RNAV GPS Approaches

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FDXDave
Posts: 202
Joined: Mon Jul 17, 2017 7:56 pm

RNAV GPS Approaches

Post by FDXDave »

Hello Fellow Pilots and enthusiasts. So I have yet another question.
So I just started using RNAV / GPS Approaches. For the longest time, I have pretty much restricted myself to either an ILS Approach
or just basic Visual Approaches. So with the majority of RNAV Approaches there is a RVAN Glide Slope. I notice it the most when i fly
my Eclipse 550. I Just select the GPS Approach and when I see that I'm under the GS I press APPR the same way you would on an ILS APPR.
All the plane will start to descend with the GS marker.

So today I flew from DEN to EGE. I selected the RNAV / GPS "D" 25 Approach (IAF) Kremmling VOR. So I was guiding my self down all the way till around
3 NM to NEPRY 9860 feet. I never saw the GS on this APPR. So I just leveled out around 9860 Feet thinking the GS would catch up and start me down. Nope !
Had to switch to Visual approach. So my question is i guess, most of the other flights I do in this aircraft will show a GS even in RNAV....why did
this flight not display any GS ?? Is it published somewhere on the Approach plate that this RNAV APPR does not have a GS? If so where do I look? Or is it possible it
could be just an X-Plane thing, where the X-plane platform just did not enter all the GPS APPR information into the coding. Because I know it's not my plane
model, because it works on several others.

Thanks for any light you can shed on this.

Dave.
rtataryn
Posts: 344
Joined: Wed Mar 04, 2015 10:19 pm
Location: Spokane, WA

Re: RNAV GPS Approaches

Post by rtataryn »

Dave,

Not all RNAV approaches offer vertical guidance or a "glide path". (Technically, to pick nits, the term glide slope is specific to ILS or ground-based electronic components that emit a fixed angle signal, so for RNAV/GPS approaches the vertical guidance is termed a glide path.) The only RNAV approaches with glide paths are LPV approaches and LNAV/VNAV. There is also one other RNAV approach type, LNAV+V that offers an advisory only glide path, not approved, so you need to use LNAV minima for these. The approach you were on at KEGE, the RNAV(GPS)D has only CIRCLING minima. It is not an LPV or LNAV/VNAV approach, so it only offers lateral guidance with no vertical guidance, hence your GPS box wouldn't send a glide path signal to your instruments.

So I was guiding my self down all the way till around 3 NM to NEPRY 9860 feet. I never saw the GS on this APPR. So I just leveled out around 9860 Feet thinking the GS would catch up and start me down.

The approach plate allows you to descend to circling minimums after 3 NM to NEPRY, or down to 8900 feet. Had you been in the soup still and unable to go visual, you could have legally and safely dropped down to that altitude rather than leveling at 9860 feet.

Is it published somewhere on the Approach plate that this RNAV APPR does not have a GS? If so where do I look?

Yes, If the approach had vertical guidance (glide path) it would say LPV or LNAV/VNAV in the landing minimums section of the approach plate. Since your approach only has "CIRCLING" listed, there is no vertical guidance offered. That's how you'll know on future approaches. There's one more clue. Any approach plate that has a low alphabet letter like A,B,C or D after it indicates that it only offers circling minimums. So you can instantly know that these will only offer lateral guidance with no vertical path.
Rod
PPL, Instrument, ASEL, ASES
2013 Cirrus SR22T N877MS
2018 Icon A5 N509BA
1946 Piper J3 Cub N7121H
1942 Stearman N2S N6848
FDXDave
Posts: 202
Joined: Mon Jul 17, 2017 7:56 pm

Re: RNAV GPS Approaches

Post by FDXDave »

rtataryn wrote:Dave,

Not all RNAV approaches offer vertical guidance or a "glide path". (Technically, to pick nits, the term glide slope is specific to ILS or ground-based electronic components that emit a fixed angle signal, so for RNAV/GPS approaches the vertical guidance is termed a glide path.) The only RNAV approaches with glide paths are LPV approaches and LNAV/VNAV. There is also one other RNAV approach type, LNAV+V that offers an advisory only glide path, not approved, so you need to use LNAV minima for these. The approach you were on at KEGE, the RNAV(GPS)D has only CIRCLING minima. It is not an LPV or LNAV/VNAV approach, so it only offers lateral guidance with no vertical guidance, hence your GPS box wouldn't send a glide path signal to your instruments.

