GPS for a VOR approach

M

meritflyer

Well-Known Member
In conversation today, another CFI (friend) and I were discussing approaches. He mentioned that you could use GPS such as the G1000 (the autopilot will fly the approach for you) to fly a VOR approach legally and that there was an Advisory Circular that discussed this in detail.

I was always under the assumption that the navigation system had to be appropriate to the type of approach.

Anyone care to shed any light on this including the Advisory Circular would be great.
 
meritflyer said:
In conversation today, another CFI (friend) and I were discussing approaches. He mentioned that you could use GPS such as the G1000 (the autopilot will fly the approach for you) to fly a VOR approach legally and that there was an Advisory Circular that discussed this in detail.

I was always under the assumption that the navigation system had to be appropriate to the type of approach.

Anyone care to shed any light on this including the Advisory Circular would be great.
Click to expand...


One must use Google my friend.......

http://www.faa.gov/ASD/international/TSO_FAR_AC/AC90-94A.pdf

3. APPROACH OVERLAY PROGRAM. To accelerate the availability of instrument approach procedures to be flown using certified GPS equipment, the FAA developed the GPS Approach Overlay Program. This program allows pilots to use GPS equipment to fly existing VOR, VOR/DME, NDB, NDB/DME, TACAN, and RNAV nonprecision instrument approach procedures. The approach overlay program is limited to U.S. airspace. GPS instrument approach operations outside the U.S. must be authorized by the appropriate sovereign state.
Click to expand...
page 15 I believe.

at least I think this is the answer you're looking for.
 
meritflyer said:
In conversation today, another CFI (friend) and I were discussing approaches. He mentioned that you could use GPS such as the G1000 (the autopilot will fly the approach for you) to fly a VOR approach legally and that there was an Advisory Circular that discussed this in detail.

I was always under the assumption that the navigation system had to be appropriate to the type of approach.

Anyone care to shed any light on this including the Advisory Circular would be great.
Click to expand...
This is somewhat of a grey area. Normally, this is not allowed unless the approach is labeled (VOR or GPS).

The way to get around this, is to pull up a RMI needle and fly the approach using the GPS, but 'monitor' the VOR. This is what most people in bigger equipment with a FMS do. The only thing you have to be careful of, is to make sure any step down fixes are actually in the GPS database. Otherwise, you have to rely on along track distance to identify step downs, and if you do this, you run a higher risk of making a mistake.

In my airplane, if I pull up an RMI needle to a VOR, it will give me a DME readout if it is available, so this is less of an issue. Another way you can make good use of your avionics, is to use the primary navaid for the approach, but switch to the GPS for the missed. This works great for the ILS where you have to use the primary navaid, and can ease workload for those other approaches as well.
 
JEP said:
One must use Google my friend.......

http://www.faa.gov/ASD/international/TSO_FAR_AC/AC90-94A.pdf

page 15 I believe.

at least I think this is the answer you're looking for.
Click to expand...

That AC is no longer valid, it looks like it was written before all the GPS info was included in the AIM.

From the current AIM at http://www.faa.gov/ATPubs/AIM/Chap1/aim0101.html#1-1-19

3. The GPS Approach Overlay Program is an authorization for pilots to use GPS avionics under IFR for flying designated nonprecision instrument approach procedures, except LOC, LDA, and simplified directional facility (SDF) procedures. These procedures are now identified by the name of the procedure and "or GPS" (e.g., VOR/DME or GPS RWY 15). Other previous types of overlays have either been converted to this format or replaced with stand-alone procedures. Only approaches contained in the current onboard navigation database are authorized. The navigation database may contain information about nonoverlay approach procedures that is intended to be used to enhance position orientation, generally by providing a map, while flying these approaches using conventional NAVAIDs. This approach information should not be confused with a GPS overlay approach (see the receiver operating manual, AFM, or AFM Supplement for details on how to identify these approaches in the navigation database).

NOTE-
Overlay approaches are predicated upon the design criteria of the ground-based NAVAID used as the basis of the approach. As such, they do not adhere to the design criteria described in paragraph 5-4-5j, Area Navigation (RNAV) Instrument Approach Charts, for stand-alone GPS approaches.




The FAA no longer allows the overlay program, except for the approaches with 'or GPS' in the title. If you have the avionics, the trick is to fly using the GPS, but 'monitor' the navaid. If they ask, you are flying using what ever underlying navaid you are supposed to be using.
 
ananoman said:
This is somewhat of a grey area. Normally, this is not allowed unless the approach is labeled (VOR or GPS).
Click to expand...

Garmin's position is that it's ok to use GPS up until the FAF for any approach, ILS included. When I asked Garmin to show me how that was in compliance with the regulations or the AIM, the representative I was corresponding with got pretty testy and discontinued our email relationship.;)

For the ILS, the Garmin will lead you outbound, through the PT, and then turn over to the localizer once it's intercepted. However, the approach is actually constructed to fly the localizer backcourse outbound; where is the authorization to use GPS instead?

Real-world usage of GPS seems to greatly exceed what the AIM expressly permits. I can't tell that anyone in the FAA really cares.
 
