Localizer HILPT with GPS?

[Marc_B]

Watched a webinar that stated you cannot use your GPS for navigating a procedure turn for ILS/LOC approach if GPS isn't in the title.  I thought that I understood that you MUST be navigating with raw LOC data by the time you hit the FAF/final approach course, but this lecture from Gary GPS stated that you must be on LOC/green needles for the procedure turn.  Is that correct?

So with the GTN/GFC500 in order for the AP to fly a coupled HILPT on an approach it will fly this with GPS, then switch to the LOC (green needles) when the FAF becomes the next waypoint.  NOTE: for GTN, this is when the aircraft is turning inbound and about to intercept the LOC course leading up to the FAF.  So I make sure that I've switched by the time I hit the final approach course.  But I did not take that to mean you can't use GPSS for the PT/HILPT leading up to this...

edit: in my scenario, I do have the LOC "bearing pointer" turned on, have tuned and am monitoring the LOC that appears on my HSI during the HILPT even when GPS is the primary source for AP navigation.

https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/946030

8.  Uses of suitable RNAV systems not allowed by this AC. An otherwise suitable RNAV system cannot be used for the following:

a.  NOTAMed Procedures

b.  Substitution on a Final Approach Segment

c.  Lateral Navigation on LOC-Based Courses. Lateral navigation on LOC-based courses
(including LOC back-course guidance) without reference to raw LOC data.

[PeteMc]

Looks like you're reading an older AC that is specific to "RNAV" systems, not GPS.

"...NOTE: This AC does not address the use of RNAV systems on RNAV routes and RNAV terminal procedures. The current edition of AC 90-100, U.S. Terminal and En Route Area Navigation (RNAV) Operations, applies to those operations. This AC also does not address the use of RNAV systems on instrument approach procedures (IAP) titled RNAV (GPS) and GPS..."

 

Edited May 23, 2024 by PeteMc

[midlifeflyer]

It’s about that last part of what you quoted. If Gary said you can’t fly any portion of the procedure turn with GPS, I disagree. After all, those were designed as dead reckoning segments and that’s how we flew them before GPS.

But if he’s saying that you have to intercept a green LOC inbound course, even if outside the FAF, I agree.

[Marc_B]

https://www.nafisummitcourses.site/2023/5.html/
 

A lot of his remarks were about using auto switch but at 17:25 he says you can’t use GPS for ANY part of localizer approach including the procedure turn. I’ve never read or understood that.

@PeteMc I may have linked the wrong AC. Was trying to find the proper reference and was having trouble finding it this morning. 

[donkaye]

As mentioned above those references are waaaay out of date.  It used to be that you could use GPS as a monitor to VOR approaches from the FAF to the MAP.  Within in the past several years that has been replaced with you can use GPS as the primary nav source from the FAF to the MAP if you monitor the underlying nav source.  WRT HILPT, they wouldn 't be in the database if they were illegal.  I'll continue to teach their use when available in conjunction with ILS approaches.

Actually, AIM 1-2-3c seems explain it all.  

I see a distinction between 1-2-3c4 and 1-2-3c5.  The first was flying the approach in lieu of the underlying navaid and was used initially as an overlay approach before new GPS approaches were designed.  The second is used when the underlying navaid IS available and can be used in conjunction with it to fly the final approach segment.  1-2-3c2 specifically excludes GPS in lieu of ILS, LOC, and back course approaches.

[Marc_B]

@donkaye Main thing I recall for reference was from AIM 1-2-3 c. Uses of suitable RNAV Systems.  I was trying to find this and came across the AC linked above that read similar. Disregard old reference.

[Marc_B]

54 minutes ago, PeteMc said:

This AC also does not address the use of RNAV systems on instrument approach procedures (IAP) titled RNAV (GPS) and GPS..."

What I’m talking about is an “ILS or LOC” approach. Not referring to approaches with GPS in the title. 

