VOR Approaches Using GPS

[donkaye, MCFI]

Can a stand alone VOR (Not "or GPS") approach be completely flown using GPS as the primary source of navigation--especially on the final approach segment?  Too many people either don't know the answer to that question, answer it incorrectly, or are confused by AIM 1-2-3 Notes (4) and (5).  Careful reading of AIM 1-2-3 with support from AC 90-119 (draft) provides the answer.

My intention is just to provide the answer without going into a long dissertation.  The answer is a qualified, YES.

Qualifications:  1. A WAAS RNAV system TSO'd under TSO-C129 capable of navigating the final approach segment.  2. The underlying VOR must be operational.

Confusion arises by misinterpreting Note (4) in AIM 1-2-3.  It states, "Pilots may not substitute (my highlight) for the NAVAID providing lateral guidance for the final approach segment).  Note (5) says, "Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN, or NDB signal, is allowable.  The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment".

At first glance it appears that Notes (4) and (5) are contradictory.  They are not.  The critical word it SUBSTITUTE.  Substitute in Note (4) means using GPS exclusively for the approach.  Note (5) refers to using a "suitable navigation system" (for example a GTN 750) used in conjunction with the underlying VOR to run the approach.

Thus a VOR approach can be run using "a suitable navigation system" (WAAS GPS certified under TSO-129) as the primary source of navigation as long as the underlying VOR is operational and monitored along the final approach segment with either a CDI or bearing pointer.

[DCarlton]

I’ve actually wondered about this recently so….   I’ll be the dumb guy.   Why would WAAS be required when vertical guidance is not consistent with a VOR approach?  

[MikeOH]

I believe WAAS also provides more accurate lateral guidance; not just vertical.

[donkaye, MCFI]

14 minutes ago, DCarlton said:

I’ve actually wondered about this recently so….   I’ll be the dumb guy.   Why would WAAS be required when vertical guidance is not consistent with a VOR approach?  

I'd refer you to  AC 90-119.  PBN, Performance Based Navigation.  Read especially Chapter 12.

AC_90-119_Coord_Copy.pdf

[toto]

3 hours ago, donkaye, MCFI said:

Can a stand alone VOR (Not "or GPS") approach be completely flown using GPS as the primary source of navigation--especially on the final approach segment?  Too many people either don't know the answer to that question, answer it incorrectly, or are confused by AIM 1-2-3 Notes (4) and (5).  Careful reading of AIM 1-2-3 with support from AC 90-119 (draft) provides the answer.

My intention is just to provide the answer without going into a long dissertation.  The answer is a qualified, YES.

Qualifications:  1. A WAAS RNAV system TSO'd under TSO-C129 capable of navigating the final approach segment.  2. The underlying VOR must be operational.

Confusion arises by misinterpreting Note (4) in AIM 1-2-3.  It states, "Pilots may not substitute (my highlight) for the NAVAID providing lateral guidance for the final approach segment).  Note (5) says, "Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN, or NDB signal, is allowable.  The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment".

At first glance it appears that Notes (4) and (5) are contradictory.  They are not.  The critical word it SUBSTITUTE.  Substitute in Note (4) means using GPS exclusively for the approach.  Note (5) refers to using a "suitable navigation system" (for example a GTN 750) used in conjunction with the underlying VOR to run the approach.

Thus a VOR approach can be run using "a suitable navigation system" (WAAS GPS certified under TSO-129) as the primary source of navigation as long as the underlying VOR is operational and monitored along the final approach segment with either a CDI or bearing pointer.

It’s an interesting topic. My immediate thought was that Garmin provides guidance on use of the GTN as primary for a VOR approach on the final approach segment.. I grabbed my GTN manual (screenshot below). Garmin suggests that VLOC mode is “required” and that the pilot “must” switch from GPS to VLOC before the final approach segment.

If the AFMS for the navigator requires using the ground-based nav source as primary for the final approach segment, does the AFMS control the decision?

[donkaye, MCFI]

2 hours ago, toto said:

It’s an interesting topic. My immediate thought was that Garmin provides guidance on use of the GTN as primary for a VOR approach on the final approach segment.. I grabbed my GTN manual (screenshot below). Garmin suggests that VLOC mode is “required” and that the pilot “must” switch from GPS to VLOC before the final approach segment.

If the AFMS for the navigator requires using the ground-based nav source as primary for the final approach segment, does the AFMS control the decision?

