Why higher LPV minimums?

[poadeleted20]

My understanding is that the TSO C146AR WAAS GPS may fly any minimum line approved on the approach chart. There is a hierarchy in the annunciations on the WAAS GPS (LPV, L/VNAV, LNAV). You cannot fly any minimum line that is higher than the one annunciated, but you can fly anyone below the one annunciated.

First, let's make sure we're all aware that when you say "higher" and "below," you're talking about the location of the line on the approach chart, i.e., that the LNAV/VNAV line is located below the LPV line.

The main difference in the annunciation is the integrity values that are required to be met. The vertical and lateral guidance is the same. So with LPV annunciated, you can fly to the LPV DA minimums, the LNAV/VNAV DA minimums, or ignore the vertical guidance all together and fly to the LNAV MDA. This approach is one of the unusual cases where flying the LNAV/VNAV has an advantage with the WAAS GPS.

I'd sure like to see that in writing somewhere, because it's contrary to my reading of the manual.

 

[aterpster]

Actually, it's both -- the DA you see on your altimeter, and the DH you are above touchdown when you see DA on your altimeter. So, at Salisbury MD (KSBY) on the RNAV(GPS) 32, when operating in LPV mode, your DA is 253 MSL and your DH is 200 feet above the touchdown zone elevation, or TDZE, of 53 feet MSL.

I guess. But, there was no such thing as DA for a good part of my career. It was DH (and AH for fail-active CAT III). Then, Jeppesen went to DA to conform with ICAO and eventually the FAA caught up.

 

[Dave Siciliano]

Ron: Please be kind enough to point out where that is in the AIM or Instrument Procedures Manuel. We spend a lot of time looking. All we saw for DH was in Cat approaches. DA for others. And it lead us to believe DH is determined by RADAR altimeter. I'd like to point it out to the SIMCOM fellas if it's there somewhere. I always used DH on an ILS and was corrected.

Dave

 

[Brad Z]

Ron: Please be kind enough to point out where that is in the AIM or Instrument Procedures Manuel. We spend a lot of time looking. All we saw for DH was in Cat approaches. DA for others. And it lead us to believe DH is determined by RADAR altimeter. I'd like to point it out to the SIMCOM fellas if it's there somewhere. I always used DH on an ILS and was corrected.

Dave

DH is simply the old name for a DA.

 

[Dave Siciliano]

Yes, I know, minor stuff, but at recurrent they explained it and when I do on here, some folks don't seem to be up to speed on it. If memory serves correctly, on an ILS where minimums were shown, it used to say DH; that's not there anymore on the approaches I looked at. Admit, I didn't check them all.
Everyone can't go to recurrent each year; just pointing it out.

(resistance if futile (g)).

Best,

Dave

 

[Captain]

DA is a 'Decision Altitude' read off your altimeter. DH is a 'Decision Height' read off your radar altimeter assuming the ground below the plane is the exact same elevation as the TDZ.

The two are interchangeable. It is a point in space defined two ways...what your altimeter says and how high above the touch down zone. Why do we need two? Easy...clouds are measured as 'AGL' and your missed approach point is based on MSL. Pilots need to know both in order to plan and execute.

 

[gismo]

There are no downgrades from LPV to LNAV/VNAV. All downgrades are to LNAV without ever any vertical guidance. Unless an approach has LNAV/VNAV as the highest service available on the chart (better look for one soon as all of them are slated for adding a LPV), you will never see L/VNAV annunciated.

According to Eckalbar, if the LPV mins are 200 AGL the VAL drops from 50 to 35m and if the VPL is greater than 35m and equal to or less than 50m or on any LPV approach if the HAL is between the 40m HPL for LPV and the 556m HPL for LNAV/VNAV a WAAS GPS is supposed to downgrade from LPV to LNAV/VNAV if both exist. I don't know if any TSO C146s boxes will do that but the PG for my GNS480 indicates that it will always downgrade from LPV or LNAV/VNAV to LNAV if a protection limit is exceeded.

 

[Dave Siciliano]

DA is a 'Decision Altitude' read off your altimeter. DH is a 'Decision Height' read off your radar altimeter assuming the ground below the plane is the exact same elevation as the TDZ.

The two are interchangeable. It is a point in space defined two ways...what your altimeter says and how high above the touch down zone. Why do we need two? Easy...clouds are measured as 'AGL' and your missed approach point is based on MSL. Pilots need to know both in order to plan and execute.

