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AIRPORT MASTER PLAN <br />that aircraft can fly to when they are in close proximity to theNDB 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 />nautical miles northwest of the Airport directly under the flight path for Runway 13. <br />The NDB is used as the basis for the NDB approach to Runway 13 and as the outer <br />marker associated with the ILS approach for Runway 13. It is expected that the NDB <br />will eventually be decommissioned as the FAA plans to phase out NDB systems <br />nationwide. <br />Instrument Landing System (ILS) <br />Instrument Landing Systems (ILS) are a ground-based navigation system, composed <br />of a localizer and glideslope that provide vertical and horizontal guidance to pilots <br />when conducting an instrument approach to a runway during inclement weather. <br />Today, ILS systems are still the primary instrument approach system utilized at <br />commercial service airports across the United States. However, with t <br />migration to GPS based approaches and enroute navigation, the need for ILS <br />systems is expected to decrease in the future. <br />Currently, San Marcos Regional Airport only has an ILS approach to Runway 13. <br />Based on the IFR wind coverage analysis previously shown in Table 4-9, Runway 13 <br />has the best IFR wind coverage of all the individual runway ends at the San Marcos <br />Regional Airport and, consequently, is the ideal runway end to be equipped with an <br />ILS system. The ILS system is in good condition and is maintained by the FAA. Due <br />expected that an additional ILS system will be needed at the San Marcos Regional <br />Airport. <br />Automated Weather Observation Systems (AWOS) and Automated Surface <br />Observation Systems (ASOS) consist of various types of sensors, a processor, a <br />computer-generated voice subsystem, and a transmitter to broadcast minute-by- <br />minute weather data from a fixed location directly to the pilot. The information is <br />transmitted over the voice portion of a local NAVAID (VOR or DME), or a discrete <br />VHF radio frequency. The transmission is broadcast in 20-30 second messages in <br />Facility Requirements Chapter Page 52 of 70 <br />October 2020 <br /> <br />