LPV vs LP+V

[midlifeflyer]

5 minutes ago, donkaye said:

Again, I said a Baro-Corrected Altimeter Source was required for VNAV enroute descents on the GTNs and AP coupled VNAV descents for the GFC 500.  This is independent of the AiM.  It is dependent on what Garmin says works for their units. 

Obviously, what is available to the GPS and what the GPS/autopilot interface is capable of depends on the manufacturers of both and may depend on connections to other equipment. 

[donkaye]

1 hour ago, donkaye said:

Again, I said a Baro-Corrected Altimeter Source was required for VNAV enroute descents on the GTNs and AP coupled VNAV descents for the GFC 500.  This is independent of the AiM.  It is dependent on what Garmin says works for their units. 

This thread was originally talking approaches with vertical navigation.  Someone brought up VNAV so I chimed in about that.  With a baro-corrected altimeter and one of the GTN series GPSs and PFDs, VNAV is available with or without the GFC 500 and can be flown manually or on an autopilot such as the KFC 150 in V/S mode.  With a non Garmin AP it just requires more work to follow the step-downs.

[Marauder]

I thought I would share the following. My airport (N57) was serviced by a VOR approach that was NA’d this year. The FAA has agreed to develop two GPS approaches. I signed up for the FAA notifications to receive the details of the TERPS development. Thought I would share this so you can get an idea of what is involved in developing an approach.

You will note that the LPV version is not depicted on the preliminary chart. We have been informed that LPV approaches are added after the others are implemented. Our belief this is due to the additional development and flight testing required to meet the LPV requirements.

Enjoy!




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[Marauder]

The rest of the story...




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[Marauder]

NOTE: For some reason, Tapatalk loaded these in reverse order. For my first post, start at the bottom and work up from the approach plate. Same for the second post.


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[RobertGary1]

5 minutes ago, Marauder said:

NOTE: For some reason, Tapatalk loaded these in reverse order. For my first post, start at the bottom and work up from the approach plate. Same for the second post.


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Just curious does this get you lower than the mva? One of my home fields has no approach but atc can usually get you to 2,500 ft which is likely the lowest an approach would be due to terrain. But there could be other benefits to having an approach. . 

 

-Robert 

[midlifeflyer]

11 hours ago, RobertGary1 said:

But there could be other benefits to having an approach. . 

Are you asking about something other than a legal way to fly with no visibility to the 365' AGL minimums (better if they get LPV) with terrain and obstruction clearance guaranteed all the way down, and assessment for terrain and obstruction clearance on the way up?

[RobertGary1]

2 hours ago, midlifeflyer said:

Are you asking about something other than a legal way to fly with no visibility to the 365' AGL minimums (better if they get LPV) with terrain and obstruction clearance guaranteed all the way down, and assessment for terrain and obstruction clearance on the way up?

If you can get 365 agl that’s pretty good and worth it. I’m sure that’s lower than the mva.  
 

-Robert

[John Mininger]

21 hours ago, midlifeflyer said:

We have been talking about two completely different things, so let's make sure we are not talking about apples and oranges.

LPV - localizer performance with vertical guidance. FAA TERPS standards used for vertical guidance.

LNAV/VNAV - an approach with vertical guidance using FAA TERPS standards. It was originally designed for airlines with Baro-VNAV equipment but our WAAS boxes are designed to be capable of flying them without the old airline equipment. 

LNAV+V - From the FAA standpoint a pure lateral GPS approach. The +V only means a GPS manufacturer added a glidepath usually based on the standard 3° stabilized approach. Use at your own option and your own risk. No one flight tested it for obstacles.

I believe this is correct. LNAV/VNAV approaches were originally designed for certified Baro-VNAV equipment. Then when WAAS came along, and since these approaches were already certified, they just designed them into the WAAS GPS approach databases.

I've never read this in an AC or the AIM, but my understanding from various seminars that I've attended is that both ILS and LPV (if you stay on them) will give you obstacle clearance to the threshold. Whereas LP+V and RNAV+V will give you an obstruction free path to the MDA, but no guarantees beyond that. 

[midlifeflyer]

2 hours ago, RobertGary1 said:

If you can get 365 agl that’s pretty good and worth it. I’m sure that’s lower than the mva.  
 

-Robert

I didn't make up the number. It's the LP MDA in the pro forma chart he posted.

[midlifeflyer]

1 hour ago, John Mininger said:

Whereas LP+V and RNAV+V will give you an obstruction free path to the MDA

No. On an approach with no stepdowns, sure. But with stepdowns, don't even count on it for that. It is a purely lateral navigation approach with an advisory vertical guidance which does nothing more than hand you  a glidepath in the standard 3 degree range to assist you in maintaining a stabilized approach. Period. It provides nothing else. In fact, the only place you will see LNAV+V is where the FAA has decided there should not be a vertical glidepath.  If there is an LNAV/VNAV or LPV option, there is no LNAV+V.

