negate the requirement for the navaid.
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Ok, how about this?
Do you agree that an overlay approach is an RNAV approach? If yes, then:
Do you agree that if a VOR is unavailable but there is an overlay you can still fly the approach using the overlay (RNAV)? If so, then:
Do you agree that if the VOR is unavailable and there is no overlay, you may not fly the approach, since there is no RNAV procedure?
If you understand all that, and understand that an RNAV has as much relationship to a VOR approach as an ILS does, what is this discussion about? You can do RNAV, or ILS, or VOR, or NDB. You can't do a combination of them.
ILS requires a functioning ILS transmitter
VOR requires a functioning VOR transmitter
NDB requires a functioning NDB transmitter
and RNAV requires a specific navigation performance be met along with crew qualification etc.
Do you agree that an overlay approach is an RNAV approach? If yes, then:
Do you agree that if a VOR is unavailable but there is an overlay you can still fly the approach using the overlay (RNAV)? If so, then:
Do you agree that if the VOR is unavailable and there is no overlay, you may not fly the approach, since there is no RNAV procedure?
If you understand all that, and understand that an RNAV has as much relationship to a VOR approach as an ILS does, what is this discussion about? You can do RNAV, or ILS, or VOR, or NDB. You can't do a combination of them.
ILS requires a functioning ILS transmitter
VOR requires a functioning VOR transmitter
NDB requires a functioning NDB transmitter
and RNAV requires a specific navigation performance be met along with crew qualification etc.
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Sadly it is not as simple as that, and additionally a lot depends on local regulations. Lets think about some tiny airport out there that has only one IFR approach, lets say it is a VOR approach. No RNAV approach, no ILS, GLS or MLS.
Now, according to what we are allowed to use we would set up the VOR approach in the FMC and fly it using IAN which makes it look and act like an ILS, autopilot or not and flight director or not doesn't matter, i can fly it either way. However we do not tune the VOR as we are not required to do that, perhaps set up the approach for our alternate, or some nav aids used during the missed approach or simply forget about it all since we do not need to tune anything, we just have to make sure there is no ILS tuned, but that is simply an autoflight system restriction (approach mode would try to intercept the tuned ILS instead of the IAN approach if one is tuned).
The VOR on the ground has to be serviceable of course or ATC could not clear us for the approach. But we won't use it, except as backup, since all we need to fly the VOR approach is one FMC, and we got two of those. Now, how do we now that we are still within the limits of the approach? By using a generic RNP of 0.3 which is database coded into the approach. The approach in itself does not have any RNP, however if you want to fly it using the FMC as sole guidance you have to use an RNP and it is part of your companies approved procedures and therefore part of the AOC.
The need to tune, identify and display the navigation source for a non precision approach is not there anymore. That bit of legislation may not have reached your company or country yet, but it will. The aircraft we use are certified for it for quite some time now, the 737 since it turned into the NG.
Now, according to what we are allowed to use we would set up the VOR approach in the FMC and fly it using IAN which makes it look and act like an ILS, autopilot or not and flight director or not doesn't matter, i can fly it either way. However we do not tune the VOR as we are not required to do that, perhaps set up the approach for our alternate, or some nav aids used during the missed approach or simply forget about it all since we do not need to tune anything, we just have to make sure there is no ILS tuned, but that is simply an autoflight system restriction (approach mode would try to intercept the tuned ILS instead of the IAN approach if one is tuned).
The VOR on the ground has to be serviceable of course or ATC could not clear us for the approach. But we won't use it, except as backup, since all we need to fly the VOR approach is one FMC, and we got two of those. Now, how do we now that we are still within the limits of the approach? By using a generic RNP of 0.3 which is database coded into the approach. The approach in itself does not have any RNP, however if you want to fly it using the FMC as sole guidance you have to use an RNP and it is part of your companies approved procedures and therefore part of the AOC.
The need to tune, identify and display the navigation source for a non precision approach is not there anymore. That bit of legislation may not have reached your company or country yet, but it will. The aircraft we use are certified for it for quite some time now, the 737 since it turned into the NG.
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You don't need any FMG to fly the approach because you have the VOR.
If you use the RNP as sole guidance you are doing an RNAV approach, and must comply with all of the requirements therein.
You should probably get your hands on an ICAO PBN manual. It sounds to me like your company is doing RNAV approaches without RNAV approval and without complying with any RNAV requirements.
To use RNAV as a reference the approach must be encoded in the database as such, the tracks and distances must be checked, and nothing from the FAF in can be changed laterally for LNAV, or vertically if you're going to use VNAV. GNSS is required for any 0.3 approach (for now anyway) and RAIM must be confirmed before completing the procedure. There must also be an alerting function in the airplane that warns you when GPS is lost or the EPU exceeds the RNP for the approach.
