ILS vs LPV

[ilovecornfields]

I’ve noticed a lot of airports have ILS and LPV approaches to the same runway with similar minimums. I usually pick the LPV approach but I’m wondering what other people do and the reasons for it.

My thoughts are that the LPV approaches have better monitoring and the missed approach is usually easier. Not sure if there are any advantages to the ILS.

[Jeff_S]

Given the choice, I would take the LPV most times, but with my G1000 equipment the methods of flying them are so similar it really doesn’t matter. Most times I’m at the discretion of Approach or Tower control anyway so they generally select the ILS as a greater percentage of planes are so equipped...even with a /G transponder code, not all these planes have a WAAS receiver whereas almost all IFR planes will have ILS capabilities.

[Jim Peace]

16 minutes ago, ilovecornfields said:

I usually pick the LPV approach but I’m wondering what other people do and the reasons for it.

I would take the ILS over an LPV, I want to follow the tractor beam directly from the source vs space based magic....I am a bit older school and not a millennial, I am sure others will disagree with some valid points.

[milotron]

4 minutes ago, Jim Peace said:

I would take the ILS over an LPV, I want to follow the tractor beam directly from the source vs space based magic....I am a bit older school and not a millennial, I am sure others will disagree with some valid points.

I have this preference also. I can dial in the ILS on the second NAV and CDI as a backup to the HSI and VOR/GPS signal.

It is helpful as I have been known to not switch from GPS to VLOC on the GNS 430 on occasion also....

 

iain

[Marauder]

Not that in all cases, but most, the ILS has lower minimums. I prefer to setup the LPV on the primary HSI and monitor the ILS on the second HSI. Especially if I am flying the whole approach including procedure turns.


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[gsxrpilot]

I'll take the ILS, thanks.

[M016576]

I normally fly the LPV (in the Mooney)- but only because I pay so much frickin money to Jeppeson for nav data that I feel like I need to get my moneys worth.

as was mentioned above- minimums are sometimes lower for an ILS... but the 100-200’ difference between the two is kind of irrelevant for me- I don’t relish shooting approaches down to 200’ or 300’ unless it’s a low, stable layer and VFR on top.

either way- the approaches are TERPsed for a safe approach at the minimums on the plate... the difference? Sensitivity as you get close to the ILS ground antennas changes, whereas with the WAAS approach- sensitivity on the needles remains constant (it’s linearly scaled) throughout the final portion of the approach.

[Danb]

I’d rather take the ILS for similar reasons as JimP

[thinwing]

In mountainous terrain..I prefer the lpv due to signal scalloping of the localizer signal on the ILS...also lpv share a common "T" layout that is very familiar.

[M016576]

2 hours ago, Jim Peace said:

I would take the ILS over an LPV, I want to follow the tractor beam directly from the source vs space based magic....I am a bit older school and not a millennial, I am sure others will disagree with some valid points.

Ok, I’ll bite for the sake of argument.  But I’m not a millennial— just want to get that out there.

1:  the JDAM reached IOC back in ‘97.  In my experience dropping laser guided bombs (beam riders) vs gps guided bombs (JDAMs)- the GPS guided bombs are more accurate.

subjective- yes- but a data point.

2:  if a truck drives through the ILS critical area (or a plane taxis in front of the antennas), your ILS signal will either drop entirely, or bounce... which (and I have seen this before) will cause your needles to display inaccurate glideslope or localizer.  Also, if you are high or right/left enough of the station, or if there is enough terrain nearby- it is possible to get a bad signal too, which appears to be accurate.  You have no way of knowing this via the instrument alone.

with a WAAS receiver- the unit is continually performing error checking and RAIM calculations.  If the receiver detects an error- it notifies the pilot and downgrades the approach for you- basically- the units are required to detect if they can’t meet precision accuracy, and then automatically revert to a non-precision profile while telling the pilot.  That’s a pretty nice safety feature IMO.

3: I paid a TON of money for this fancy panel mount WAAS gps.  I have to continue to pay a TON of money for nav data... the ONLY thing this panel mounted waas gps gives me over a hand held(+infinitely cheaper basic panel gps) is the ability to shoot these waas approaches... I can get gps airways navigation from a bunch of cheaper sources...... so... I’m using the LPV approaches that I paid for!  

 

Edited December 9, 2018 by M016576

[thomas1142]

I prefer the LPV approach since I’m using the GPS for navigation and I have the approach loaded, and activated. No need to enter any more info, or push any buttons on the GPS, or Any other instrument, to execute  the approach.

[Deb]

5 hours ago, M016576 said:

Sensitivity as you get close to the ILS ground antennas changes, whereas with the WAAS approach- sensitivity on the needles remains constant (it’s linearly scaled) throughout the final portion of the approach.