I think we are in violent agreement, but most GA folks aren't flying with a RADAR altimeter. The baro altimeter is what they look at and make their decision on. Yes, they may know what the AGL altitude is, but the point being made for most GA folks is they are looking at what's now called DA.

'Nough said. I'll move along

Best,

Dave

 

[Captain]

I think we are in violent agreement, but most GA folks aren't flying with a RADAR altimeter. The baro altimeter is what they look at and make their decision on. Yes, they may know what the AGL altitude is, but the point being made for most GA folks is they are looking at what's now called DA.

'Nough said. I'll move along

Best,

Dave

No I agree. DH is important when you're setting up for the approach. The field is calling 100' Overcast? Okay...it's going to be tight on the ILS. Skip past the RA and look and my point about the relationship between going missed and knowing where the cloud layer is.

 

[John Collins]

First, let's make sure we're all aware that when you say "higher" and "below," you're talking about the location of the line on the approach chart, i.e., that the LNAV/VNAV line is located below the LPV line.

I'd sure like to see that in writing somewhere, because it's contrary to my reading of the manual.

To your first assumption, I specified the order of the hierarchy of annunciations (LPV, L/VNAV, LNAV) in my statement, but you are correct that it is also the same as the AeroNav Charts order from top line to the lowest line of minimums and on the Jeppesen charts it is from left to right.

It should not be controversial that when flying a RNAV approach with LPV minimums, it is a pilot option to fly the procedure to the LNAV minimums if they are charted on the same procedure. There are frequent instances where the LNAV minimums have a lower visibility requirement and might make a better choice for the pilot in a given situation. Occasionally, the LNAV minimums also have a lower MDA than the LPV DA on the same procedure, for example when a step down fix permits a descent after a obstacle is passed. When LNAV/VNAV minimums are the highest service, there are many more situations where the LNAV MDA is a better choice for a given situation. The same argument can be made when circling minimums are available, it may be the best choice to fly the LNAV to the circling MDA and then circle to land, even though the GPS is annunciating LPV or LNAV/VNAV. You are not claiming that this can't be done, but I doubt you will find a specific reference in any supporting documentation.

The vertical and horizontal flight path for a LPV and a LNAV/VNAV are the same if they are charted on the same chart and flown by a WAAS TSO C146AR GPS. The differences are in the minimum lines, specifically the DA and visibility requirements. Any LPV approach requires a tighter HAL and either the same or tighter VAL than the co-charted LNAV/VNAV requires, so the integrity requirements will always be met for the LNAV/VNAV if they are met for the LPV. When LPV is annunciated, integrity is better than required for the LNAV/VNAV and the path is the same, both vertically and horizontally. So what would be the argument for not permitting the LNAV/VNAV to be flown as the installation is approved to fly this exact same procedure if the LPV minimum was not charted with looser integrity standards.

The only reference that I could find is in the AIM 5−4−5. Instrument Approach Procedure Charts, paragraph k. ... "ATC clearance for the RNAV procedure
authorizes a properly certified pilot to utilize any minimums for which the aircraft is certified". Most WAAS GPS are certified for LPV, LNAV/VNAV, and LNAV and some are certified for LP.

 

[olasek]

Occasionally, the LNAV minimums also have a lower MDA than the LPV DA on the same procedure,

if at all possible I would like to see an example of that, please ...

But I agree that quite frequently visibility requirements are lower for LNAV as compared to ILS/LPV.

 

[John Collins]

if at all possible I would like to see an example of that, please ...

But I agree that quite frequently visibility requirements are lower for LNAV as compared to ILS/LPV.

View attachment lpv da higher than lnav mda kwt.pdf

 

[olasek]

John, most obliged. I could definitely claim I learned something new today.

 

[aterpster]

According to Eckalbar, if the LPV mins are 200 AGL the VAL drops from 50 to 35m and if the VPL is greater than 35m and equal to or less than 50m or on any LPV approach if the HAL is between the 40m HPL for LPV and the 556m HPL for LNAV/VNAV a WAAS GPS is supposed to downgrade from LPV to LNAV/VNAV if both exist. I don't know if any TSO C146s boxes will do that but the PG for my GNS480 indicates that it will always downgrade from LPV or LNAV/VNAV to LNAV if a protection limit is exceeded.

