If you HAVE to shoot an approach, would you choose an ILS or an LPV?

Captain said:
What I'm pointing out is an ILS has a tighter deviation than GPS....even GPS with WAAS. It proven by the lower DA's published.
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Hmm, no I don't think that is quite correct. There was a study done by Raytheon that demonstrated WAAS accuracy at 3m and vertical accuracy at 4m whereas a Cat III ILS is accurate only to 7.6 meters in both planes at the middle marker. There is a difference between the GPS WAAS specification that was intended and what we are achieving today.

My personal experience is that at least in my plane the LPV approaches take me right down the center and not the case with ILS. My last ILS approach two days ago I did down to minimums and I was clearly offset. Perhaps some interference? When I left that same airport later I noticed the ILS hold short line was quite far back from the runway perhaps there was a plane sitting there when I landed.

Also most of the time I see an LPV and an ILS they have the same DA.
 
LPV backed up by ForeFlight SV fed by my Stratus. 50' would be more than enough to flare enough for a safe arrival.
 
It would definitely depend on which ILS. I'm sure the ones that are tested to CatIII standards are good but there are some with erratic signals. You're not even supposed to couple the ILS 10R into KMRY, and it says it's unusable from IMRY 1.8 DME inbound.
 
Re LPV and WAAS GPS, a CFII I know told me he was giving an owner an instrument checkout under the hood, and they decided to shoot an LPV to the ground, which went well. But at that point, the owner asked if he could keep his hood on while taxiing. The instructor said sure, why not, just go slow. Well, according to the instructor, the owner kept taxiing right on the taxiway centerlines, and eventually stopped right in front of his T-hangar before taking the hood off.
 
mscard88 said:
I ran PARs when I was an USAF controller. DH was 100' but we continued giving GS and azimuth info all the way down. I didn't work this flight but 5 F5s (Agressor Sqdn) went missed approach and immediately declared an fuel emergency. Approach vectored the flight in tight turning them onto a 4-5 mile PAR final. I happened to be in the tower where there were 3 parallel runways. Out of the fog came the F5s, actually landing on each runway safely.
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Had something similar only with ANG F-15s. All of them were emergency fuel diverts from SAV. What a mess. Hand offs inside my airspace; some automated, some a primary target. They started going missed then it was getting really serious. Last one in actually went missed, turned on his own for a crossing runway, made a handoff to GCA (SA) at 3 miles. Totally jacked up but we got them all down in one piece. Went downstairs afterwards and all of them soaked in sweat, chain smoking and doing the usual pilot hand gestures.

I agree with Fearless. I'll still take needles over a PAR. That is unless I was in position. I'll beat a LPV / ILS any day.:D
 
RotorDude said:
RNP is just bureaucratic nonsense created by people who don't fly the system.
My WAAS GPS gives me accuracy down to a couple of feet, and that's all I need in an emergency.
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All those pilots who do fly the system and who are trained and qualified in airplanes that can fly RNP AR would likely take strong exception to your view of RNP.

RNP AR was not intended to be a precision approach system. It was designed to get by or around critical terrain.

Unquestionably, LPV is far more precise the last two miles, or so, on final approach than any RNP AR approach.

There are plans to eventually meld RNP AR with LPV and even GLS.
 
aterpster said:
All those pilots who do fly the system and who are trained and qualified in airplanes that can fly RNP AR would likely take strong exception to your view of RNP.

RNP AR was not intended to be a precision approach system. It was designed to get by or around critical terrain.

Unquestionably, LPV is far more precise the last two miles, or so, on final approach than any RNP AR approach.

There are plans to eventually meld RNP AR with LPV and even GLS.
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I'd be one of those RNP AR folk and your assessment is correct.
 
First off I'd take whichever has lower minimums. However just about everywhere I go these days, and my base airport the LPV mins are the same as the ILS mins. In that case I'll go with the LPV every time, Whenever I'm flying and it's that low and they are advertising the ILS I always request the RNAV. I personally find the glideslope and lateral track to be more constant with an LPV and I find the automation in my airplane, (G1000, flight director and autopilot) to couple much better with the LPV than the ILS. If an LPV is available and as low as the ILS I'll take the LPV
 
I personally take vectors to final on a LPV over an ILS whenever it's an option. If the airplane has the ability to tune an ILS at the same time and display that information to me I set that up as well.
 
