SIMPLIFIED DIRECTIONAL FACILITY

The SDF is another instrument approach system that is not as accurate as the LOC approach facilities. Like the LOC type approaches, the SDF is an alternative approach that may be installed at an airport for a variety of reasons, including terrain. The final approach course width of an SDF system is set at either 6 or 12 degrees. The SDF is a nonprecision approach since it only provides lateral guidance to the runway.

For straight-in SDF approaches, the angle of convergence for the final approach course and the extended runway centerline is 30 degrees or less, and if the angle of convergence is beyond 30 degrees, the SDF will only have circling minimums. An SDF approach is provided a minimum of 250 feet obstacle clearance for straight-in approaches while in the final approach area, which is an area defined for a 6 degrees course: 1,000 feet at or abeam the runway threshold expanding to 19,228 feet 10 NM from the threshold. The same final approach area for a 12 degrees course is larger. This type of approach is also designed with a maximum descent gradient of 400 feet per NM, unless circling only minimums are authorized. [Figure 5-59]

Figure 5-59. Newark-Heath (KVTA), Newark, Ohio, SDF RWY 9.