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GPS is more accurate than a VOR or NDB signal. Can we use a GPS to fly a VOR or NDB approach from the initial approach fix through the missed approach and hold?

I know there are two types of approaches that deal with GPS and VOR/NDBs:

I'm specifically asking about the first type or approach without the wording "or GPS in the title.

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No, you still have to monitor the underlying NAVAID. You just have to read further in that same section of the AIM. Reference the most recent edition of the AIM, which has Change 3 dated April 27, 2017. In section 1-2-3-c-5 it 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.

That last sentence in the quote above is the important part.

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In the US they can (Effective: May 26, 2016). This change allows for the use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure (IAP) based on a VOR, TACAN, or NDB signal. The underlying NAVAID must be operational and monitored for the final segment course alignment.

Still can’t fly an ILS or localizer approaches.

Update: 2017-04-19 Max Trescott has a good explanation of how to use GPS in conjunction with ground-based navaids on ILS and VOR approaches.

AIM Section 2. Performance−Based Navigation (PBN) and Area Navigation (RNAV)

1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes

  1. Use of a suitable RNAV system as an Alternate Means of Navigation when a VOR, DME, VORTAC, VOR/DME, TACAN, NDB, or compass locator facility including locator outer marker and locator middle marker is operational and the respective aircraft is equipped with operational navigation equipment that is compatible with conventional navaids. For example, if equipped with a suitable RNAV system, a pilot may fly a procedure or route based on operational VOR using that RNAV system without monitoring the VOR.

NOTE− 4. The navigation database should be current for the duration of the flight.

c. Uses of Suitable RNAV Systems. Subject to the operating requirements, operators may use a suitable RNAV system in the following ways. 1. Determine aircraft position relative to, or distance from a VOR (“VOR” includes VOR, VOR/DME, and VORTAC facilities and “compass locator” includes locator outer marker and locator middle marker.), TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course.

  1. Navigate to or from a VOR, TACAN, NDB, or compass locator.

  2. Hold over a VOR, TACAN, NDB, compass locator, or DME fix.

  3. Fly an arc based upon DME.

None of the substitutions mentioned above include the localizer portion of an ILS. So you may not substitute GPS/WAAS for and ILS or localizer approach, but you may still use it for situational awareness.

You need to dig into the AIM to find out what they mean by “suitable RNAV system” but basically both certified GPS or WAAS count.

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    $\begingroup$ I believe a key factor in the "suitable RNAV system" is that the desired approach must be in the nav database for the system. You can't manually enter approach fixes to create an approach. $\endgroup$ – Gerry Feb 28 '17 at 15:26
  • $\begingroup$ @Gerry That’s true, the approach has to be in your database, but what they say about "Suitable RNAV Systems’ is "the following systems qualify as a suitable RNAV system: 1. An RNAV system with TSO−C129/ −C145/−C146 equipment, installed in accordance with AC 20−138,… and 2. An RNAV system with DME/DME/IRU inputs that is compliant with the equipment provisions of AC 90−100A" For most people, that means certified GPS or WAAS systems. $\endgroup$ – JScarry Feb 28 '17 at 19:45
  • $\begingroup$ Agreed, but I raised the point as it's entirely possible to have an approved "Suitable RNAV System" installed in your aircraft and not have the desired approach in your database. I think it's an important factor when trying to determine "Can I fly a particular approach?" Having an approved system won't help if the approach you want isn't in the database. $\endgroup$ – Gerry Mar 1 '17 at 12:35
  • $\begingroup$ Reading at section in the AIM, the first note stipulates to read AC 90-108. That AC says you cannot substitute a GPS/RNAV system on a Final approach segment. What does that mean? $\endgroup$ – wbeard52 Mar 1 '17 at 19:32
  • $\begingroup$ AC No: 90-108 Change: 1 is Dated: 4/21/15. The AIM change is Effective: May 26, 2016. I’m guessing that the AC has not been updated yet OR there is another AC that the AIM is based on. $\endgroup$ – JScarry Mar 1 '17 at 19:55

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