Grand Canyon Air Tour Coalition v. FAA et al.
Cite as: 154 F.3d 455



GRAND CANYON TRUST et al., Intervenors

No. 97-1003
Consolidated with
Nos. 97-1014, 97-1104, 97-1112, 97-1279

On Petitions for Review of an Order of the Federal Aviation Administration

Argued November 6, 1997
Decided September 4, 1998


Walter A. Smith, Jr. argued the cause for petitioners Grand Canyon Trust, et al., with whom Michael L. Kidney and Robert Wiygul were on the briefs.

E. Donald Elliott argued the cause for petitioner Grand Canyon Air Tour Coalition, with whom Michael A. Wiegard and Christopher A. Cole were on the briefs.

Jill E. Grant argued the cause for petitioner Hualapai Indian Tribe, with whom Joshua S. Grinspoon was on the briefs.

Eliot R. Cutler argued the cause for petitioners Clark County Department of Aviation, et al., with whom John E. Putnam and Stacie Brown were on the briefs.

Ronald M. Spritzer, Attorney, U.S. Department of Justice, argued the cause for respondents. Lois J. Schiffer, Assistant Attorney General, Nancy B. Firestone, Deputy Assistant Attorney General, Albert M. Ferlo, Jr., Attorney, and Patricia Lane, Office of the Chief Counsel, Federal Aviation Administration, were on the brief. Anne S. Almy, Attorney, U.S. Department of Justice, entered an appearance.

Walter A. Smith, Jr., Michael L. Kidney and Robert Wiygul were on the brief for intervenors Grand Canyon Trust, et al.

Jill E. Grant and Joshua S. Grinspoon were on the brief for intervenor Hualapai Indian Tribe.

John E. Putnam, Eliot R. Cutler and Stacie Brown were on the brief for intervenors Clark County Department of Aviation, et al.

Before: Silberman, Rogers and Garland, Circuit Judges.

Garland, Circuit Judge:

In response to an Act of Congress, the Federal Aviation Administration (the "FAA") developed a three-part plan to reduce aircraft noise from sight-seeing tours in the Grand Canyon National Park (the "Park"). On December 31, 1996, the FAA issued the first final rule and proposed two further rules to implement the balance of the plan. In this case, we consider attacks on the final rule by four groups of petitioners: the Grand Canyon Air Tour Coalition (the "Coalition"), a group of 13 air-tour operators that fly visitors over the Park; the Clark County Department of Aviation and the Las Vegas Convention and Visitors Authority ("Clark County"); the Hualapai Indian Tribe (the "Tribe" or "Hualapai"); and seven environmental groups led by the Grand Canyon Trust (the "Trust").

Three of the four petitioners -- the Coalition, Clark County, and the Hualapai -- essentially argue that the FAA's rule does "too much, too soon." The Trust, on the other hand, charges that the rule does "too little, too late." We reject both lines of attack and uphold the rule. We do so not because we necessarily believe the rule is "just right," but because we defer to the agency's reasonable exercise of its judgment and technical expertise, and because many of petitioners' attacks are not yet ripe in light of the phased nature of the FAA's proposed solution to the problem of aircraft noise.


The rule now before the court has a tortuous and complex history. In this Part of the opinion, we recount only so much of that history as is necessary to aid in our discussion.


In June 1987, the FAA issued Special Federal Aviation Regulation ("SFAR") No. 50-1, which regulated aircraft flying below 9,000 feet in the Park. See Special Flight Rules in the Vicinity of the Grand Canyon National Park, 52 Fed. Reg. 22,734 (1987). The regulation, set to expire on June 15, 1992, established minimum altitudes, routes, and noise-sensitive areas from which aircraft were barred. See id. at 22,739. The FAA promulgated the regulations to address safety concerns and because it "believe[d] that there is also a public interest in promoting a quiet environment in the canyon and minimizing the intrusion of aircraft noise on this environment...." Id. at 22,735.