I was fooling around with my 430 today. Had it set up to do an ILS full procedue. Prior to the OM inbound, the box said "tune proper nav aid", or something to that effect, as a reminder that you needed to have the ILS as the primary nav and not the GPS. I thought that was pretty high tech, that it knew I needed to switch from GPS to the ILS.

I believe the FAA has blessed GPS for terminal navigation and that it's allowed as a substitue for VOR/DME/ADF/OM fixes. As far as approaches, you could do a GPS approach or an "overlay" approach. This is all assuming you have an IFR approach legal box.
 
DE727UPS said:
I believe the FAA has blessed GPS for terminal navigation
Click to expand...

That they have, but it's not clear to me that the initial segment of an instrument approach qualifies as "terminal navigation", any more than the final approach segement does.
 
John and Martha say the same thing about using the GPS until the FAF. I have no idea where they came up with that though unless its in an AC somewhere.

I am going to say that you are NOT able to use a GPS overlay for a VOR approach unless it is titles "VOR XX or GPS XX". As for navigating to the IAF or IF, you are able to use such navigation to those fixes but once the FAC is intercepted, you must use the type of navigation appropriate to the approach.

Agreed?
 
meritflyer said:
As for navigating to the IAF or IF, you are able to use such navigation to those fixes but once the FAC is intercepted, you must use the type of navigation appropriate to the approach.

Agreed?
Click to expand...

That's my belief based on the regulations and what the AIM says, but I gather I'm in the minority.
 
I would agree with this as well. It makes sense to transition to the propper navaid as soon as you are able to intersept the final approach course, but using the GPS can make it easier to fly any required arc, procedure turn, etc. It can also make life easier on the missed to switch back to GPS after the MAP.

If you are able to monitor the navaid with a RMI or some other indication, there is nothing wrong with using the GPS to fly NDB or VOR approaches as well. I would probably not advise students to try this for a checkride though. Who knows what the DE would do? There is even some argument when we take 135 checks about what is allowed and what is not. Most people don't care if you use the FMS to fly a NDB approach, but some want to see it 'raw data'.
 
tgrayson said:
That's my belief based on the regulations and what the AIM says, but I gather I'm in the minority.
Click to expand...
Gosh, I =hope= you're not in the minority since you're right.

Heck, just load a VOR-only approach in a newer Garmin or King GPS and you'll even get a warning about it.
 
MidlifeFlyer said:
Heck, just load a VOR-only approach in a newer Garmin or King GPS and you'll even get a warning about it.
Click to expand...

Yeah, but the documentation seems pretty wishy-washy about it. That warning seems clear to me, but then the docs say that as long as you use the underlying navaid from the FAF onward, you're legal. So that sends a mixed message to me.
 
tgrayson said:
Yeah, but the documentation seems pretty wishy-washy about it. That warning seems clear to me, but then the docs say that as long as you use the underlying navaid from the FAF onward, you're legal. So that sends a mixed message to me.
Click to expand...
The difficulty with the AIM discussion of the use of GPS for IFR terminal/approach operations is that you really have to read all of it to get the context. They didn't make it as simple as they could have.

But, combining the discussion of the overlays with the discussion of use as substitution for ADF and DME in 1-1-19.1.b.(6)

==============================
Charted requirements for ADF and/or DME can be met using the GPS system, except for use as the principal instrument approach navigation source.
==============================

probably comes the closest to a full explanation.
 
Here's a question for you smart guys.

My avionics tech says you can't use a stand alone IFR GPS box (GNC300XL) as a sole source of navigation and have it be a legal IFR setup. In other words, you still need VOR as a backup (for the alternate airport, he says). My thinking is the regs say you need "nav capability suitable for the navaids you're gonna use" I see nothing wrong with the legality of having ONLY GPS on board (not saying it would be smart). I haven't looked very deeply into this. Is my avionics tech right?
 
DE727UPS said:
Here's a question for you smart guys.

My avionics tech says you can't use a stand alone IFR GPS box (GNC300XL) as a sole source of navigation and have it be a legal IFR setup. In other words, you still need VOR as a backup (for the alternate airport, he says). My thinking is the regs say you need "nav capability suitable for the navaids you're gonna use" I see nothing wrong with the legality of having ONLY GPS on board (not saying it would be smart). I haven't looked very deeply into this. Is my avionics tech right?
Click to expand...

Yes he's right because there is a requirement that your alternate airport have an approach OTHER than GPS, and you must be able to fly it. I'll find the source later if someone else doesn't beat me to it.
 
Sorry Don.

AIM 1-1-19(b) states -

"Aircraft using GPS navigation under IFR must be equipped with an approved and operational alternate means of navigation appropriate to the flight. Active monitoring of alternate navigation equipment is not required if the GPS uses RAIM. Active monitoring of an alternate means of navigation is required when RAIM capability of the GPS is lost".
 
Ralgha said:
Yes he's right because there is a requirement that your alternate airport have an approach OTHER than GPS, and you must be able to fly it. I'll find the source later if someone else doesn't beat me to it.
Click to expand...

There is nothing that says a GPS approach cannot be filed as an alternate unless I am mistaken. For instance, KSDL has published alternate mins for their GPS approaches.
 
You must log in or register to reply here.
Back
Top