Definition
A straight-in localizer approach: a non-precision instrument approach that uses only the localizer (lateral guidance) portion of an ILS, without glideslope information. It is flown to the runway aligned with the final approach course, using step-down altitudes rather than a continuous descent path.
Plain English
It's an approach that lines you up with the runway using a radio beam for left-right guidance, but does not give you any up-down guidance. You manage the descent yourself using published altitudes.
Context Anchor
Seen in the minimums section of an instrument approach chart, including charts used in timed approaches from a holding fix.
Derivation
S' stands for 'straight-in' (aligned with the runway, no circling required). 'LOC' is short for 'localizer,' the radio signal that provides left-right guidance to the runway centerline. Together, S-LOC labels the minimums for flying the localizer straight to the runway without using the glideslope.
Why Pilots Care
Knowing whether you are flying to S-ILS or S-LOC minimums determines your decision altitude or minimum descent altitude, the descent technique you'll use, and how much margin you have above terrain and obstacles. Mistaking one for the other can put you below safe altitude.
Intuition Check
Do not read the “S” as “south” or “standard.” In this chart label, “S” means “straight-in.”
Example Sentence 1
With the glideslope reported out of service, the controller cleared us for the S-LOC approach to runway 27.
Example Sentence 2
Aircraft were released at two-minute intervals for the S-LOC to maintain proper spacing on final.