GPS approach requests

[Jim_CAK]

Great Thread! I learned a lot from it. I have a non-WAAS 430 and never sorted out the differences in LPV and LNAV/VNAV because I could not use them.
Very good information.
Thanks guys =

 

[midlifeflyer]

Now that LPV is coming into significant use in Europe, I suspect there will be a lot more pressure put on ICAO to back off their stance on LPV.

Yup. Hence my bolding of the word "current."

 

[coloradobluesky]

There is more to an approach than the radar guidance. There is the runway environment, lights, missed and so forth. I agree, an RNAV approach with vertical guidance should be considered a precision approach. At least some of them. I dont really even know why there is a difference. Is there some function that a precision approach lets the airplane do that an equivalent non-precision approach that gets you down the same minimums wont let you do? I think the FAA wrote it off to "politics" and succumbed to the ICAO, which is mostly European. Some long story like that.

 

[fiveoboy01]

Is there some function that a precision approach lets the airplane do that an equivalent non-precision approach that gets you down the same minimums wont let you do?

In the case of an LPV approach I'd say no. Minimums are close to the ILS.. in many cases the same.. and this was rehashed in another thread but the consensus is that either would get you to the TDZ in a zero zero situation.

In fact, some LPV approaches get you lower than the ILS. Just a quick look in my terps book shows that the LPV DA is 50 feet lower than the ILS DA to RW21 at MSN. Go figure on that one. The "NPA" has a lower DA than the precision approach

 

[John Collins]

Vertical guidance is based on two different things in a GPS approach (from what I've read).

If you're flying an LNAV+V (which is a LNAV/VNAV approach): The Vertical Navigation (VNAV) utilizes an internally generated glideslope based on WAAS or baro-VNAV systems. Minimums are published as a DA. If baro-VNAV is used instead of WAAS, the pilot may have approach restrictions as a result of temperature limitations and must check predictive RAIM.

LNAV+V is not the annunciation for an LNAV/VNAV approach although it was on earlier versions of the software for the GNS480. The annunciation for LNAV/VNAV is L/VNAV on most GPS WAAS systems and it has a DA. LNAV+V is an LNAV approach with an MDA where the +V signifies advisory vertical guidance is available. It may not be used below the MDA as there may be obstacles on that path. For the newer GNS430W/530W software, there is also an annunciation of LP+V which is an LP procedure with advisory vertical guidance and it is flown to an MDA.

 

[John Collins]

And it's really annoying, since most GPSs are WAAS these days, so you really only see LPV and LNAV.

I'm sure LP approaches exist somewhere, but I've never seen one. I've seen a lot of LNAV/VNAV minimums, but I haven't seen an airplane with Baro-aided VNAV, and with WAAS, you can just use LPV.

Truckee and Rio Vista are two in California. There are about 600 LP procedures in the US. Although your WAAS GPS does not use baro-vnav for the vertical guidance, it is approved to fly an approach that has LNAV/VNAV minimums using the WAAS for the vertical guidance. They will annunciate as L/VNAV on most WAAS GPS systems, although you can chose to fly to these minimums if they are on the approach chart and you have either LPV or L/VNAV annunciated.

 

[petrolero]

I'm just guessing, but is it possible that you have not read the new Instrument Procedures Handbook? Available on the faa.gov website.

Bob Gardner

It's possible I haven't either. Lord knows I tried. It is impenetrable. I prefer the instrument flying handbook.

 

[petrolero]

In training we never distinguished between ILS and LOC as far as requests go. It's the same procedure and ATC holds open the same airspace and you can switch between one and the other without any further request. Just because they clear you for the ILS doesn't preclude you from flying it as a LOC-only procedure.

Same with RNAV approaches. Just call it RNAV and fly it to whatever limits you choose - ATC doesn't care as long as you follow instructions on the plate and instructions given by ATC.

 

[fiveoboy01]

I don't know how you can say that an ILS and a LOC approach are the same procedure(even to the same runway) with a straight face.

As far as RNAV limits, fly to the minima on the plate dictated by the GPS' annunciation, not whatever you choose.

 

[petrolero]

I don't know how you can say that an ILS and a LOC approach are the same procedure(even to the same runway) with a straight face.

As far as RNAV limits, fly to the minima on the plate dictated by the GPS' annunciation, not whatever you choose.

Pedantic reply.

