Simplified Directional Facility (SDF)
A Simplified Directional Facility (SDF) is a type of navigation aid used for nonprecision instrument approaches. The final approach course is similar to that of an ILS localizer; however, the SDF course may be offset from the runway, typically not exceeding 3°, and the course may be wider than the localizer, resulting in a lower degree of accuracy. Despite the decreased accuracy, SDF is still a reliable means of navigation, providing pilots with valuable guidance during instrument approaches. SDFs are typically used in areas where terrain or other obstacles make it difficult to operate an ILS. The SDF ground equipment consists of a directional antenna and a communication facility. When aircraft receive the signal, it provides the pilot with information that enables them to fly a predetermined course towards the targeted runway.
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