Garmin WAAS navigators will downgrade from LPV to LNAV/VNAV. Having said that, the Garmin engineer I work with said the chances of seeing it happen are very unlikely.

 

[aterpster]

Ron: Please be kind enough to point out where that is in the AIM or Instrument Procedures Manuel. We spend a lot of time looking. All we saw for DH was in Cat approaches. DA for others. And it lead us to believe DH is determined by RADAR altimeter. I'd like to point it out to the SIMCOM fellas if it's there somewhere. I always used DH on an ILS and was corrected.

Dave

DH and DA are identical. The only IAP where the radar altimeter is authorized to determine minimums is on most Cat II IAPs. In that case it is RA, not DH or DA. RA is surveyed and often different than that CAT II DA. Some CAT II IAPs do not have RA because the terrain is too rough for an acceptable RA reading.

 

[John Collins]

Garmin WAAS navigators will downgrade from LPV to LNAV/VNAV. Having said that, the Garmin engineer I work with said the chances of seeing it happen are very unlikely.

Not according to the AFMS, the pilot guide and the messages that support fail-down, it is only to LNAV without any vertical guidance possible, so fail-down to LNAV/VNAV is not supported.

Here is what the TSO C146AR reference specification DO-229C/D has to say on the subject, emphasis is mine:

In approach mode the current approach type shall be continuously annunciated in accordance with the database (see section 2.2.4.5.1 and 2.2.5.5.1) and switches to LNAV during fail-down from LNAV/VNAV or LPV.

Any GPS that did a fail down to LNAV/VNAV would be in violation of the TSO.

 

[poadeleted20]

Ron: Please be kind enough to point out where that is in the AIM or Instrument Procedures Manuel. We spend a lot of time looking. All we saw for DH was in Cat approaches. DA for others. And it lead us to believe DH is determined by RADAR altimeter. I'd like to point it out to the SIMCOM fellas if it's there somewhere. I always used DH on an ILS and was corrected.

Dave

It's in the pilot/controller glossary and 14 CFR 1.1.

 

[poadeleted20]

I think we are in violent agreement, but most GA folks aren't flying with a RADAR altimeter.

Radar altitude is something else entirely. It is the height above the ground below you at the MAP for a Cat II ILS, and it is the controlling value for missed on a Cat II. Since the ground elevation at that point short of the runway may not be the same as the TDZE, RA is not necessarily the same as DH. The Cat II
Rwy 10 at BWI is a good example, where the ground at the MAP is 4 feet lower than the runway, so the RA is 104 for a DH of 100.
http://155.178.201.160/d-tpp/1204/00804I10C2.PDF
And if you use your radar altimeter to determine arrival at decision height on a Cat I ILS at a hilltop airport like Wilkes-Barre, you may hit something hard.

 

[poadeleted20]

DH and DA are identical.

Only if the touchdown zone elevation is sea level (0 MSL).

 

[aterpster]

Not according to the AFMS, the pilot guide and the messages that support fail-down, it is only to LNAV without any vertical guidance possible, so fail-down to LNAV/VNAV is not supported.

Here is what the TSO C146AR reference specification DO-229C/D has to say on the subject, emphasis is mine:



Any GPS that did a fail down to LNAV/VNAV would be in violation of the TSO.

I'll have to ding the Garmin senior engineer I work with.:wink2:

I have DO-229 here somewhere. I'll have to do a phrase search.

 

[aterpster]

Only if the touchdown zone elevation is sea level (0 MSL).

Do you have a reference?

Added: I see the distinction in Part 1. But, it makes no sense because that is that definition of HATh, formerly HAT.

DH was around for many, many years, and it was based on MSL.

 

[Dave Siciliano]

It's in the pilot/controller glossary and 14 CFR 1.1.

Thanks! I'll take a look.
Sure is getting technical and confusing. A reasonable pilot shouldn't have to dig through all of this for things that should be pretty clear and simple. Even the professionals seem to have valid concerns/disagreements. Don't know how the part time GA folks can be expected to keep this clear.

Best,

Dave

 

[Captain]

DH and DA are identical.

I assume you mean they are an identical point in space. Clearly DA is an MSL altitude and DH is the number of feet above the TDZE the point in space is.

That's what you meant, right?

 

[Everskyward]

I assume you mean they are an identical point in space. Clearly DA is an MSL altitude and DH is the number of feet above the TDZE the point in space is.