In August 1987, Congress enacted what is commonly referred to as the Overflights Act (the "Act"), see Pub. L. No. 100-91, 101 Stat. 676 (1987) (codified at 16 U.S.C. 1a-1 note (1992)). The Senate Report accompanying the Act stated that SFAR 50-1 did "not adequately address the adverse effects caused by low flying aircraft" above the Park and that "section 3 of this bill rectifies this inadequacy." S. Rep. 100-125, at 8 (1987). Section 3 of the Act itself stated that:

[n]oise associated with aircraft overflights at the Grand Canyon National Park is causing a significant adverse effect on the natural quiet and experience of the park and current aircraft operations at the Grand Canyon National Park have raised serious concerns regarding public safety, including concerns regarding the safety of park users.
Overflights Act 3(a).

To address this problem, Congress required the Secretary of the Interior to submit to the Administrator of the FAA, within 30 days after the enactment of the Act,

recommendations regarding actions necessary for the protection of resources in the Grand Canyon from adverse impacts associated with aircraft overflights. The recommendations shall provide for substantial restoration of the natural quiet and experience of the park and protection of public health and safety from adverse effects associated with aircraft overflight.
Id. 3(b)(1) (emphasis added). Although it left the content of the recommendations largely open-ended, Congress specifically required the Secretary to prohibit flights below the canyon rim, subject to certain exceptions, and to designate "flight free zones." Id. "Such zones shall be flight free," Congress said, "except for purposes of administration and for emergency operations," including the transportation of supplies and people to and from specified Indian villages. Id.

Next, Congress established an implementation schedule for the Secretary's recommendations:

Not later than 90 days after receipt of the recommendations ... and after notice and opportunity for hearing, the [FAA] shall prepare and issue a final plan for the management of air traffic in the air space above the Grand Canyon. The plan shall, by appropriate regulation, implement the recommendations of the Secretary without change unless the [FAA] determines that implementing the recommendations would adversely affect aviation safety.
Id. 3(b)(2). If the FAA were to find an adverse effect on aviation safety, it was required, within 60 days and in consultation with the Secretary, to "eliminate the adverse effects on aviation safety and issue regulations implementing the revised recommendations in the plan." Id.

Finally, Congress directed the Secretary to submit to it, within two years after the effective date of the plan, "a report discussing (A) whether the plan has succeeded in substantially restoring the natural quiet in the park; and (B) such other matters, including possible revisions in the plan, as may be of interest." Id. 3(b)(3).


In response to the Overflights Act, the Secretary of the Interior submitted recommendations to the FAA in December 1987. In June 1988, the FAA adopted the majority of those recommendations, modified slightly for safety reasons, and implemented them in the form of SFAR 50-2. See Special Flight Rules in the Vicinity of the Grand Canyon National Park, 53 Fed. Reg. 20,264 (1988). The regulation applied to aircraft flying below 14,500 feet and established, inter alia, minimum altitudes, four flight free zones covering 44% of the Park, four flight corridors through those zones, and specified flight routes. [FN 1] Although the regulation was set to expire on June 15, 1992, the FAA twice extended the expiration date, [FN 2] first because the Secretary of the Interior's required report was not yet completed, and then because the FAA needed time to review the Secretary's recommendations and develop a new rule. See Special Flight Rules in the Vicinity of Grand Canyon National Park, 61 Fed. Reg. 40,120, 40,121 (1996) [hereinafter "Proposed Final Rule"].

[FN 1] A flight free zone is an area of the Park in which aircraft may not fly. A flight corridor is a passage, typically two to four miles wide, through which aircraft may traverse a flight free zone. Id. at 20,268. A flight route is the path a plane must follow for its entire tour, from its initial embarkation point to its final destination, including its path between and through any flight corridors. A route structure is the set of all the routes operators may fly in the Park. Although the FAA did not initially establish specific flight routes in the 1988 rule, the FAA's Flight Standards District Office in Las Vegas later created 29 routes, allowing commercial air tour operators access to designated areas of the Park. See National Park Service, U.S. Dep't of the Interior, Report on Effects of Aircraft Overflights on the National Park System 182 (1995).

