Author: Williams, Bradford T

Introduction
The San Marcos Municipal Airport is experiencing a period for growth potential and wants the capacity to accommodate larger aircraft to realize this long-term goal. Certain guidelines exist that limit construction and expansion efforts, per the Federal Aviation Administration (FAA). These guidelines help guide the parties involved in maintaining safety for both pilots and local residents. Local Land use and Obstructions causing a hazard or concern to both entities have been located and analyzed for future development of this project. Geo-Air
Consulting was consulted to develop a planning model to help derive possible expansion possibilities.
The Texas Department of Transportation (TXDOT) is helping to facilitate this task in coordination with local government officials and Airport management.

San Marcos Municipal Airport Runway Extension

Figure 1. San Marcos Airport Image

Image of San Marcos Municipal Airport

Source: Geo-Air Consulting

Figure 2. Controlled Compatibility Land Use Area

Table 1. Land Use Percentage

Figure 3. Approach Surface Obstruction Distribution

The table above shows the amount of obstructions and penetration percentage within each approach surface.
The map to the left shows the obstruction distribution in relation to the penetrable surface.

Analysis Procedure

Figure 4. Imaginary Surface Analysis Model

Land Use Compatibility Analysis
The creation and adoption of a controlled compatible land use map is critical for any airport looking to expand. Upon the completion of all analysis pertaining to land use, it was apparent what types of land use were most dominate in the controlled area created during analysis (See Figure 2 ). In addition, the attached table (See Table 1) defines the total count for each of the land use types in the controlled area.
Regarding the area in and around the San Marcos airport, most of the land use is agricultural land. There are some circumstances existing that could affect the expansion of the airport regarding available for land acquisition.

Imaginary Surfaces Methodology
The shape file data for this project was acquired from TXDOT. The construction of the two-dimensional Approach Surface polygons was based on FAA criteria and were manufactured accordingly. The Approach Surface polygons ground vertices were then assigned elevation values based on the Digital Elevation Model. The vertices for the upper end of the surface were assigned elevation value based on rise over run
calculation. The next procedure was to run a triangulated irregular network on the Approach Surface. This allowed a further conversion into a usable continuous surface of elevation values (Raster). The obstruction points were then interpolated with the Z value of the Approach Surface Raster at the points spatial location beneath the continuous elevated surface. (See Figure 4.) Subtracting the total elevation of each point (elevation + above ground height) - (Raster Z value) in the point’s attribute tables gave the level of
obstruction. Negative values showed no penetration, while positive values showed perforation of the
Approach Surface.

Conclusion
Geo-Air Consulting has provided the Texas Department of Transportation and the city of San Marcos with a controlled compatibility land use area map. This map takes into account pertinent statutes of the Texas Airport Zoning Act and has been reclassified for use as a zoning guide. Obstruction penetrations of FAA imaginary surfaces have been identified and tabulated into a matrix for use in eliminating those
obstructions. The penetration matrix provides detailed spatial location and the magnitude of the
penetrations in feet. Perforations of each imaginary surface have been accounted for.
After the penetration analysis, the suggested extension for runway 13-31 on the 31 end of the runway is 400 feet, bringing the overall length of the runway to 6,003 feet. This length will accommodate flight operations for the Gulfstream G450 which is the critical aircraft for this study. For runway 17-35, Geo-Air Consulting recommends an extension of 780 feet on the 35 end of the runway bringing the total length of that runway to 6,222 feet.

3D View of Approach Surface and Penetrations

Figure 5. Three - dimensional view of Approach Surface

Runway 13/31 was the area for consideration for expansion. This model shows the 50:1 Approach Surface for Runway 31. The obstructions are visualized as
vertical bars with the penetrating section highlighted in yellow.

Team Members:
Pete Binion, Project Manager
Marcus Pacheco, GIS Analyst
Michael Tebo, GIS Analyst/Web Design
Bradford Williams, GIS Analyst

Acknowledgements: Dr. Yongmei Lu, Ryan
Shuermann, and Mr. Daniel Benson (TXDOT)