Travis Air Force Base Mid-Air Collision Avoidance pamphlets (MACA) for 2007, 2011, 2017, and 2020. In 2011, the MACA was amended to warn about the area over a wind turbine facility as being high-risk for mid-air collisions due to the impact of spinning turbine blades on radar. This warning did not appear in the 2007 MACA. At that time, the impact of the blades on digital radar systems was not well understood. Analog radars are not impacted by the turbines. The area continues to be a high risk for collision and pilots are required to fly with transponders turned on. The pamphlets can be downloaded by clicking the document links on this page. The single page shown below is taken from the 2011 pamphlet.