[FN 2] See Special Flight Rules in the Vicinity of the Grand Canyon National Park, 57 Fed. Reg. 26,764 (1992) (extending expiration date from June 15, 1992 to June 15, 1995); Special Flight Rules in the Vicinity of the Grand Canyon National Park, 60 Fed. Reg. 31,608 (1995) (extending expiration date from June 15, 1995 to June 15, 1997).

On September 12, 1994, more than four years late, [FN 3] the National Park Service ("the Park Service" or "NPS"), on behalf of the Secretary of the Interior, submitted the report to Congress required by section three of the Overflights Act. See National Park Service, U.S. Dep't of the Interior, Report on the Effects of Aircraft Overflights on the National Park System (1995) [hereinafter "NPS Report"]. In that report, the Park Service made three important definitional determinations. First, it decided that the appropriate measure for quantifying aircraft noise was the percentage of time that aircraft are audible ("percent of time audible"). See NPS Report at 60. Second, the Park Service determined that an aircraft was audible if it increased the ambient noise level by three decibels, the smallest change perceptible to the human ear. See FAA, U.S. Dep't Transp., Environmental Assessment: Special Flight Rules in the Vicinity of Grand Canyon National Park 4-4 to -5 (1996) [hereinafter "Environmental Assessment"] (adopting Park Service criteria and noting that the three-decibel detectability criterion is "commonly accepted in the acoustics community"). Finally, the Park Service concluded that the key statutory phrase, "substantial restoration of the natural quiet," "requires that 50% or more of the park achieve 'natural quiet' (i.e., no aircraft audible) for 75-100 percent of the day." NPS Report at 182.

[FN 3] Section 3 of the Overflights Act directed the Secretary to submit the report within two years after the effective date of the FAA's plan, which itself was required within 120 days after the statute's enactment. See Overflights Act 3(b)(2), (3). The Act was enacted on August 18, 1987, but SFAR 50-2 was not implemented until June 1988. Thus, the September 12, 1994 submission of the report to Congress was more than four years late. A separate section of the Overflights Act, section 1, required the Secretary to submit an additional report to Congress within three years that would evaluate the impact of overflights in other national parks and make recommendations for legislative and regulatory action. See id. at 1(d). The Park Service combined the section 1 report with the section 3 report and submitted them at the same time in a single document.
Using these definitions, the NPS Report found that, although "compliance with SFAR 50-2 has been excellent, natural quiet is not yet substantially restored." Id. at 195. Instead, the Park Service found that only 34% of the Park enjoyed "a substantial restoration of natural quiet," by which it meant that in only 34% of the Park was aircraft noise no more than three decibels above ambient levels for at least 75% of the day. Id. at 13. [FN 4] Moreover, the NPS Report predicted that without revisions to the regulation, the predicted growth in the number of flights would cause the percentage of the Park enjoying "substantial restoration" to drop to less than 10% by the year 2010. See id.
[FN 4] As this usage indicates, when the Park Service discusses its current progress toward "a substantial restoration of natural quiet," it refers to the percentage of the Park enjoying natural quiet for 75% of the day. When it discusses the overall statutory goal of "substantial restoration of the natural quiet," however, it refers to a situation in which at least 50% of the Park achieves natural quiet for 75% of the day. Depending upon the context, we will use the phrase in the same two ways in this opinion.
The Park Service concluded that it was "obligated, in pursuit of both its Congressionally mandated and defined management responsibilities, to seek a further restoration of natural quiet." Id. at 198. Accordingly, the NPS Report recommended that the FAA revise SFAR 50-2. It said that noise reductions could be achieved by the expansion of flight-free zones, the operation of flights along paths taking advantage of natural land contours, the phase-in of quieter airplanes, the use of larger planes (on the assumption that larger numbers of people per flight would result in fewer total flights), and the limitation of flights to certain times of the day. See id. at 199-200.

