Noob question about flying a VOR/DME approach using a GNS430

BenWA

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I am new to using the 430 for IFR and I am confused on a couple of points. Let's use the following approach as an example for the sake of discussion: http://204.108.4.16/d-tpp/0910/00142VD16R.PDF

Let's first assume that it is a simple aircraft equipped with one GNS430 linked to a CDI/glideslope, and one other independent VOR receiver (NAV2). The aircraft does not have an ADF or DME.

We want to fly the 9 DME arc to the IF (FETOL), and then fly the remainder of the approach inbound. Assuming this approach is in the GNS430 database as an overlay approach that can be flown entirely using the GPS (which I am pretty certain is the case, but I haven't checked this approach in the 430 database specifically), would I be correct in saying that the approach could be set up and flown legally with the 430 in either of two ways:

1) Put the localizer frequency 110.6 MHz (PAE) in the active VLOC with the 430 in CDI mode, while also setting up PAE as the active waypoint to receive DME information, or

2) Select and activate the VOR/DME RWY 16R approach as an overlay approach and fly it with the 430 set in GPS mode.

Is this correct? Does the first option that I listed satisfy acceptable substitution of DME with the GPS, as described in AIM 1-1-19(f)?

If I am way off on anything here, please let me know. This is all new to me!
 

Green Banana

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You are on the right track! Both are acceptable, but there is a BEST answer!

1) shooting a VOR approach using GPS as your DME. You do not want the GPS in CDI mode. You want the active way point to be the PAE VOR/DME, but the CDI will be in the VOR/LOC setting. Fly the ARC using the DME readout off the GPS and CDI to track progress until intercepting the inbound course. CDI based on ground VOR and GPS/DME are independent.

2) Overlay approach using the GPS information on the #1 CDI. The CDI in GPS mode will show lateral deviation from center line based on GPS data.

Both work, one is a VOR app using GPS substituted DME and the other is an overlay GPS approach both using only #1 CDI. The BEST way to shoot is to set up and shoot the approach using option #2 (GPS overlay) on your NAV/CDI #1 and set up your NAV #2 as a RAW DATA backup using PAE VOR.

Read on in the AIM. It states (monitoring of the underlying approach is suggested when equipment is available and functional). Again, not required, but suggested.

Fly Safe Puget Sound Pilot!
 

Lynxman

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Great question I just started using the GNS430 full time now. Only problem I have is now the plane has one CDI/GS that's it.
 

BenWA

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Thanks GB...

1) shooting a VOR approach using GPS as your DME. You do not want the GPS in CDI mode. You want the active way point to be the PAE VOR/DME, but the CDI will be in the VOR/LOC setting. Fly the ARC using the DME readout off the GPS and CDI to track progress until intercepting the inbound course. CDI based on ground VOR and GPS/DME are independent.

Yup, I'm with you. Thanks for clarifying.

The BEST way to shoot is to set up and shoot the approach using option #2 (GPS overlay) on your NAV/CDI #1 and set up your NAV #2 as a RAW DATA backup using PAE VOR.

With you again.


Here's another question about using an IAP as an overlay: if the approach in the GPS database has "GPS" in diagonally descending letters next to the approach name, but the published paper approach plate does not have "or GPS" in the title, is it legal to fly the approach as an overlay using the GPS as the primary NAV source? Or does the paper approach plate superceed the GPS database, even if it may potentially be pending update?
 
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time builder

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Hate to be nit picky, but I've seen recent FAA guidance on this matter stating that on an approach such as this, you may not use the GPS for primary navigation on the final approach segment. However, you may use it for other portions such as the DME arc and the intermediate segment leading up to it.

There are approaches where you can use either the GPS or another navaid interchangeably on all segments, but such have both in the name of the approach, like this:
http://204.108.4.16/d-tpp/0910/05638NGA.PDF
 

BenWA

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Hate to be nit picky, but I've seen recent FAA guidance on this matter stating that on an approach such as this, you may not use the GPS for primary navigation on the final approach segment. However, you may use it for other portions such as the DME arc and the intermediate segment leading up to it.

Nothing wrong with being nitpicky.

I suppose as long as you can use the GPS as primary NAV on the arc, who cares if you have to use the VLOC for the final approach segment -- it's no more difficult to set up or fly than it would be using the GPS, right? Moot, really. At least as the VOR/DME approach is concerned.
 

Green Banana

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Here's another question about using an IAP as an overlay: if the approach in the GPS database has "GPS" in diagonally descending letters next to the approach name, but the published paper approach plate does not have "or GPS" in the title, is it legal to fly the approach as an overlay using the GPS as the primary NAV source? Or does the paper approach plate superceed the GPS database, even if it may potentially be pending update?

The simple answer is NO. The FAA has named all the overlay approach plates "OR GPS". If you can see the approach in the GPS as you state, this is used for orientation purpose only. It is to show you a little map and help in situational awareness. The approach is not a GPS approach and ATC will not clear you for it as a GPS approach. If you want to set up the approach on the NAV 1 OBS, that is fine, but you must have the RAW DATA VOR approach in NAV 2, and this is your PRIMARY REFRENCE. You are shooting a VOR approach.
 

Green Banana

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Hate to be nit picky, but I've seen recent FAA guidance on this matter stating that on an approach such as this, you may not use the GPS for primary navigation on the final approach segment. However, you may use it for other portions such as the DME arc and the intermediate segment leading up to it.

There are approaches where you can use either the GPS or another navaid interchangeably on all segments, but such have both in the name of the approach, like this:
http://204.108.4.16/d-tpp/0910/05638NGA.PDF

You are absolutely correct. The PAE VOR/DME approach that is used in the first post of the thread is not an overlay approach. You may use the GPS as a DME substitute, but not for course information. As I stated in my other post, the GPS approach in the database is used for situational awareness only. Thanks for the catch, and sorry for the confusion.
 

BenWA

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Thanks Green Banana and time builder for the clarification. This has helped immensely.

You are correct, GB -- that VOR/DME approach is not an overlay. I was mistaken in my original post.
 

illinipilot

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I tried reading through this but my attention span wandered. What about an ILS approach that requires ADF? It seems that we can identify the outer-marker (LOM) just as easily with a GPS as we can with an ADF. Are we able then to substitute the GPS when an ADF is required per the approach plate?
 

Green Banana

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Yes, you may substitute IFR-certified GPS receivers for DME and ADF avionics for all operations except NDB approaches without a GPS overlay. GPS can be used in lieu of DME and ADF on all localizer-type approaches as well as VOR/DME approaches, including when charted NDB or DME transmitters are temporarily out of service. These operations are allowable even when the facility is explicitly identified as required (e.g., "Note ADF Required")!

Want to read more? AIM 1-2-3 c
 
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