can you use waas GPS for vor/dme approach?

[eman1200]

yes or no?  just in case, I think AC 90-108 is the one to reference.  

[Steve W]

As the VOR, no. As the DME yes(except Martin State). As 'VOR/DME or GPS', yes.

[eman1200]

it's just listed as 'VOR/DME', not 'vor/dme or gps'

[Steve W]

8. USES OF SUITABLE RNAV SYSTEMS NOT ALLOWED BY THIS AC. An otherwise suitable RNAV system cannot be used for the following:

b. Substitution on a Final Approach Segment (FAS). Substitution for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the FAS.

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

Edited September 22, 2019 by Steve W

[PT20J]

You are not allowed to "make up" an approach with GPS -- you have to use the ones loaded in the  database. The FAA won't allow a database to include an approach that the GPS is not approved to use. So, as far as the GPS is concerned, if it's in the database, you use it; if it's not, you can't.

Skip

[larryb]

You must monitor the actual VOR indicator during the approach. But you can also look at the GPS and your autopilot can be coupled to the GPS. So, you cannot fly a VOR approach with your GPS if you don’t also have and use a working NAV receiver.

[kortopates]

Absolutely Yes for both, same goes for NDB, but the navaid has to operational and you have to monitor the raw data while flying by the GPS lateral guidance. 

This is per a 2016 update to AIM 1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes:...
5. 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.

WAAS is not required, just an approved GPS. GPS substitution for DME has never been a problem (in the US).

Edited September 22, 2019 by kortopates

[Steve W]

So the actual answer is "needs more information". If you buy a plane with a fancy GNC 355 as your sole nav device, no you can't fly an VOR/DME only approach(or ILS, or LOC). 

[EricJ]

It gets tricky when they don't agree, too.   When I did my IR we'd practiced the VOR-C approach into Scottsdale since it was likely to be used in the checkride.   The GPS and the VOR disagreed significantly (like a mile or something).   The GPS was more consistent, and when I got that approach during my checkride I pulled both up but told the examiner I knew that they didn't agree but I was more comfortable flying the GPS guidance since it was more consistent and I knew it still got me to the right place.    He was fine with that.

[eman1200]

So the actual answer is "needs more information". If you buy a plane with a fancy GNC 355 as your sole nav device, no you can't fly an VOR/DME only approach(or ILS, or LOC). 

GTN650. DPE wouldn’t let me use the approach points loaded in the database , wanted me to use the home/nearest/vor function for dme.

[Steve W]

10 minutes ago, eman1200 said:

GTN650. DPE wouldn’t let me use the approach points loaded in the database , wanted me to use the home/nearest/vor function for dme.

 

Now the truth comes out. I'd argue he's wrong but I have no regulatory guidance to back that up. I'd always use published waypoints in preference to a distance readout if they're available.

[tgardnerh]

49 minutes ago, eman1200 said:

GTN650. DPE wouldn’t let me use the approach points loaded in the database , wanted me to use the home/nearest/vor function for dme.

Did the DPE make it clear that he was telling you what he thought the rules required, or did he just want to make sure you could do it without the GPS?

[kortopates]

2 hours ago, eman1200 said:

 

GTN650. DPE wouldn’t let me use the approach points loaded in the database , wanted me to use the home/nearest/vor function for dme.

 

 

1 hour ago, Steve W said:

Now the truth comes out. I'd argue he's wrong but I have no regulatory guidance to back that up. I'd always use published waypoints in preference to a distance readout if they're available.

 

1 hour ago, tgardnerh said:

Did the DPE make it clear that he was telling you what he thought the rules required, or did he just want to make sure you could do it without the GPS?

As a CFI, I am well aware that not all DPE's embrace technology and all have things in mind that they want  you to show you know how to do on an IFR checkride. For example, virtually all want you to show you can still do ground based navigation even though you have a fancy GPS. Admittedly I like to make sure my IR candidates can master their GPS by the time they take their checkride, but you still need to be able to perform basic ground based navigation if you lose your GPS.

I suspect, just as @tgardnerh was hinting at, the DPE was merely ensuring you know can navigate without the GPS. 

Folks, don't confuse what a DPE wants to see on a IR checkride as having anything to do with how you want to fly instruments real world! They are two entirely different things. The DPE wants to make sure you have a solid foundation in all forms of navigation, not just GPS. For example,  I don't think there are any DPE's out there that would allow you to demonstrate a hold using a GTN or Avidyne programmed hold, (i.e. where you set up the GPS to give you guidance for holding at any fix). Instead they want you set it up using OBS on the GPS and some even want you to do the hold using ground based nav with VORs or VOR/DME - typically if they haven't yet demonstrated you can navigate without the GPS, the hold is one way you can. IMO, its best not to be displaying a magenta line at all on a moving map on your checkride - expect that it will get covered up real fast. But real world there is never a reason not to use GPS until you lose GPS; especially for VOR approaches since its far more accurate. Just be able to still revert to ground based nav in the rare case of an GPS outage or more likely a personal GPS equipment failure.  

