Would you give up ILS for LPV approaches?

[Chip Sylverne]

I have not flown an ILS since 2008 in actual conditions. I regularly practice an ILS, but if ATC is using an ILS, I will request the RNAV. I have never been turned down, although vectors to final is the normal method of joining the approach because the path will overlay the ILS and I won't interfere with others flying the ILS. All that said, I would keep my ILS/VOR system as a backup. In the older installations with a separate GPS and Nav/Com, the primary CDI is usually switched between GPS and Nav and in most cases, the relay has spare poles to add the GS signals. If not, update the relay and keep the SL30, after all you still need a Com unit.

The fly in that ointment is the 175/375 isn't approved in the AFMS as a switched source, and it doesn't have the required annunciation pinouts. But I think I've decided to go with the 175 to drive my 525A and stec 60-2 for lpv appchs. Keep one sl30 as a separate loc/ils capability, and the second SL30 as a nav/com without a cdi, so if tshtf I can cross check radials using the integrated display and be on my merry way /A.
Thanks for the input, John.

 

[John Collins]

The AFMS does not limit if the CDI source is switchable from GPS or VLOC. So there is no reason not to have one of your SL30 as a VLOC source and a switch/relay/Source annunciator to switch between GPS and VLOC.

The external CDI is mentioned in a few places in the Limitations section of the AFMS, see this partial quote (reformatted):

2.2 Minimum Equipment
The GPS 175/GNX 375 must have the following system interfaces fully functional in order to be used for primary navigation during IFR operations:
External HSI/CDI/EHSI:, Number installed: 1 or more: Required for IFR: 1
External APPR and LOI Annunciator; Number Installed: See Note 1; Number required for IFR: 1

Note 1: Certain installations require an external APPR and LOI annunciator light. If installed, these
annunciators must be fully functional to use the GPS 175/GNX 375 GPS navigation for IFR
operations

2.6 System Use
The only approved sources of course guidance are on the external CDI, HSI, or EHSI display.
The moving map and CDI depiction on the GPS 175/GNX 375 display are for situational awareness only and are not approved for course guidance.

Although not a limitation (which is a legal requirement), section 4 of the AFMS for Normal Procedures deals with the topic of HSI/EHSI Operation. The caution note make no sense unless the installation supported a capability to select the source of GPS or VLOC on the same HSI.

4.3 HSI and EHSI Operation
If an HSI is used to display navigation data from the GPS 175/GNX 375 the pilot should rotate the course pointer as prompted on the GPS 175/GNX 375. If an EHSI is used to display navigation data from the GPS 175/GNX 375 the course pointer may autoslew to the correct course when using GPS navigation. For detailed information about the functionality of the EHSI system, refer to the
FAA approved Flight Manual or Flight Manual Supplement for that system.

CAUTION: The pilot must verify the active course and waypoint for each flight plan leg. The pilot must verify proper course selection each time the CDI source is changed from GPS to VLOC.

 

[Chip Sylverne]

The AFMS does not limit if the CDI source is switchable from GPS or VLOC. So there is no reason not to have one of your SL30 as a VLOC source and a switch/relay/Source annunciator to switch between GPS and VLOC.

The external CDI is mentioned in a few places in the Limitations section of the AFMS, see this partial quote (reformatted):



Although not a limitation (which is a legal requirement), section 4 of the AFMS for Normal Procedures deals with the topic of HSI/EHSI Operation. The caution note make no sense unless the installation supported a capability to select the source of GPS or VLOC on the same HSI.

Then I'm a little confused as to why the source switching wasn't spec'd in the external switching section, as it was in the GNS 4xx/5xx manual or the GTN 6xx/7xx manual, nor are there any interconnect diagrams as there are in the GX series IM's. The only source switching shown in the IM is for the Ki208A and 209A.

As a practical matter, 12v remote solenoids are difficult to find and very expensive, and add significantly to the complexity of the install. I'm not sure the juice is worth the squeeze.