If you follow it, it does not guarantee you wont bust stepdown minimums inside the FAF. It does not guarantee you won't hit something on the way to the MDA. 

It is so incredibly important to completely understand and accept that an approach with "+V" is not a vertical navigation approach. It is a purely lateral nav approach.

[RobertGary1]

I guess we really don’t know how gps manufacturers compute the advisory glide slope but I wouldn’t assume it’s 3 degrees. That wouldn’t even make sense because it could put you a long way from the runway.  I assume they’re taking two points (maybe iaf and runway) and making a slope out of that whatever angle it may be. 
 

-Robert 

[Marauder]

17 hours ago, RobertGary1 said:

Just curious does this get you lower than the mva? One of my home fields has no approach but atc can usually get you to 2,500 ft which is likely the lowest an approach would be due to terrain. But there could be other benefits to having an approach. . 

 

-Robert 

The MVA for our area is 2200'. The approach for RWY24 is currently close to the MDA for the terminating VOR approach. Our runway 6 never had an approach and the 365 MDA will be great to have. Our 24 runway has some obstacles in the approach path so I am not surprised to see a higher MDA.

[midlifeflyer]

51 minutes ago, RobertGary1 said:

I guess we really don’t know how gps manufacturers compute the advisory glide slope but I wouldn’t assume it’s 3 degrees. That wouldn’t even make sense because it could put you a long way from the runway.  I assume they’re taking two points (maybe iaf and runway) and making a slope out of that whatever angle it may be. 
 

-Robert 

All I can go by is what the device manufacturers say it is. That graphic is from the 750 manual. 

But why does it not make sense? An An ILS glideslope and a LNAV/VNAV and LPV glidepath bring you right down to the runway from the FAF on a 3° vertical path.  Besides, LNAV+V is not designed to bring you to the runway Only to the nonprecision MDA hopefully at or before the VDP (which is also based on a 3° glide path). 

 

[RobertGary1]

11 minutes ago, midlifeflyer said:

All I can go by is what the device manufacturers say it is. That graphic is from the 750 manual. 

But why does it not make sense? An An ILS glideslope and a LNAV/VNAV and LPV glidepath bring you right down to the runway from the FAF on a 3° vertical path.  Besides, LNAV+V is not designed to bring you to the runway Only to the nonprecision MDA hopefully at or before the VDP (which is also based on a 3° glide path). 

 

Because if you drew a 3 degree slope from some point (FAF, IAF) in many cases it could end up not even at the airport, especially if we know the airport already has some terrain (since the FAA didn't just publish a LPV). 

In every case I've flow in my Garmin system the +V ends up at the runway threshold. 

-Robert

[midlifeflyer]

24 minutes ago, RobertGary1 said:

Because if you drew a 3 degree slope from some point (FAF, IAF) in many cases it could end up not even at the airport, especially if we know the airport already has some terrain (since the FAA didn't just publish a LPV). 

In every case I've flow in my Garmin system the +V ends up at the runway threshold. 

-Robert

I can only suggest you look at the profile view of a few vertical guidance approaches and see what the angle is. Same for lateral-only approaches where some guidance is given. What does the one you flew say? Anything like this?

When you flew yours and followed the advisory path, what were your airspeed and descent rate?

[RobertGary1]

31 minutes ago, midlifeflyer said:

I can only suggest you look at the profile view of a few vertical guidance approaches and see what the angle is. Same for lateral-only approaches where some guidance is given. What does the one you flew say? Anything like this?

When you flew yours and followed the advisory path, what were your airspeed and descent rate?

Yours is a bit unique because the FAA has designed the approach for a 3 degree slope. That only works when terrain allows, not the norm in my experience. 

[RobertGary1]

59 minutes ago, Hyett6420 said:

Being the brand new owner of an IFD540 this is the most interesting thread on here.  To me, because i have to relate to known knowns, things are as follows:-

• LPV = ILS in old school speak
• LNAV = VOR approach
• LNAV + V = VOR plus guess your own glidepath.

Ive learnt that the +V is definitely to be taken with a pinch of salt of or you might find the odd tower block or mountain  in the way.  
im still learning LOADS.  this stuff is still very new in europe.

 

And LP+V

Be careful there are some legal differences between ILS and LPV though.

-Robert

[John Mininger]

2 hours ago, midlifeflyer said:

No. On an approach with no stepdowns, sure. But with stepdowns, don't even count on it for that. It is a purely lateral navigation approach with an advisory vertical guidance which does nothing more than hand you  a glidepath in the standard 3 degree range to assist you in maintaining a stabilized approach. Period. It provides nothing else. In fact, the only place you will see LNAV+V is where the FAA has decided there should not be a vertical glidepath.  If there is an LNAV/VNAV or LPV option, there is no LNAV+V.