Sources of VOR error that are eliminated by GPS Nav on a VOR approach:

• The pilot has to twist the OBS to the exact radial (remember the rule of 60's for each degree your off based on distance from the VOR), most pilots flying a VOR approach are only close. In contrast on the GPS, it doesn't matter where you leave the OBS twisted to, GPS still gives proper guidance.
• The +/- error from your last VOR or VOT test, if it wasn't +/- 0 from your last test are you correcting for the error when you dial in the radial? In contrast the GPS has no such error, again it doesn't matter where the OBS is twisted to. 

 

Edited September 22, 2019 by kortopates

[eman1200]

1 hour ago, tgardnerh said:

Did the DPE make it clear that he was telling you what he thought the rules required, or did he just want to make sure you could do it without the GPS?

the gps was going to be used one way or another.  I was either going to use the waypoint info supplied by the gps (waypoint name, distance to the next waypoint..) OR use the GPS as dme FROM the vor.  she wouldn't let me do the first method.

[PT20J]

9 hours ago, kortopates said:

Absolutely Yes for both, same goes for NDB, but the navaid has to operational and you have to monitor the raw data while flying by the GPS lateral guidance. 

This is per a 2016 update to AIM 1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes:...
5. 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.

WAAS is not required, just an approved GPS. GPS substitution for DME has never been a problem (in the US).

Perhaps I misunderstood the OP's question as wanting to know if GPS could be used in lieu of the VOR or NDB. There's a nuance here. While Paul correctly points out that paragraph 5 allows the use of GPS to navigate a final approach segment if the the NAVAID is operational and you monitor it for the final course alignment, the preceding paragraph 4 states that "Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment."  So to do this correctly, you have to set up and monitor two navigation systems during the final approach. That's a lot of workload and if I really needed to do it for some reason I'd have the autopilot flying the GPS and me monitoring the VOR (or NDB). 

[kortopates]

2 hours ago, PT20J said:

Perhaps I misunderstood the OP's question as wanting to know if GPS could be used in lieu of the VOR or NDB. There's a nuance here. While Paul correctly points out that paragraph 5 allows the use of GPS to navigate a final approach segment if the the NAVAID is operational and you monitor it for the final course alignment, the preceding paragraph 4 states that "Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment."  So to do this correctly, you have to set up and monitor two navigation systems during the final approach. That's a lot of workload and if I really needed to do it for some reason I'd have the autopilot flying the GPS and me monitoring the VOR (or NDB). 

Skip, it surely doesn't have to be much added workload and its surely a big improvement. The extra workload is to tune in the Freq and identity it which should be  done before you get to the final approach segment, which you would be doing already flying a VOR approach. Then it's easiest to monitor the VOR using a bearing pointer on a glass HSI - that makes it downright trivial!  Without the glass, you'll need to twist in the Final approach course radial on a second CDI and upon passing final you can keep kit in your scan while navigating off the GPS taking you to the MAWP. But by monitoring you'll know if you lose the raw data. But by setting it up before you get to the FAF you won't have any extra twisting to do as you pass the FAF (remember you'll be navigating to the FAF with GPS, no need to use the VOR for that unless you really do want to increase your workload).  Only thing we can't do is navigate past the FAF off the GPS if the VOR (or NDB) goes down. 

Edited September 23, 2019 by kortopates

[PT20J]

7 hours ago, kortopates said:

Skip, it surely doesn't have to be much added workload and its surely a big improvement. The extra workload is to tune in the Freq and identity it which should be  done before you get to the final approach segment, which you would be doing already flying a VOR approach. Then it's easiest to monitor the VOR using a bearing pointer on a glass HSI - that makes it downright trivial!  Without the glass, you'll need to twist in the Final approach course radial on a second CDI and upon passing final you can keep kit in your scan while navigating off the GPS taking you to the MAWP. But by monitoring you'll know if you lose the raw data. But by setting it up before you get to the FAF you won't have any extra twisting to do as you pass the FAF (remember you'll be navigating to the FAF with GPS, no need to use the VOR for that unless you really do want to increase your workload).  Only thing we can't do is navigate past the FAF off the GPS if the VOR (or NDB) goes down. 

Good points, Paul. I agree that setting up two nav systems should not be overly challenging since I can do this at a low workload time. My thought is that the workload to monitor two navigation systems during a non-precision approach with no vertical guidance (I won't get LNAV+V on this) while descending close to the ground may be more workload than I might want. This is a nit perhaps, but I don't believe using the HSI bearing pointer on the VOR (it would be OK for an NDB) is what the FAA had in mind when it stated that the underlying NAVAID must be "monitored for final segment course alignment." You really need a second CDI to do that with accuracy. So now I am modifying my scan, trying to correlate two CDI indications (with the VOR perhaps scalloping a bit) while descending close to the ground. It absolutely can be done. And, if I had an operational need to do it, I would. I just think it's not the best situation.