 

[N1120A]

Unless you were based at VNY, MCC or any other of the very rare airports that don't have a decent (or any) GPS approach, you are getting much more if you choose LPV over ILS. Not only are you getting LPV, but all the non-LPV GPS approaches. Those are generally superior to some crappy VOR or even LOC only approach.

I prefer to use an LPV approach over an ILS approach. The LPV approaches tend to be more stable and less susceptible to issues like prop shadowing (the 310 was very bad about this). Plus LPVs are more available at a larger number of airports than ILSs are. Pretty much all airports with an ILS also have an LPV to equal minimums, but many airports with LPVs do NOT have an ILS.

That said, I would not want to give up ILS for the simple reason that at busier airports you will often be assigned an ILS, and in some cases if you ask for the LPV you will be told "No." So then that puts you in the position of having to say "Unable" and wondering what NY approach will do with you, or else shooting the LPV approach to the same one (assuming there is one) and hoping you don't get in trouble for it. I don't like that position.

On the first point, I totally agree. GPS approaches simply don't have the radio sensitivity issues that ILS approaches do, and light aircraft with GPSS autopilots fly them much better when you need to shoot with a little help than they do an ILS. Your information from the CDI is always going to be correct, no matter how close you get to the radio.

On the second, when you have an LPV overlaid on an ILS, there is zero reason for a controller to deny. They use the same waypoints and even FAFs. More and more, I'll even have controllers clearing "ILS or RNAV." If a controller is denying in that situation, they are just being jerks.

Having just retaken the IR written, if you file for an LPV approach, and you require an alternate, the alternate (assuming less than VMC from MEA to runway) must be a different approach type, (ILS or LOC) correct? That alone would be enough reason to me.

If you have WAAS and an LPV approach, you don't need a backup.

I'd be a lot more concerned about the actual interference testing by the U.S. military than a hypothetical attack by the Russians.

We get those all the time and I've never (knock wood) had an issue.

 

[JohnAJohnson]

I wonder if that includes the cost of satellite maintenance, Air Force staff required to monitor the system, and other required GPS costs. I think you'd have to for an apples to apples.

Cost to maintain ILS: ~$100,000
Cost to maintain LPV: ~$3,000

I'd give up ILS for LPV.

That said, I'd fight pretty hard to have both.

 

[flyingcheesehead]

I wonder if that includes the cost of satellite maintenance, Air Force staff required to monitor the system, and other required GPS costs. I think you'd have to for an apples to apples.

Not from an FAA perspective. The GPS constellation is going to exist for the military regardless of other users. Might as well take advantage of it if you're the FAA. No more electronic stuff to maintain, just flight test it every so often and you're good.

 

[Martin Horton]

I am preparing to be disappointed in the Garmin 175. Looking over the IM, it looks like it will support my HSI and A/P, but won't share it with my SL30. There are a couple dedicated pins missing on the J connector to support the ACU, like OBS HOLD/Susp, term, wpt. The only two outputs are LOI and APPCH. No interconnect diagram either. Not a good sign, I think.

So that leaves the question. If the 175 won't support sharing an HSI, would it be worth the trade off, LPV for ILS?

I'm just getting back into flying again, so not totally up to speed, so I might be way off. But I am looking to buy an airplane that is equipped with two NavComs but lacks a GPS and ADSB.
So it occured to me that a GNX 375 would be great. But then I realized it wouldn't do ILS. But the ILS approaches are in the database, just come with a warning that it's for monitoring only. So it occurred to me that you could allow the GPS to provide guidance to the AP but you would have to have a NavCom tuned to the ILS and displayed on an indicator. Then you could let the AP fly the LPV provided you monitor the ILS indicator to be sure you are following LOC and GS.

Am I crazy, misinformed, or would that work and be legal. It seems to me that as long as the ILS indications are in the right place, how you achieve that is up to you.

