Plain English Meaning

It's a coded label used inside flight management systems to mark the very first point of a procedure. The 'I' part means 'this is the starting fix' and 'SNA' is the name of that starting fix. It tells the FMS where the procedure begins, without describing how the airplane got there.

Full Definition

I-SNA is the ICAO/ARINC 424 path terminator code for an Initial Fix (IF) leg at a procedure beginning with the identifier SNA (typically referencing a fix, waypoint, or navaid named SNA, such as Santa Ana). The 'I' designates the leg type as an Initial Fix — a defined point that establishes the start of a procedure leg with no flight path before it — and 'SNA' is the fix identifier the leg terminates at.

Context Anchor

Seen on instrument approach charts and in examples of coded approach paths, often near the localizer frequency or information.