Same plate (IAP - Instrument Approach Procedure) is what I mean. ATC doesn't give a rat's which limit you're flying. I think you could have tried a tiny bit harder to understand what I meant. It was pretty clear from context.

 

[bobmrg]

It's possible I haven't either. Lord knows I tried. It is impenetrable. I prefer the instrument flying handbook.

Apples and oranges. You need to read both in order to cover all the bases, and "all the bases" is a moving target. Read John Collins posts here and in the BeechTalk forum and you will quickly realize that there are more players in the game than just the FAA.


Bob

 

[petrolero]

Apples and oranges. You need to read both in order to cover all the bases.

(And "all the bases" is a moving target.)

Bob

I know they are apples and oranges. Big time. And no, you don't need to read them both - at least not in order to fly safely in the system. Perhaps if you want to really understand how terps come to be, yes. And that is the subject of this thread, I know.

The procedures handbook deals with the minutia of how procedures are created. I can get by just fine with what's in the AIM, IFH, etc. I don't need to know all that crap in the procedures book.

 

[c310flyr]

I don't know how you can say that an ILS and a LOC approach are the same procedure(even to the same runway) with a straight face.

As far as RNAV limits, fly to the minima on the plate dictated by the GPS' annunciation, not whatever you choose.

Not always.
Even though you have LPV annunciated there are special circumstances where the lnav mins can be more favorable ( for instance, lower visibility mins)

You can choose to fly to those mins if you wish

 

[fiveoboy01]

Pedantic reply.

Same plate (IAP - Instrument Approach Procedure) is what I mean. ATC doesn't give a rat's which limit you're flying. I think you could have tried a tiny bit harder to understand what I meant. It was pretty clear from context.

If it was clear I wouldn't have questioned what you said. What you said("same procedure") and what you meant ("same plate) have patently different meanings, at least to me.

That the two use the same plate is obvious, anyone can see that where it says "ILS or LOC"...

Anyways wasn't trying to start an argument. I really didn't interpret your post that way. Maybe you could make it more pedantic next time

 

[RussR]

On checkrides in LPV equipped airplanes, sometimes the examiner requests that the approach be flown as an LNAV (using the appropriate stepdowns and altitudes instead of the GS) - since you can't turn off the GS.
In the 'old days' most planes had a LOC and and ILS head so you just used the one for the approach the examiner wanted you to do.

I've often turned off the GS in WAAS-equipped airplanes for training purposes.

In the Garmin 430/530, it's under Aux/SBAS selection.

In the Garmin 650/750, it's in the System/GPS Status/SBAS menu.

In both cases, turn it off and you've now dumbed down the GPS to non-WAAS.

I'm not an examiner, but I'd be surprised if they don't know this too.

 

[midlifeflyer]

The procedures handbook deals with the minutia of how procedures are created. I can get by just fine with what's in the AIM, IFH, etc. I don't need to know all that crap in the procedures book.

Are we talking about the same Instrument Procedures Handbook? The FAA publication with that name I am familiar with is intended for pilots and is sort of an expanded AIM that deals with instrument flight from airport ground operations to emergencies.

I don't think it has anything about the minutia of how IAPs are created, other than mentioning that design is based on TERPS requirements (the primary source of the minutiae of approach design). Of course, we might have differing views of whether such things as

An instrument approach may be divided into as many as four approach segments: initial, intermediate, final, and missed approach. Additionally, feeder routes provide a transition from the en route structure to the IAF. FAA Order 8260.3 (TERPS) criteria provides obstacle clearance for each segment of an approach procedure as shown in Figure 4-29 .
​

is minutiae or unnecessary crap.

Personally, while I would hardly think of it as vacation reading material, I've found it very helpful as a reference for explanations on instrument flight that go beyond the IFH.

 

[rocketflyer84]

I've often turned off the GS in WAAS-equipped airplanes for training purposes.

In the Garmin 430/530, it's under Aux/SBAS selection.

In the Garmin 650/750, it's in the System/GPS Status/SBAS menu.

In both cases, turn it off and you've now dumbed down the GPS to non-WAAS.

I'm not an examiner, but I'd be surprised if they don't know this too.

You can disable it although if flying the approach with steps downs as just an LNAV approach one is usually so far off the glide slope anyway that it's hardly a distraction (or aid).

 

[flyingron]

Probably TAS calculations.

The 480 doesn't do TAS calculations.

For approaches, the encoder and baro information input allows the system to function with one fewer satellite in view, so it improves the reliability.