 

[Chip Sylverne]

I'm just getting back into flying again, so not totally up to speed, so I might be way off. But I am looking to buy an airplane that is equipped with two NavComs but lacks a GPS and ADSB.
So it occured to me that a GNX 375 would be great. But then I realized it wouldn't do ILS. But the ILS approaches are in the database, just come with a warning that it's for monitoring only. So it occurred to me that you could allow the GPS to provide guidance to the AP but you would have to have a NavCom tuned to the ILS and displayed on an indicator. Then you could let the AP fly the LPV provided you monitor the ILS indicator to be sure you are following LOC and GS.

Am I crazy, misinformed, or would that work and be legal. It seems to me that as long as the ILS indications are in the right place, how you achieve that is up to you.

Martin, apparently great minds think alike

 

[Daniel Lobb]

Chip did you finish your Garmin 175 install and do you have pictures of your panel? I'm installing one in my Skyhawk and also decided to give up ILS in favor of LPV. I'd love to have an additional CDI installed at some point to have the redundancy of ILS but that's an investment I'll have to hold off on for now.

 

[Chip Sylverne]

Chip did you finish your Garmin 175 install and do you have pictures of your panel? I'm installing one in my Skyhawk and also decided to give up ILS in favor of LPV. I'd love to have an additional CDI installed at some point to have the redundancy of ILS but that's an investment I'll have to hold off on for now.

Yes, I did and it's working out great. Such a leap forward from the GX50 worth every penny. Couples up great to the S-Tec for vertical guidance. The touch screen is very sensitive, so turbulence is an issue. Need to get more proficient at manually entering stuff using the knobs. The 175 is connected to the HSI, Nav 1 to the CDI, nav 2 has just the display CDI and numeric.

 

[Daniel Lobb]

Wow, that's awesome. Can you fly LOC or ILS approaches on your NAV 1 CDI indicator?

 

[Chip Sylverne]

Wow, that's awesome. Can you fly LOC or ILS approaches on your NAV 1 CDI indicator?

Yeah, but not coupled. My home drone is LPV, as are most of the places I go. I figure if I need to fly a LOC or ILS, I'll load the approach into the 175, and monitor the with nav 1. If the 175 goes TU, then I'll just hand fly the CDI. If enroute and the 175 craps out, I'll just use the navs and continue /A. With 3 separate radios, I figure I've got a good redundancy if shtf. Only have about 15 hours behind it now, and not yet comfortable enough with all the tricks for hard IFR, but I like it a lot.

 

[Jesse Tait]

I've got the SL30 using a TKM MC60 CDI - works perfectly. Called Garmin last week to find out if the 175 will talk to the MC60 - they're not sure and are researching it. Because, I've got a second MC60 CDI on the shelf that would be the display for LPV with the 175.

Looking at the docs, the 175 is an ADS-B out....I'm assuming it can be turned off, since I have the GTX 335.

How is your SL30 connected to the MC60? I've been trying to set this up but can't figure out the wiring. TKM doesn't know, either.

 

[murphey]

How is your SL30 connected to the MC60? I've been trying to set this up but can't figure out the wiring. TKM doesn't know, either.

TKM can't provide any info on the MC60 since 1) it was discontinued years ago and 2) no one at TKM remembers anything about it. TKM got new owners/management a few years ago. I'll go back over my emails with them - I think they mentioned one of the electronics techs who retired and does stuff like this on the side. I'll try and dig up his details.

 

[Ryan Klems]

How is your SL30 connected to the MC60? I've been trying to set this up but can't figure out the wiring. TKM doesn't know, either.

I would guess the SL30 is connected via composite (pin 19 SL 30 to pin 4 MC60) and ILS enable (pin 33 SL 30 to pin 19 MC60). And the SL30 should be configured to converter.

 

[Martin Pauly]

This shouldn't be about whether LPV is as good as ILS.
This should be about whether you need a backup in case there is an issue with GPS, such as jamming, spoofing, or the government degrading it temporarily.
I love LPV, but I won't bet my life on having 100% availability of GPS.

