Let's be precise

Those names don’t convey the key distinction between the two basic types of procedures—namely, whether you follow a glideslope or approved glidepath to a decision altitude (DA) or manage the descent along the final approach segment on your own, perhaps with advisory (+V) vertical guidance, to a minimum descent altitude (MDA). Certainly, you must fly both types of approaches with precision. But like “stall,” a term that befuddles pilots and nonaviators alike, we’ve been stuck with these labels since the beginning of instrument flying.

The International Civil Aviation Organization (ICAO) based in Montreal may be the folks who gave us “BR” for “mist” in METARs (brume is the French word), but they have adopted new clear, common-sense descriptions for approaches. In ICAO-speak, there are now two fundamental types: 2D, which offer lateral guidance to an MDA; and 3D, which provide both lateral and approved vertical guidance to a DA.

The first indications that the FAA is slowly supplanting the venerable “nonprecision approach” (NPA) and “precision approach” (PA) with the updated ICAO definitions are in the Instrument Rating-Airplane ACS and notes in the legends for the terminal procedures publication (TPP) and the Aeronautical Chart User’s Guide.

Appendix 3 in the IFR ACS states under Task A that, “A non-precision approach is a standard instrument approach procedure to a published minimum descent altitude without approved vertical guidance.” Under Task B, the appendix explains, “A precision approach is a standard instrument approach procedure to a published decision altitude using provided approved vertical guidance.” That language makes the precision approach task on IFR practical tests feasible in areas where an ILS isn’t readily or reliably available, and it removes a previous exception that allowed substituting an RNAV (GPS) approach with LPV minimums for an ILS only if the DA was 300 feet or less height above touchdown.

The TPP and Aeronautical Chart User’s Guide legends for the profile views of approach charts also distinguish between 2D and 3D approaches. Notes emphasize that stepdown altitudes along the final approach segment apply only when you’re flying the 2D version of an approach: “Altitude restrictions at stepdown fixes on final approach not applicable to Precision (LPV or LNAV/VNAV) Approaches.” Note the use of “precision” when referring to LPV minimums. (For more about stepdown fixes, see “Watch Your Step (Downs),” April 2025 Flight Training.)

The forthcoming AC 90-119 about Performance-Based Navigation Operations goes further. Section 12 of that AC, which should be published in 2025, explicitly adds the 2D and 3D terminology. Paragraph 12.3.1.1 NPA Operations explains that: “Two-dimensional (2D) operations use GPS-derived lateral guidance…These 2D procedures typically have LNAV lines of minima to a minimum descent altitude (MDA).”

The same document describes precision approaches (PA) thus: “These 3D operations use either ground-based, GPS-derived, and/or integrated electronic vertical guidance…to enable lateral and vertical navigation to decision altitude (DA)/decision heights (DH) at or below 250 feet above ground level (AGL) (depending on the presence of obstacles). Typically, these are shown as LPV or LNAV/VNAV (and ILS/GLS) DA/DHs.” The draft AC further emphasizes that all GPS approaches that rely on WAAS to provide an LPV DA “regardless of height above touchdown (HAT) are 3D PA operations.” 

Adopting the 2D and 3D labels should reduce the confusion caused when approaches with LPV and LNAV/VNAV minimums were introduced. As Aeronautical Information Manual 1−1−18 still explains, those procedures originally did not meet the old ICAO standards for precision approaches, so they were dubbed approach with vertical guidance (APV).

The 2D and 3D names don’t, however, have much significance for GA pilots unless you’re training for an instrument rating or completing an instrument proficiency check. Specifically, if you need to file an alternate per FAR 91.167, the “1-2-3 rule,” you still can’t consider an approach with LPV minimums a precision approach and use the 600-2 standard ILS alternate minimums as a general guide. Indeed, the draft language in AC 90-119 preserves the existing requirements, perhaps because not all LPV minimums match the standard 200 feet DA and one-half statute mile visibility for a Category 1 ILS.

“Operators with WAAS-enabled RNP systems [that is, an IFR approved GPS] may qualify both the destination and alternate with a GPS-based IAP,” says the AC, “but are restricted to planning for the nonprecision (2D) LNAV or circling line of minima at the alternate.” That language matches the requirements for specifying alternates in AIM 1-1-18.

Nevertheless, you can now demonstrate your precise understanding of the evolving nature of IFR operations by name-dropping “2D” and “3D” when talking about approaches.

Bruce Williams is a CFI. Find him at youtube.com/@BruceAirFlying and bruceair.wordpress.com