Why is LPV not considered precision approach
- Thread starter WannFly
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MauleSkinner
Touchdown! Greaser!
because the definition of a precision approach isn't broad enough to make LPV a precision approach.
Brad Z
Final Approach
For technical reasons. Curious, does it operationally make a difference to you?
WannFly
Final Approach
It doesn’t , I am just curious of those technical reasons
More foolish compliance with ICAO.
Brad Z
Final Approach
How much would you like to learn about horizontal and vertical alert limits (HALs and VALs)?
Kristin
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It matters in Part 135 training and certification. If you are not near an ILS, you have to travel for training and checkrides as the LPV doesn't count for a precision approach, which seems to make no sense.
WannFly
Final Approach
I came across those in the GTN manual, but haven’t had a chance to look up the tech specs ... I will do some reading
MauleSkinner
Touchdown! Greaser!
Depends on the POI and the training program.
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tonycondon
Gastons CRO (Chief Dinner Reservation Officer)
Instrument Rating ACS clearly allows LPV to sub for the precision approach if the DA is below 300'...
MauleSkinner
Touchdown! Greaser!
Keep in mind that under 135, the training program determines what you can and can’t do...the ACS is just the standard for the maneuver.
labbadabba
Pattern Altitude
It does when determining your alternate
Brad Z
Final Approach
True, but not because it is or is not considered precision.
You are required to use non-precision minimums when planning an alternate because it is assumed that you are using the alternate without WAAS integrity, thus falling back to LNAV. See AC 90-107. The limitation is based on the technical standards order, and the legal prohibition on using LPV as a planned alternate is in your Flight Manual Supplement. The Garmin 530W flight manual supplement says the following: "It is not acceptable to flight plan a required alternate airport based on RNAV(GPS) LP/LPV or LNAV/VNAV approach minimums. The required alternate airport must be flight planned using an LNAV approach minimums or available ground-based approach aid."
If you read the definition of a precision approach versus non-precision approach in 14 CFR 1.1, a precision approach simply requires an electronic glide slope. If it weren't for the flight manual supplement limitation, you could use precision minimums for alternate planning. Conversely, even if ICAO considered APV to be a precision approach, it wouldn't change the flight manual supplement limitation.
Depends what you mean by "technical."
Currently, "Precision approach procedure means a standard instrument approach procedure in which an electronic glide slope is provided, such as ILS and PAR." The LPV is a calculated glide path not an electronic glide slope.
If you are wondering why the definition has not be adjusted, the answer is that they don't meet current ICAO standards for a precision approach. In what way don't they? It takes someone smarter and more interested than I to read ICAO Annex 10 requirements for precision approaches and find out.
Brad, that seems to assume the AFMS limitation is a manufacturer decision independent of the rules and guidance. I'm curious. Any support for that?
My assumption is the opposite; the AFMS limitation is because of the current guidance. For an example, there's the prohibition on using GPS as primary on a VOR or NDB approach. As soon as the FAA limitation went away, the FMS limitation was edited, with, AFAIK, the only change in the hardware, software or firmware being the removal of the warning.
Brad Z
Final Approach
My apologies, I've been out of the WAAS business for about 12 years, so it's been a while since I've tried to walk through this. It's actually not the TSO that drives the prohibition, it is the FAA policy on airworthiness approval of navigation systems, as described in AC 20-138 that drives the limitation. The point that I was trying to make is the regulatory hook is the requirement for an operator to abide by the aircraft flight manual. Basically the FAA tells manufacturers if you want to get your device certified, you have to to include that limitation.
See the following relevant parts of AC 20-138:
From 5-3.2(b)...
b. GPS/SBAS equipment that complies with the standards implemented by TSO-C145(AR)/C146(AR) does not have an equipment limitation for the aircraft to be equipped with other navigation systems appropriate to the operation. With GPS/SBAS equipment it is also acceptable to flight plan an alternate using an RNAV(GPS) approach to LNAV minimums at the alternate airport rather than a ground-based approach aid (see paragraph 15-7.1).
