Satellite-guided instrument approaches arrived way back in the 1990s. This technology has provided greater accuracy and ultimate economy for pilots – once that $50K panel is installed. Combined with moving map technology for situational awareness, this whole world of instrument approaches has changed for the better. Just describe an NDB approach to an IFR newbie to witness confusion and fear; *that* is “non precision!”
“GPS Alphabet Soup” Take an L and a V and even a NAV. Add a P and mix em all around. What do you get? You get a total of five different GPS approaches to sort out. IFR Mag
This constantly evolving SBAS “alphabet soup” has created confusion and led to an occasional lack of safety. The flight training and testing world struggles daily seeking clarity: “What are the ‘legal minimums’ for this approach?”, “What equipment and data verification are necessary to be ‘legal?‘” and “What are the approach and alternate requirements given the installed equipment?” Applicants for flight tests and senior pilots alike suffer from the confusing “designation of the week” as the satellite technology continuously evolves. Hybrid satellite/ground-based approaches have appeared with little explanation and training (“How do we enter this ILS 23 at KMMU?”) Pilots struggle to set up and fly these approaches safely. But at least most of the “scud-runner” IFR approaches (proceed visual) are mostly gone now.
Some clarity is finally coming with the FAA’s integration of the ICAO 2D/3D clarification. Lateral guidance to an MDA (baro-dependent) will soon be designated “2D” and approved vertical path guidance to a DA (RNAV point in space) will be defined “3D” in future FAA documents.
The non-precision approach definition in the Instrument ACS FAA-S-ACS-8C is almost there: ” a published minimum descent altitude without approved vertical guidance.” (2D) That 300-foot limitation is now gone for training. Unfortunately for training/testing, it is almost impossible to find an approach when testing *without* some form of vertical guidance; e.g. an approach *requiring* step downs. (Serious safety concerns for a real MON situation – Green Needles!)
The ACS definition of an precision approach is simply: “a standard instrument approach procedure to a published decision altitude using provided approved vertical guidance.” (3D). These nicely match the ICAO 2D/3D distinction. This is made even clearer with the notes found in the Terminal Procedures Publication (TPP):
The actual 2D/3D FAA terminology will be published in the forthcoming revision of AC 90-119 “Performance-Based Navigation” available now in draft format. Section 12.3.1 finally distinguishes the 2D/3D approach definitions clearly. This should be published in final form later this year. Clarify your alphabet and fly safely out there (and often)!
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Given that the TPP says that LPV and LNAV/VNAV approaches are “precision,” and a pending AC that says the LPV – though not LNAV/VNAV – approaches, when do they update the Alternate Airport Minimum rules that say that none of that is true?