- Martin

 

[CA182R]

Is it possible to mix-and-match these 2" Garmin navigators with a GTN? I already have a GTN 750 unit and a GNC 255. I would rather my #2 unit be a GPS unit and not a NAV unit, especially since my home airport has LPV and not ILS. Along those lines, I'm thinking next year to upgrade the GNC 255 to GNC 355 or to GTN 635/650. But I think I heard Garmin say the 2" navigators can't be used with another navigator...

 

[Ryan Klems]

Is it possible to mix-and-match these 2" Garmin navigators with a GTN? I already have a GTN 750 unit and a GNC 255. I would rather my #2 unit be a GPS unit and not a NAV unit, especially since my home airport has LPV and not ILS. Along those lines, I'm thinking next year to upgrade the GNC 255 to GNC 355 or to GTN 635/650. But I think I heard Garmin say the 2" navigators can't be used with another navigator...

Not sure what you mean by mix and match. You can certainly install both a GTN and a 2” Navigator, but currently you can’t cross fill between them. Garmin has indicated they will probably bring that in a future software update though

 

[CA182R]

Not sure what you mean by mix and match. You can certainly install both a GTN and a 2” Navigator, but currently you can’t cross fill between them. Garmin has indicated they will probably bring that in a future software update though

I saw that the latest GTN software can cross-fill to these units, at least for database transfer. Could a GTN 750 and a GNC 355 both connect to a GAD 29b?

Please see 3:40:

Not sure what "Interfacing to another navigator" means...

 

[Ryan Klems]

I saw that the latest GTN software can cross-fill to these units, at least for database transfer. Could a GTN 750 and a GNC 355 both connect to a GAD 29b?

Please see 3:40:

Not sure what "Interfacing to another navigator" means...

Sure, you can easily connect both a GTN750 and a GNC355 to a GAD29B. You would have to have a garmin autopilot (or no autopilot) to do so however, as dual nav interface is not approved when interfacing with a 3rd party autopilot.

 

[kayoh190]

What does it cost to keep a NAV radio and indicator installed? I’m as big a fan of GPS as anyone, but it seems like there’s not a lot of downside to having a NAV radio installed for redundancy.

 

[CA182R]

I'm glad to have a NAV/GPS/COM for navigation unit #1, but for backup purposes (if unit #1 breaks) I would prefer to have to have GPS over ILS because most airports have RNAV approaches. My home airport has LPV. But with all that said, I sometimes wonder if redundancy is even required at all for me, just plan enough fuel to include a VFR alternate.

 

[hindsight2020]

What does it cost to keep a NAV radio and indicator installed? I’m as big a fan of GPS as anyone, but it seems like there’s not a lot of downside to having a NAV radio installed for redundancy.

Bingo. I can always shoot the IPAD GPS RWY XX approach if need be. I rather have the VOR/ILS CDI for a #2, it's so much cheaper to keep, especially in most inherited airplanes (resale) of today. Sometimes the capability diversification is indeed inverse the cost. But in this case, the capability case and the cost case both point in the same direction.

 

[asicer]

I'm glad to have a NAV/GPS/COM for navigation unit #1, but for backup purposes (if unit #1 breaks) I would prefer to have to have GPS

I would hazard a guess that the odds of a modern GPS box breaking is far less than the odds of a jammer depriving both GPS #1 and GPS #2 as well as your iPad of satellite signal.

I sometimes wonder if redundancy is even required at all for me, just plan enough fuel to include a VFR alternate.

I wholeheartedly agree with this sentiment.

 

[Jesse Saint]

There are currently 3998 LPV and 1549 ILS. Pretty much all runways that have an ILS also have an LPV.

Yes, and often they have an LPV going both directions, while few have an ILS both directions, so if the wind is wrong for the ILS, the opposite LPV will get you several hundred feet lower than circling ILS minimums or a Loc Back Course, if that airport has one. Also, many airports that used to have a VOR approach have lost it and now only have a GPS approach.

Would I give up ILS for RNAV/GPS? Absolutely! It sounds, however, like the OP will still have ILS capability, just not coupled to the auto pilot.

