The alliance, which filed suit to overturn the FAA's approval of Cape Wind, obtained the agency documents after filing a Freedom of Information Act request in 2010. The group allowed The Associated Press to independently review the documents.
Many of the documents fall within a 15-month period from Feb. 13, 2009, when the FAA determined the wind farm could present an airplane navigation hazard, to May 17, 2010, when the agency reversed itself.
During that period, the FAA was attempting to address concerns shared by local air traffic controllers about radar reflections, or "clutter," expected from the wind farm's rotating turbines. The clutter makes it extremely difficult for air traffic controllers to spot planes over the wind farm that aren't equipped with the transponders that signal their location — usually smaller planes.
The FAA documents indicate that about 12 percent of the area's air traffic doesn't have transponders. A study commissioned by the FAA indicated that less than 1 percent of local air traffic passed over the proposed Cape Wind site.
The FAA eventually decided Cape Wind would pose no navigation hazard but only if modifications were made to the existing analog radar system at Otis Airfield, the center of local air traffic control, that would essentially help filter out the radar clutter.
The order said that in the "unlikely" event the modification didn't work as well as the FAA thought it would, a more advanced digital radar system would need to be installed and paid for by Cape Wind. But the documents also indicate significant uncertainty the modification would be sufficient.
Some documents refer to difficulties testing the selected fix. One noted no existing turbine fields match Cape Wind's planned configuration.
An official at the FAA's Operations Support Center, writing before Cape Wind agreed to pay for any needed upgrade, asked, "Who is the decision maker that puts the agency at (economic) risk if the decision if the (fix) doesn't work?"
Notes from an April 22, 2010, teleconference indicate that managers were still getting conflicting reports on the modification. "We hear that (the modification) will adequately address the issue. However, we hear that they won't," one note read.
After the FAA decision was overturned, an FAA engineer wrote, "We may never have to worry about getting rid of the clutter that may be created." He also expressed doubts that air traffic control could keep a low-flying search plane from "running into a wind turbine."
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