Coming to an approach plate near you, Summer 2009...

[TangoWhiskey]

Add another entry to the "L"-alphabet in your minimums section:

Future WAAS Approaches

LP. The term “localizer performance” is one you will see on future approach charts. As with ILS approaches, there may be places where an obstruction would require a high DA. Just as there are localizer-only approaches, in the future there will be equivalent WAAS procedures with “LP” minimums. A WAAS LP approach will provide accurate lateral guidance, but no vertical guidance.

The improved lateral accuracy of the LP approach will allow minimums as low as 300 feet AGL without any vertical guidance. The first LP approaches are scheduled for publication in summer 2009.

Source: http://www.faa.gov/news/aviation_news/2009/media/marapr2009.pdf (paper page 13, PDF page 15)

 

[Trapper John]

Add another entry to the "L"-alphabet in your minimums section:



Source: http://www.faa.gov/news/aviation_news/2009/media/marapr2009.pdf (paper page 13, PDF page 15)

Maybe I'm becoming a chicken in my old age, but the thought of flying down to 300 AGL in IMC without precision vertical guidance just isn't very appealing.


Trapper John

 

[Kaye]

There's a "V" that goes with that, and I just flew one of those LPV's to minimums this past Saturday in a 182.....what a hoot!!! No ILS at JYO, so we wouldn't have made it in with just the LOC.

 

[TangoWhiskey]

There's a "V" that goes with that, and I just flew one of those LPV's to minimums this past Saturday in a 182.....what a hoot!!! No ILS at JYO, so we wouldn't have made it in with just the LOC.

LPVs are different than LPs; the former has vertical guidance to a DA, the latter has no vertical guidance, but a VERY low (300' AGL, sometimes) MDA (not DA) is possible due to lack of conflicting terrain or obstacles.

 

[Bob Noel]

a bit of trivia: the word "precision" in "precision approach" doesn't say anything about accuracy. "Precision" only means veritical guidance.

 

[Kaye]

LPVs are different than LPs; the former has vertical guidance to a DA, the latter has no vertical guidance, but a VERY low (300' AGL, sometimes) MDA (not DA) is possible due to lack of conflicting terrain or obstacles.

Aack, I missed that nuance as my quick "scan" sucked. My bad. Based on what I think I understand about LP, which ain't a whole lot, the MDA doesn't seem that out of whack as compared to a LOC- DME, and so it makes some sense to me.

 

[TangoWhiskey]

a bit of trivia: the word "precision" in "precision approach" does say anything about accuracy. "Precision" only means veritical guidance.

Just to expand on that, Bob... another quote from the same FAA-published article:

Since APV approaches include vertical guidance and can, in some cases, provide approach minimums equivalent to Category I ILS, you may wonder why FAA doesn’t simply classify them as precision approaches. Here’s the answer. Officially, the APV is different because it does not meet the International Civil Aviation Organization (ICAO) and FAA precision approach definition. That definition applies mostly to localizer and glide-slope transmitters. In addition, FAA and ICAO definitions for a “precision approach” carry a great deal of documentation, definition, and associated costs.

Rather than try to change these standards and the associated international agreements, both ICAO and FAA adopted the term APV.

 

[Let'sgoflying!]

why would they choose a name (LP) that is so very near another but different name(LPV)? I guess the hazard is minimal, but the confusion!

 

[gismo]

why would they choose a name (LP) that is so very near another but different name(LPV)? I guess the hazard is minimal, but the confusion!

Because the 'L' and 'P' refer to the same words in both cases?

Localizer Performance, Localizer Performance with Vertical guidance.

 

[poadeleted20]

I've flown a few LPV approaches where there's also an ILS to the same runway, and tuned up the LPV in the 530 and the ILS on the Narco nav 122. The LPV gives better guidance every time, and is dead-nuts accurate and stable down to about 20 feet AGL. The ILS tends to bend and wander a little bit here and there. Given the choice...I'm just sorry the FAA hasn't worked a way to give 200-foot DH's to the LPV approaches yet.

 

[write-stuff]

Hey Trapper John - it's that album cover that's REALLY showing your age! A Thousand Days of Yesterdays....

- Russ

 

[gismo]

I've flown a few LPV approaches where there's also an ILS to the same runway, and tuned up the LPV in the 530 and the ILS on the Narco nav 122. The LPV gives better guidance every time, and is dead-nuts accurate and stable down to about 20 feet AGL. The ILS tends to bend and wander a little bit here and there. Given the choice...I'm just sorry the FAA hasn't worked a way to give 200-foot DH's to the LPV approaches yet.

I'm pretty sure they have, but only at runways with the full Monty approach lighting system.

 

[Let'sgoflying!]

Because the 'L' and 'P' refer to the same words in both cases?.

My answer was going to be lack of imagination and failure to anticipate the impending confusion.

 

[bbchien]

My answer was going to be lack of imagination and failure to anticipate the impending confusion.

Well, then AFS 400 will simply issue a corrective notam, which will contain an error, and completely confuse everyone.

Worse, the Instrument procedures handbook will now need yet another revision. And it is written by english majors.

 

[John Collins]

I've flown a few LPV approaches where there's also an ILS to the same runway, and tuned up the LPV in the 530 and the ILS on the Narco nav 122. The LPV gives better guidance every time, and is dead-nuts accurate and stable down to about 20 feet AGL. The ILS tends to bend and wander a little bit here and there. Given the choice...I'm just sorry the FAA hasn't worked a way to give 200-foot DH's to the LPV approaches yet.

Ron,

They have! There were a few LPV approaches with a DH of 200 feet issued in late 2007 and many more in 2008, at last count there were over 90 LPV approaches with a DH of 200 feet. They require an approach lighting system to the runway and the same survey requirements as an ILS.

Any LPV with a DH under 250 feet requires the VPL (Vertical Protection Limit) to be lower than 35 Meters, whereas the ones at 250 feet and above require a VPL of 50 Meters. In most of the US, the VPL is better than 17 meters for more than 99.9 percent of the time. It is not as good on the far west coast and I haven't seen any LPV approaches with a DH below 250 feet there. If you don't have VPL displayed on the satellite page, you can normally get an indication by looking at VFOM (Vertical Figure of Merit). A value below 40 feet will generally support LPV approaches with a DH of 200 feet and a value below 60 feet will support a DH of 250 feet or more. I typically see VFOM values under 23 feet.

Note that there is no graceful degradation of WAAS GPS performance if you don't have the required VPL for the approach. You either meet the requirements and have vertical guidance or you don't and have no vertical guidance. If you don't have the required VPL, the approach will downgrade to an LNAV MDA if there is one for the approach, it will never downgrade from LPV minimums to LNAV/VNAV minimums.