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AIRPORT MASTER PLAN <br />Very High Frequency Omni-Directional Range/Tactical Aircraft Control <br />(VORTAC) <br />Currently, Very High Frequency Omni-Directional Ranges (commonly referred to as <br />VORs) are still used for aerial navigation. These systems emit a signal that aircraft <br />can follow or track to move from point-to-point and conduct an instrument <br />approach for landing at an airport. Tactical Aircraft Control systems (commonly <br />referred to as TACANs) are similar systems used for military purposes. When these <br />systems are co-located together, they are referred to as a VORTAC. <br />The closest VORTAC for the San Marcos Regional Airport, the Randolph VORTAC, is <br />located 31.4 miles southeast of the airport. The Centex VORTAC is located 33.9 <br />miles north of the field and is used as part of the ILS/LOC approach to Runway 13. <br />The 215-degree radial from the Centex VORTAC is used to define the outer marker <br />for the ILS approach for Runway 13. <br />Non-Directional Beacon (NDB) <br />NDBs are an older ground based navigational technology that is still used in some <br />places to provide redundant navigational capabilities at airports. NDBs emit a signal <br />that aircraft can fly to when they are in close proximity to the NDB station. <br />Currently, NDBs are used as a basis for instrument approach procedures and for <br />marker locations (e.g. typically the outer marker) associated with ILS approaches. <br />The San Marcos Regional Airport currently has an NDB located approximately 5.5 <br />NM northwest of the airport directly under the flight path for Runway 13. The NDB <br />is used as the basis for the NDB approach to Runway 13 and as the outer marker <br />associated with the ILS approach for Runway 13. <br />Instrument Landing System (ILS) <br />ILS are the most accurate ground based runway approach navigation system <br />currently in the industry. ILS are composed of two ground based navigation aids: a <br />localizer (LOC) and a glide slope (GS). When conducting an ILS approach, these two <br />systems (the LOC and the GS) provide horizontal and vertical guidance in concert to <br />aid a pilot in executing an instrument approach to a runway end. <br />Currently, the San Marcos Regional Airport only has an ILS approach to Runway 13. <br />The glideslope associated with the approach is located at the approach end of <br />Inventory Chapter Page 20 of 52 <br />October 2020 <br /> <br />