Skip

[Marauder]

Good points, Paul. I agree that setting up two nav systems should not be overly challenging since I can do this at a low workload time. My thought is that the workload to monitor two navigation systems during a non-precision approach with no vertical guidance (I won't get LNAV+V on this) while descending close to the ground may be more workload than I might want. This is a nit perhaps, but I don't believe using the HSI bearing pointer on the VOR (it would be OK for an NDB) is what the FAA had in mind when it stated that the underlying NAVAID must be "monitored for final segment course alignment." You really need a second CDI to do that with accuracy. So now I am modifying my scan, trying to correlate two CDI indications (with the VOR perhaps scalloping a bit) while descending close to the ground. It absolutely can be done. And, if I had an operational need to do it, I would. I just think it's not the best situation.
Skip

A glass HSI gives you a few options. On an Aspen (and I believe Garmin has this as well), you can use the CDI portion for the VOR and use the RMI for the GPS course.

One feature I like on the Aspen 2000 setup I have is the ability to run dual HSIs. Here is a shot of RNAV practice approach with the ILS on the second HSI (right side).






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[PT20J]

44 minutes ago, Marauder said:

 

A glass HSI gives you a few options. On an Aspen (and I believe Garmin has this as well), you can use the CDI portion for the VOR and use the RMI for the GPS course.

One feature I like on the Aspen 2000 setup I have is the ability to run dual HSIs. Here is a shot of RNAV practice approach with the ILS on the second HSI (right side).

 

 

I like my Aspen, though I've only got one tube. Do you fly instruments using it with synthetic vision? I find the pitch axis and horizon line a little indistinct for flying precisely with SV on and don't use it on approaches. Wonder if the MAX is better?

Skip

[Marauder]

I like my Aspen, though I've only got one tube. Do you fly instruments using it with synthetic vision? I find the pitch axis and horizon line a little indistinct for flying precisely with SV on and don't use it on approaches. Wonder if the MAX is better?
Skip

I don’t like flying IFR with the synthetic vision on. I have a flight director which makes it easier to see the correct attitude. My FD is set up to be shown with or without the autopilot servos on. That helps, but having flown for so many years with the classic blue/brown depiction, SV will probably take some time to get used to. Sort of like what it took to get used to the tapes.




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[Oscar Avalle]

58 minutes ago, Marauder said:

 

I don’t like flying IFR with the synthetic vision on. I have a flight director which makes it easier to see the correct attitude. My FD is set up to be shown with or without the autopilot servos on. That helps, but having flown for so many years with the classic blue/brown depiction, SV will probably take some time to get used to. Sort of like what it took to get used to the tapes.




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Interesting. I am so used to flying IFR with SV... I feel vulnerable without it. On the other hand I just can not get used to the tape... Any suggestion on how to get more used to them?

[flyboy0681]

22 hours ago, EricJ said:

It gets tricky when they don't agree, too.   When I did my IR we'd practiced the VOR-C approach into Scottsdale since it was likely to be used in the checkride.   The GPS and the VOR disagreed significantly (like a mile or something).   The GPS was more consistent, and when I got that approach during my checkride I pulled both up but told the examiner I knew that they didn't agree but I was more comfortable flying the GPS guidance since it was more consistent and I knew it still got me to the right place.    He was fine with that.

Same here. When I did my instrument work and flew a practice VOR approach to my home drome, I kept the GPS selected and monitored the VOR on NAV2 and the needles were not nearly aligned. And yes, the VOR receiver was accurate.

[Bob - S50]

12 minutes ago, flyboy0681 said:

Same here. When I did my instrument work and flew a practice VOR approach to my home drome, I kept the GPS selected and monitored the VOR on NAV2 and the needles were not nearly aligned. And yes, the VOR receiver was accurate.

One thing that might make a difference.  The GPS course is a calculated course.  It does not care about the actual magnetic variation dialed into the VOR.  When you fly the course using your GPS, you'll set HSI/CDI to the desired course calculated by the GPS.  This could be a couple degrees different than the actual course depicted on the approach plate.  Be sure to set up the #2 Nav by setting the course depicted on the plate, not the course calculated by the GPS.

[kortopates]

25 minutes ago, Bob - S50 said:

One thing that might make a difference.  The GPS course is a calculated course.  It does not care about the actual magnetic variation dialed into the VOR.  When you fly the course using your GPS, you'll set HSI/CDI to the desired course calculated by the GPS.  This could be a couple degrees different than the actual course depicted on the approach plate.  Be sure to set up the #2 Nav by setting the course depicted on the plate, not the course calculated by the GPS.

Exactly ^^ , and be sure to add or subtract any error that you recorded from your current VOT or VOR test - if there was any.

[Marauder]

Interesting. I am so used to flying IFR with SV... I feel vulnerable without it. On the other hand I just can not get used to the tape... Any suggestion on how to get more used to them?

Before I was able to remove the mechanical ASI, I had to resort to covering it up to force myself to learn the tape. Now it feels natural.


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