Can a pilot use their GPS/FMS to fly a VOR or NDB approach?

Question

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:

• NDB RWY 35L (KCOS RWY 35L) without GPS in the title
• VOR or GPS-A (KGUC VOR or GPS-A) with "or GPS" in the title

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

Answer 1

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

2. 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.

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

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

4. 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.

Answer 2

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.

Answer 3

In reference to the OP’s original question about VOR and NDB procedures:

Yes for a Missed Approach Segment or Hold.

&

NO for a Final Approach Segment WITH LATERAL GUIDANCE.

The answer as it pertains to the final approach segment is NO if the Navaid is providing lateral guidance. And, you do not have to monitor the underlying Navaid EXCEPT for the final approach segment.

In other words, you can fly to, from, and around a Navaid without tuning in to the Navaid. You can even use GPS to fly to the runway while monitoring the Navaid. As soon as you are using Lateral guidance to align the plane with the runway for landing purposes, you have to use your Nav radio.

I imagine that the only time a VOR would provide lateral guidance by scaling would be if the VOR were located on the field. This is probably making a distinction between VOR/DME and NDB approaches not providing alignment guidance, and all other approaches. Probably since a VOR not located on the field will point you to the runway. But, it will not funnel or lead/guide you down to it (scaling).

And, your database must be current and contain the desired procedure to legally use the GPS.

See the below excerpt from the latest FAR/AIM as of 26 Jan 20. Specifically AIM 1-2-3 Notes section 2 & 4.

The FAR/AIM says:
Notes

1. The allowances described in this section apply even when a facility is identified as required on a procedure (for example, “Note ADF required”).

2. These operations do not include lateral navigation on localizer-based courses (including localizer back-course guidance) without reference to raw localizer data.

3. Unless otherwise specified, a suitable RNAV system cannot be used for navigation on procedures that are identified as not authorized (“NA”) without exception by a NOTAM. For example, an operator may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory flight inspection, or a procedure that is based upon a recently decommissioned NAVAID.

4. Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment. This restriction does not refer to instrument approach procedures with “or GPS” in the title when using GPS or WAAS. These allowances do not apply to procedures that are identified as not authorized (NA) without exception by a NOTAM, as other conditions may still exist and result in a procedure not being available. For example, these allowances do not apply to a procedure associated with an expired or unsatisfactory flight inspection, or is based upon a recently decommissioned NAVAID.

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.

6. For the purpose of paragraph c, “VOR” includes VOR, VOR/DME, and VORTAC facilities and “compass locator” includes locator outer marker and locator middle marker.

d. Alternate Airport Considerations. For the purposes of flight planning, any required alternate airport must have an available instrument approach procedure that does not require the use of GPS. This restriction includes conducting a conventional approach at the alternate airport using a substitute means of navigation that is based upon the use of GPS. For example, these restrictions would apply when planning to use GPS equipment as a substitute means of navigation for an out-of-service VOR that supports an ILS missed approach procedure at an alternate airport. In this case, some other approach not reliant upon the use of GPS must be available. This restriction does not apply to RNAV systems using TSO-C145/-C146 WAAS equipment. For further WAAS guidance, see paragraph 1-1-18.

Answer 4

Good info here, but I'd add a little interpretation and implied requirements as follows, as I don't see conflict between AIM 1-2-3(c) Notes 4 & 5 - though that is less than completely obvious.

1. AIM 1-2-3 (c) note 4: "lateral guidance" has nothing to do with runway alignment. It is simply the left/right guidance provided by the NAVAID to follow a final approach course as depicted on the chart. Runway alignment does not impact this note; the NAVAID must be referenced as provided in the note during the final approach segment, period. So we are not allowed to simply fly a VOR or NDB approach using GPS needles and ignore the "raw" VHF data. That's always been true.
2. AIM 1-2-3 (c) note 5: we can navigate with the GPS provided "the underlying NAVAID [is] operational and the NAVAID monitored for final segment course alignment." So here's an example of a practical way of doing this: some AP systems can be flown in GPSS mode (navigating directly off the GPS) while the primary CDI still displays the VHF course information (i.e. the Avidyne PFD w/ separate GPS heads can do this; however, many systems, including G1000-based systems, cannot). That gives a rock steady flight path (don't we love GPSS?) while showing the "raw" VOR data right on the HSI's CDI. Why do I think it should be a CDI type display (for VOR approaches) showing the "raw" data and not just the RMI style bearing pointer on your PFD pointing to the VOR? Because pilots aren't expected to do math in their heads much and the requirements for "on course" (and "established") during the final approach segment are based largely on CDI deflection (3/4 max deflection for VHF approaches) and stability on the course and converting a bearing pointer to an off-course number of degrees or a rate of departure from a course (that is, a rate of lateral tracking error) and then knowing when too much is too much and time to go missed is much more difficult. So without two CDIs available (and many do have that, but not all) then I think one has to go with the VOR indication on the one CDI. Our local DPE's expect to see the VHF device on a CDI during an approach (FAF inbound), including VOR approaches - not just a bearing pointer. So depending on your equipment you may or may not be able to actually fly the GPS and still monitor the VOR appropriately. My $0.02; good thread, all.