Plain English Meaning

An instrument approach that gives you a left/right needle to follow toward the runway, but no glide path. The signal is less precise than a localizer and may point slightly off the runway centerline, so you fly down using published altitudes rather than a smooth glide.

Full Definition

A non-precision instrument approach that uses a Simplified Directional Facility to provide lateral (left/right) guidance to a runway. The SDF transmits a single course signal similar to a localizer, but with a wider course width (typically 6° or 12°) and a course alignment that may not be exactly aligned with the runway centerline. It provides no vertical guidance; descent is flown using published to a ().