15-7.1 Limitations.
a. When installing equipment that uses GPS/SBAS for integrity during instrument meteorological conditions, there must be a performance limitation in the installation instructions (or equivalent installation documentation) for inclusion as a limitation in the AFMS/RFMS. This limitation must indicate the equipment has a performance limitation necessitating an alternate airport flight planning operational mitigation (see appendix 5 for an example). The Aeronautical Information Manual provides some operational flexibility regarding the flight planning operational mitigation for operators that also have baro-VNAV capability. Refer to paragraphs 1-1-18c.9 and 5-4-5m.7(h) in the Aeronautical Information Manual for specific operational guidance.
From appendix 5, sample flight manual...
<Limitation for all GNSS equipment:>
4. The TSO-C<insert number and revision> equipment has a performance limitation necessitating an alternate airport flight planning operational mitigation. In the U.S., refer to sections 1-1-17, 1-1-18, 1-2-3 and 5-4-5 in the Aeronautical Information Manual for specific operational guidance. In other states, refer to their operational guidance for RNAV(GNSS) approaches.
Kristin
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No, not really! The FSIMS, etc, make it pretty clear that any training program and ops specs are going to differentiate between precision and non-precision approaches. As the ILS is the only precision approach by definition, to include precision approaches in the ops specs, it has to be in the training program and the training program is going to require demonstration of the ability to fly the precision approach on a regular basis. Thus if you are an operator in a remote location that does not regularly go to an airport with an ILS, the training costs to add precision approaches to the ops specs can be prohibited. I ran into that in SE Alaska.
MauleSkinner
Touchdown! Greaser!
Most of the 135 training programs I deal with mirror the ACS with regard to allowing LPV to be considered a “precision approach” for training and checking purposes...we don’t have to do two ILSs, we can do one ILS and one LPV.
you are correct that if you’re authorized an approach type, it has to be demonstrated, but it has nothing to do with whether or not LPVs are precision approaches.
tonycondon
Gastons CRO (Chief Dinner Reservation Officer)
In our Training Manual, GPS w/Vertical Guidance is listed under Precision Approaches
Kristin
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Sometimes Alaska is its own thing, but usually they are more lenient than in the Lower 48. We would have had to fly about 170nm to demonstrate a precision approach, and that just didn't make financial sense. It certain did seem to have something to do with LPV's not be precision approaches as we could not demonstrate one routinely in a cost effective manner. In truth, if something unexpected happened with the weather and we needed to go to KTN as they only place open, we would just had done it on emergency authority. ad we been able to use the LPV as a stand-in for a precision approach, we would have gotten authority for it.
Kristin
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In our ops specs, it was listed under non-precision.
WannFly
Final Approach
even +V ?
MauleSkinner
Touchdown! Greaser!
+V isn’t considered an approach with vertical guidance.
Brad Z
Final Approach
+V is advisory vertical guidance--a feature from your avionics, not a type of approach. It is an LNAV procedure with your box giving you a vertical path to the visual descent point (VDP).
Kenny Phillips
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I though that the ground-based systems (LAAS) were going to replace the ILS, with a calculated but very accurate glideslope. But I've certainly not seen that.
Tarheelpilot
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Because it doesn’t have an electronic GS.
Brad Z
Final Approach
FAA dropped the term LAAS about a decade ago, and went with the ICAO term GBAS. There are some GLS approaches at Newark and Houston, probably a bunch in Europe too.
Interesting that there’s very little cross-over between GBAS and SBAS with heavy commercial ops versus GA. The only explanation I ever got was that operators of Boeing and Airbus equipment rarely operate at airports not fully supported by ILS. Already being RNAV equipped, WAAS offers nothing that the heavies aren’t already capable of. GBAS is of interest because it offers the promise of CAT 2 and CAT 3 approaches; something WAAS LPV will never be able to accomplish.
tspear
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Timothy
aterpster
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aterpster
Unlike an ILS, LPV is not monitored.