It’s actually a bit more nuanced; here’s the definitive answer from John Collins:

The LPV CDI FSD (Full Scale Deflection) is 1 NM until reaching a point 2 NM prior to the FAF. The FSD then transitions to the value for the FAF to threshold. At the FAF, this is equivalent to +/- 2 degrees measured from a calculated point beyond the threshold such that when at the threshold, the FSD is +/- 350 feet. It continues at a fixed value of +/- 350 feet until reaching a reference point (about 1000 feet from the threshold) and after that, is changes to a fixed value of +/- 0.3 NM.

So as a practical matter, it is similar to an ILS with a runway length of about 10000 feet. It is angular for the final approach course (+/- 2 degrees) and not a fixed value. It is +/- 350 feet at the threshold and continues at this value for another 1000 feet before increasing back to 0.3 NM.

My reference for this is from RTCA DO229D, which is the technical specification for a TSO C145/146 WAAS GPS Navigator. You have to be a member of RTCA to get this document for free or must pay $370 for a copy.

Here is some description from the 10/12/2017 AIM 1-1-18, d 4 (page 1-1-34):

4. Both lateral and vertical scaling for the LNAV/VNAV and LPV approach procedures are different than the linear scaling of basic GPS. When the complete published procedure is flown, ±1 NM linear scaling is provided until two (2) NM prior to the FAF, where the sensitivity increases to be similar to the angular scaling of an ILS. There are two differences in the WAAS scaling and ILS: 1) on long final approach segments, the initial scaling will be ±0.3 NM to achieve equivalent performance to GPS (and better than ILS, which is less sensitive far from the runway); 2) close to the runway threshold, the scaling changes to linear instead of continuing to become more sensitive. The width of the final approach course is tailored so that the total width is usually 700 feet at the runway threshold. Since the origin point of the lateral splay for the angular portion of the final is not fixed due to antenna placement like localizer, the splay angle can remain fixed, making a consistent width of final for aircraft being vectored onto the final approach course on different length runways. When the complete published procedure is not flown, and instead the aircraft needs to capture the extended final approach course similar to ILS, the vector to final (VTF) mode is used. Under VTF, the scaling is linear at ±1 NM until the point where the ILS angular splay reaches a width of ±1 NM regardless of the distance from the FAWP.

[vorlon1]

5 hours ago, M016576 said:

..... so... I’m using the LPV approaches that I paid for!  

Not to sound snarky, but don't you mean "paid extra" for? As a taxpayer,  you paid for the ILS as well. 

 

 

[David Lloyd]

Recently been flying with a Garmin GTN750.  Either ILS or LPV, this thing makes an approach so easy, a piece of cake.  If an ILS minimums are 200 & 1/2 and LPV minimums are 300 & 1 and reported weather is 400 & 1, I will go for the ILS every time.  Reason: Far to many times I have flown an approach and found the ceiling to be lower than reported.  If I'm flying in low weather, I'm going to play my best card first.

[midlifeflyer]

Both are easy to fly, but I prefer LPV. I won't refuse the ILS at a towered airport, but if asked what approach I want, I will choose LPV. Besides, there are more of them and they provide straight in low minimums in situations where the ILS is to the opposite runway. I haven't found the minimums between colocated ILS and LPV to be substantially different. If they are and the weather is low, of course I will choose the ILS, but no real reason to otherwise.

Edited December 9, 2018 by midlifeflyer

[aviatoreb]

I agree with all that said there are reasons to choose the LPV when given a choice.

But I have noticed that it seems like almost always at a towered airport they are assigning the ILS approaches unless the pilot asks for something else.  Why is that?

[kpaul]

7 hours ago, M016576 said:

1:  the JDAM reached IOC back in ‘97.  In my experience dropping laser guided bombs (beam riders) vs gps guided bombs (JDAMs)- the GPS guided bombs are more accurate.

Yet, the military went back and designed a laser JDAM...Why?  Because while GPS only is good for specific targets, laser guidance has its advantages as well. Although, this has nothing to do with LPV vs ILS.

 

LPV approaches are a WAAS/GPS based approach, and they're very similar to the ILS. But there is a difference. Even though LPV approaches have vertical guidance, they're not considered precision approaches. Instead, they're an approach with vertical guidance (APV).

So what's the difference? APV approaches don't meet the ICAO and FAA precision approach definitions, which apply mostly to localizer and glideslope transmitters. The precision approach definition also carries a lot of documentation, definition, and cost with it, so the FAA and ICAO adopted the APV definition, so they could build new approaches and not be burdened with the cost and paperwork.

[Raptor05121]

10 hours ago, Jim Peace said:

I would take the ILS over an LPV, I want to follow the tractor beam directly from the source vs space based magic....I am a bit older school and not a millennial, I am sure others will disagree with some valid points.

Millennial here, I'd take an ILS over an LPV any day. Same logic.

