Charting Two for One

The note is correct as written-and an IFR GPS alone is fine. Now follow me down a logical rabbit hole to understand why, as well as see how GPS and digital tech in general are changing how we fly IFR.

jwanwest

Friday, March 03, 2017 at 12:00 AM ET

Verified

Key Takeaways:

Confusing notes like "GPS and DME required" on approach charts arise because a single chart title (e.g., "ILS Z or LOC Z") actually represents two distinct approaches co-charted for efficiency, each with specific equipment requirements.
In the given example, GPS is required for the missed approach procedure of both the ILS Z and LOC Z, while DME (or GPS in lieu of DME) is *only* required for the LOC Z approach to identify specific points, clarifying the conditional nature of the "and" requirement.
The FAA plans to introduce clearer briefing strip information to specify equipment requirements for different approach versions, and GPS databases are evolving to better support distinct localizer approach waypoints, which currently can be missing from ILS-loaded approaches.

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Someone asked me about a note on the ILS Z or LOC Z Rwy 23 at Walterboro, SC (KRBW). The note says: “GPS and DME required.” (Emphasis added.) How can that be? GPS can be used in lieu of DME, but it can’t be a typo because it would just say “DME required.”

The note is correct as written—and an IFR GPS alone is fine. Now follow me down a logical rabbit hole to understand why, as well as see how GPS and digital tech in general are changing how we fly IFR.