DA (MSL) and DH (AGL) are the identical point in space. The thing is that you don't have a way of measuring DH in the cockpit. You can't use the radar altimeter because the level of the ground in advance of the threshold fluctuates.

 

[aterpster]

DA (MSL) and DH (AGL) are the identical point in space. The thing is that you don't have a way of measuring DH in the cockpit. You can't use the radar altimeter because the level of the ground in advance of the threshold fluctuates.

Exactly. And, in TERPs terms its about DA and HATh. There are more than a few airports where the elevation is significantly lower below the DA point than at the threshold.

 

[poadeleted20]

A reasonable pilot shouldn't have to dig through all of this for things that should be pretty clear and simple.

I agree -- that's why I teach it as part of the program when training someone for an IR. Learn it early and it stickes -- Law of Primacy.:wink2:

 

[olasek]

I'll have to ding the Garmin senior engineer I work with.:wink2:

I have DO-229 here somewhere. I'll have to do a phrase search.

I also recall from Trescott's books and from other sources that when downgrade occurs you are automatically at LNAV, there are no 'intermediate' downgrades that would put you say at LNAV/VNAV or LNAV+V.

 

[aterpster]

Not according to the AFMS, the pilot guide and the messages that support fail-down, it is only to LNAV without any vertical guidance possible, so fail-down to LNAV/VNAV is not supported.

Here is what the TSO C146AR reference specification DO-229C/D has to say on the subject, emphasis is mine:



Any GPS that did a fail down to LNAV/VNAV would be in violation of the TSO.

I only have DO-229C. I did a word search for "fail-down," which returned no results. Garmin WAAS navigators are presently certified to DO-229C. Perhaps the prohibition came with 229D.

 

[aterpster]

Attached is a page from the Cessna Mustang G-1000. The underlined statement implies that downgrade is allowed prior to the FAF.

 

[John Collins]

I only have DO-229C. I did a word search for "fail-down," which returned no results. Garmin WAAS navigators are presently certified to DO-229C. Perhaps the prohibition came with 229D.

I went thru DO-229C and agree that the wording was not there, it was introduced in DO-229D. In looking at other related wording, one can read it such that it might be possible to permit at the time of approach selection that a lower level of service be provided if the HPL and VPL permit it. Assuming an approach has a LPV, LNAV/VNAV, and LNAV line of minimums, with the LPV being of the 200 DH variety which has a HAL of 40 meters and a VAL of 35 meters, one could have a situation where the VPL was lower than the LPV VAL, but still below the LNAV/VNAV VAL of 50 meters. In theory, it would be possible that the LNAV/VNAV would be permitted to be annunciated. In practice, I don't see it. What I see if the integrity is not met at the time of the approach selection is that LPV would be selected as the annunciation, but that it would not be green and would be yellow instead.

I don't have a way of testing this on the GNS series or the G1000 series, but do on the GTN series. I can manually set the HPL and VPL on the GTN series trainer to this condition, and it works as I described above, LPV is annunciated, but it is yellow. A subsequent downgrade or fail down at 1 minute prior to the FAF occurs. On the GNS or G1000 trainer, all I can do is turn off SBAS, in which case at the time of selection LNAV is the service level offered. If I turn off SBAS after the approach selection, a downgrade occurs immediately after the FAF fix becomes the active fix, it does not wait for the 1 minute to go point to fail-down.

At the one minute prior to the FAF, the only downgrade option is to LNAV without any vertical guidance.

The AFMS and Pilot Guides are consistent that the only downgrade is to LNAV. I have quoted the relevant sections from the documents I have available to me.

G1000 Messages:

APR DWNGRADE – Approach downgraded - Use LNAV minima when approach is downgraded.

GNS480 AFMS:

f) During a GPS LPV precision approach, or GPS LNAV/VNAV approaches, the GNS480 will downgrade the approach if the Horizontal or Vertical Alarm Limits are exceeded. This will cause the vertical guidance to flag unavailable. The procedure may be continued using LNAV only minimums.

GNS530W AFMS Text:

c) During a GPS LPV precision approach or GPS LNAV/VNAV approach, the 500W Series unit will downgrade the approach if the Vertical alarm limits are exceeded. This will cause the vertical guidance to flag as unavailable. The procedure may be continued using the LNAV only minimums.
d) During a GPS LP approach, the 500W Series may downgrade the approach prior to the Final Approach Fix if alarm limits are exceeded. If this occurs, a message will be displayed advising the pilot to use LNAV minimums. If alarm limits are exceeded after the Final Approach Fix, the 500W Series unit will flag the lateral guidance and generate a system message “ABORT APPROACH loss of navigation”. Immediately upon viewing the message the unit will revert to Terminal alarm limits. If the position integrity is within these limits lateral guidance will be restored and the GPS may be used to execute the missed approach, otherwise alternate means of navigation should be utilized.
e) During any GPS approach in which precision and non-precision alarm limits are exceeded, the 500W Series unit will flag the lateral guidance and generate a system message “ABORT APPROACH loss of navigation”. Immediately upon viewing the message the unit will revert to Terminal alarm limits. If the position integrity is within these limits lateral guidance will be restored and the GPS may be used to execute the missed approach, otherwise alternate means of navigation should be utilized.

GNS530W Pilot Guide:

Annunciation: LPV

Description:Localizer Performance with Vertical guidance (LPV) approach. Fly to LPV minimums. A yellow background indicates that the approach is safe to continue but a downgrade to LNAV may occur.

Sixty seconds prior to reaching the FAF (LOTKE), the unit will check the required Horizontal Alarm Limit (HAL) and Vertical Alarm Limit (VAL) to ensure the GPS position integrity is within limits to complete the LPV precision approach. In the event the HAL or VAL limits are exceeded, the approach will be downgraded to a nonprecision approach indicated by “Lnav ” on the moving map, a message that the approach is downgraded (“Approach downgraded - Use LNAV minima”), and the glideslope indicator will be flagged. You may continue the approach using LNAV non-precision minimums if there are LNAV minimums for this approach. In the rare event the GPS integrity cannot meet the non-precision HAL limits, the unit will send a message to the pilot to abort the approach (“Abort Approach - Loss of Navigation”). The
unit will revert to terminal limits to support navigation to the missed approach when the message is acknowledged.

5. Sixty seconds prior to reaching the FAF, the 500W-series unit will check the required Horizontal Alarm Limit (HAL) to ensure the GPS position integrity is within limits to complete the LP non-precision approach. In the event the HAL limits are exceeded, the approach will be downgraded, when available, indicated by “LNAV” on the moving map, otherwise the approach will be aborted. A message will note that the approach is downgraded and the NAV indicator will be flagged. You may continue the approach using LNAV non-precision minimums if there are LNAV minimums for this approach. In the rare event the GPS HAL limits cannot meet non-precision limits, the 500W-series unit will notify the pilot with a message to abort the approach. The 500W-series unit will revert to terminal limits of 1.0 NM to support navigation
to the missed approach.

Approach downgraded — Use LNAV minima — This message will occur 60 seconds prior to the FAF if flying LNAV+V, L/VNAV, LP, or LPV approaches and WAAS integrity parameters have fallen below minimal limits. As a result, vertical guidance has been discontinued and the LP, LPV, LNAV+V, or L/VNAV approach you were flying has been downgraded.

GTN AFMS:

3.2.2 GPS APPROACH DOWNGRADE
During a GPS LPV, LNAV/VNAV, or LNAV+V approach, if GPS accuracy requirements cannot be met by the GPS receiver, the GTN will downgrade the approach. The downgrade will remove vertical deviation indication from the VDI and change the approach annunciation accordingly from LPV, L/VNAV, or LNAV+V to LNAV. The approach may be continued using the LNAV only minimums.

During a GPS approach in which GPS accuracy requirements cannot be met by the GPS receiver for any GPS approach type, the GTN will flag all CDI guidance and display a system message “ABORT APPROACH-GPS approach no longer available”. Immediately upon viewing the message, the unit will revert to Terminal navigation mode alarm limits. If the position integrity is within these limits lateral guidance will be restored and the GPS may be used to execute the missed approach, otherwise alternate means of navigation must be utilized.

GTN Pilot Guide _ Messages:

Message:Approach Downgrade - Approach downgraded. Use LNAV Minima.

Description: Approach has been downgraded from LPV or LNAV/VNAV, to an LNAV approach. Vertical guidance will be removed from the external CDI/HSI display.

Action: Continue to fly the approach using LNAV minimums.

 

[poadeleted20]

GNS530W AFMS Text:

Annunciation: LPV

Description:Localizer Performance with Vertical guidance (LPV) approach. Fly to LPV minimums. A yellow background indicates that the approach is safe to continue but a downgrade to LNAV may occur.

That's the part I was speaking of. It says "Fly to LPV minimums," and that's it. As I see it, flying to lower published LNAV/VNAV minimums would violate that section of the AFMS, with which, by regulation, compliance is mandatory.

 

[John Collins]

That's the part I was speaking of. It says "Fly to LPV minimums," and that's it. As I see it, flying to lower published LNAV/VNAV minimums would violate that section of the AFMS, with which, by regulation, compliance is mandatory.

That only permits flying to the LPV minimums, it doesn't prohibit flying to the other approved minimums. Clearly you don't mean one can't fly the approach to LNAV MDA minimums or LNAV circling minimums if they choose to just because LPV is annunciated. If you disagree, we will just have to agree to disagree.

According to your logic, I could not use the LNAV minimums or circle to land using category A minimums on this approach.

View attachment lpv da higher than lnav mda.pdf

 

[poadeleted20]

That only permits flying to the LPV minimums, it doesn't prohibit flying to the other approved minimums. Clearly you don't mean one can't fly the approach to LNAV MDA minimums or LNAV circling minimums if they choose to just because LPV is annunciated.

Obviously you can stop before reaching the LPV mins if appropriate, but it does not authorized flying to lower mins, such as the lower LNAV/VNAV mins in the chart that started this whole thread.

 

[John Collins]

Obviously you can stop before reaching the LPV mins if appropriate, but it does not authorized flying to lower mins, such as the lower LNAV/VNAV mins in the chart that started this whole thread.

I edited my prior post with an example and have repeated it here.

According to your logic, I could not use the LNAV minimums or circle to land using category A minimums on this approach if LPV was annunciated. I would have to wait for a day when the approach downgraded to a lower accuracy so I could circle, sorry that is not logical. You can't show anything to support your position other than your limited interpretation of those few words.

View attachment lpv da higher than lnav mda.pdf

 

[aterpster]

G1000 Messages:

I can only speak to the G-1000. The message you show is because of a GIA fault, not because of a degrading of the WAAS geometry or signal, if you will. The reference I posted above is absent a hardware failure and is included in the main body of the manual.

As my engineer friend stated, and I quote indirectly, if geometry is less than required for LPV but at least what is required for LNAV/VNAV, then the LNAV/VNAV level of service is technically possible. But, the chances of that happening are very remote.

 

[aterpster]

I edited my prior post with an example and have repeated it here.

According to your logic, I could not use the LNAV minimums or circle to land using category A minimums on this approach if LPV was annunciated. I would have to wait for a day when the approach downgraded to a lower accuracy so I could circle, sorry that is not logical. You can't show anything to support your position other than your limited interpretation of those few words.

View attachment 25923

I think you guys are saying the same thing. I also suspect, but would have to check to be certain, that this particular chart violates policy.

 

[John Collins]

I think you guys are saying the same thing. I also suspect, but would have to check to be certain, that this particular chart violates policy.

Ron and I are saying something quite different. He claims that you cannot use any other minimum if it is a lower DA/MDA than the annunciated minimum. I claim you can fly either minimum.

I will be interested if you find anything regarding policy on the MDA being lower than the DA on the same chart. This issue comes up much more often with the LNAV/VNAV verses VNAV and circling minimums being lower. The issue started when LNAV/VNAV minimums began being added to existing LNAV approaches, causing the circling minimums to go up for users that only had GPS NPA capability. Complaints from users (mostly GA) who saw their circling minimums rise to meet the higher LNAV/VNAV DA's caused the FAA to reevaluate the criteria for circling minimums so that the lowest value was determined by the lowest straight in minimum.

The IPG-ACF reported the following in their minutes:

MEETING 11-01: Tom Schneider, AFS-420, briefed that discussion is on-going between AFS-420 and 470 to determine whether not publishing LNAV/VNAV minimums when there is a large difference in DA and MDA is of value. There is also discussion of whether a maximum value should be established when there is a difference, and if so, what that value should be. To date, the issue is still under discussion to determine whether there is any benefit in eliminating LNAV/VNAV minimums in this situation. Lev Prichard, APA, asked if LNAV/VNAV minimums are taken away, will some operators lose the approach. JD Hood, Horizon Air stated that most pilots will use LNAV/VNAV to set up the approach and use vertical guidance to fly to the LNAV MDA. Brad Rush, AJV-3B, stated that under current policy, if the airport meets GQS standards, LNAV/VNAV minimums will be published. The issue will continue to be worked by AFS-42 and 470 through the US-IFPP. ACTION: AFS-420 (US-IFPP) and AFS-470.