In anticipation of the NPS Report, the Park Service and the FAA had issued an advance notice of proposed rulemaking seeking public comment on regulatory actions for all national parks, and specifically for the Grand Canyon National Park. See Overflights of Units of the National Park System, Advanced Notice of Proposed Rulemaking (ANPRM), 59 Fed. Reg. 12,740 (1994). The agencies sought comments on several proposals, including altitude restrictions, flight free periods, flight free zones, and incentives to use quieter aircraft. See id. at 12,744-45. The FAA received over 600 substantive comments on the Grand Canyon National Park, but two years later still had not proposed regulations, let alone finalized any.

In an Earth Day memorandum, issued on April 22, 1996, President Clinton directed the Secretary of Transportation, in conjunction with the relevant departments and agencies, to issue

proposed regulations within 90 days to place appropriate limits on sightseeing aircraft over the Grand Canyon National Park to reduce the noise immediately and make further substantial progress toward restoration of natural quiet, as defined by the Secretary of the Interior, while maintaining safety in accordance with the Overflights Act (Public Law 100-91). Action on this rulemaking to accomplish these purposes should be completed by the end of 1996.
Memorandum of April 22, 1996, Additional Transportation Planning to Address Impacts of Transportation on National Parks, 3 C.F.R. 278-79 (1996). The President also directed the FAA and National Park Service to achieve the substantial restoration of the natural quiet by 2008. See id. at 279.

In response to the President's directive, the FAA issued proposed regulations on July 31, 1996. In those regulations, the FAA proposed to expand the horizontal and vertical area covered by the existing regulations, create new and modify existing flight free zones to cover 87% of the Park, create new and modify existing flight corridors, develop specific flight routes for each operator, set a curfew for flights, establish a temporary cap on the number of flights, and require operators to submit flight reports. See Proposed Final Rule, 61 Fed. Reg. at 40,123-28.


On December 31, 1996, the FAA issued the final rule now before this court, and proposed two additional rules. See Special Flight Rules in the Vicinity of Grand Canyon National Park, 61 Fed. Reg. 69,302 (1996) [hereinafter "Final Rule"]. In the Final Rule and its associated Environmental Assessment, the FAA adopted the definitional determinations contained in the NPS Report. See id. at 69,306-10; Environmental Assessment at 4-4 to -5. The FAA also established new and modified existing flight free zones, established new and modified existing flight corridors, instituted flight curfews, set caps on the number of aircraft that can fly in the park, and established reporting requirements.

The Final Rule adopted most of the flight free zones proposed on July 31, 1996. See Final Rule, 61 Fed. Reg. at 69,311, 69,330-31. It enacted a curfew for the eastern portion of the Park, prohibiting flights during the summer season from 6 p.m. until 8 a.m. and in the winter season from 5 p.m. to 9 a.m. Id. at 69,316, 69,332. It established a cap on the number of aircraft that could fly in the Park, limiting each operator to the highest number it had used between July 31, 1996 and December 31, 1996, but did not establish a cap on the number of flights. See id. at 69,317, 69,332. The FAA concluded that, although the best way to address the noise problem "is through reducing noise at the source (i.e. quieter aircraft)," the aircraft cap was a necessary interim measure to ensure that the deterioration of the natural quiet would not continue prior to the implementation of the noise limitation rule proposed on the same day. See id. at 69,317. Finally, the FAA adopted reporting requirements for operators. See id. at 69,324-25, 69,332. The FAA stated that this Final Rule, in combination with the proposed quieter aircraft rules, would substantially restore the natural quiet as required by the Overflights Act. See id. at 69,329.