You are correct.  If you have an older GTN 750 and not the Xi there may be an issue, if the AFMS says you must change to VOR for the FAS, as it doesn't look like Garmin updated their manual.  That is not the case with the latest GTN 750 Xi version.  See attached.  Since both models were certified to TSO C-129 standards, you would think they could both fly the VOR approach similarly.  I deliberately left off a Localizer type approach, since the FAS must be flown with the CDI in localizer mode, as there is no way to monitor it with a bearing pointer.

 

[midlifeflyer]

5 hours ago, toto said:

If the AFMS for the navigator requires using the ground-based nav source as primary for the final approach segment, does the AFMS control the decision?

If the Limitations section of the AFMS limits its use, it controls. This is from Revision 8 of the GTN (not Xi) AFMS Limitations, so no such limitation.

“2.10. When using the VOR or ADF receiver to fly the final approach segment of a VOR or NDB approach, GPS may be the selected navigation source so long as the VOR or NDB station is operational and the signal is monitored for final approach segment alignment.”

OTOH, Rev E for the older GNS W units does in 2.6

“GPS guidance can only be used for approach procedures with GPS or RNAV in the procedure title. When using the Garmin VOR/LOC/GS receivers to fly the final approach segment, VOR/LOC/GS navigation data must be selected and presented on the CDI of the pilot flying.”

AFAIK, the GNS limitations were never updated to the newer AIM guidance.

Edited Saturday at 11:01 AM by midlifeflyer

[Jackk]

Oddly I’ve been required to be in “green needles” on many a 135 & 121 ride

[midlifeflyer]

3 hours ago, Jackk said:

Oddly I’ve been required to be in “green needles” on many a 135 & 121 ride

I don't think that's odd. In part, the limitations of your equipment controls. Or A company's operations manual may require green needles on the CDI when flying those approaches. 

But aside from that, Examiners and check pilots may want a demonstration of flying green needles. That seems to be fairly common for VOR radial interception tasks on instrument check rides.  Personally, if I have a pilot fly a VOR approach for an IPC, I insist on green needles on the CDI. My reasoning is, the only time a pilot might ever fly a VOR approach in real life is during a GPS failure. I often see problems with with pilots who are used to flying GPS forgetting that VOR needles don't auto slew. You have to tune, identify, and twist. 

 

Edited Saturday at 06:20 PM by midlifeflyer

[PeteMc]

21 hours ago, donkaye, MCFI said:

VOR is operational and monitored

Back when the first GPS came out, I *believe* you could only shoot the Approach if it actually said VOR (GPS) in the title (that's the way we were taught and what was told in all the FAA seminars I attended).  You've zeroed in on some changes over the years and pointed out you're good to shoot the approach using the GPS as your primary source IF the VOR is being MONITORED.  You can't just have a VOR in the plane. 

 

[midlifeflyer]

10 hours ago, PeteMc said:

Back when the first GPS came out, I *believe* you could only shoot the Approach if it actually said VOR (GPS) in the title (that's the way we were taught and what was told in all the FAA seminars I attended).  You've zeroed in on some changes over the years and pointed out you're good to shoot the approach using the GPS as your primary source IF the VOR is being MONITORED.  You can't just have a VOR in the plane. 

 

Yes. That’s a reason the GNS and GTN Limitations are different. It was originally, no RNAV for lateral guidance on the FAS. (Still says that in AC90-108). It was later changed to the current, ok if you monitor, in the AIM. 

I recall discussions around the time if the change like, what if they look different? 

[Jackk]

On 8/23/2025 at 2:18 PM, midlifeflyer said:

I don't think that's odd. In part, the limitations of your equipment controls. Or A company's operations manual may require green needles on the CDI when flying those approaches. 

But aside from that, Examiners and check pilots may want a demonstration of flying green needles. That seems to be fairly common for VOR radial interception tasks on instrument check rides.  Personally, if I have a pilot fly a VOR approach for an IPC, I insist on green needles on the CDI. My reasoning is, the only time a pilot might ever fly a VOR approach in real life is during a GPS failure. I often see problems with with pilots who are used to flying GPS forgetting that VOR needles don't auto slew. You have to tune, identify, and twist. 

 

 It’s really a nothing burger, for a LOC I can fly it LNAV/VNAV with the last altitude hard in the FMS, it draws the path and executes, I set altitude preselect to mins, right before the FAF go green needles and hit/capture that VS, shy of a massive power or wind change it’ll hit the target perfect at MDA and the AP will capture MDA.

 

 Still funny as the WAAS system will fly a cleaner approach than the LOC/VOR, outside of a ILS, or major spoofing or jamming, real world it’s just silly 

Edited yesterday at 08:04 PM by Jackk

[Vance Harral]

On 8/22/2025 at 11:07 PM, toto said:

I grabbed my GTN manual (screenshot below). Garmin suggests that VLOC mode is “required” and that the pilot “must” switch from GPS to VLOC before the final approach segment.