So I was guiding my self down all the way till around 3 NM to NEPRY 9860 feet. I never saw the GS on this APPR. So I just leveled out around 9860 Feet thinking the GS would catch up and start me down.

The approach plate allows you to descend to circling minimums after 3 NM to NEPRY, or down to 8900 feet. Had you been in the soup still and unable to go visual, you could have legally and safely dropped down to that altitude rather than leveling at 9860 feet.

Is it published somewhere on the Approach plate that this RNAV APPR does not have a GS? If so where do I look?

Yes, If the approach had vertical guidance (glide path) it would say LPV or LNAV/VNAV in the landing minimums section of the approach plate. Since your approach only has "CIRCLING" listed, there is no vertical guidance offered. That's how you'll know on future approaches. There's one more clue. Any approach plate that has a low alphabet letter like A,B,C or D after it indicates that it only offers circling minimums. So you can instantly know that these will only offer lateral guidance with no vertical path.
@rtataryn Thanks !! This is great. I had no idea. Thank you for the RNAV Lesson.
I see most major airports use GPS either X or Y Approaches So I know these have vertical guidance.
So if you are able to answer this in a few words...I dont want to take up to much of your time lol... what
is the difference between say Porland's GPS X 28L and GPS Y 10R Approaches. Same runway different letters.
I do see that they both offer vertical navigation by your explanation above.

Thank you for your help.

Dave.
Keith Smith
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Location: Pompton Plains, NJ
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Re: RNAV GPS Approaches

Post by Keith Smith »

Dave,

The presence of an X or Y approach at a given airport just means there are multiple RNAV approaches to the same runway. It says nothing at all about whether there is vertical guidance on a given approach. The only way to know if there is vertical guidance on a given approach is to look at the plate and examine the minimums.
rtataryn
Posts: 344
Joined: Wed Mar 04, 2015 10:19 pm
Location: Spokane, WA

Re: RNAV GPS Approaches

Post by rtataryn »

Yes, as Keith said, the X, Y and Z suffix is no indicator of vertical guidance; it just indicates that there is more than one RNAV approach for that runway. Take a look at the RNAV(GPS) Z RWY 8 approach into KBUR. The minimums section list three approach types, LP, LNAV and Circling. None of these offer vertical guidance. Like a LOC approach, they are lateral guidance only. Unless there is an LPV or LNAV/VNAV offered, you will not get a glide path. (With the exception of the advisory glide path in an LNAV+V gps box).

It's also important to confirm while actually flying the approach that you are getting that level of service. It's not guaranteed just because the approach plate has it listed. I've been on LPV approaches and lost WAAS signal, forcing me to downgrade my approach to LNAV minima, begin step downs, and lose my glide path.
Rod
PPL, Instrument, ASEL, ASES
2013 Cirrus SR22T N877MS
2018 Icon A5 N509BA
1946 Piper J3 Cub N7121H
1942 Stearman N2S N6848
FDXDave
Posts: 202
Joined: Mon Jul 17, 2017 7:56 pm

Re: RNAV GPS Approaches

Post by FDXDave »

OK. So the letters are only saying more than one GPS type of approach and that is how the Controller identifies exactly which one you have chosen. I get that part. now.

Good example using KBUR. Just LNAV, LP, and Circling. I now have it in my notes for quick reference, to look for LPV or LNAV/VNAV at the bottom of a plate.

Thanks Keith and Rtataryn. Very good information. : )

Dave.
Keith Smith
Posts: 9939
Joined: Sat Oct 09, 2010 8:38 pm
Location: Pompton Plains, NJ
Contact:

Re: RNAV GPS Approaches

Post by Keith Smith »

Dave,

FWIW, the nuances of approach plates and how they're named are all covered in the workshops. All of the information that is presented is there because it's practical, useful, and will come in handy at some point in your day to day flying :)
FDXDave
Posts: 202
Joined: Mon Jul 17, 2017 7:56 pm

Re: RNAV GPS Approaches

Post by FDXDave »

Keith Smith wrote:Dave,

FWIW, the nuances of approach plates and how they're named are all covered in the workshops. All of the information that is presented is there because it's practical, useful, and will come in handy at some point in your day to day flying :)
I'm guessing instrument approaches part 4 would be the workshop. I'll have to take a look.
I found IFR pretty easy to learn. When i was away last month a watched a few workshops you
Did on VFR. i found that very interesting. I'm now doing more VFR flying now
that i understand it better. I finally did a " pop up" IFR while flying VFR. Great source of info.
It will take me a while. But I'll make my way through those work shops.

Thanks
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