Whichever one I used on the previous attempt because I know it's working.
 
fiveoboy01 said:
Whichever one I used on the previous attempt because I know it's working.
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optimist - it's gonna break when ya need it the most*


*I'm sure that is somebody's corollary to Murphey's Law
 
Given my current situation, if the ILS or GPS approach stops working correctly just a few minutes after I went missed, then it's just my time to die.

In all seriousness, I'd probably fly the LPV approach. I'm pretty comfortable with either, but it always seems I'm just a hair more precise with the LPV approach.
 
Bottom line...any of it will get you there. I've built course and VNAV plans into a VFR GPS on the fly that got me to 50 feet over the threshold.:dunno:

I recall reading once that KLM used to do the equivalent of Cat II or III approaches with DC-3s and NDBs.
 
ILS because I don't have WAAS certified GPS
 
MauleSkinner said:
Bottom line...any of it will get you there. I've built course and VNAV plans into a VFR GPS on the fly that got me to 50 feet over the threshold.:dunno:

I recall reading once that KLM used to do the equivalent of Cat II or III approaches with DC-3s and NDBs.
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I recall reading that they used to takeoff without clearance in 0/0 weather. :(
 
I would have the LPV approach on NAV1 and have the ILS on NAV2. I would use the LPV as a primary and switch to the ILS if the GPS went out
 
Has anyone ever rode both to the asphalt on the same runway? It'd be interesting to compare actual data. I still suspect the ILS would do better but am open to evidence otherwise.

WAAS/ non-WAAS should be stipulated. Also needle deflection at 10' should be noted (or some representative altitude prior to flare)
 
WAAS is a given. The question was ILS vs LPV.

Edit - I am thinking you mean whoever tries it should make that note.

I'd be the Guinea pig but my airplane has no engine right now. Boo.
 
Not sure I'd give a single duck which one I used. Either way, I'm taking it all the way down, and putting the wheels somewhere on the airport proper. On, or very near, the runway would be good, but not required. Can't say I'd have gone missed the first time even, given the fuel state. Or declare, unless it would buy me some time - otherwise, it's a conversation/distraction I don't have time for. Definitley a gruesome situation. Backing one up with the other sounds good, but I think I'd probably be zeroed in on the primary.
 
Maybe I didn't see this quite right, as my focus was elsewhere, but it seemed to me that the GS was not well behaved below minimum when landing in VMC. Multiple full scale deflections, which I presumed to be false glide slopes, presumably closely packed together that close in.

I'd expect CAT II/III to be different. Never flew one.
 
Captain said:
Has anyone ever rode both to the asphalt on the same runway? It'd be interesting to compare actual data. I still suspect the ILS would do better but am open to evidence otherwise.

WAAS/ non-WAAS should be stipulated. Also needle deflection at 10' should be noted (or some representative altitude prior to flare)
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Yes there is actual data. ;) It's in the Raytheon study I mentioned earlier.
 
Gubbins said:
Yes there is actual data. ;) It's in the Raytheon study I mentioned earlier.
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Cliff notes? Or a link....I'd prefer cliff notes as honestly I'm not that interested. I don't see this actually happening to me and if it did I know I'd ride the ILS...to an autoland.
 
MAKG1 said:
Maybe I didn't see this quite right, as my focus was elsewhere, but it seemed to me that the GS was not well behaved below minimum when landing in VMC. Multiple full scale deflections, which I presumed to be false glide slopes, presumably closely packed together that close in.

I'd expect CAT II/III to be different. Never flew one.
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Might be technique. I've never had a problem.
 
Captain said:
Cliff notes? Or a link....I'd prefer cliff notes as honestly I'm not that interested. I don't see this actually happening to me and if it did I know I'd ride the ILS...to an autoland.
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Cliff notes in Post #41.

If you have a big ol' "autoland" button that only works with ILS, that will probably bias you towards ILS. :lol: If I had that I'd just make a note to never use it at HKS because you will end up landing off the runway. On the other hand why would you even be landing an A320 at HKS? No Cat III approaches there. OMG the pressure to have to land it with no assurances that it has been actually tested down to the asphalt! Maybe you'd elect to do the LPV as well ;)
 
MAKG1 said:
Maybe I didn't see this quite right, as my focus was elsewhere, but it seemed to me that the GS was not well behaved below minimum when landing in VMC. Multiple full scale deflections, which I presumed to be false glide slopes, presumably closely packed together that close in.

