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 co-charted ILS/LOC approaches signifies that GPS is needed for the specific missed approach procedure (applicable to both ILS and LOC), while DME (or GPS in lieu) is an additional requirement only for the localizer approach's FAF/MAP identification.
"ILS Z or LOC Z" indicates two distinct approaches on a single chart, each with potentially different requirements, rather than one approach with an optional glideslope, which is key to interpreting complex equipment notes.
GPS databases are improving to differentiate and include specific waypoints for localizer approaches previously co-charted with ILS, enhancing precision for localizer-only operations, especially for non-WAAS units or during WAAS outages.

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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.