Grand Canyon air tours face restrictions By Andrew Compart / July 13, 1999 Share 1 -- WASHINGTON -- Air tours over the Grand Canyon would face more restrictions under new rules proposed by the Federal Aviation Administration aimed at helping to enhance the "natural quiet" of the national park. Under the proposals, the aircraft would fly modified routes at higher altitudes. The agency also is proposing a new system for limiting the number of flights for each operator and an expansion of the park's flight-free zones.Aircraft would be able to fly through an "incentive corridor" in one of the zones, however, if they meet stricter noise standards currently under development. Public hearings on the proposals are planned for this summer.Even if the rules are adopted, however, the restrictions would fall short of the National Park Service definition of "substantial restoration of natural quiet," so more proposals are in the works.Under the NPS definition, more than half the park must be free of aircraft noise 75% to 100% of the day. Currently, 32% of the park meets that standard. The FAA proposals would increase the amount to 41%.