The first one or two letters of the four‑letter code represent the State or region (e.g., E for Northern Europe, K for the contiguous United States, V for Southeast Asia). The remaining two or three letters identify the specific aerodrome (e.g., C for Chicago O’Hare → KORD ).

(Note: Always verify you are downloading the most recent edition. The keyword "doc 7910 pdf" can lead to outdated versions from 2012 or 2015, which are unsafe for operational use.)

It is common to confuse the various "7910" numbers. Let’s clarify: