Travis Air Force Base midair collision avoidance pamphlets (MACA) from 2007 and 2011. The 2011 pamphlet was amended to address the impact of spinning turbine blades on radar. Both pamphlets can be downloaded by clicking on the links below. The third 1-page document shown below is taken from the 2011 MACA.
Documents filed under Safety from California
On January 10, 2011, at 1057 Pacific standard time, a Rockwell International S-2R, impacted a meteorological tower (met tower) during an aerial application on Webb Tract Island, Oakley, California. The airplane sustained substantial damage and the pilot was killed. The met tower was erected for the purposes of planning a wind energy facility. The preliminary NTSB report can accessed at the link(s) below.
The California Wind Energy Collaborative was tasked to look at barriers to new wind energy development in the state. Planning commissions in the state have developed setback standards to reduce the risk of damage or injury from fragments resulting from wind turbine rotor failures. These standards are usually based on overall turbine height. With the trend toward larger capacity, taller towers and longer blades, modern wind turbines can be "squeezed out" of parcels thus reducing the economic viability of new wind developments. Current setback standards and their development are reviewed. The rotor failure probability is discussed and public domain statistics are reviewed. The available documentation shows rotor failure probability in the 1-in-1000 per turbine per year range. The analysis of the rotor fragment throw event is discussed in simplified terms. The range of the throw is highly dependent on the release velocity, which is a function of the turbine tip speed. The tip speed of wind turbines does not tend to increase with turbine size, thus offering possible relief to setback standards. Six analyses of rotor fragment risks were reviewed. The analyses do not particularly provide guidance for setbacks. Recommendations are made to use models from previous analyses for developing setbacks with an acceptable hazard probability.