I'd expect CAT II/III to be different. Never flew one.
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Only with CAT II/III ILS installations can you be assured of a rock-solid LOC and GS to touchdown. In CAT I ILS installations it is all over the map, so to speak. Keep in mind ILS is a 1930s concept that requires a large area around it to be a ground plane antenna. Notice that some ILSes are not authorized for auto-flight coupling. That tells you something.

An unrestricted Category I ILS has to perform to a DA of 200 feet. All bets are off below 200 feet. Some are rock-solid; others are not.

LPV is the same everywhere. It is a derived system, with no airport issues affecting its performance. In an emergency I would elect a couple LPV approach every time. The big advantage of a CAT II/III runway would be the great runway lighting. But, there just aren't that many of those great runways.
 
I'd be all over the LPV. I've shot hundreds of them and have never seen anything that didn't have me on a wire down to the thousand-footers. I'm sure it's all in what you're used to.
 
Personally I would monitor both, and toss in a third LOC or ILS if equipped. The antenna offset of the ILS is within a realistic margin of error for the GPS, so as long as the needles are close, I know I'm heading for the runway environment, and that's good enough for survival if not a nice landing.
 
Henning said:
Personally I would monitor both, and toss in a third LOC or ILS if equipped. The antenna offset of the ILS is within a realistic margin of error for the GPS, so as long as the needles are close, I know I'm heading for the runway environment, and that's good enough for survival if not a nice landing.
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So... let's say you're monitoring both. You blow below the DA because you're out of fuel and you've got to go the whole way down to the asphalt and they start disagreeing with each other A LOT (which they will at some airports). Now what?
 
Gubbins said:
So... let's say you're monitoring both. You blow below the DA because you're out of fuel and you've got to go the whole way down to the asphalt and they start disagreeing with each other A LOT (which they will at some airports). Now what?
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Super question.
 
Gubbins said:
So... let's say you're monitoring both. You blow below the DA because you're out of fuel and you've got to go the whole way down to the asphalt and they start disagreeing with each other A LOT (which they will at some airports). Now what?
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No RAIM faults? I'll pick the LPV to follow.
 
fiveoboy01 said:
WAAS is a given. The question was ILS vs LPV.

Edit - I am thinking you mean whoever tries it should make that note.

I'd be the Guinea pig but my airplane has no engine right now. Boo.
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Mine has an engine. If someone wants to give me a WAAS IFR certified GPS and install it, I would happily be the guinea pig and post video of my results.:yes:
 
Turningfinal said:
No RAIM faults? I'll pick the LPV to follow.
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RAIM is not an issue if within WAAS coverage. Also, if the annunciation is "LPV" then all types of checks and validations have been passed. Otherwise it will downgrade to LNAV/VNAV or even just LNAV.
 
Where's the bottom of the LPV slope? Does it go to the threshold or the TDZ? That alone might be reason enough to follow an ILS glide slope.
 
Captain said:
Where's the bottom of the LPV slope? Does it go to the threshold or the TDZ? That alone might be reason enough to follow an ILS glide slope.
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With a 200 AGL minimum it damn well had better be pointed at the TDZ.

LPVs are supposed to be "just like" ILSs. Though the FAA considers them non precision.
 
aterpster said:
RAIM is not an issue if within WAAS coverage. Also, if the annunciation is "LPV" then all types of checks and validations have been passed. Otherwise it will downgrade to LNAV/VNAV or even just LNAV.
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What about when the military decides to block or spoof GPS signals?
 
EdFred said:
What about when the military decides to block or spoof GPS signals?
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If that happens to occur on the day you run yourself low on fuel and miss the first approach, it's just not your day.
 
Everskyward said:
If that happens to occur on the day you run yourself low on fuel and miss the first approach, it's just not your day.
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Hazardous Attitude!!! Burn her at the stake. Hazardous Attitude! Hazardous Attitude!

*Cue FastEddie with his little chart*
 
Captain said:
Where's the bottom of the LPV slope? Does it go to the threshold or the TDZ? That alone might be reason enough to follow an ILS glide slope.
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As I understand it, both the ILS and LPV GS are supposed to bring you to a touchdown on the thousand foot markers (TFMs). However, that depends on where the receiver antenna is installed on the aircraft relative to the bottom of the wheels. I also heard that ILS GS typically "flares" a bit over the runway, whereas LPV is a laser-straight line from the FAF to the TFMs. Both are supposed to cross the threshold at around 50' (not sure if that's antenna height or wheel height), which is how the (typically 3 degree) descent angle is defined.
But as always, I stand to be corrected on all these points by the experts.
 
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