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RNAV (GNSS)

Old 29th Nov 2014, 12:06
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No. It is considered to be a NPA. Because the visual segment area does not have significant obstacle penetrations, it does have what the FAA calls a vertical descent angle (VDA). But, the VDA is advisory; does not meet APV criteria. If it were an APV, there would be an LNAV/VNAV line of minimums.
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Old 29th Nov 2014, 12:58
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Thanks, an other question:
RNAV (GPS) do not require a specific RNP (eg. 0.3). On my AOC I' m authorized to operate down to RNP 0.3 but we are not authorized for RNP approaches ( coded RNAV(RNP) ).
Where can I use my RNP 0.3 ??
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Old 29th Nov 2014, 13:34
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Topper80:

Thanks, an other question:
RNAV (GPS) do not require a specific RNP (eg. 0.3). On my AOC I' m authorized to operate down to RNP 0.3 but we are not authorized for RNP approaches ( coded RNAV(RNP) ).
Where can I use my RNP 0.3 ??
I can only speak for the US. LNAV and LNAV/VNAV are RNP 0.3, but the lateral obstacle clearance areas are larger than RNP AR 0.30, and don't require the avionics redundancy required for RNP AR.

Then, we also have LPV and LP, which are predicated on SBAS augmentation. Western Europe is also doing SBAS augmentation.
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Old 29th Nov 2014, 13:53
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No. It is considered to be a NPA.
The latest ICAO concept that has reached us, 2D and 3D approaches, has NPAs that are flown with an FMS-derived approach path may be classed as a 3D approach. It won't have a DA, so it's up to the operator to not go below the MDA.

Last edited by Capn Bloggs; 30th Nov 2014 at 22:11. Reason: Reference to "Precision" removed at Peekay's suggestion later down the page.
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Old 29th Nov 2014, 14:40
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Captain Bloggs:

The latest ICAO concept that has reached us, 2D and 3D approaches, has NPAs that are flown with an FMS-derived approach path may be classed as a 3D ie "precision" approach. It won't have a DA, so it's up to the operator to not go below the MDA.
Be that as it may be, FAA flight inspection is continuing to remove or not accept VDAs on many NPAs in the U.S. If the runway doesn't have an APV there are obstacle issues in the visual segment. If flight inspection judges them significant the VDA is removed (or disapproved on new NPAs, such as LP and LNAV), thus there will be no vertical path such NPAs in the FMS.
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Old 29th Nov 2014, 14:50
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Underfire:

RNP-AR with a single GPS.?
As you know the missed approach segment is often not critical. The only clue the pilot has is when the chart states RNP of less than 1.0 is required for the missed approach.

Since Rifle, Colorado Runway 8 has been an example of low minimums but not a critical missed approach (other than climb performance) here is a more "terpsy" look at RNAV Z Runway 26. The missed approach is critical. By continuing past the FAF with one GPS receiver, the odds of having to conduct an IRU coasting missed approach are certainly increased significantly; probably reducing the target level of safety below the presumed value for this IAP.

I have pasted the missed approach "telescoping" values on the Jepp chart, followed by the actual FAA TERPS map. Not a friendly environment for coasting on IRU(s).



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Old 30th Nov 2014, 16:34
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RNAV (GPS) Y 08
Minima in only LNAV, not LNAV/VNAV: is consider anyway to be a APV approach?
An APV approach will always list a DA instead of an MDA, so that's an easy way to tell if the approach is considered an APV or an NPA.

Currently the only APV approaches are: LNAV/VNAV, LPV and RNP.

The latest ICAO concept that has reached us, 2D and 3D approaches, has NPAs that are flown with an FMS-derived approach path may be classed as a 3D ie "precision" approach. It won't have a DA, so it's up to the operator to not go below the MDA.
That's not exactly right. Some countries are operating with a special waivers / ops specs / procedures allowing approved operators flying certain NPA approaches using Continuous Descent Final Approach (CDFA) to treat MDA as DA. Under this procedure the operator may actually descend below the published MDA during a missed approach.

However such an approach is still not considered a "precision approach" under ICAO definition. Currently only ILS, MLS and GLS approaches meet the criteria for "precision approach".
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Old 30th Nov 2014, 17:21
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Under this procedure the operator may actually descend below the published MDA during a missed approach.
This surprises me and I find it hard to believe. Why don't they just add 50ft like they do in NZ and Australia if they are going to treat an MDA as a DA?
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Old 30th Nov 2014, 18:15
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This surprises me and I find it hard to believe. Why don't they just add 50ft like they do in NZ and Australia if they are going to treat an MDA as a DA?
The point is to reduce minimums when safe practices allow it.

Examples:

1. FAA OpSpec C073 VNAV MDA as DA:

"The certificate holder is authorized to use minimum descent altitude (MDA) as a decision altitude (DA)/decision height (DH) with vertical navigation (VNAV) on a Nonprecision Approach (NPA)."

8900.183 - OpSpec/MSpec/LOA C073, Vertical Navigation (VNAV) Instrument Approach Procedure (IAP) Using Minimum Descent Altitude (MDA) as a Decision Altitude DA)/Decision Height (DH) ? Document Information

2. Transport Canada Special Exemption from 602.128(2)(b)

"The purpose of this exemption is to permit pilots-in-command of IFR aircraft operated by holders of an air operator certificate or a temporary private operator certificate to descend below the minimum descent altitude (MDA), when conducting a non-precision approach ... following a stabilized constant descent angle (SCDA) non-precision approach."

