While the use of Runway 4 has grown over the last several years, the SDP technical alternatives evaluation found that there are several limitations to further increasing its use, including:
- airspace conflicts with Randolph AFB arrivals and departures;
- the intersection with Runway 13R-31L which has been deemed a safety “hot spot” by the FAA;
- and to a lesser extent, Lackland AFB/Kelly Airfield interference with Runway 4 arrivals.
In other words, making Runway 4-22 SAT’s main runway would increase the current airspace conflicts. It would make the SAT operation mostly dependent on the Joint Base San Antonio aircraft operations at Randolph AFB and Lackland AFB/Kelly Airfield. This is not acceptable, given SAT’s role as a growing air carrier airport and important contributor to the regional economy.
Also, because Runway 4-22 will ultimately go away as an air carrier runway (some time after a parallel runway is built, between 2038 and 2048), investing in extending it versus extending one of the 13-31 runways would not be a sound infrastructure investment. As such, it is likely to be ineligible for FAA funding. It should also be noted that there is not sufficient space off the ends of Runway 4-22 for a full extension to the ultimately needed 10,700 feet. To the south, limitations include the space needed for a runway safety area (overrun) and airspace clearance over the elevated portion of Loop 410. Limitations to the north include the Salado Creek and Mud Creek floodplain and wetland areas, as well as the Salado Creek Greenway. So-called special purpose environmental laws mandate that impacts to these areas are only allowable if no alternative exists that avoids such impacts. In our case, the final SDP alternatives avoid special purpose environmental impacts.
Lastly, once a closely-spaced parallel runway will have been built, SAT’s airfield will be an efficient two-runway parallel traffic flow in the 13-31 direction. Like other US parallel-runway airfields with good wind coverage, Runway 4-22 could not be used much anymore at that time, because its traffic would cross with two parallel traffic flows on the 13-31 runways.
For these reasons, the seven-month long technical alternatives evaluation process eliminated alternatives that would extend Runway 4-22, build a parallel to it, or build other air carrier runways in the general northeast-southwest orientation.