In addition to the Final Rule now before us, the FAA proposed two further rules: one to establish new and modify existing flight routes; the other to require operators to use quieter aircraft. See Proposed Air Tour Routes for the Grand Canyon National Park, 61 Fed. Reg. 69,356 (1996) [hereinafter "Proposed Air Tour Routes"]; Noise Limitations for Aircraft Operations in the Vicinity of Grand Canyon National Park, 61 Fed. Reg. 69,334 (1996) [hereinafter "Proposed Noise Limitations" or "Quiet Technology Rule"]. The FAA said the proposed new routes were necessitated by the new flight free zones adopted in the Final Rule. It said that "the use of quieter, larger aircraft would provide two-fold benefits in reducing [the] noise of each operation and reducing the number of operations to carry the same number of passengers." Quiet Technology Rule, 61 Fed. Reg. at 69,340.

The FAA explained that its tripartite regulatory action was necessary because from 1988 to 1994, "that part of the Park experiencing a substantial restoration of natural quiet declined from 43% to 31%," and because the NPS Report had predicted that it would further decline to 10% by 2010. Final Rule, 61 Fed. Reg. at 69,317. The FAA predicted that the Final Rule, in conjunction with the two proposed rules, would meet the statutory goal of substantial restoration of the natural quiet by the year 2008. See id. at 69,329. The Final Rule alone, it said, would nearly achieve the statutory goal (raising the percentage to 49.3% in 1997), while implementing the proposed quieter aircraft rule as well would bring natural quiet to 57.4% of the Park by the year 2008. Environmental Assessment at 4-11

The FAA set May 1, 1997 as the effective date for the Final Rule, anticipating that the new route structure would be in place by that time.


By February 1997, after reviewing comments on its proposed new routes, the FAA determined that it could develop better routes that would yield more noise reduction and have fewer adverse effects on tour operators and neighboring Indian tribes. To facilitate exploration of the best possible routes, the FAA stayed the effective date of the portions of the Final Rule that established the flight free zones, corridors, and related minimum altitudes from May 1, 1997 to January 31, 1998. See Special Flight Rules in the Vicinity of Grand Canyon National Park, 62 Fed. Reg. 8862 (1997). The agency subsequently extended the effective date again, to January 31, 1999, "to allow the FAA time to establish a route structure" for the Park. See Special Flight Rules in the Vicinity of Grand Canyon National Park, 62 Fed. Reg. 66,248 (1997). The FAA did not stay the effective date for the curfew, cap, or reporting requirements and found that the curfew alone would contribute to the substantial restoration of the natural quiet. See 62 Fed. Reg. at 8863. [FN 5]

[FN 5] On May 15, 1997, the FAA proposed the addition of two new flight corridors. See Establishment of Corridors in the Grand Canyon National Park Special Flight Rules Area, 62 Fed. Reg. 26,902, 26,904 (1997). In conjunction with the proposed corridors, the FAA also proposed a new route structure, subject to future modifications. See Notice of Availability of Commercial Air Tour Routes for the Grand Canyon National Park and Disposition of Comments, 62 Fed. Reg. 26,909 (1997). More recently, however, the FAA withdrew its proposal for the two corridors issued on May 15, 1997. The Federal Register withdrawal notice states that the agency is "presently considering alternatives to the National Canyon area for air tour routes." 63 Fed. Reg. 38,233 (July 15, 1998).
By October 1997, the FAA also discovered that it had significantly underestimated the number of aircraft operating in the Park. Shortly before oral argument in this case, the FAA issued a clarification of the Final Rule, stating that its original estimate of 136 aircraft was incorrect and that there were actually 260 aircraft. See Special Flight Rules in the Vicinity of Grand Canyon National Park, 62 Fed. Reg. 58,898, 58,900 (1997) [hereinafter "Clarification"]. The FAA concluded that, although this did not warrant a revision of the Final Rule itself, it did mean that the Final Rule would be less effective than previously thought. The FAA nevertheless found that the Final Rule would still meet the goal of substantially restoring natural quiet "after implementation of the revised air tour routes and completion of the [Quiet] Technology rulemaking." See id.

