Definition
The standard lateral width of the usable signal produced by a Simplified Directional Facility (SDF), measured as the total angle from the full-scale left deflection of the course deviation indicator to the full-scale right deflection. SDF course widths are fixed at either 6° or 12°, depending on the installation, and are not adjustable to provide an optimum runway alignment as an ILS localizer course is.
Plain English
The SDF's guidance signal is 6° wide from one edge to the other. If your course needle is fully to the left, you're 3° off course on one side; fully to the right, you're 3° off on the other side. Anywhere in between, you're somewhere inside that 6° fan.
Context Anchor
Seen when studying Simplified Directional Facility approach guidance and how sensitive the course needle will be on an SDF approach.
Derivation
Course means the path to be followed. Width usually suggests a physical distance, but here it means angular width: how wide the radio guidance fan spreads out from the center course.
Why Pilots Care
The narrower 6° width increases course sensitivity, requiring more precise tracking but delivering tighter alignment with the final approach course than the 12° setting.
Grounding Statement
Picture the SDF guidance as a narrow V-shaped radio path aimed along the approach course, with the airplane trying to stay in the middle of that V.
Intuition Check
Do not read “width” as runway width or miles across. Here, “width” means an angle in the guidance signal, measured in degrees.
Example Sentence 1
Because this SDF has a 6° course width, a half-scale needle deflection means you are about 1.5° off the final approach course.
Example Sentence 2
When briefing the approach, the pilot confirmed the facility was using 6° course width rather than the wider 12° option.