If the AFMS for the navigator requires using the ground-based nav source as primary for the final approach segment, does the AFMS control the decision?

Just to be clear, the screenshot you posted is from the Pilot's Guide, not the AFMS.  Two different documents with different legal status.

There is a lot of understandable confusion about this.  The voluminous "Pilot's Guide" may be nice to have with you, but it's not legally required in the airplane, and nothing it contains is regulatory.  In contrast, the pamphlet-like Airplane Flight Manual Supplement (AFMS) is required to be in the aircraft, and anything found in its LIMITATIONS section is binding from a regulatory standpoint.  The AFMS is not only serial-number specific, it is also software revision specific - you're supposed to get a new one with each software upgrade.

I've been invited into several clients' airplanes in which the required AFMS is nowhere to be found.  Sometimes the installation shop didn't provide it.  But in other cases the owner is just confused - they put the not-required Pilot's Guide in the cockpit while filing away the required AFMS along with their invoice, warranty paperwork, and so forth.

Here's a screenshot of the first page of a "generic" GTN650 AFMS, awaiting the make/model/registration/serial number info to be filled in.  If you don't have this in your airplane with your Garmin navigator (GNS, GTN, etc.), you're failing the "weight of paperwork must equal weight of airplane" rule. 

[toto]

4 minutes ago, Vance Harral said:

Just to be clear, the screenshot you posted is from the Pilot's Guide, not the AFMS.  Two different documents with different legal status.

There is a lot of understandable confusion about this.  The voluminous "Pilot's Guide" may be nice to have with you, but it's not legally required in the airplane, and nothing it contains is regulatory.  In contrast, the pamphlet-like Airplane Flight Manual Supplement (AFMS) is required to be in the aircraft, and anything found in its LIMITATIONS section is binding from a regulatory standpoint.  The AFMS is not only serial-number specific, it is also software revision specific - you're supposed to get a new one with each software upgrade.

I've been invited into several clients' airplanes in which the required AFMS is nowhere to be found.  Sometimes the installation shop didn't provide it.  But in other cases the owner is just confused - they put the not-required Pilot's Guide in the cockpit while filing away the required AFMS along with their invoice, warranty paperwork, and so forth.

Here's a screenshot of the first page of a "generic" GTN650 AFMS, awaiting the make/model/registration/serial number info to be filled in.  If you don't have this in your airplane with your Garmin navigator (GNS, GTN, etc.), you're failing the "weight of paperwork must equal weight of airplane" rule. 

Fair enough. Here’s the relevant section from my AFMS:

[Ibra]

21 hours ago, midlifeflyer said:

I recall discussions around the time if the change like, what if they look different? 

Does that happen very often?

I had the impression in US you are required to have VOR checks and the magnetic variation at VOR station is freezed. So the bias between GPS Track-To-Fix (TF leg) and VOR Course-To-Fix (CF leg) is very minimal 

In any case, you legally required to carry VOR if the plate require it for final segment (FAS leg) and monitor VOR guidance on final segment to stay within the protected area (or go-missed which can be done using GPS RNAV1, or on magnetic vector or heading to altitude) 

How you display, fiddle with buttons, or how you hook auto-pilot is largely irrelevant? especially, in Part91 where you are the only person in the cockpit 

These days digital autopilots use "GPS-aiding" to intercept VLOC for pure conventional VOR, LOC and ILS. So I can't see why pilot can do this on raw data while handflying? 

I recall GFC500 can't fly conventionel ILS with coupled glide when GPS is jammed, no LPV, well no ILS for you  time to go back to heading and vertical speed modes 

Edited 13 hours ago by Ibra

[midlifeflyer]

7 hours ago, Vance Harral said:

The voluminous "Pilot's Guide" may be nice to have with you, but it's not legally required in the airplane

Check out the very first Limitation in the AFMS you posted a picture of. 

[midlifeflyer]

3 hours ago, Ibra said:

Does that happen very often?

Almost always  There are two types of discrepancies. One is the very minor one you mentioned, the acceptable range of VOR error. 

The other is numerical. Since VOR radials are not recalibrated to magnetic often, there can be a discrepancy between the radial and course number displayed in the GPS. 

Even that “should” not be a big deal, but I was approached a few years ago by an instructor whose student failed their instrument checkride because of it. In that case, the VOR had last been calibrated in 1965 when the magnetic variation was 6° different. The 215° GPS course on the 209° radial threw him.