To further assess the impact of the changed data, the FAA prepared a written reevaluation of its original Environmental Assessment. See FAA, U.S. Dep't of Transp., Written Reevaluation, Notice of Clarification, Environmental Assessment: Special Flight Rules in the Vicinity of Grand Canyon National Park (1997) [hereinafter "Reevaluation" or "Written Reevaluation of Environmental Assessment"]. Instead of achieving natural quiet in 49.3% of the Park as projected in the original Environmental Assessment, the Reevaluation concluded the Final Rule would achieve substantial restoration of the natural quiet in only 41.7% of the Park in 1997, decreasing to 34.2% in 2008. See id. at 20. At oral argument, the FAA acknowledged that this meant the proposed rule on quiet aircraft technology, and other alternatives, would have to make up the gap in order to achieve the 50% requirement contained in the Park Service definition. See Oral Arg. Tr. at 82, 84-85; FAA Supplemental Br. at 4. Although the FAA concluded in the Reevaluation that it could not also effectively cap the number of flights, as opposed to the number of aircraft, see Written Reevaluation of Environmental Assessment at 3, after oral argument the FAA informed this court that it is reconsidering a cap on the number of flights as well. See Letter from Ronald M. Spritzer, counsel for FAA, at 2 (Nov. 12, 1997) [hereinafter "FAA Letter"].


In this Part, we consider the challenges of the three groups of petitioners who essentially argue that the FAA did too much, and that what it did do was done too soon. These petitioners do not seriously challenge three of the provisions of the Final Rule: the curfew, aircraft caps, and reporting requirements. See Oral Arg. Tr. at 74-75. The Air Tour Coalition contends, however, that the government adopted a definition of "substantial restoration of the natural quiet" that is too restrictive of aircraft overflights, in contravention of the language and legislative history of the Overflights Act. The Coalition also contends that the FAA committed a series of errors that are fatal under the Administrative Procedure Act (APA). Clark County argues that the FAA should not have promulgated flight free zones until it was ready to issue final routes and corridors, and until it had more adequately assessed their environmental impact. Finally, the Hualapai Tribe maintains that the FAA issued its rule without adequately considering whether implementation of the expanded flight free zones would simply push the noise off the Park and onto the Hualapai Reservation, causing damage to its sacred sites and cultural resources.


The Air Tour Coalition contends that the Park Service and FAA interpretation of the key statutory phrase, "substantial restoration of the natural quiet and experience of the park," is overly restrictive of aircraft overflights because it is contrary to the "plain meaning" of the statute and its legislative history. The Coalition has identified four principal problems with the agency's interpretation.

First, the Coalition contends that the agencies erred in defining the term "natural quiet" without regard to other sounds in the Park. "Natural quiet," the Coalition argues, is not the absence of audible sound. According to the Coalition, the government's definition of "natural silence" as sound of up to three decibels ignores this point because it does not consider "prevailing sound conditions in the Park." Coalition Br. at 10. "The faint, barely audible hum of a light plane," the Coalition maintains, "will not be noticed by, much less disturb, a visitor to roaring river rapids." Id. at 11.

We may dispense with this first argument without any statutory analysis, because it simply misapprehends the agencies' definition. The Final Rule does not define "natural quiet" as sound of up to three decibels; it defines it as sound of up to three decibels above "the ambient level." See Environmental Assessment at 4-4; see also NPS Report at 60 ("[P]ercent of time audible is a measure of how long aircraft sound levels protrude above all other sounds."). That is, an aircraft breaks the natural silence only when it is three decibels louder than the ambient sound -- whether that sound is the roar of the river or the song of the birds.

Second, the Air Coalition contends that the government erred because it equated "quiet" with the absence of detectable sound, rather than with the absence of "noise" that would disturb visitors or disrupt their experiences of the park. See Coalition Br. at 12. The statute does not authorize the agencies to eliminate noise for its own sake, the Coalition insists, but only to increase the enjoyment of people on the ground. This assertedly follows from the plain language of the statute, which refers to the "natural quiet and experience of the park." Overflights Act 3(b)(1) (emphasis added). It further follows from the legislative history which indicates, the Coalition says, that the Act was intended only to ensure " 'a location where visitors can experience the park' free of disturbing aircraft noise." Coalition Br. at 12 (quoting 133 Cong. Rec. S10799 (daily ed. July 28, 1987) (statement of Sen. McCain)).