Editor's Note: A telcon was held on May 3, 2011 with participation from the managers of AFS-470, AFS-420, AJW-913, and AJV-3B, as well as staff specialists from AFS-420. It was agreed that in order to continually support Commercial Aviation Safety Team (CAST) initiatives, LNAV/VNAV minimums will continue to be established wherever possible regardless of the difference in LNAV minimums. The associated circling MDA must be no lower than the lowest straight-in MDA. A policy clarification memo has been prepared.

MEETING 11-02: Tom Schneider, AFS-420, briefed that per the secretary's post-meeting note in the minutes of the last meeting, AFS-400 issued a policy memorandum on August 10, 2011, clarifying that LNAV/VNAV minimums must always be published whenever the glidepath qualification surface (GQS) is clear. A copy of the memo was included in the meeting folder and is attached here Tom recommended the issue be closed. Rich Boll, NBAA questioned that the memorandum appears to address the potential disconnect between Straight-In and Circling, but does not address the other related concern where LNAV/VNAV minimums (in accordance with applicable criteria) may be noticeably higher than LNAV-only. Bruce McGray, AFS-410, confirmed
that it is confusing for pilots to see precision minimums that are excessively higher than the non precision minimums. Rich referred to the Harrisburg, PA RNAV (GPS) RWY 13 approach that prompted the original issue paper. The LNAV/VNAV DA is 392 feet higher than the LNAV and circling MDAs. Additionally, the visibility requirement is 5 miles, much higher than the LNAV and circling visibility requirements. Rich suggested we may be giving pilots the message that it is safer to make a circling approach rather than a vertically guided straight-in approach. JD Hood, Horizon Air, interjected that it is not a safety discrepancy adding that there are other locations with the same situation. He emphasized that his airline does not want to lose LNAV/VNAV minimums and capability. Rich responded that using baro-VNAV under OpsSpec C-073 will provide the same vertical guidance benefit to the lower LNAV MDA. Rich added that an alternative to his recommendation would be to provide an explanation for this minima in the AIM and Instrument
Procedures Handbook (IPH). Tom Schneider asked whether this would resolve the issue for NBAA. Bruce McGray, AFS-410, took the action item to develop and coordinate proposed wording for the AIM and IPH with the concerned parties (NBAA, APA, and Horizon Air). ACTION: AFS-410.

I attended the IPG-ACF last week and will try to get a copy of the minutes on this item. I don't recall any change, but I was not taking notes on it.

 

[aterpster]

Ron and I are saying something quite different. He claims that you cannot use any other minimum if it is a lower DA/MDA than the annunciated minimum. I claim you can fly either minimum.

I will be interested if you find anything regarding policy on the MDA being lower than the DA on the same chart. This issue comes up much more often with the LNAV/VNAV verses VNAV and circling minimums being lower. The issue started when LNAV/VNAV minimums began being added to existing LNAV approaches, causing the circling minimums to go up for users that only had GPS NPA capability. Complaints from users (mostly GA) who saw their circling minimums rise to meet the higher LNAV/VNAV DA's caused the FAA to reevaluate the criteria for circling minimums so that the lowest value was determined by the lowest straight in minimum.

The IPG-ACF reported the following in their minutes:



I attended the IPG-ACF last week and will try to get a copy of the minutes on this item. I don't recall any change, but I was not taking notes on it.

The minutes will appear on the FAA site before too long. I recall that it was Harrisburg that prompted Rich to write that issue paper. I found some new IAPs with both LPV and LNAV-VNAV higher than CTL. So, I guess that is the way it is to be.

 

[olasek]

Originally I was convinced that Ron was correct but then John showed that plate for an airport in Alaska and this convinced me that it is not higher/lower that matters since if this was true we would end up with a paradox - downgrade from LPV to LNAV would not be possible at that airport - an obvious nonsense. So clearly it is not higher/lower but rather type of an approach. The way I understand it now there are only two possibilities - either you have the WAAS part in which case you may fly any type of approach that provides GP guidance or you don't have it and LNAV is your only option, and you can forget abut the higher/lower stuff.

 

[Captain]

I don't have WAAS and I fly LNAV/VNAV all the time.