Edited 10 hours ago by midlifeflyer

[midlifeflyer]

8 hours ago, toto said:

Fair enough. Here’s the relevant section from my AFMS:

That was updated in later AFMS revisions. I think it was Revision 8 in 2018.

Edited 10 hours ago by midlifeflyer

[toto]

16 minutes ago, midlifeflyer said:

That was updated in later AFMS revisions. I think it was Revision 8 in 2018.

Thanks for that. Honestly, I didn’t intend to open a question about any particular supplement or manufacturer’s guidance - I really just meant to ask about a conflict between the manufacturer and the regulation. It sounds like in Garmin’s case they had no reason to require the use of the ground-based nav source for the final approach segment aside from wanting to align their guidance with the regulation. So when the regulation was updated, they updated their guidance?

[midlifeflyer]

2 hours ago, toto said:

Thanks for that. Honestly, I didn’t intend to open a question about any particular supplement or manufacturer’s guidance - I really just meant to ask about a conflict between the manufacturer and the regulation. It sounds like in Garmin’s case they had no reason to require the use of the ground-based nav source for the final approach segment aside from wanting to align their guidance with the regulation. So when the regulation was updated, they updated their guidance?

When you're talking about this subject, you can't help but look at the particular unit supplement involved. 

On the part I bolded, that's basically correct. But just to get the terminology correct...

when the regulation FAA guidance on GPS use was updated, they updated their guidance regulatory Limitations.

That's not as picky as it sounds. There are some important consequences to the way the FAA handles GPS use. Can you imagine what it would be like if every time a manufacturer came up with a new GPS function or the FAA became more comfortable with a particular function, the FAA had to go through the entire notice and comment period to approve it. Instead, there's really only two regulations on the subject. 91.205 which requires  "navigation equipment suitable for the route to be flown" for IFR and 1.1 which includes "Information on suitable RNAV systems is published in FAA guidance material" in the definition of "Suitable RNAV system."

 

[skykrawler]

The FAAs super conservative approach to the introduction of new technology has a lot to do with the regulations and guidance and the slow pace of change.

In this case - before RAIM, the FAA concern was probably you would arrive to a VOR approach and attempt to fly it with a bad GPS signal, thus the VOR must be operating.

Now, there you are wanting to fly the GPS version of the VOR approach, the VOR is OTS and you can't legally do the approach.  Seems silly.

 

[Ibra]

6 hours ago, midlifeflyer said:

there can be a discrepancy between the radial and course number displayed in the GPS

Indeed, that makes a discrepancy but as you said it's purely numerical artefact for Track-To-Fix: the leg go from VOR fix to RWY or VOR-VOR, having differences in magnetic track make no real difference on aircraft position between two coordinates.

For Course-To-Fix leg, indeed, the number on GPS database vs VOR charts are not the same, especially, if VOR stations are not regularly updated. So, I can see how an examiner would make a fuss out of it (as it matter for VOR  holds and separation, say two aircraft one using GPS and one using VOR).

The funny and nerdy bit is that the numbers for magnetic tracks shown in GTN are calculated on-the-fly while using magnetic variation at aircraft position rather than VOR station (this would be reason to fail written exam). While ago, I was checking if the procedure is available, I noted that numbers in plates for some aiport in Norway were way off versus magnetic track in GTN while aircraft was sitting in UK. Garmin replied, "if you cross-check them near destination it will be fine", they were right as Norway aligns their VOR or paint their runways every few years, it sounds like lot of work and waste go into such maintenance 

Edited 4 hours ago by Ibra

[Vance Harral]

10 hours ago, midlifeflyer said:

Check out the very first Limitation in the AFMS you posted a picture of. 

Yes, here we go down the rabbit hole.

This is well and good, but the Reference Guide is yet another pamphlet-like document that is not the voluminous Pilot's Guide often found in the cockpit.  Even the Reference Guide is not required unless "navigation is predicated on the use of the GTN."  I think most would agree that flying IFR departure/enroute/approach procedures using guidance from the GTN triggers that clause.  I'm less sure about VFR ops and lean toward arguing those do not trigger the clause.

Getting a bit off topic here, but an AFMS limitation that comes up in CFII debates from time to time is this one:

I've had fellow instructors claim there is nothing in FAA literature which prohibits flying an instrument approach with an expired database provided you "verify each waypoint for accuracy".  That may be true, but if you're Garmin equipped it doesn't matter, because the AFMS for Garmin navigators explicitly prohibits it, allowing the "verify each waypoint" trick only for terminal and enroute ops.  I don't know if other navigators (e.g. Avidyne) contain this same AFMS limitation.