There is also less than meets the eye to this second asserted dispute over statutory interpretation. We need not decide whether the Overflights Act would permit the government to ensure silence for silence's sake, because the agencies did not try to do so. To the contrary, this characterization of the agencies' views rests on a misreading of the FAA's brief and Federal Register notice, and of the NPS Report. The Coalition contends, for example, that the FAA's brief "unabashedly concedes its belief that 'people' and people's experiences of the park are irrelevant under its approach." Coalition Reply Br. at 2. To support this contention, the Coalition cites a portion of the FAA's brief that responds to the Coalition's argument that the agency can only regulate those areas of the park "where people are more likely to be." But the FAA did not respond by saying the experience of Park visitors was irrelevant. Instead, it said that "the Overflights Act was ... intended to address the problem of aircraft noise on a Park-wide basis in recognition of the fact that there may be 'back country users and other sensitive park resources.' " FAA Br. at 20 (quoting 133 Cong. Rec. at S10799 (statement of Sen. McCain)).

The Coalition also misreads the Federal Register notice accompanying the Final Rule. That notice, according to the Coalition, confirms that the FAA intends to protect natural quiet, irrespective of visitor experience. See Coalition Reply Br. at 2 & n.5 (citing 61 Fed. Reg. at 69,308). But the cited page of the Federal Register says nothing of the sort. To the contrary, it is replete with agency references to the manner in which its definition of substantial restoration of the natural quiet responds to "visitors' experience." [FN 6]

[FN 6] See, e.g., Final Rule, 61 Fed. Reg. at 69,308 ("The NPS definition of 'substantial restoration of natural quiet' involves time, area, and acoustic components. Because many park visitors typically spend limited time in particular sound environments during specific park visits, the amount of aircraft noise present ... can have great implications for the visitors' opportunity to experience >natural quiet in those particular times and places."); id ("Based on its studies, the NPS concluded that the visitors' opportunity to experience natural quiet during their visits and the extent of noise impact depends on a number of factors.").
It is true, as the Coalition contends, see Coalition Reply Br. at 2 n.4, that the NPS Report refers to "natural quiet" as a "resource." See NPS Report at 10. But the full context of the reference makes clear that in the Park Service's view, natural quiet is a resource because it is relevant to visitor enjoyment: "Intangible qualities" like "natural quiet ... are important components of visitors' overall enjoyment of parks and are thus valued resources." Id. (emphasis added). [FN 7] This concern for visitors' experience permeates the report. Indeed, the NPS explains that it chose "percent of time audible" as an appropriate index because it "found this metric to be best correlated with visitors' response to sound." Id. at 60. [FN 8]
[FN 7] See also id. at 78 ("Quiet itself ... is an important element of the feeling of solitude. Quiet also affords visitors an opportunity to hear faint or very distant sounds.... Such an experience provides an important perspective on the vastness of the environment in which the visitor is located.") (emphases added).

[FN 8] See also id. ("As will be discussed in Chapter 6, 'Effects on Visitor Experience,' percent of time audible is useful because it can be related to visitor reactions to the sound of aircraft overflights.").