Do you comply with any of this when you do your VOR approach using the FMGS as the only reference?
If you use the RNP as sole guidance you are doing an RNAV approach, and must comply with all of the requirements therein.
You should probably get your hands on an ICAO PBN manual. It sounds to me like your company is doing RNAV approaches without RNAV approval and without complying with any RNAV requirements.
To use RNAV as a reference the approach must be encoded in the database as such, the tracks and distances must be checked, and nothing from the FAF in can be changed laterally for LNAV, or vertically if you're going to use VNAV. GNSS is required for any 0.3 approach (for now anyway) and RAIM must be confirmed before completing the procedure. There must also be an alerting function in the airplane that warns you when GPS is lost or the EPU exceeds the RNP for the approach.
Do you comply with any of this when you do your VOR approach using the FMGS as the only reference?
Guys,
There exists a breach between the FAA and ICAO on this issue. Initially, when the FAA started the "GPS overlay" approvals, they required the underlying approach navaid to be tuned and monitored. This requirement went away in FAA World sometime ago, if the FMS meet TSO-specific requirements as an approach aid, the need to tune, monitor or even to have the underlying navaid was eliminated. The ICAO and EU countries, as I understand it, have kept the requirement to tune and display the underlying navaid, unless it is a RNAV approach.
In my plane, we can fly any NPA, using FMS approach, without the navaid tuned or displayed, as long as "APP" or "GPS APPR" is annunciated before the FAF. This is common in the US, but not so in many regulatory regimes.
This from FAA AC 90-94, 1994
This authorization is expressly limited to FAA regulated airspace. Also, the TERPs standard used to designed the approach was that for the ground-based navaid, not RNAV. So, one can fly a VOR approach, with approved equipment, as an FMS approach without use of the ground-based navaid in US airspace. It will not be an RNAV approach, it will be a VOR standard approach flown using FMS.
GF
There exists a breach between the FAA and ICAO on this issue. Initially, when the FAA started the "GPS overlay" approvals, they required the underlying approach navaid to be tuned and monitored. This requirement went away in FAA World sometime ago, if the FMS meet TSO-specific requirements as an approach aid, the need to tune, monitor or even to have the underlying navaid was eliminated. The ICAO and EU countries, as I understand it, have kept the requirement to tune and display the underlying navaid, unless it is a RNAV approach.
In my plane, we can fly any NPA, using FMS approach, without the navaid tuned or displayed, as long as "APP" or "GPS APPR" is annunciated before the FAF. This is common in the US, but not so in many regulatory regimes.
This from FAA AC 90-94, 1994
(1) Phase I. This phase ended in February 1994, the date when
the FAA declared GPS operational for civil operations.
(2) Phase II. This phase began on February 17, 1994 when the FAA
declared the system suitable for civil operations. Certified GPS
equipment can be used as the primary IFR flight guidance to fly an
overlay to an existing nonprecision approach without actively
monitoring the applicable navaid(s) which define the approach being
used. However, the underlying ground-based navaid(s) required for the
published approach must be operational and the associated avionics
must be installed and operational. The avionics need not be operating
during the approach if RAIM is providing integrity. Pilots can tell
that Phase II applies because "GPS" is not included in the title of
the approach.
(3) Phase III. Phase III began April 28, 1994, when the first
instrument approach procedures were published to include "or GPS" in
the title of the published approach procedure. Neither the aircraft
traditional avionics nor the underlying ground station navaid(s) need
be installed, operational, or monitored to fly the nonprecision
approaches at the destination airport. For GPS systems that do not use
RAIM for integrity, the ground-based navaid(s) and the airborne
avionics that provide the equivalent integrity must be installed and
operating during the approach. For any required alternate airport, the
traditional ground-based and airborne navigational equipment that
defines the instrument approach procedure and route to the alternate
must be installed and operational.
the FAA declared GPS operational for civil operations.
(2) Phase II. This phase began on February 17, 1994 when the FAA
declared the system suitable for civil operations. Certified GPS
equipment can be used as the primary IFR flight guidance to fly an
overlay to an existing nonprecision approach without actively
monitoring the applicable navaid(s) which define the approach being
used. However, the underlying ground-based navaid(s) required for the
published approach must be operational and the associated avionics
must be installed and operational. The avionics need not be operating
during the approach if RAIM is providing integrity. Pilots can tell
that Phase II applies because "GPS" is not included in the title of
the approach.
