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:

The note "GPS and DME required" on charts like "ILS Z or LOC Z" signifies distinct equipment needs for two co-charted approaches, not a single one with optional glideslope.
Specifically, 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 required for identifying fixes on the localizer (LOC Z) approach.
This complex phrasing stems from historical charting practices, but the FAA plans to introduce clearer equipment requirement sections on future approach charts.
Modern GPS databases are evolving to better support distinct localizer approach data, including previously missing waypoints, enhancing navigation accuracy for these procedures.

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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.