I often get questions about how and when a pilot can substitute a GPS receiver/navigator for ground-based navigation aids when flying under IFR.
For a detailed discussion of this topic, see my presentation: Using GPS on Conventional Procedures.
Fortunately, an update to the AIM (dated 25 August 2011) included revisions to section 1-2-3: Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes, specifically to clarify the use of RNAV systems (especially IFR-approved GPS units) as substitutes for ground-based navaids.
For information about a further change to this section of the AIM in 2016, see
Use of IFR GPS on Conventional Approaches and Use of GPS on Conventional Approaches (Update) at BruceAir. And for additional suggestions, see Setting the CDI on a Conventional Approach (The “Kill Switch”).
Note 1 of that section also explains that “Additional information and associated requirements are available in Advisory Circular 90-108 titled ‘Use of Suitable RNAV Systems on Conventional Routes and Procedures.'”
New AIM section 1-2-3 explains that:
…b. Types of RNAV Systems that Qualify as a Suitable RNAV System. When installed in accordance with appropriate airworthiness installation requirements and operated in accordance with applicable operational guidance (e.g., aircraft flight manual and Advisory Circular material), 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, Airworthiness Approval of Global Positioning System (GPS) Navigation Equipment for Use as a VFR and IFR Supplemental Navigation System, or AC 20-130A, Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors, and authorized for instrument flight rules (IFR) en route and terminal operations (including those systems previously qualified for “GPS in lieu of ADF or DME” operations), or
2. An RNAV system with DME/DME/IRU inputs that is compliant with the equipment provisions of AC 90-100A, U.S. Terminal and En Route Area Navigation (RNAV) Operations, for RNAV routes. A table of compliant equipment is available [here] (Microsoft Excel worksheet. That worksheet lists details about the specific capabilities of various units (subject, of course, to any limitations in the AFM supplement for your aircraft).
For most GA pilots, only item 1 applies. “RNAV system with TSO-C129/ -C145/-C146 equipment…” basically means IFR-approved GPS units, either non-WAAS or WAAS-capable boxes.
The updated language in the AIM includes the following explanations:
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 (see NOTE 5 below), 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.
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. 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.
I also have links to several useful resources about GPS and WAAS on my Aviation Resources page.
8 thoughts on “Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes”
This page needs updating. Your AIM 1-2-3 quote is out of date. The latest version introduces some ambiguity. I started a discussion thread here:
You’ll find a couple of updates, one from 2016, that address that section of the AIM.