Finally, the Air Tour Coalition suggests two further, related ways in which the government's interpretation of the Overflights Act is invalid. First, the Coalition argues that the Park Service's decision to define "natural quiet" based on the decibel level a human ear can hear is unreasonable because it does not consider whether sound at that level would be disturbing. What the agency should have done instead, the Coalition insists, is looked to surveys of park visitors which show that only 34% report hearing aircraft, and only 5% report being "annoyed" by them. See NPS Report at 139. [FN 9] Second, the Coalition contends, the government's effort to ensure quiet in 50% of the park for 75-100% of the day is also unreasonable because it does not consider "whether there will be any visitors present to be disturbed" in those areas. Coalition Br. at 10. Instead of trying to protect more than 50% of the Park, what the FAA should have done is simply re-routed air tours away from places where visitors concentrate, thus creating a "location where visitors can experience the park free of disturbing aircraft noise." See id. at 5.
[FN 9] The same surveys indicate that 10% of park visitors report aircraft noise interferes with the natural quiet. Id.
Chevron U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837 (1984), governs our analysis of the validity of an agency's interpretation of a statute. Following the familiar Chevron two-step, we first ask whether Congress "has directly spoken to the precise question at issue," in which case we "give effect to the unambiguously expressed intent of Congress." See id. at 842-43. But if Congress has been silent or ambiguous about the meaning of the specific question at issue, we defer to the agency's interpretation so long as it is "based on a permissible construction of the statute." Id. at 841. In the latter circumstance, the agency need only establish that its construction is "reasonable in light of the Act's text, legislative history, and purpose." Southern Cal. Edison Co. v. FERC, 116 F.3d 507, 511 (D.C. Cir. 1997); see also Chevron, 467 U.S. at 844; Appalachian Power v. EPA, 135 F.3d 791, 800 (D.C. Cir. 1998).

There is nothing in the Overflights Act's reference to "natural quiet" that requires the FAA to define the term by survey results rather than decibel level. Indeed, the Coalition itself concedes that "the words 'natural quiet' are not self-defining" and that there is "ambiguity inherent in the term." See Coalition Reply Br. at 5. That being so, the only question for us is whether the agency has acted reasonably. We find nothing unreasonable in the agency's explanation for relying on acoustical measurements rather than visitor surveys. [FN 10] Nor is there anything unreasonable about giving visitors the experience of silence by barring noise above the three-decibel level, even if "only" 34% of all Park visitors report hearing aircraft noise.

[FN 10] See Final Rule, 61 Fed. Reg. at 69,306 ("[T]he threshold of audibility used in the NPS model is louder than the level which would be detected by an attentive listener, guaranteeing that virtually all visitors would notice the noise while engaged in normal visitor activities."); NPS Report at 138 ("The nature and severity of impacts at specific sites within parks may not be captured by the judgments gathered in the exit visitor survey.").
Similarly, nothing in the statute instructs the FAA to create only one or more locations of quiet and to herd all visitors into those quiet zones. Moreover, the statute speaks of the "substantial" restoration of the natural quiet. That term is also inherently ambiguous, and supports the agency's effort to regulate not only for the benefit of those visitors who prefer to congregate at visitors' centers, but also of those who prefer to see the back-country. Protecting 50% of the Park for 75% of the day gives the latter at least a reasonable chance of seeing the less-traveled areas in peace.

Nor is there anything in the legislative history that is inconsistent with the agency's approach or that renders it unreasonable. The Coalition principally relies on a quotation from Senator McCain of Arizona for the proposition that the purpose of the Overflights Act was only "to provide a location where visitors can experience the park essentially free from aircraft sound intrusions." 133 Cong. Rec. at S10799 (statement of Sen. McCain), cited in Coalition Br. at 4, 9, 12. Although we ordinarily do not attach controlling weight to the "remarks of a single legislator, even the sponsor," Chrysler Corp. v. Brown, 441 U.S. 281, 311 (1979), it is worth noting that the Coalition has mischaracterized the Senator's position. It has done so, first, by failing to emphasize that the "purpose" Senator McCain was speaking of was not that of the Overflights Act as a whole, but rather of "flight free zones" -- which are only one part of the regulatory regime envisioned by the statute. See 133 Cong. Rec. at S10799. The Coalition also has mischaracterized the Senator's position by omitting his next sentence: "The boundaries of these flight-free zones are meant to be drawn to maximize protection to the back country users and other sensitive park resources." Id. (emphasis added). This is fully in accord with the essence of the FAA's position: it can draw flight free zones, and otherwise regulate aircraft noise, in order to protect not only those who choose the well-worn path, but also those who prefer the road less taken.

Continued in Part Two