Definition
The standard total angular width of the usable signal of a Simplified Directional Facility (SDF) approach course, measured from the full-scale left deflection of the course deviation indicator to the full-scale right deflection. SDF courses are fixed at either 6° or 12°, with 12° being one of the two permitted widths.
Plain English
The SDF approach beam is 12 degrees wide from one edge to the other. If your needle is centered, you are in the middle of that 12-degree slice of sky. If it swings fully to one side, you have drifted 6 degrees off the centerline.
Context Anchor
Seen when reading about SDF approaches and how their lateral guidance compares with a localizer.
Derivation
Course comes from a Latin word meaning a running or path. Width means how broad something is. A degree is one of 360 equal parts of a circle, so 12° course width describes how broad the radio guidance path is as an angle.
Why Pilots Care
The wider signal means full-scale needle deflection occurs farther from centerline, so pilots must monitor position carefully to avoid large deviations during final approach.
Analogy
Think of it like following a wide road instead of a narrow lane. You can still tell whether you are left or right of the center, but the guidance does not pinpoint your position as tightly.
Intuition Check
Do not read “width” as a physical runway or ground distance here. It is an angle: 12 degrees total, measured across the SDF guidance signal.
Example Sentence 1
The approach plate showed an SDF with a 12° course width, so the pilot used gentler heading corrections than on a typical localizer.
Example Sentence 2
Because of the 12° course width, the pilot maintained a slightly wider heading tolerance on final than would be used on an ILS.