Grand Canyon Air Tour Coalition v. Federal Aviation Administration

United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued November 6, 1997 Decided September 4, 1998

No. 97-1003

Grand Canyon Air Tour Coalition,

Petitioner

v.

Federal Aviation Administration,

Respondent

Grand Canyon Trust, et al.,

Intervenors

Consolidated with

Nos. 97-1014, 97-1104, 97-1112, 97-1279

On Petitions for Review of an Order of the

Federal Aviation Administration

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 Patri-
cia 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 Wi-
ygul 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.

Opinion for the Court filed by Circuit Judge Garland.

Garland, Circuit Judge: In response to an Act of Con-
gress, the Federal Aviation Administration (the "FAA") de-
veloped 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 Au-
thority ("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.

I

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.

A

In June 1987, the FAA issued Special Federal Aviation
Regulation ("SFAR") No. 50-1, which regulated aircraft fly-
ing 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 environ-
ment...." Id. at 22,735.

In August 1987, Congress enacted what is commonly re-
ferred to as the Overflights Act (the "Act"), see Pub. L. No.
100-91, 101 Stat. 676 (1987) (codified at 16 U.S.C. s 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 s 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 ad-
verse impacts associated with aircraft overflights. The
recommendations shall provide for substantial restora-
tion of the natural quiet and experience of the park and
protection of public health and safety from adverse ef-
fects associated with aircraft overflight.

Id. s 3(b)(1) (emphasis added). Although it left the content
of the recommendations largely open-ended, Congress specifi-
cally 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 sup-
plies 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 recommenda-
tions ... 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 regula-
tion, implement the recommendations of the Secretary
without change unless the [FAA] determines that imple-
menting the recommendations would adversely affect
aviation safety.

Id. s 3(b)(2). If the FAA were to find an adverse effect on
aviation safety, it was required, within 60 days and in consul-
tation with the Secretary, to "eliminate the adverse effects on
aviation safety and issue regulations implementing the re-
vised 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 substantial-
ly restoring the natural quiet in the park; and (B) such other
matters, including possible revisions in the plan, as may be of
interest." Id. s 3(b)(3).

B

In response to the Overflights Act, the Secretary of the
Interior submitted recommendations to the FAA in Decem-
ber 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.1 Although the regulation was set

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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,

to expire on June 15, 1992, the FAA twice extended the
expiration date,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"].

On September 12, 1994, more than four years late,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

__________
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).

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).

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 s 3(b)(2), (3). The Act
was enacted on August 18, 1987, but SFAR 50-2 was not imple-
mented 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 s 1(d). The Park Service combined the section 1

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 determi-
nations. 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 Assess-
ment: 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 accept-
ed in the acoustics community"). Finally, the Park Service
concluded that the key statutory phrase, "substantial restora-
tion 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.

Using these definitions, the NPS Report found that, al-
though "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 13.4 Moreover, the NPS Report
predicted that without revisions to the regulation, the predict-
ed growth in the number of flights would cause the percent-

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report with the section 3 report and submitted them at the same
time in a single document.

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.

age of the Park enjoying "substantial restoration" to drop to
less than 10% by the year 2010. See id.

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 advan-
tage of natural land contours, the phase-in of quieter air-
planes, 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 rulemak-
ing seeking public comment on regulatory actions for all
national parks, and specifically for the Grand Canyon Nation-
al 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 Nation-
al Park, but two years later still had not proposed regula-
tions, 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 appro-
priate limits on sightseeing aircraft over the Grand Can-
yon 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 Over-
flights Act (Public Law 100-91). Action on this rulemak-

ing 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 opera-
tors to submit flight reports. See Proposed Final Rule, 61
Fed. Reg. at 40,123-28.

C

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 Assess-
ment, the FAA adopted the definitional determinations con-
tained in the NPS Report. See id. at 69,306-10; Environ-
mental 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 cur-
fews, 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 "Pro-
posed 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 reduc-
ing 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 de-
clined 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.

D

By February 1997, after reviewing comments on its pro-
posed 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, corri-
dors, 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 8863.5

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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 Can-
yon 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 conclud-
ed 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 Re-
evaluation, Notice of Clarification, Environmental Assess-
ment: 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 restora-
tion 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 argu-
ment, 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 Environ-
mental Assessment at 3, after oral argument the FAA in-
formed 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"].