If you follow it, it does not guarantee you wont bust stepdown minimums inside the FAF. It does not guarantee you won't hit something on the way to the MDA. 

It is so incredibly important to completely understand and accept that an approach with "+V" is not a vertical navigation approach. It is a purely lateral nav approach.

 

[John Mininger]

I've heard of pilots getting extremely close to obstructions when they treated a LNAV+V like a LPV or ILS and busted the MDA. But I have never heard of anyone getting close to obstructions when flying the +V to the MDA.

The advisory vertical guidance seemed to appear in the operating system of the 430W with little fanfare. Then, maybe 10 or so years ago it was taken out for a while. My understanding was that the FAA pressured Garmin take it out because pilots while using it, were getting a false sense of security and busting the MDA. I'm not sure why it came back, but I'm very glad that it did. There are some LNAV approaches that don't have it. Could it be that they're the ones where you could get close to an obstruction if you followed the +V from the FAF to the MDA?

[midlifeflyer]

2 hours ago, John Mininger said:

But I have never heard of anyone getting close to obstructions when flying the +V to the MDA.

 

[kortopates]

John is right, because he explicitly caveated with following it to MDA - not below. 

I think the video example may be confusing the real issue. The real issue is following an advisory glidepath below MDA - NOT TO MDA. We are afforded obstacle protection following it to MDA - just not below MDA. The video example cited the problem when a pilot descends below the MDA when obstacles are present on the visual portion of the approach. 

Advisory glide path, +V,  comes from the Continuous Descent from Final Approach (CDFA) principal that defines stabilized approach - the stabilized approach and CDFA are detailed in AC 120-08. Before we can have +V, the TERPSters that design the approach chart, have to publish a glide path angle from the FAF to runway. The FAA for years has been encouraging pilots to make one continuous descent from the FAF rather than the old "Dive and Drive" between step down fixes. By publishing a glide path angle that is able to meet all the step down fix requirements between the FAF and threshold, pilots can use that charted angle to make a continuous descent.  We can do that on every approach when we trying to follow a 3 degree glide path, for example, by maintaining a stable descent rate that matches the required feet per minute to a 3 degree descent rate.

Then Garmin came along and implemented the charted Glide path angle to make it easy for GA pilots to follow CDFA - but only when charted (as Mark showed in an example above). Of course, no manufacturer is making these up and they aren't necessarily always 3 degrees (they may range from 2.75º–3.77º) . Nor is there any danger in following these above MDA; only when a the pilot follows them below MDA/MDH as if it was a real glideslope (ILS or LPV).

Robert provides another good example above at Columbia of an approach where it would be dangerous to follow +V below MDA. One of the government charts deficiencies IMO is they don't always show the published glide path angle such as on the Columbia O22 RNAV 35.  The government chart shows no GPA on that approach. So therefore you won't know till you load an approach if it will have +V, or worse not until you fly it on a GNS navigator and see the GS come alive. But if you look at the corresponding Jepp chart you'll see the GPA is 3.04 degrees and thus you'll know as soon as you see the chart that the approach will have +V.  Plus the savvy pilot will also understand the note on the plan view that says "Visual Segment - Obstacles 34:1 is not clear" as well as symbology, or lack thereof, in the profile view that tells us about potential obstacles on the visual portion. 

Unfortunately with respect to the visual portion below minimums, when it comes to government charts, its more about a lack of symbology that tells us when we need to be extra careful. For example if we see a VDP (visual descent point) we know we should be good descending from the VDP to the threshold. Well almost, if the VDP also includes a grey stipple, then yes we have similar protection afforded just like a VASI or PAPI in that the 34:1 slope from the VDP is clear of obstacles. A 34:1 slope, or 178 FPNM, is much shallower than 3 degree and thus just like a VASI we could similarly drop a bit below the GPA,  like seeing 3 reds and 1 white, and still be okay. But without the grey stipple on the VDP, then we only have a 20:1 slope, or 304 FPNM, which is right at 3 degrees, so unlike the prior VASI comparison, we have no safe margin below the 3 degree slope and need to be more careful. But in the absence of a VDP its telling us that the visual path below MDA, following a charted GPA is not clear of obstacles! This isn't always clearly charted. 

Remember also too even VASI and PAPI's both have limits for obstacle protection, with lateral limits of +/- 10 degrees and distance limits of 4nm for VASI and 3 nm for PAPI.

 

Edited October 13, 2020 by kortopates

[John Mininger]

Just for the record, I have NEVER suggested going beyond the MDA on an advisory vertical glidepath without a good and legal visual view of the runway. Just like any other non-precision approach.