Aha! That makes sense. One of those things that affects the use of even an ILS for alternate planing.
Brad Z
Final Approach
FAA-Federal Aviation Administration
ICAO-International Civil Aviation Organization
ILS- Instrument Landing System
WAAS- Wide Area Augmentation System
LPV- Localizer Performance with Vertical Guidance
LAAS- Local Area Augmentation System (term no longer used)
GBAS- Ground Based Augmentation System (same thing as LAAS)
GLS- GBAS Landing System (ground based equivalent of an RNAV (GPS) LPV approach)
SBAS- Satellite based augumentation system (ICAO term for WAAS)
CAT 2 and 3 approaches: my shorthand, it's actually CAT-I and CAT-II. The typical ILS approach you or I fly is a CAT-I precision approach. CAT-II and CAT-III get you even lower DA and visibility requirements. CAT-III basically requires auto-land capability.
For more on GBAS, check out FAA's FAQs.
Brad Z
Final Approach
Physics. The inherit time-to-alert is much greater for WAAS than GBAS. For a GPS signal correction to take place, the WAAS reference station (WRS) receives the GPS signal, compares the calculated GPS location with it's known location, transmits the correction to the WAAS Master Station (WMS), which is sent to the Ground Uplink Station, combined with data from other WMS, transmitted to a WAAS satellite 22,000 miles away in geostationary orbit. The satellite rebroadcasts the message in a format your WAAS receiver can pick up.
In contrast, GBAS has a few reference stations located on the airport, transmitting corrections to a single computer which transmits the corrections on a VHF frequency to the aircraft. There is much less processing and data transmission taking place, so the GBAS receiver is alerted to integrity issues sooner, a necessity the faster and closer your are to the ground.
Larry in TN
En-Route
I've flown the GLS approaches at both EWR and IAH. Works just like an ILS. I've never had the opportunity to fly an LPV.
tspear
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Timothy
I am curious how much is transmission lag vs computing lag; especially with how much computing capacity has continued to push forward. I wonder how much the time delta is legacy thought process vs modern reality.
Considering the impact speed with the runway on a cat 2/3 landing; and the plane is in a stable approach, what is an "acceptable" error time and how does that affect the landing height?
Tim
Basically the same thing as an ILS. It’s nice because you can fly to a podunk airport and go down to ILS mins.
Ryan F.
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Ryan Ferguson 1974
Eureka. Thanks for sharing that. I hadn't connected the dots on that one.
Nathan Miller
Pre-takeoff checklist
Instrument noob here. Hi. What does monitoring an ILS mean? What are the operational considerations for flying a non-monitored ILS?
My home field (HEF - Manassas, VA) recently had the tower hours cut back to 8a-4p with a slew of accompanying notams. One of which is a notam stating the ILS is not monitored from 4p - 8a.
I'd ask my CFII, but the state ended my IFR training since I only bore holes in the sky recreationally.
It also begs the question - if the ILS is only monitored by tower personnel, who monitors the ILS at non towered fields? Arg. So confused.
That means there's some device that's verifying the integrity of the signal that will notify ATC (and then the pilot) when the system is out of limits. With LPV, your GPS receiver determines the integrity as you are receiving it.
Well strictly, it means little to you other than you need to be careful flying that ILS. However, what will usually happen with unmonitored navaids is they'll be publicized or notam'd against being usable for designation as an alternate. Note that the "alternate" rules are purely a filing/fuel planning exercise. If you can't make your destination for whatever reason, it's the discretion of the pilot where to go instead.
The monitor can be remote to a nearby ATC facility such as the overlying approach control. If it's not monitored, again, that doesn't mean it's unusable, but typically blocked from being a designated alternate.