The National Park Service has released the draft Environmental Impact State for Special Flight Rules Area in the Vicinity of Grand Canyon National Park. The public comment period is open from Feb 4 through June 6, 2011. From the Executive Summary:
Since 1987 Overflights Act passage, steps have been taken to restore natural quiet in GCNP. In compliance with the 20 1987 Overflights Act and in 1995 Report to Congress, “substantial restoration of natural quiet” in Grand Canyon 21 National Park was defined as “50% or more of the park achieving natural quiet (i.e., no aircraft audible) for 75% to 22 100% of the day.” In an April 9, 2008 Federal Register notice (73 Federal Register 55130), the NPS clarified that
23 Substantial Restoration of Natural Quiet in GCNP will be achieved when reduction of noise from aircraft operations 24 below 18,000 feet mean sea level (MSL) results in 50% or more of GCNP achieving restoration of the natural quiet 25 (i.e., no aircraft audible) for 75% to 100% of the day, each and every day. The NPS also clarified that 50% of GCNP 26 is a minimum in the restoration goal.