What is an SDF?

• A. Simplified Directional Facility; provides final approach course similar to a localizer; may not be aligned with runway and may be wider than LOC (up to 35 degrees)
• B. Standard Directional Facility; provides a straight final course identical to LOC
• C. Simple Directional Front; used to align with runway centerline
• D. Special Directional Facility; used only with GPS overlays and always aligned with runway

Answer: (A)

An SDF is a Simplified Directional Facility. It provides a final approach course that is similar to a localizer, but with a wider course width and the possibility of being offset from the runway centerline. Because the final course can be offset and the guidance is only lateral (no vertical guidance like a glideslope), it is less precise than a standard localizer approach. The key point is that the course may not be aligned with the runway and can be wider than a localizer, up to about 35 degrees offset in some cases. The other descriptions either give an incorrect name or imply features (such as always aligning with the runway or requiring GPS overlays) that aren’t part of what an SDF provides.