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20 CHAPTER FOUR WIND ENERGY AND POTENTIAL IMPACTS This section describes the existing body of information on space Review, 2010). An example of this latter case is the the potential impacts of wind energy on airports and aviation. Wild Horse Wind Farm in Washington State located 13 miles Impacts of wind turbines on aviation include physical pene- away from Bowers Airport (ELN). After the wind farm was trations of airspace, communication system interference, and constructed, the FAA flight procedures office assessed the rotor blade-induced turbulence. Although wind turbines like potential impact of the constructed wind farm on instru- other electricity generation emit electromagnetic fields, owing ment approach and missed approach procedures. It deter- to the design and size of the generator they do not cause elec- mined that the wind farm presented an Adverse Obstacle tromagnetic interference (CAA 2010). An additional issue and raised the height above airport minimums from 421 ft noted in this section is the increased propagation of meteoro- to 801 ft (Rowbothan 2010). Chain of communication break- logical test towers (also known as met towers) erected to mea- down can also occur. For example, in the Shepherd Flats sure the potential wind energy generating capacity of an area. review, the local Air Force base initially signed off on the project, when it required review from other people in the agency (Robyn 2010). PHYSICAL PENETRATION OF AIRSPACE Although utility-scale wind turbines exceed 200 ft above The FAA undertakes a systematic review of projects that ground triggering an airspace review, met towers often do not. physically penetrate airspace. Project review is coordinated Met towers have even been positioned at heights just under by the Obstruction Evaluation Office and reviews are under- 200 ft, specifically to avoid triggering an airspace review taken by different divisions within the FAA that have spe- and marking requirements. As a result, state agencies have cialized expertise, including airports, technical operations, expressed concern about the potentially undocumented haz- services, frequency management, flight standards, and flight ard posed by met towers (Bingner 2010; S. Brummond, per- procedures office (see Regulatory Review Processes in chap- sonal communication, 2010). However, the FAA has informed ter two). The FAA also coordinates with the military and local South Dakota that federal law preempts the states on any airports, and the review is subject to a 30-day public com- matter of regulating airspace (Whitlow 2009). ment period. The FAA issued a notice in the January 5, 2011, Federal Utility-scale wind turbine generators rise above 200 ft (see Register requesting comments on proposed revisions to AC Figure 14) and therefore are subject to FAA review under 70/7460-1, Obstruction Marking and Lighting, that provide Part 77 regardless of a project's proximity to an airport. The guidance for voluntary marking of met towers under 200 ft FAA may issue a Notice of Presumed Hazard if a wind tur- above ground level. The FAA is recommending that met bine is located in an approach area to a runway if the wind towers include alternate orange and white painting, and also turbine exceeds the approach minimums. Wind turbines that seeks comments on sleeves around the guy wires to make are not proposed in airport approach areas are often issued a the facilities more visible ("Marking Meteorological Evalu- No Hazard Determination with the conditions that the wind ation Towers" 2011). Just two weeks after the FAA's notice, turbine be equipped with FAA-approved marking and/or light- a crop dusting aircraft hit a met tower in the Sacramento ing (FAA 2007). The FAA does not require all wind turbine San Joaquin River Delta of California and crashed killing generators in a wind farm to be marked. the pilot. The met tower was 197 ft tall and therefore did not require FAA airspace review or obstruction marking The volume of wind turbine applications to the FAA has ("NTSB: Pilot . . ." 2011). increased dramatically in recent years, from 3,030 in 2004 to 25,618 in 2009 (Kaufman 2010). There have been uncom- mon cases where the Part 77 review overlooked information COMMUNICATIONS SYSTEMS INTERFERENCE suggesting that a project will impact procedures and systems. In those cases, the FAA will attempt to modify approvals There has been a considerable amount of study on the poten- before construction begins. Where construction has already tial impacts of wind turbines on aviation navigation and com- occurred, the FAA is limited to making adjustments to flight munications systems. Initial concern came from the DoD and procedures (F. Beard, personal communication, FAA Air- the potential effect of wind turbines on military training. In a

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21 FIGURE 14 Wind turbines from Klondike Wind Farm, Oregon (courtesy: Stephen Barrett). report issued in 2006, the DoD concluded that wind turbines have an effect on primary radar and have the potential to "negatively impact the readiness of U.S. forces to perform the air defense mission" (DoD 2006). Data collection efforts have accelerated since and the DoD and FAA have worked with the wind industry to identify areas sensitive to military training and the nation's radar system. Individual projects continue to require detailed evaluation and consideration of mitigation options. The DoD recently reported in a statement to Congress on the effects of wind turbines on military readi- ness that "the vast majority of all wind turbines proposed through the OE/AAA process raise no concerns for the Depart- ment, and for those that do raise concerns, we can generally FIGURE 15 Department of Defense screening tool, Topeka, find a way to mitigate the problem" (Robyn 2010). Kansas (courtesy: FAA website). For the purpose of this discussion, communications sys- tems include radar and NAVAIDS. Radar can be divided to Air Defense and Homeland Security radars, aeronautical between primary and secondary systems. The FAA operates study required; yellow impact likely to Air Defense and two basic radar systems: airport surveillance radar (ASR) and Homeland Security radars, aeronautical study required; and air route surveillance radar (ARSR), both of which include green no anticipated impact to Air Defense and Homeland primary and