I.e. KGXY ILS or LOC Rwy 35

https://skyvector.com/files/tpp/2405/pdf/00325IL35.PDF

[donkaye]

35 minutes ago, Marc_B said:

@donkaye Main thing I recall for reference was from AIM 1-2-3 c. Uses of suitable RNAV Systems.
 

I was trying to find this and came across the AC linked above that read similar. Disregard old reference. What is the current reference pertaining to this besides AIM?

I saw the document and may have saved it, but I can't find it now.

[Rick Junkin]

3 hours ago, Marc_B said:

Watched a webinar that stated you cannot use your GPS for navigating a procedure turn for ILS/LOC approach if GPS isn't in the title.

I just watched the same video after reading your post - I'm assuming it was the recording of Gary's presentation at the NAFI Summit?

BLUF (bottom line up front): His context was mistakes instructors make when teaching GPS (in his opinion), how to best teach GPS so your student doesn't fail his/her check ride (in his opinion),  and implies his methods will prevent common oversights when things don't go optimally on approach, which they will. He says "Don't do it" but doesn't say you can't do it, with the intent of encouraging instructors to teach their students using raw LOC data for the entirety of a non-GPS approach. His opinion and technique, and not necessarily what is legal and not legal.

3 hours ago, Marc_B said:

So with the GTN/GFC500 in order for the AP to fly a coupled HILPT on an approach it will fly this with GPS, then switch to the LOC (green needles) when the FAF becomes the next waypoint.  NOTE: for GTN, this is when the aircraft is turning inbound and about to intercept the LOC course leading up to the FAF.  So I make sure that I've switched by the time I hit the final approach course.  But I did not take that to mean you can't use GPSS for the PT/HILPT leading up to this...

edit: in my scenario, I do have the LOC "bearing pointer" turned on, have tuned and am monitoring the LOC that appears on my HSI during the HILPT even when GPS is the primary source for AP navigation.

This is the way I do it as well. Gary's implication, and I think he even says it at one point, is that the student on a check ride will only be looking at the PFD and not at the NAV 2 CDI, and will not catch that the system has not auto-switched from GPS to VLOC. Of course this assumes the PFD can't display both the GPS course and the LOC info you have on your bearing pointer, and that the student won't be cross-checking a separate NAV 2 CDI with the LOC course. There are other ways to teach it to achieve the same results.

Cheers,
Junkman

[Marc_B]

@Rick Junkin I agree with your thoughts above.  Yes, this was from the NAFI Summit directed at instructors teaching students.  But from the video Gary says, “You may not use GPS as your primary reference for ANY part of a localizer-based approach, ESPECIALLY the procedure turn.  That is NEVER allowed.  Why?  Because you don’t have the obstacle clearance you think you do.”

This is what confused me.  I was not taught this and couldn't find a reference that would suggest you can't use GPS for the HILPT.  I was under the impression that you could use GPS while you're monitoring the LOC up until the FAF when you must be on primary LOC data (I'm always on green needles prior to this).  However, reading the AIM further it sounds like you should be on Green Needles with raw localizer data anywhere along the localizer course / anywhere on the final approach course.

From Pilot/Controller Glossary:  FINAL APPROACH COURSE- A bearing/radial/track of an instrument approach leading to a runway or an extended runway centerline all without regard to distance.

From AIM 1-2-3:

[midlifeflyer]

3 hours ago, Marc_B said:

@donkaye Main thing I recall for reference was from AIM 1-2-3 c. Uses of suitable RNAV Systems.  I was trying to find this and came across the AC linked above that read similar. Disregard old reference.

The AIM is generally more up to date than the older AC.

[Rick Junkin]

1 hour ago, Marc_B said:

@Rick Junkin I agree with your thoughts above.  Yes, this was from the NAFI Summit directed at instructors teaching students.  But from the video Gary says, “You may not use GPS as your primary reference for ANY part of a localizer-based approach, ESPECIALLY the procedure turn.  That is NEVER allowed.  Why?  Because you don’t have the obstacle clearance you think you do.”