EXEMPTION FROM PARAGRAPH 602.128(2)(b) OF THE CANADIAN AVIATION REGULATIONS - Transport Canada

(SCDA is the Canadian term for CDFA).
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Old 30th Nov 2014, 22:21
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Interesting stuff, PK. I've amended my earlier post re "precision".
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Old 1st Dec 2014, 01:05
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Peekay4,
Thanks for posting that.
It's interesting how different regulators around the world view different subjects and what they are willing to provide exemptions for.
I understand that the lower the minima the better commercially but can't ever imagine our regulators " down under" being willing to sign off on certain operators descending below MDA even if it is just 50 feet or so.
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Old 2nd Dec 2014, 07:33
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mel question

I found that this is in my opinion is the best place to ask the question because it seems that the real experts are here.

Two weeks ago during a ramp check the only complaint they had was on the RNAV subject and the complaint was that we didnt specific which systems (DME, VOR and GPS) affect the navigation and any combination in between. Is this the way your MEL written/deigned ?
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Old 5th Dec 2014, 01:21
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Short answer is "within half-scale deflection" of the CDI.

Generally, to be established on a segment implies all of the below:

1. You've passed the segment's defining fix
2. You are receiving "positive course guidance" (PCG) from the navigation system
3. You are within half-scale deflection on the CDI **
4. You are "stable" in the segment (i.e., with a positive trend to track the centerline)

** The "+/- 5 degrees" is mostly for NDBs (since there's no CDI).
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Old 5th Dec 2014, 02:03
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Have you met all four criteria listed above? (Including #1)

If not, you're not established.

You have to be within half-scale of the centerline defining the segment your are joining, not your route to the segment.
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Old 5th Dec 2014, 02:53
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Hmm, sorry, I have to take back some of I wrote above.

For RNAV and RNP:

1. Instead of "half-scale deflection", the guidance for established is: "An aircraft is considered to be established on-course during RNAV and RNP operations anytime it is within 1 times the required accuracy for the segment being flown." (The scale will depend on your FMS but this seems to imply full-scale deflection).

2. Instead of waiting to "pass" the segment's defining fix, the exact standard is: "(a) Pilots flying FMS equipped aircraft with barometric vertical navigation (Baro-VNAV) may descend when the aircraft is established on-course following FMS leg transition [to the next segment]. Leg transition normally occurs at the turn bisector for a fly-by waypoint [...] (b) Pilots flying TSO-C129 navigation system equipped aircraft without full automation should use normal lead points to begin the turn. Pilots may descend when established on-course on the next segment of the approach."

The italicized quotations are from revised FAA AIM 5-5-16. RNAV and RNP Operations:

https://www.faa.gov/air_traffic/publ...m/aim0505.html

Last edited by peekay4; 5th Dec 2014 at 03:11.
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Old 5th Dec 2014, 13:55
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There is another part of the AIM which discusses passing the bisector of a course change to be considered in the succeeding segment of an IFP.

That's how the avionics work.
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Old 8th Dec 2014, 23:11
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Be that as it may be, FAA flight inspection is continuing to remove or not accept VDAs on many NPAs in the U.S. If the runway doesn't have an APV there are obstacle issues in the visual segment. If flight inspection judges them significant the VDA is removed (or disapproved on new NPAs, such as LP and LNAV), thus there will be no vertical path such NPAs in the FMS.
What do they achieve by doing this?

The whole point of providing VDA's is to give those without FMS's a flighting chance of flying a stable approach, and those with FMS's the ability to use vertical guidance...which according to ICAO is more safe.

Have they not just increased the risk of instability on the approach?

There are other ways to deal with obstacles in the visual segment. Removing the VDA is a poor option.

Alpha
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Old 8th Dec 2014, 23:25
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There are other ways to deal with obstacles in the visual segment. Removing the VDA is a poor option.
I review every FAA IFP as they are posted for public review. It appears that it is flight inspection that removes them, not the initial designers.

The FAA position is that the airport either remove the 20:1 penetration, or mitigation (sometimes) with a VGSI. But, when flight inspection doesn't like what they see for daytime operations the VDAs go.

I feel they are more concerned about FAA liability than safety.
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Old 9th Dec 2014, 00:15
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KRIL RNP based minima could safely still be even lower

The KRIL RNP based approach minima at RNP .1 could still safely be even lower, if the present obsolete and unnecessary limitations were removed that are still being placed on RNP procedure design. The fully allocated real VEB could easily provide for DA(H) down to and even somewhat below 200' HAT compared to the higher DA(H) shown for the RNAV(RNP) Z Rwy 8. The present 250' HAT floor limit was only put there for largely political reasons, not due to any technical limitation of engineering or physics. That potential additional advantage for RNP is particularly valid considering that any aircraft with RA available could also use an RA floor to additionally bound improbable to extremely improbable VNAV non-normal events. Unlike with TERPS or PANS-Ops, with [real] RNP, particular non-normal as well as rare-normal events are already suitably addressed and accommodated.
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Old 9th Dec 2014, 00:28
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Aterpster, I wasn't criticising you. I was just questioning the FAA logic

It would be interesting to know the logic and what they think they are achieving.
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