 

[N1120A]

Leaving aside the issue of having a backup navigation source not reliant on solely radio or satellite navigation, there are still a limited, but meaningful, number of places where having ILS/radio NAV capability is necessary or preferable. Don't have radio navigation into VNY? Better be VFR. Want to get better mins at MRY or BUR? Need ILS.

Is it possible to mix-and-match these 2" Garmin navigators with a GTN? I already have a GTN 750 unit and a GNC 255. I would rather my #2 unit be a GPS unit and not a NAV unit, especially since my home airport has LPV and not ILS. Along those lines, I'm thinking next year to upgrade the GNC 255 to GNC 355 or to GTN 635/650. But I think I heard Garmin say the 2" navigators can't be used with another navigator...

They can absolutely be used together..

What does it cost to keep a NAV radio and indicator installed? I’m as big a fan of GPS as anyone, but it seems like there’s not a lot of downside to having a NAV radio installed for redundancy.

I mean, you can get an all in one box anyway...

 

[iamtheari]

Leaving aside the issue of having a backup navigation source not reliant on solely radio or satellite navigation, there are still a limited, but meaningful, number of places where having ILS/radio NAV capability is necessary or preferable. Don't have radio navigation into VNY? Better be VFR. Want to get better mins at MRY or BUR? Need ILS.

Thanks for pointing out some examples. I looked at all the airports I thought I might fly into and never found one with an ILS that lacked an LPV with the same minimums as the ILS. I just pulled up KBUR, and it turns out that they do exist.

 

[N1120A]

Thanks for pointing out some examples. I looked at all the airports I thought I might fly into and never found one with an ILS that lacked an LPV with the same minimums as the ILS. I just pulled up KBUR, and it turns out that they do exist.

Even crazier is KVNY. You cannot shoot an instrument approach there without radio NAV in your airplane. Also, KBUR actually doesn't have LPV minimums, but only LP minimums (my guess is due to obstacles). There are others too. KSBA and KMRY both have higher LPV mins than ILS.

 

[Martin Pauly]

Even crazier is KVNY. You cannot shoot an instrument approach there without radio NAV in your airplane.

Crazy indeed. What's the story? Van Nuys is such a busy airport, surely there must be interest in having a diverse selection of approaches.

- Martin

 

[IK04]

No.

And, if you have a gazillion dollar certified navigator that is not compatible with your displays, you need to keep shopping until you find one that is.

 

[asicer]

Even crazier is KVNY. You cannot shoot an instrument approach there without radio NAV in your airplane.

Here's the list I came up with searching my database for airports with ILS* and nothing with GPS or RNAV in the procedure name: (No guarantees of accuracy, some are not public, did not hand check these, etc etc)
(Edit, ok, almost all .mil)

KBAD KDMA KDYS KHIF KLRF KLSV KMCC KMIB KMMT KMTC KMUO KMXF KNOG KNQI KNUQ KRCA KSSC KVBG PASY PPG

And the list for VOR* but no GPS, RNAV or ILS
12G 1X1 2J9 2P7 3F9 4I9 56D 8G1 C25 C77 F14 F51 K59 LZD N57 U69

And finally, the list for NDB* but no GPS, RNAV, ILS or VOR:
KPHH PACZ WTK

Well that's odd. Any idea why KVNY did not show up in your search, @chartbundle ?

 

[chartbundle]

Well that's odd. Any idea why KVNY did not show up in your search, @chartbundle ?

Looks like when I ran that report there was a 'VOR/DME OR GPS B' approach at VNY in addition to possibly others. Unfortunately I don't keep history so I don't know when they went away.

 

[bluesky74656]

I know I’ve brought this up before, but BKL in Cleveland has two approaches: an ILS and an RNAV to 24R. The RNAV is NOTAMed NA for the next two years.

I wish I knew why. They raised the circling minimums on the ILS, so something must have become an obstacle, but I don’t see why they wouldn’t just raise the RNAV minimums too rather than disallowing the procedure entirely.

 

[N1120A]

Crazy indeed. What's the story? Van Nuys is such a busy airport, surely there must be interest in having a diverse selection of approaches.