 He then described the difference between the GPS course width guidance and the LOC angular course guidance, which is the same consideration that prevented GPS approaches from being termed "precision" approaches. I believe his point is that the LOC bounds the PT or HILPT on the approach course side, and the GPS course width can allow you to be beyond the LOC course on the wrong side of the line. That would explain his statement about obstacle clearance. If you aren't on the PT/HILPT side of the LOC course you aren't guaranteed obstacle clearance.

 

My bottom line understanding from the AIM is the LOC course line is the ground truth and must be referenced for final course determination and guidance. That said, I can use my GPS to steer through the PT/HILPT as long as I am monitoring the LOC course to ensure I stay on the PT/HILPT side. As @midlifeflyer said above, this is a DR portion of the approach. You can use the guidance you want (DR, GPS, RNAV, etc) to execute it, but you need to be referencing the LOC for the final course.

Cheers,
Junkman

[Rick Junkin]

TL;DR Me editorializing.

Getting back to the source that generated all of this discussion - I need to be mindful when reading or viewing Gary's products. He has a lot of good points and perspectives, but also makes some statements up front that set the stage for potential misinterpretation of his opinions as facts. He clearly states that some of what he is going to tell us is his opinion and contrary to what we know or think we know and that we should maintain an open mind and listen to his arguments. Then after we get into the meat it's easy to get caught up in his presentation style and forget he's opining. He's got some really good techniques developed from vast experience, and he comes across as motivated to help us all be better.

We had a catch phrase when I was in flight school all those years ago. "Technique only". It referred to A way to execute something, not THE way. A technique that fits the rules and works for the person using it is a good technique. There's no need to abandon what works for you without a compelling reason to do so.

Cheers,
Junkman

[Pinecone]

FYI, he is a good guy to talk to.  He was at Mooney Max and I had some comments about a couple things he said.  Had a very nice talk with him and he explained his concept, but acknowledged my points and we came to a mutual agreement.

[Rick Junkin]

35 minutes ago, Pinecone said:

FYI, he is a good guy to talk to.

Thanks for that, I'll look forward to meeting him some day.

Cheers,
Junkman

[PeteMc]

8 hours ago, Marc_B said:

A lot of his remarks were about using auto switch but at 17:25 he says you can’t use GPS for ANY part of localizer approach including the procedure turn. I’ve never read or understood that.

@PeteMc I may have linked the wrong AC. Was trying to find the proper reference and was having trouble finding it this morning. 

I had a chance to watch the video.  I think you took him out of context.  He was specifically talking about Checkrides and what DPEs were failing people for.  He never referenced any Reg that says you can't do the PT with a GPS.  And if there were one, I think Garmin's lawyers would not allowed their devices to fly the PT on GPS and THEN switch to VLOC.  

He also makes a great point about NOT relying on the Auto Switch.  You need to monitor it or just go ahead and switch over once you are Inbound.

 

Edited May 24, 2024 by PeteMc

[midlifeflyer]

9 hours ago, PeteMc said:

He also makes a great point about NOT relying on the Auto Switch.  You need to monitor it or just go ahead and switch over once you are Inbound

I absolutely agree with Gary on that point. Auto switch is for when you screw up and forget to manually switch.  And even then…

I saw a checkride failure by a pilot who relied on auto switch. Blew right through the localizer course. Twice, since the DPE was kind enough to vector the applicant around for a second attempt.  As the students instructor described the checkride sequence, I could see the bust coming.

[midlifeflyer]

14 hours ago, Rick Junkin said:

bottom line understanding from the AIM is the LOC course line is the ground truth and must be referenced for final course determination and guidance. That said, I can use my GPS to steer through the PT/HILPT as long as I am monitoring the LOC course to ensure I stay on the PT/HILPT side.

Not even that. You need to remain in the protected area. Remember that the parallel entry as described by the AIM takes place on the non-holding side, not on the LOC course. There is enough protected area on the nonholding side to account for a parallel entry that crosses the holding fix almost perpendicular at max holding speed with a 50 it tailwind.