If you have a MX20, the baro is also used to key the obstacle/terrain function.

 

[taters]

A note on LNAV+V: If I'm reading correctly (links below), that is an LNAV approach for all intents and purposes and should be flown as such. The +V is vertical guidance calculated by the GPS unit and is only advisory. It helps avoid dive and drive. It is not LNAV/VNAV and all step down altitudes are still mandatory.

https://www.faa.gov/about/office_or...nss/library/factsheets/media/RNAV_QFSheet.pdf

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC 90-107.pdf

LPV: use LPV DA (flown like ILS)
LP: use LP MDA (flown like LOC)
LNAV: use LNAV MDA (flown like LOC)
LNAV+V: use LNAV mins (again, +V is advisory only)

^^ This,

and on LNAV + V flown in a non- standard atmosphere you can find quite a difference between the "advisory glide-path" and the actual one. It basically provides some big picture help in predictive monitoring required to be performed by the PIC when using the CANPA technique on a non-precision approach.

I have seen people trust the "advisory glide-path" like the spoken gospel, don't fall into that trap, you must still honor any step downs with your own altimeter/brain power.

 

[petrolero]

If it was clear I wouldn't have questioned what you said. What you said("same procedure") and what you meant ("same plate) have patently different meanings, at least to me.

That the two use the same plate is obvious, anyone can see that where it says "ILS or LOC"...

Anyways wasn't trying to start an argument. I really didn't interpret your post that way. Maybe you could make it more pedantic next time

Is a "plate" also known as an "instrument approach procedure" or are those "patently different" in your world?

Also... no **** you fly to the "minima on the plate". But which one? There are several. That's exactly what I was referring to and what the thread is discussing. But you "choose" which one you are descending to. The point in that post is that it doesn't change how you refer to the approach vis-a-vis ATC. You just call it by the name on the plate.

You just took my post entirely out of context and then chose to nitpick it to mean something out of the wild blue yonder. I don't know why so many guys on this board do that. I guess it's the internet and that's what people do here.

Jesus H.

 

[petrolero]

Are we talking about the same Instrument Procedures Handbook? The FAA publication with that name I am familiar with is intended for pilots and is sort of an expanded AIM that deals with instrument flight from airport ground operations to emergencies.

I don't think it has anything about the minutia of how IAPs are created, other than mentioning that design is based on TERPS requirements (the primary source of the minutiae of approach design). Of course, we might have differing views of whether such things as

An instrument approach may be divided into as many as four approach segments: initial, intermediate, final, and missed approach. Additionally, feeder routes provide a transition from the en route structure to the IAF. FAA Order 8260.3 (TERPS) criteria provides obstacle clearance for each segment of an approach procedure as shown in Figure 4-29 .
​

is minutiae or unnecessary crap.

Personally, while I would hardly think of it as vacation reading material, I've found it very helpful as a reference for explanations on instrument flight that go beyond the IFH.

Yes that's the one. Don't get me wrong, there is some very detailed info in there and it is a fantastic reference. But my point is that it's dense and full of minutia and it's not necessary to read that as any kind of pre-req for safe IFR flight.

I did read some of it and quickly realized that the important one for me to read and know well was the Instrument Flying Handbook, not the procedures one.

 

[fiveoboy01]

Is a "plate" also known as an "instrument approach procedure" or are those "patently different" in your world?

Also... no **** you fly to the "minima on the plate". But which one? There are several. That's exactly what I was referring to and what the thread is discussing. But you "choose" which one you are descending to. The point in that post is that it doesn't change how you refer to the approach vis-a-vis ATC. You just call it by the name on the plate.

You just took my post entirely out of context and then chose to nitpick it to mean something out of the wild blue yonder. I don't know why so many guys on this board do that. I guess it's the internet and that's what people do here.

Jesus H.

 

[midlifeflyer]

Yes that's the one. Don't get me wrong, there is some very detailed info in there and it is a fantastic reference. But my point is that it's dense and full of minutia and it's not necessary to read that as any kind of pre-req for safe IFR flight.

I did read some of it and quickly realized that the important one for me to read and know well was the Instrument Flying Handbook, not the procedures one.

I think we agree on a lot. I see them and being different with different purposes and uses.

I think of one (IFH) as a textbook one reads for a course and the other (IPH) as a reference manual one uses to look stuff up when one is interested in more detail about something.