Definition
Non-precision instrument approaches that use the localizer portion of an Instrument Landing System (ILS) to provide lateral (left-right) guidance to a runway, but do not provide electronic vertical (glideslope) guidance. The pilot follows published step-down altitudes to a Minimum Descent Altitude (MDA) and must visually acquire the runway environment before descending to land.
Plain English
An instrument approach where a radio signal lines you up with the runway side-to-side, but you have to manage your own descent using altitudes printed on the chart. There's no electronic beam telling you when to go down.
Context Anchor
Seen on instrument approach charts and used during instrument flying when the approach is labeled LOC or when only the localizer portion of an ILS is being flown.
Derivation
Localizer' comes from 'localize' -- to pinpoint a position. The localizer signal pinpoints the extended centerline of the runway, allowing the aircraft to be located laterally relative to it.
Why Pilots Care
It lets pilots fly precise approaches to lower weather minimums than non-precision approaches without localizer guidance.
Analogy
Think of the localizer like a centerline guide extending out from the runway. It helps you stay lined up left and right, but it does not by itself tell you how steeply to descend.
Intuition Check
Do not read approach here as just any way of getting closer to an airport. A localizer approach is a specific published instrument procedure. Also, a localizer approach is not automatically a full ILS; localizer-only guidance normally means left-right guidance without a glideslope.
Example Sentence 1
When the glideslope was reported out of service, the crew briefed the localizer approach to Runway 27 and reviewed the step-down altitudes.
Example Sentence 2
Localizer approaches require the pilot to monitor altitude manually using step-down fixes on the chart.