II

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 as-
sessed their environmental impact. Finally, the Hualapai
Tribe maintains that the FAA issued its rule without ade-
quately 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.

A

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 con-
trary 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 agen-
cies' 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 detecta-
ble 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 s 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 govern-
ment 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 "una-
bashedly concedes its belief that 'people' and people's experi-
ences of the park are irrelevant under its approach." Coali-
tion 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." 6

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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 typical-
ly 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).7 This
concern for visitors' experience permeates the report. In-
deed, 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 60.8

Finally, the Air Tour Coalition suggests two further, relat-
ed 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 139.9 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 "wheth-
er there will be any visitors present to be disturbed" in those

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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).

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.").

9 The same surveys indicate that 10% of park visitors report
aircraft noise interferes with the natural quiet. Id.

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.

Chevron U.S.A., Inc. v. Natural Resources Defense Coun-
cil, 467 U.S. 837 (1984), governs our analysis of the validity of
an agency's interpretation of a statute. Following the famil-
iar 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 ques-
tion 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 Coali-
tion 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 sur-
veys.10 Nor is there anything unreasonable about giving

__________
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 virtu-
ally all visitors would notice the noise while engaged in normal

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.

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 (state-
ment 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 "pur-
pose" 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. (em-
phasis added). This is fully in accord with the essence of the

__________
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.").

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.

B

The Air Tour Coalition also maintains that the FAA's Final
Rule should be remanded because the FAA committed a
series of errors under the Administrative Procedure Act.
Specifically, the Coalition contends the FAA failed to: permit
comment on the definition of "substantial restoration of the
natural quiet," respond to comments on that definition, ade-
quately justify the definition, consider the interests of the air
tour industry, explain its departure from prior regulations,
and respond to comments in connection with the Regulatory
Flexibility Act, 5 U.S.C. s 601 et seq. We reject all of these
challenges for a mix of factual and legal reasons.

The APA requires agencies to provide notice and an oppor-
tunity to comment on proposed rules. See 5 U.S.C. s 553(c);
see also McLouth Steel Prod. Co. v. Thomas, 838 F.2d 1317,
1322-23 (D.C. Cir. 1988). The FAA did that here. The Final
Rule was proposed in a Federal Register notice on July 31,
1996, and numerous comments were submitted. See Final
Rule, 61 Fed. Reg. at 69,305-18 (summarizing and responding
to comments). The Air Coalition's true complaint is not that
it lacked an opportunity to comment, but that it was not
permitted to comment meaningfully because the FAA viewed
itself as bound to adopt the Park Service's 1995 definition,
and so neither took the Coalition's comments into consider-
ation nor responded to them. See generally Final Rule, 61
Fed. Reg. at 69,306 ("[T]he terms do not need additional
comment under the Administrative Procedure Act."). Ordi-
narily, this would be a potentially winning administrative law
argument. An agency is required to provide a meaningful
opportunity for comments, which means that the agency's
mind must be open to considering them. See McLouth, 838
F.2d at 1323. An agency must also demonstrate the rationali-
ty of its decision-making process by responding to those

comments that are relevant and significant. See Professional
Pilots Fed'n v. FAA, 118 F.3d 758, 763 (D.C. Cir. 1997);
Home Box Office, Inc. v. FCC, 567 F.2d 9, 35 (D.C. Cir. 1977).

But the Overflights Act is not the ordinary statute. It
envisions a regulatory program that is the product of two
agencies and clearly divides the institutional responsibilities
between them. It instructs that the "Secretary [of the Interi-
or] shall submit to the Administrator [of the FAA] recommen-
dations ... [which] shall provide for substantial restoration of
the natural quiet and experience of the park." Overflights
Act s 3(b)(1). And it directs that the Administrator, after
providing notice and an opportunity to be heard, "shall ...
implement the recommendations of the Secretary without
change unless the Administrator determines that implement-
ing the recommendations would adversely affect aviation safe-
ty." Id. s 3(b)(2) (emphasis added). Under this statutory
scheme, the FAA was correct in believing that it had no
choice but to adopt the Park Service's recommendations
(except for any safety concerns the FAA might have), and
hence that it did not need to provide additional comments of
its own on the Interior Department's definition of the statuto-
ry terms. See Final Rule, 61 Fed. Reg. at 69,306.