secondary radar capabilities (FAA 2008a). The Security radars, aeronautical study required. Figure 15 shows difference between the two systems is that ASR is focused the output for a fictitious wind turbine proposed in Topeka, on near airport activities whereas ARSR is a long-range radar Kansas. deployed at about 100 locations across the country. There are other supplemental radar systems throughout the air naviga- tion system that provide additional information to pilots. Primary Radar Interference Two primary areas of impact are blockage and clutter. Primary radar transmits a signal that is reflected back to the Two areas of impact analysis from DoD's perspective are radar receiver when it contacts an object within the radar (1) impacts on long-range radar used for airspace surveillance line-of-sight. Modern day WTGs present a significant obsta- and air defense, and (2) impacts on testing and training mis- cle with a high potential to reflect radar signals and produce sions that require electromagnetically pristine environments images on aircraft and airport radar deemed to be unwanted to collect baseline data and assess weapon performance (DoD returns (referred to as clutter) on radar screens. The taller 2006; Robyn 2010). The DoD has provided a red-yellow- the WTG, the greater is the risk of clutter. Multiple WTGs green map on the FAA's OE/AAA website to alert devel- in wind farms increase the potential for clutter and the closer opers about potential problem areas for wind turbine siting wind farms are to a radar station the greater potential of false (FAA OE/AAA 2011). Red signifies impact highly likely radar returns. Impacts of WTGs on primary radar can be more

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22 difficult to predict because the wind turbine rotor position Presenting an Obstruction--As with primary radar, a changes with wind direction and as a result its potential to WTG can present a physical obstruction to locating reflect radar signals will also change. The following types of aircraft on the backside of the structure, thereby block- impacts from WTGs on primary radar have been identified ing the signal and preventing its identification by the (CAA 2010): secondary radar system. Receiver Saturation--This condition occurs where the NAVAIDs Interference wind facility, because of its location, size, and extent, reflects enough energy back to the primary radar to sat- NAVAIDs are systems that support aircraft and pilot nav- urate the receiver. This effect can be caused by any large igation and location identification. There are more than structure and the likelihood of saturation from a wind 2,000 ground-based NAVAIDs available to pilots across farm is considered to be low. the continental United States (FAA 2008b). They include Constant False Alarm Rate--The Constant False Alarm instrument landing systems and very high frequency omni- Rate affects radar signal processing whereby the filter- directional radar. Although adoption of SATNAV (satellite- ing adjustments tuned to receive signals from aircraft are based navigation) has been evolving since the 1980s, some masked by new signals produced by the wind turbines ground-based system may be retained as a back-up for satel- resulting in a masking of the aircraft targets. lite system failure or during periods when satellite signals Defeating Moving Target Processing (obscuration)-- are interrupted by distortions in the Earth's atmosphere. Filters are used to distinguish between objects based NAVAIDs also include visual markings used by pilots oper- on rate of movement with aircraft radar trained to pick ating under visual flight rules. All NAVAIDs have the poten- up typical aircraft speeds while effectively filtering out tial to be impacted by inappropriately sited development stationary and slow moving objects. Because the speed including new energy technologies. of the wind blade tip travels at rates within the range of aircraft speed, spinning wind turbines cannot be fil- tered and removed producing clutter. Regulatory Review Thresholds False Radar Returns (clutter)--The clutter produced by the wind blade tips shows up on radar as a "twinkling" The FAA provides guidance on criteria used for determining if that can be distracting to controllers looking for aircraft a structure will have an adverse effect. The first trigger is if the targets and easily cause confusion. High levels of clutter structure exceeds the obstruction standards of Part 77 and/or is can obscure tracking of aircraft targets and pathways. found to have physical, electromagnetic, or other line-of-sight Plot Extractor/Filter Memory Overload--Some radar impact on aviation prompting the FAA obstruction evaluation systems are equipped with a plot extractor that filters review (see Figure 16). In its review, the FAA will determine and processes all identified targets. Constant unwanted that an obstruction results in an adverse effect if it: returns from wind facilities can overload the memory of the plot extractor clutter and cause it to shut down. 1. Requires a change to an existing or proposed instru- Presenting an Obstruction (shadow)--A WTG, even ment flight rules (IFRs) minimum flight altitude, a pub- when stationary, will block and reflect a radar signal lished or special flight procedure, or an IFR departure such as any solid structure, limiting detection of objects procedure for a public-use airport; on the opposite side from the radar receiver. 2. Requires a visual flight rule (VFR) operation to change its regular flight course or altitude; Secondary Radar Interference Secondary surveillance radar (SSR) identifies and commu- nicates with aircraft that are equipped with transponders. Although clutter is not an issue with secondary radar, two interference issues can occur. SSR Reflections--Reflections from secondary radar can occur if the object is in the line-of-sight between the receiver and the transponder. The likelihood of this occurring would be greater the closer the WTG is to the secondary radar receiver. The line-of-sight assessment is more difficult to determine however because aircraft response from the transponder can reflect off of a struc- ture and back to the receiver under certain operating conditions, even if the structure is not directly in the FIGURE 16 Wind Farm at Altamont Pass, California (courtesy: line-of-sight. U.S. DOE, Lawrence Berkeley National Laboratories).