(3) Phase III. Phase III began April 28, 1994, when the first
instrument approach procedures were published to include "or GPS" in
the title of the published approach procedure. Neither the aircraft
traditional avionics nor the underlying ground station navaid(s) need
be installed, operational, or monitored to fly the nonprecision
approaches at the destination airport. For GPS systems that do not use
RAIM for integrity, the ground-based navaid(s) and the airborne
avionics that provide the equivalent integrity must be installed and
operating during the approach. For any required alternate airport, the
traditional ground-based and airborne navigational equipment that
defines the instrument approach procedure and route to the alternate
must be installed and operational.
GF
Last edited by galaxy flyer; 21st Jan 2011 at 19:14.
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The ICAO and EU countries, as I understand it, have kept the requirement to tune and display the underlying navaid, unless it is a RNAV approach.
Of course you can fly it using the old fashioned procedures by tuning the VOR, calculating your rate of descent (drive and dive is not allowed anymore) and flying it in VORLOC using V/S. But that is not necessary anymore of course. And of course we are certified for RNPs down to 0.3 with either GPS or only DME/DME and down to CAT I (currently flying CAT IIIb tests) using GBAS or anything inbetween.
Last edited by Denti; 21st Jan 2011 at 20:16.
Zeffy
Yes, it was and AC 90-105 doesn't address the issues of AC 90-94 directly, but state, "However, previous approvals under these two ACs (AC 90-94 and AC 90-97) are still valid for the operations and conditions stated."
I posted the reference to point out the historical background as to how the use of GPS and FMS evolved.
GF
Yes, it was and AC 90-105 doesn't address the issues of AC 90-94 directly, but state, "However, previous approvals under these two ACs (AC 90-94 and AC 90-97) are still valid for the operations and conditions stated."
I posted the reference to point out the historical background as to how the use of GPS and FMS evolved.
GF
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1. In which european countries exactly is it allowed to fly VOR or NDB approaches without referring to the basic navaid? (assuming FMGC is certified to fly NPAs in nav mode)
2. Even if what Denti says is right, the instructor mentioned RNP for ILS approaches as well, so I don' t think all these make any sense.
My vote goes for engfireleft
2. Even if what Denti says is right, the instructor mentioned RNP for ILS approaches as well, so I don' t think all these make any sense.
My vote goes for engfireleft
There is simply no way RNP relates to ILS. Unless one forces the issue and tries to apply RNP calculations to LOC accuracy, a bit like calling MNPS RNP 12.6. If track spacing works out to a bit under 60 nm, then 95% of the time the plane must be within 12.6 nm of actual position because it must be within 60nm 99% of the time.
GF
GF
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Now I'll agree with you there, Avenger!
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Changer, I am not sure how autoland has creeped into this thread, as you are aware, not all ILS end in autoland, are you suggesting the aircraft cannot land without a traditional Glide slope and localiser signal? Our caompany procedure is to fly all approaches using the FMS as the primary source of nav if the RNP is achieved and " where available, monitor raw data" , this is referred to in the Boeing FCTM. I believe, Avenger was referring to the orignal question, and the fact that generally, it is not a good idea to tell the interviewer they are talking rubbish, when clearly, as demonstrated by the answers here, he/she had a vaild question.
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kitks gusset:
Because you state "fly all approaches using FMS as the primary source..." does this include ILS? If so, what do you use to replace the ILS glideslope?
Our caompany procedure is to fly all approaches using the FMS as the primary source of nav if the RNP is achieved and "where available, monitor raw data"
Because you state "fly all approaches using FMS as the primary source..." does this include ILS? If so, what do you use to replace the ILS glideslope?
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"Our caompany procedure is to fly all approaches using the FMS as the primary source of nav if the RNP is achieved and " where available, monitor raw data" , this is referred to in the Boeing FCTM."
If you are conducting an approach using the FMS as the primary source of navigation you are doing an RNAV approach. The requirements for doing those are pretty much universal and becoming more refined as time goes along and the world converts to PBN. You're suggesting your company does conventional NPA's and if the signal is not available, no problem, we'll just use the FMS.
If you don't mind my asking, what country is your company based in? Also if you don't mind saying what company is it?
If you are conducting an approach using the FMS as the primary source of navigation you are doing an RNAV approach. The requirements for doing those are pretty much universal and becoming more refined as time goes along and the world converts to PBN. You're suggesting your company does conventional NPA's and if the signal is not available, no problem, we'll just use the FMS.
If you don't mind my asking, what country is your company based in? Also if you don't mind saying what company is it?
I beg to differ, engfireleft, if the approach is on a ground-based navaid (for the pendants: VOR, VOR/DME, TACAN, NDB, that is non-LOC) it is an FMS approach flying an overlay. The approach is drawn to TERPS, PANS-OPS standards for the terrestrial navaid, not to RNAV or RNP standards. There is no specified RNP because it is a conventional approach flown on the FMS. the crew must be trained appropriately, the database current and used. The Canadian-built and trained business aircraft is flown and trained thusly.
GF
GF