Image: Grand Canyon
Joe Cavaretta  /  AP
A tour helicopter lifts off inside the Grand Canyon in Arizona. Sound levels at the canyon are being measured to determine whether current regulations on tour flights adequately address concerns at the canyon.
updated 6/2/2005 6:31:24 PM ET 2005-06-02T22:31:24

Mounted at about ear level on tripods, microphones are capturing the sound of quiet at the Grand Canyon.

The four microphones are attached to sound level meters and computers that will later screen out all manmade sounds, such as the chatter of hikers, the rumble of cars and the buzz of sightseeing planes and helicopters. All that will be left will be the sounds of nature: the wind in the trees, the chirping of birds, for example.

Park officials are doing this because they need to establish the natural decibel level at the Grand Canyon before policymakers can decide whether the current noise-reduction regulations governing flights over America's most breathtaking natural wonder are adequate.

Although the listening devices are new, the effort to determine whether the park is as quiet as it should be goes back a generation.

Congress said in 1975 that natural quiet is a resource at the Grand Canyon, just like the animals and the vegetation, and must be protected.

At the time, flights over the canyon were virtually unregulated. But little was done about the aircraft until a helicopter and a sightseeing plane collided 2,000 feet above the canyon floor in 1986, killing 25 people.

The federal National Parks Overflights Act passed the following year, establishing flight corridors, altitude requirements and caps on the number of flights. The law also required that natural quiet be substantially restored to the park.

The problem was that no one defined "substantial restoration" and no one knew what "natural quiet" sounded like at the canyon. That has contributed to years of fighting among air tour operators, environmentalists and policymakers.

What constituted substantial restoration of quiet remained unsettled until 1994. The standard was set at half or more of the park having no audible aircraft noise at least 75 percent of the day. That did not settle the issue, though.

"Even what we meant by the `day' was a contentious issue for many years," said Ken McMullen, overflights and natural soundscape manager for the park. Officials finally defined "day" as 7 a.m. to 7 p.m., a standard the air tour operators still do not like.

But without knowing what decibel level constitutes "natural quiet" at the Grand Canyon, it is impossible to say whether substantial restoration has occurred over the park, which had about 83,000 sightseeing flights in 2003.

So in April, canyon officials began gathering data using microphones placed in the four major types of vegetation, away from developed areas of the park. The sounds will then be plugged into a computer model that will determine the Grand Canyon's natural decibel level.

Many computer models for determining noise levels are designed for big cities and airports, not the unique terrain of the Grand Canyon. It took four years of study before the National Park Service and the Federal Aviation Administration found a model that seemed valid for the Grand Canyon.

By next winter, Grand Canyon officials should have an idea of how close they are to natural quiet in the summer and whether the current regulations are adequate. By next year, they hope to have an assessment that covers the winter months.

After that, it could still take years before the Park Service, air tour operators, environmentalists, Indian tribes and others can come to terms on the flight regulations.

But Steve Bassett, president of the U.S. Air Tour Association, expressed optimism. "It just seems like all the stars are starting to align, and we will get something done," he said.

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