FAA Obstruction Lighting Standards for Wind Energy Plants
Publication Number: CEC-500-2005-180
Publication Date: December 2005
PIER Program Area: Renewables Program Area
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Proposed structures that exceed 200 ft (61 m) above ground level (AGL) in height in the United States are considered obstructions to navigable airspace according to the Code of Federal Regulations (CFR, United States 2005a). Although these structures are not specifically regulated by the Federal Aviation Administration (FAA), the FAA must be notified of proposed construction. Other authorities, such as the Federal Communications Commission (for antenna structures), and local Counties, provide regulatory language that FAA recommendations for obstruction lighting must be followed.
Although early stand-alone MOD-series wind turbines exceeded 200 ft (61 m) in total height (see Figure 1 for dimensions) and required obstruction lighting, only in the last decade has there been large-scale manufacturing of turbines over 200 ft. Nearly every utility scale wind turbine sold today exceeds 200 ft (61 m) in height. Wind plants are now constructed with up to 200 of these large turbines. Obstruction lighting now becomes a formidable permitting issue, which impacts the scheduling and economics of the development, and will have a community visual impact.
Figure 1. Wind Turbine Dimensions
The primary goal of the FAA recommendations is to ensure pilot safety. In the United States, there are no known incidents of an aircraft striking a utility-grade wind turbine. There is one reported case of an aircraft striking a farmers wind turbine (Maller 2000), however the accident report for the crash does not mention the aircraft crashing into the turbine (NTSB 2000).
The California Wind Energy Collaborative (CWEC) has undertaken a study of wind turbine obstruction lighting under its Windplant Optimization task. Obstruction lighting was determined to be an issue of concern for California wind plant developers and operators. By studying the issues of obstruction lighting, perhaps solutions to overcome the issues could be determined.
The scope of this study is limited to obstruction lighting of wind plants away from airports where different considerations can take effect. This boundary is a 20,000 ft (6096 m) according to the CFR (United States 2005a). Low flying military operations are also not discussed; for this topic the reader is referred to a report by the British Department of Trade and Industry (Department of Trade and Industry 2002) on this subject.
With heights of modern utility-scale wind turbines exceeding 200 ft (61 m), wind energy developers in recent years have had to submit lighting proposals for wind plants to the Federal Aviation Administration (FAA). The current FAA guidelines for wind plant obstruction lighting have not been developed to a level where developers can know with some certainty what lighting scheme the FAA will approve for proposed construction. The California Wind Energy Collaborative (CWEC) initiated a study of FAA obstruction lighting for wind plants to determine the issues surrounding the subject. A literature survey and interviews on the subject were conducted. During the period of investigation, the CWEC was able to observe flight tests with the FAA of a wind farm configured for new lighting standards. Key elements of the proposed standards are synchronization of the flashing lights and maximum 0.5 mi. (0.8 km) spacing between lighted turbines. It is expected that the new standards will improve flight safety and streamline the FAA recommendation and permitting processes for wind plant developments.
Table of Contents1 Summary 1
2 Nomenclature 2
3 Introduction 3
4 Obstruction Lighting and Marking Advisory Circular 5
4.2 Wind Turbine Marking 7
4.3 Wind Turbine Lighting 8
4.4 Wind Plant Lighting 11
6 Development of Obstruction Lighting for Wind Turbine Farms 14
6.2 Lighting Type 15
6.3 Wind Plant Lighting Patterns 16
6.4 Separation between Lighted Turbines 16
7.2 Description of the wind plant 17
7.3 FAA Evaluations at Blue Canyon 20
7.3.2 Ground Evaluations August 2004 20
7.3.3 Flight Evaluations December 2004 20
8.2 Recommendations for Further Study 22
8.3 Acknowledgements 23
List of Figures
Figure 1. Wind Turbine Dimensions 3
Figure 2. Typical Wind Turbine Height Comparison to 500 ft AGL 6
Figure 3. Wind turbine marking (FAA 2000) 7
Figure 4. Nacelle installation of obstruction light (photo courtesy of Jim Patterson) 8
Figure 5. Vertical beam spread with expected low-visibility maximum range (not to scale) 9
Figure 6. Aviation safety and public acceptance for light intensity (Montgomerie 2004) 10
Figure 7. Dual Lighting Representation (FAA 2000) 10
Figure 8. FAA Obstruction Lighting Application Process 12
Figure 9. Position of light on turbine nacelle for unobstructed view 15
Figure 10. Blue Canyon Wind Farm Layout 18
Figure 11. Blue Canyon Wind Plant (photo courtesy of Jim Patterson) 18
Figure 12. Along-row view of Blue Canyon Wind Plant (photo courtesy of Jim Patterson) 19
List of Tables
Table 1. Obstruction Lighting References in California County Ordinances 5
Table 2. FAA obstruction lighting types for wind turbines 8
Table 3. FAA Evaluation Wind Plant Sites 14