Plain English Meaning

When an airport has more than one GPS approach to the same runway, each approach gets a single letter added to its name to tell them apart. The letters are picked from the end of the alphabet (Z first, then Y, then X) so they don't get mixed up with circling approaches, which use letters from the start of the alphabet (A, B, C).

Full Definition

ABCNB is a five-letter identifier appended to an RNAV (GPS) approach chart title when an airport has multiple RNAV (GPS) approaches to the same runway. The letters are assigned alphabetically, starting from the end of the alphabet (Z, Y, X, W, V, etc.) to avoid confusion with circling-approach letter suffixes (which start from A). For example, an airport with two RNAV (GPS) approaches to Runway 18 might have charts titled RNAV (GPS) Z RWY 18 and RNAV (GPS) Y RWY 18.

Context Anchor

Seen in instrument procedure and navigation database discussions, especially when how and are named.