- Martin

Got me Martin. Wally mentioned that terrain and other considerations may affect things and that the ILS approaches into both airports may be grandfathered, but who knows? I know VNY doesn't even have LOC mins on their ILS approaches - glideslope or pick another approach.

Looks like when I ran that report there was a 'VOR/DME OR GPS B' approach at VNY in addition to possibly others. Unfortunately I don't keep history so I don't know when they went away.

KVNY used to have an overlay on the VOR-B, but they did away with that. @aterpster mentioned something about a potential issue with terrain in the area.

 

[asicer]

KVNY used to have an overlay on the VOR-B, but they did away with that. @aterpster mentioned something about a potential issue with terrain in the area.

I'd be curious to know how a VOR 5+ miles away keeps you out of the rocks better than a GPS.

 

[N1120A]

I'd be curious to know how a VOR 5+ miles away keeps you out of the rocks better than a GPS.

Me too

 

[Fracpilot]

Been to VNY a zillion times flying at my full time job. Not sure I’ve ever seen the visibility less than 5SM and that may have been due to smog. I don’t think VNY would be an airport you need to worry about shooting an approach to mins.

MRY is a completely different story. It seems I always have to shoot the approach to 500 MSL or so to get below the marine layer. The RNAV approach is excellent into MRY because the points navigate you around the terrain.

ILS vs LPV at other airports won’t let you navigate around the terrain as precisely since the ILS it just shoots a straight or offset signal from the point you intercept it. The intercept is usually in a heading mode on the autopilot and requires human intervention.

Using the RNAV approaches into Mexico around terrain are fantastic examples of how much better the RNAV approach is over the ILS without much human intervention. The GPS/RNAV approaches allow you to just set it, let the airplane fly the entire arrival to approach so you can sit back and monitor, greatly reducing your workload.

I’ll take GPS/RNAV/LPV over ILS anytime


Sent from my iPhone using Tapatalk

 

[Jesse Saint]

Anybody care to research how many airports have RNAV/GPS but no VLOC approaches? I think that list may exceed the maximum post length on his forum

 

[N1120A]

Been to VNY a zillion times flying at my full time job. Not sure I’ve ever seen the visibility less than 5SM and that may have been due to smog. I don’t think VNY would be an airport you need to worry about shooting an approach to mins.

MRY is a completely different story. It seems I always have to shoot the approach to 500 MSL or so to get below the marine layer. The RNAV approach is excellent into MRY because the points navigate you around the terrain.

ILS vs LPV at other airports won’t let you navigate around the terrain as precisely since the ILS it just shoots a straight or offset signal from the point you intercept it. The intercept is usually in a heading mode on the autopilot and requires human intervention.

Using the RNAV approaches into Mexico around terrain are fantastic examples of how much better the RNAV approach is over the ILS without much human intervention. The GPS/RNAV approaches allow you to just set it, let the airplane fly the entire arrival to approach so you can sit back and monitor, greatly reducing your workload.

I’ll take GPS/RNAV/LPV over ILS anytime


Sent from my iPhone using Tapatalk

The RNP AR approach is the only approach to 28L that gets you below 823' AGL and MRY has more planes arriving that don't get AR approaches than do, meaning you need to do the ILS or RNAV 10R, and the ILS takes you lower.

VNY can and does go less than VFR that would allow for a visual approach. Particularly during Marine layer season. Visibility is rarely an issue in Southern California, rather ceilings are. The IFR MVA around there is high as well.

Anybody care to research how many airports have RNAV/GPS but no VLOC approaches? I think that list may exceed the maximum post length on his forum

And then compare relative number of operations and local population?

 

[David Megginson]

I would. The only thing the ILS beats the LPV at is CatII/III ops (for now and small GA can’t do it anyways).

Stand by for the “you’ll be sorry when the Russians shoot down our satellites” comments.

No, that won't happen, but I've flown through two real wide-area GPS outages so far in 18 years, both due to military jamming exercises. I wouldn't want to be stuck in IMC with no backup when the military jammed GPS for real because of a major terror attack.