LPV approaches

[SbestCFII]

You'll occasionally see minimal ILS systems without an approach lighting system.

 

[RotorDude]

You'll occasionally see minimal ILS systems without an approach lighting system.

Presumably that will have a significant penalty in DH and/or mins?

 

[SbestCFII]

Yes - LPV approaches are considered precision approaches. Precision approaches provide a means of "approved vertical guidance" to a defined DA. AC 90-107, 4-B states:

"Approved Vertical Guidance. Actual vertical path deviation guidance indications generated by certified means for charted approach procedures that contain a U.S. Standard for Terminal Instrument Procedures (TERPS)-protected glidepath (e.g., approaches with LNAV/VNAV, LPV or ILS lines of minima)."

Therefore, each of these approach types meet the standards for precision approaches, provided of course that the required level of navigation accuracy is annunciated by the box at the time that the approach is being flown.

 

[John Collins]

Yes - LPV approaches are considered precision approaches. Precision approaches provide a means of "approved vertical guidance" to a defined DA. AC 90-107, 4-B states:

"Approved Vertical Guidance. Actual vertical path deviation guidance indications generated by certified means for charted approach procedures that contain a U.S. Standard for Terminal Instrument Procedures (TERPS)-protected glidepath (e.g., approaches with LNAV/VNAV, LPV or ILS lines of minima)."

Therefore, each of these approach types meet the standards for precision approaches, provided of course that the required level of navigation accuracy is annunciated by the box at the time that the approach is being flown.

Scott, this is a quote from the AIM, 1−1−19. Wide Area Augmentation System
(WAAS):

b. Instrument Approach Capabilities
1. A new class of approach procedures which provide vertical guidance, but which do not meet the ICAO Annex 10 requirements for precision approaches has been developed to support satellite navigation use for aviation applications worldwide. These new procedures called Approach with Vertical Guidance (APV), are defined in ICAO Annex 6, and include approaches such as the LNAV/VNAV procedures presently being flown with barometric vertical navigation (Baro−VNAV). These approaches provide vertical guidance, but do not meet the more stringent standards of a precision approach. Properly certified WAAS receivers will be able to fly these LNAV/VNAV procedures using a WAAS electronic glide path, which eliminates the errors that can be introduced by using Barometric altimetery.

2. A new type of APV approach procedure, in addition to LNAV/VNAV, is being implemented to take advantage of the high accuracy guidance and increased integrity provided by WAAS. This WAAS generated angular guidance allows the use of the same TERPS approach criteria used for ILS approaches. The resulting approach procedure minima, titled LPV (localizer performance with vertical guidance), may have a decision altitude as low as 200 feet height above touchdown with visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest minima. LPV minima is published on the RNAV (GPS) approach charts (see paragraph 5−4−5, Instrument Approach Procedure Charts).

 

[azure]

John,

I gather from that quote that LNAV/VNAV is not quite as precise as LPV although it does have vertical guidance. How precise is LNAV/VNAV, what kind of accuracy guidance does it have, both horizontal and vertical? Also, is the 480 with software revision 2.3 capable of flying LNAV/VNAV approaches? I think I recall that it is, and that the only new WAAS-enabled mode it wasn't capable of prior to 2.3 was LP, but I'm not certain of that.

I'm wondering why you didn't also highlight this part:

2. A new type of APV approach procedure, in addition to LNAV/VNAV, is being implemented to take advantage of the high accuracy guidance and increased integrity provided by WAAS. This WAAS generated angular guidance allows the use of the same TERPS approach criteria used for ILS approaches. The resulting approach procedure minima, titled LPV (localizer performance with vertical guidance), may have a decision altitude as low as 200 feet height above touchdown with visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest minima. LPV minima is published on the RNAV (GPS) approach charts (see paragraph 5−4−5, Instrument Approach Procedure Charts).

which seems to confirm part of what SBest was saying, that for all intents and purposes, LPV (but not LNAV/VNAV or LNAV+V) approaches are indeed precision approaches.

Is that correct?

 

[aterpster]

which seems to confirm part of what SBest was saying, that for all intents and purposes, LPV (but not LNAV/VNAV or LNAV+V) approaches are indeed precision approaches.

Is that correct?

The only reason the that LPV approaches are not considered to be CAT I precision approaches by the FAA is because ICAO has yet to give LPV its "royal" blessings. (the emperor has no clothes.)

 

[John Collins]

Actually, I would have highlighted this portion of the paragraph, but I had already posted it and edited it a few times.

2. A new type of APV approach procedure, in addition to LNAV/VNAV, is being implemented to take advantage of the high accuracy guidance and increased integrity provided by WAAS. This WAAS generated angular guidance allows the use of the same TERPS approach criteria used for ILS approaches. The resulting approach procedure minima, titled LPV (localizer performance with vertical guidance), may have a decision altitude as low as 200 feet height above touchdown with visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest minima. LPV minima is published on the RNAV (GPS) approach charts (see paragraph 5−4−5, Instrument Approach Procedure Charts).

There is a difference in the way the US treats an LPV verses an ILS with respect to the alternate minimums. An ILS with a localizer option has a standard precision approach minimum of 600-2 verses 800-2 for an NPA. An RNAV approach with LPV and LNAV minimums uses the 800-2 as its standard. I presume this has to do with difference in the fallback plan when vertical guidance is not available. In the case of an ILS, the localizer only minimums provide the same lateral precision whereas with the LPV the LNAV allows for the lateral guidance precision to be 0.3 NM.

 

[azure]

There is a difference in the way the US treats an LPV verses an ILS with respect to the alternate minimums. An ILS with a localizer option has a standard precision approach minimum of 600-2 verses 800-2 for an NPA. An RNAV approach with LPV and LNAV minimums uses the 800-2 as its standard. I presume this has to do with difference in the fallback plan when vertical guidance is not available. In the case of an ILS, the localizer only minimums provide the same lateral precision whereas with the LPV the LNAV allows for the lateral guidance precision to be 0.3 NM.

That's what I've assumed too. Even if it's just vertical integrity forcing the fallback, you no longer have localizer precision lateral guidance, so when considering it as an alternate you assume you'll only have non-precision minimums available.

 

[aterpster]

OK, but it isn't clear why you could not have LNAV or circling with sufficiently high minimums. Once you leave FAF behind you a big flat valley opens up with plenty of room for maneuvering.

They indeed could have provided an RNAV approach with only CTL minimums. Because in that case descent gradient has to be calculated to the CTL MDA. I suspect they saw no reason for it, though.