I remember about 10 years ago, having a rather animated discussion with a friend who was a very active 135 pilot, and was also a very active CFII. This was when WAAS and advisory vertical guidance (+V) was fairly new. He was arguing that in poor visibility, he would much rather descend to MDA quickly after the last stepdown fix, so he had more time to descend to the runway when he saw it. As opposed to getting to MDA at the intersection of +V and the MDA; which would be closer to the runway. He had a point. My point was that in the real world, the average instrument pilot was not as pristine a diver and driver as my friend, and it would be a much safer scenario for an average pilot to fly a stabilized approach to the MDA.

I think we came away not agreeing which method was best, but that we both had a point.

[John Mininger]

Paul,

Do you (or anyone else), happen to remember the circumstances behind the removal of the advisory vertical guidance on LNAV approaches, and then their subsequence return? I seem to remember that the removal coincided with the operating software update that added LP approaches. I remember being anxious to get access to the LP approaches with their lower minimums, only to find that the update took away the advisory vertical guidance.

At the time, I complained about their loss to just about anyone who would listen. Only to find that most people had no idea what I was talking about. One of the few people at the time who did know was J. Mac McClellan of Flying Magazine. He agreed with me, removing them was a mistake.

[kortopates]

3 hours ago, John Mininger said:

Paul,

Do you (or anyone else), happen to remember the circumstances behind the removal of the advisory vertical guidance on LNAV approaches, and then their subsequence return? I seem to remember that the removal coincided with the operating software update that added LP approaches. I remember being anxious to get access to the LP approaches with their lower minimums, only to find that the update took away the advisory vertical guidance.

At the time, I complained about their loss to just about anyone who would listen. Only to find that most people had no idea what I was talking about. One of the few people at the time who did know was J. Mac McClellan of Flying Magazine. He agreed with me, removing them was a mistake.

Indeed, I for one remember very well because of the local impact it had in my area. It was purely a knee jerk reaction by the FAA. The FAA had become deeply concerned with pilots that once they saw a glideslope of any kind, started flying them like a precision approach rather than a non-precision approach, and just like the example video above courtesy of Mark tried to fly it below MDA.  (I should caveat that some Operators conducting approaches authorized by operations specification (OpSpec) C073, Vertical Navigation (VNAV) Instrument Approach Procedures (IAP) Using Minimum Descent Altitude (MDA) as a Decision Altitude (DA)/Decision Height (DH), may in fact use MDA as a DA. But only with FAA authorization which likely won't apply to anyone's Mooney flying). The FAA apparently felt they needed to put a stop to this behavior immediately and and unilaterally - so they did the only thing they could do to bring effective and immediate change - they changed all the coded GPAs that they were concerned with  0º - which disabled them. Not only did it take away the charted GPA, but it did it in a way that broke the Garmin GPS firmware that also disabled the entire approach. So we didn't simply loose  the +V on many approaches, we lost the entire approach that previously had +V that the FAA coded to 0º. 

The main issue they went after was every +V where the "VGSI and descent angles not coincident". There may have been additional ones they went after, but when the Visual Glide Slope indicator was different from the charted approach descent angle is the main ones they coded to 0. They did start an education campaign too, but they obviously felt they need to remove the most "dangerous" ones first, then educate. By my limited recollection it took Garmin over a year, perhaps 1.5 years before they were able to bring back the approaches that had the coded 0º descent angle - so all that time we lost a great many LP and LNAV approaches  entirely that previously had +V. At my home base I lost an LP approach. Yet students of mine, that had an older Non-WAAS box ,actually got to fly that same approach down to LNAV minimums. But anyone that had a modern WAAS box had the entire approach disabled till they could fix the s/w to deal with the 0º descent angle.

I forget exactly how many years ago this happened, but it's been a while. But it wasn't until last fall of 2019 that we locally got back the +V in our LP approach that originally got disabled entirely back when this all started. That's right, the FAA has gone full circle on this and I assume feels more comfortable about trusting pilots to properly fly these enough to allow us to have them back - finally. As an example, on the SEE RNAV 17 approach the charted descent angle is only 3º (only shown on the Jepp version) but the VASI is 4º - so the danger is still there. So of course there is no VDP (nor grey stipple) , just the note or warning "Visual segment obstacles" .

Some additional irony on the fallout on this issue was with the very first Mooney G1000 WAAS software release. Can you believe Mooney and Garmin actually settled on the release of the first WAAS s/w version from this pre-fix days for 0º descent angle! As such, it was missing  something like over 360+ approaches disabled entirely because of this issue! How frustrating for anyone that could at least fly LNAV min's on a LP approach and where expecting to get LP min's capability with their G1000 WAAS upgrade but because of this snafu lost the approach entirely. At least that too was finally just recently fixed.