[chrisk]

Not a millennial, and I will take an LPV approach most any time.  For the airports I typically visit GPS approaches are the only options.   Why do something different just because an airport has an ILS option?  Often the minimums are the same.  And my GTN650 simply has an atrocious interface for switching between GPS and ILS.  Again, why do anything different?

Its also been my experience that the minimums are similar (if not identical) for both, at least at the airports I visit.  An example is KCOS, where LPV and ILS both have minimums to 200 agl.  ILS gives me nothing but an opportunity to screw up.  That said, if an ILS is available for the runway I am using, I tune it in on my backup radio/indicator.

[Jerry 5TJ]

Old guy & I prefer the LPV.

A technical aside: Even if the published minimum for the LPV is higher than the ILS the GPS-based steering information is valid below DA.   The ILS is surveyed to DH but not below.  

Once you have spotted “paint, pavement or lights”  (my loose paraphrase of 91.175) you may rely upon LPV steering below the DA.   Not so with the ILS needles. 

That can be a useful assist as you transition and continue visually to the runway.   

[M016576]

1 hour ago, kpaul said:

Yet, the military went back and designed a laser JDAM...Why?  Because while GPS only is good for specific targets, laser guidance has its advantages as well. Although, this has nothing to do with LPV vs ILS.

 

LPV approaches are a WAAS/GPS based approach, and they're very similar to the ILS. But there is a difference. Even though LPV approaches have vertical guidance, they're not considered precision approaches. Instead, they're an approach with vertical guidance (APV).

So what's the difference? APV approaches don't meet the ICAO and FAA precision approach definitions, which apply mostly to localizer and glideslope transmitters. The precision approach definition also carries a lot of documentation, definition, and cost with it, so the FAA and ICAO adopted the APV definition, so they could build new approaches and not be burdened with the cost and paperwork.

Laser JDAM (gbu-54) is for Moving targets.  It’s a replacement for the aging LMAV (AGm-65), which we were using to great success against technicals across Iraq,Afghanistan,Syria , etc.

I did Op Test on this weapon in 2008 when I living in the desert.  I was skeptical at first.... until we hit a towed buggy going 60 down a dirt road....

if it’s a fixed target, though- the preferred solution is a regular JDAM- more flexible fuzing options (airbursts, etc).  The GBU-54  seeker takes the place of where you’d install a DSU-33 nose prox. fuse- all you get is a single tail fuse in the LJDAM- and no nose plug (so penetrating reinforced structures isn’t really on the table.)

Edited December 9, 2018 by M016576

[Hank]

1 hour ago, aviatoreb said:

I agree with all that said there are reasons to choose the LPV when given a choice.

But I have noticed that it seems like almost always at a towered airport they are assigning the ILS approaches unless the pilot asks for something else.  Why is that?

I rather prefer GPS approaches, and I'm from the tail end of the Boom.

Tower almost always offers the ILS if it's available, because almost all IFR-equipped planes can fly it; not so with GPS approaches. 

Not long after getting my rating (in 2010), I headed over the hills from WV to KFAY, and my descent was nicely between buildups (with clear StormScope) until entering the base layer. Tower told me to expect the ILS Back Course, which I had never flown in training. I did remember reading about reverse sensing . . . So I asked for the GPS approach instead and they rapidly granted it. I'd much rather fly an approach designed for the runway I'm flying to than twist around one giving guidance to a different runway and try to keep it straight . . . .

[Piloto]

I fly both simultaneously with my KX165 tuned to the ILS and the GN S530 on the LPV. It gives me assurance that I am approaching the right runway and redundancy. Most of my approaches are autopilot coupled.

When approaching a runway with no published approach I set the OBS on the GNS 530 to the runway heading for guidance. Besides lateral and distance guidance the VNAV function on the GNS 530 is very helpful on the descent profile.

José 

Edited December 9, 2018 by Piloto

[midlifeflyer]

2 hours ago, aviatoreb said:

I agree with all that said there are reasons to choose the LPV when given a choice.

But I have noticed that it seems like almost always at a towered airport they are assigning the ILS approaches unless the pilot asks for something else.  Why is that?

Habit. And everyone has an ILS. Not everyone has on-board GPS with full WAAS capability.

Edited December 9, 2018 by midlifeflyer

[midlifeflyer]

20 hours ago, chrisk said:

Not a millennial, and I will take an LPV approach most any time. 

I suspect it's not age-related. There might be a bit of preference for the familiarity of the past - the devil you know vs the devil  you don't know -  but I haven't found even that to be particularly age related. 

I still recall the hew and cry over the airspace change (from TCA, ARSA, etc to Class B,C, etc) and from the old US weather to the ICOA METAR, TAFs, etc. Heck, you even still see whining about as simple a change as  "taxi into position and hold" to "line up and wait." Younger folks whined about those just as much as older ones.

Edited December 10, 2018 by midlifeflyer