[Rick Junkin]

34 minutes ago, midlifeflyer said:

Not even that

Yeah, I was grasping at straws to understand what he meant about not having obstacle clearance. I guess the only way to know is to ask him.

[Marc_B]

Certainly understand that Gary's main point was don't rely on autoswitch as there are scenarios that it might not switch and with regards to check ride this is a clear gotcha that I'm sure DPEs are VERY familiar with.  I just didn't/don't understand what he was talking about with regards to procedure turn other than I guess switch to raw nav early so you don't have an issue.  Also I guess if you aren't flying coupled it doesn't matter as much if you switch early.

From my understanding, the localizer course is easier for ATC to sequence you with vectors to anywhere along the LOC and separation requirements keep the ILS still in use.  So I think it's also important to understand the nuance and quirks of ILS especially with regards to what your technology is doing, and why, is important.

[Pinecone]

I just contacted him with a link to this thread.

[Ibra]

You can use anything you wish to fly a procedure, the rules are about equipment carriage and procedure monitoring(not having stopwatch for timed VOR is illegal), the rules are not about the actual usage of equipment  These questions are moot for single pilot in Part91 

You can fly the whole procedure in GPS with magenta (as long as you monitor stopwatch for turn and you stay within LOC scale deviations), there is nothing in the regulation that says what you should display and when to switch !

Checkride & DPE practices is a different matter as the goal is to test the ability to fly on raw data (GPS failure is one scenario to test)

 

 

Edited May 25, 2024 by Ibra

[midlifeflyer]

43 minutes ago, Ibra said:

You can use anything you wish to fly a procedure, the rules are about equipment carriage and procedure monitoring(not having stopwatch for timed VOR is illegal), the rules are not about the actual usage of equipment  These questions are moot for single pilot in Part91 

You can fly the whole procedure in GPS with magenta (as long as you monitor stopwatch for turn and you stay within LOC scale deviations), there is nothing in the regulation that says what you should display and when to switch !

Checkride & DPE practices is a different matter as the goal is to test the ability to fly on raw data (GPS failure is one scenario to test)

 

 

As already quoted a few times, current US regulatory guidance (most current is AIM 1-2-3) precludes using GPS to fly a localizer course.  It’s not even in the OK while monitoring raw data group. (I suspect the reason is that GPS will annunciate LNAV rather than LP, so the tolerances are not there.)

What one can get away with without ATC noticing a deviation is a different story. Heck, on a calm day, you might get away with nothing but dead reckoning. With no clouds, not even that, just shut off the avionics and look at the runway.

[Ibra]

50 minutes ago, midlifeflyer said:

As already quoted a few times, current US regulatory guidance (most current is AIM 1-2-3) precludes using GPS to fly a localizer course.  It’s not even in the OK while monitoring raw data group. (I suspect the reason is that GPS will annunciate LNAV rather than LP, so the tolerances are not there.)

If you don't have LOC equipment you can't fly LOC on final guidance for the reason you mentioned...

I meant you already have GPS equipment and LOC equipment: you can legally have GPS from NAV1 displayed on HSI1 and LOC from NAV2 displayed on CDI2, there is nothing in regulation that says you should auto-switch here and there, display loc on nav1, disable gps...

As long as CDI2 is within loc protected angles, you can fly on magenta LNAV guidance on HSI1 

The same can be said on use DTK & TRK to set wind corrected heading and stay on LOC? or use GPS ground speed data to calculate rate of descente on LOC finale with CDFA?  

Edited May 25, 2024 by Ibra

[midlifeflyer]

35 minutes ago, Ibra said:

I meant you already have GPS equipment and LOC equipment: you can legally have GPS from NAV1 displayed on HSI1 and LOC from NAV2 displayed on CDI2, there is nothing in regulation that says you should auto-switch here and there, display loc on nav1, disable gps

I will stick with, “not according to current regulatory guidance” on the use of “suitable RNAV systems” and agree to disagree on what is required for primary nav on a LOC course.

(no one even remotely suggested disabling GPS, nor did I suggest another way wouldn’t work)