Years of modeling, planning, and talks, interrupted by lawsuits and inter-agency differences, have produced an air-tour management plan proposed for Grand Canyon National Park that officials believe will restore natural quiet over much of the iconic canyon.

Is the plan outlined within the draft environmental impact statement perfect? That remains to be seen, as it notes that even under the preferred alternative the cumulative impacts to the park "would be long-term moderate to major adverse, due primarily to high levels of aircraft audibility." Also, the voluminous document with its hundreds of pages cannot be dissected overnight.

Park officials are not underestimating the complexities of the overflight plan, which Congress ordered in 1987, and are giving all interested parties 120 days -- until June 6 -- to submit their critiques of the proposal.

On its face, the plan states that it would boost the level of "natural quiet" in the park -- quiet that allows you to hear the murmuring of creeks, the roar of rapids on the Colorado River, the melodies of canyon wrens -- from 75-100 percent of the day across 50 percent of the park as is currently the case, to across 67 percent of the park within 10 years of the plan's implementation.

Outwardly, the claim doesn't seem possible. How can there be more natural quiet across Grand Canyon National Park if 8,000 more air tours a year -- and up to 50 more a day -- are allowed above the 57,000 already being flown a year?

"It is not just one component of the plan that would actually brings us to 67 percent of restoration of natural quiet, but a variety of components," Palma Wilson, the park's acting superintendent, said last week during a conference call with reporters. "One of those components is where we propose to move most of the non-air tour operations outside of the park. A second is conversion to 'quiet technology' within 10 years. A third component is curfews -- there would be no flights until one-hour after sunrise and then no flights after one hour before sunset, and there would also be some flight changes in the air tour routes that we currently have."

The much-anticipated plan arrived as efforts moved forward in Congress to legislate an air-tour plan for the park. Advocacy groups such as the National Parks Conservation Association and the Grand Canyon Trust hope that those efforts will be suspended while the draft plan is analyzed and commented upon.

“I’m cautiously optimistic that it’s as good as we can get, but there will be four months of public comment and people will be able to weigh in on this," said David Nimkin, NPCA's Southwest regional director. "We’ll take that amount of time to evaluate it and present back. A definitive response is not something we can say explicitly at this point until we’ve had a chance to review it and consult with some of our allies.

“I know some people are going to be disappointed because they’ve been fighting this and wanting the whole enchilada for the longest time.”

While the plan would allow upwards of 65,000 air-tour flights over the canyon annually if approved in its current form, there once was a time when upwards of 90,000 flights cruised the airspace over the park and when some of those flights actually dipped below the canyon's rims and helicopters hovered in place so their passengers could gaze at the red-rock wonder.

“You have to understand, you’re talking to someone who was around when the 1987 law (calling for the air-tour management plan) was passed, we don’t have a final rule yet, but we’ve got a good operating plan that’s getting better," said Roger Clark of the Grand Canyon Trust. "And we’re making progress towards what we think is a reasonable restoration of natural quiet in the park. We still need to look at all the details, but this is better than the current operating plan in terms of what it does for the park experience. For example, it puts a cap up at Marble Canyon, which is not a heavily flown area right now, but it doesn’t allow new tours to be developed, and there is pressure to start more tours up that way."

Among the plan's main components:

* Annual allowance of 65,000 air-tour flights over designated corridors over the park;

* Daily cap of 364 flights;

* Conversion of all air-tour aircraft to "quiet technology" within 10 years;

* No flights during the hour after sunrise or the hour before sunset;

* Flight-free zones in areas outside of designated flight corridors to 17,999 feet from 13,999 feet;

* A six-month rotation of short loop flights over the so-called Dragon and Zuni corridors to give those on the ground below some respite from aircraft noise.

"We had advocated that they move the Hermit flight path a little bit further to the west so that it really didn’t affect people who would take a quiet stroll down from Hermit’s Rest, down that little canyon," said NPCA's Mr. Nimkin. "That’s where you can sit there and every 90 seconds have a helicopter or a plane flying overhead. It would seem like that’s a pretty highly visited area, maybe one of the only times that people who are taking a shuttle out to the end of the road there would sort of stroll down into the canyon. To have that be the flight path seems inconsistent.”

Mr. Clark at the Grand Canyon Trust agreed.

"That’s the Dragon Corridor. As it is right now, on a busy day you’re hearing aircraft noise, primarily helicopters, continuously throughout the day," he said. "There’s one or more sounds of a helicopter in your ears throughout the daylight hours."

But despite the park's best efforts, the plan does not mitigate all aural impacts, as indicated by the acknowledgment that even under the preferred alternative there will be "long-term moderate to major adverse" impacts related to noise. However, park planner Rick Ernenwein pointed out that some of that noise comes from high-altitude commercial aircraft the park has no sway over, and that that coming from air tours will be largely restricted to designated air corridors and, if the park's modeling holds up, eventually won't be heard for most if not all of the day over 67 percent of the park.

"The direct impacts of the air tours, under the flight routes we’re liable to have major impacts in one area," Mr. Ernenwein said, "and in the middle of a flight-free zone we’ll have negligible to minor impacts."

Among the incentives to get air-tour operators' support of the plan is the prospect of an additional 8,000 flights a year and, for those who quickly invest in "quiet technology" aircraft, the prospect of running flights from January-March without them counting against their annual number of allowed flights. Additionally, those with quiet technology aircraft could fly certain routes over the North Rim year-round as well as a route over Marble Canyon.

You can find the plan at this page, and even leave your comments there.

In addition, the Park Service will host five open-house style public meetings to present the Draft EIS, gather input, and answer questions. Meetings will be held in Flagstaff, Phoenix, and Grand Canyon, Arizona; Salt Lake City, Utah; and Las Vegas, Nevada. Additional details regarding public meetings will be announced soon.