Plain English Meaning

A ground-based radio aid that gives pilots a needle showing whether they are left or right of the path to a runway. It works like a localizer but is less precise, and it does not tell you anything about how high you should be.

Full Definition

A non-precision instrument approach navigation aid that provides lateral (left/right) course guidance to a runway, similar to a localizer but with reduced accuracy. The SDF course may be offset from the runway centerline by up to 3 degrees, and the course width is fixed at either 6 or 12 degrees, rather than being tailored to produce a standard width at the runway threshold. SDF provides no glide path ().