We reached the same conclusion with respect to a similar
statute in Bangor Hydro-Electric Co. v. FERC, 78 F.3d 659
(D.C. Cir. 1996). In that case, a hydroelectric producer,
licensed by the Federal Energy Regulatory Commission
(FERC) to build a dam, challenged a FERC order requiring
it to adopt a fish passage plan conforming to one prescribed
by the Department of the Interior. FERC issued the order
pursuant to a statute providing that "[t]he Commission shall
require the construction ... of such fishways as may be
prescribed by the Secretary of the Interior." Id. at 661
(quoting 16 U.S.C. s 811). In doing so, FERC declined to
consider Bangor's arguments concerning the need for the
fishway, concluding that under the statute it had no choice
but to require Bangor to construct it. And in light of that
statute, we held, as we hold here, that it was not the agency's
"role to judge the validity of Interior's position--substantially

or procedurally." Id. at 663; see also Escondido Mut. Water
Co. v. La Jolla Band of Mission Indians, 466 U.S. 765, 778 &
n.20 (1984).11

Although the statutory scheme in Bangor relieved FERC
of its obligation to respond to comments, it did not relieve the
government of its obligation to promulgate regulations consis-
tent with the law, or immunize those regulations from judicial
review to determine whether they were arbitrary and capri-
cious. See Bangor, 78 F.3d at 663-64; see also Escondido,
466 U.S. at 778 & n.20; Southern Cal. Edison, 116 F.3d at
519. Indeed, in Bangor we reviewed the rationality of the
fishways prescription and vacated it because it lacked "rea-
sonable support" and was not "reasonably related" to its goal.
78 F.3d at 664. Similarly, although the Overflights Act
relieved the FAA of the obligation to respond to comments on
the Park Service's definition, it did not relieve the govern-
ment as a whole--that is, the Park Service and FAA togeth-
er--of its obligation not to promulgate a rule that is "arbi-
trary, capricious, an abuse of discretion, or otherwise not in
accordance with law." 5 U.S.C. s 706(2)(A). The FAA does
not dispute this point, or the Coalition's right to challenge the
definition on those grounds before this court. See Oral Arg.
Tr. at 111-13.

Moreover, in determining whether the Final Rule is arbi-
trary or capricious, we may consider only the regulatory
rationale actually offered by the agency during the develop-

__________
11 The Coalition's reliance on McLouth Steel Products Co., 838
F.2d 1317, is misplaced. In denying a petition filed by McLouth
under the Resource Conservation and Recovery Act, 42 U.S.C.
s 6901 et seq., the EPA used a computer model it had developed
previously. The agency refused to entertain or respond to com-
ments on the model, despite never having previously exposed the
model to comment. In so doing, the EPA failed to provide the
opportunity to comment required by s 553 of the APA. See 838
F.2d at 1322-23. But as this recitation indicates, McLouth is not
like either this case or Bangor: McLouth involved decision-making
by a single agency, and no statute required it to adopt the computer
model at issue.

ment of the regulation, and not the post-hoc rationalizations
of its lawyers. See Citizens to Preserve Overton Park, Inc. v.
Volpe, 401 U.S. 402, 420 (1971); SBC Communications, Inc.
v. FCC, 138 F.3d 410, 418 (1998); see also Bangor, 78 F.3d at
662 (holding that the FERC licensing requirement would
have to be supported by the record before the agency).
Hence, although the FAA would not have violated any APA
procedural or quasi-procedural requirement by failing to re-
spond to comments about the Park Service definition, the
government would have risked the possibility that the justifi-
cation for the definition previously offered by the Park Ser-
vice (and submitted to the FAA) might not satisfy the APA's
substantive requirement of agency rationality. See Motor
Vehicles Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co., 463
U.S. 29, 43 (1983). For example, if any of those comments
exposed a previously unrecognized irrationality in the Park
Service definition, it would now be too late for the agency's
lawyers to plug the gap.

Fortunately for the government, the Park Service did offer
an adequate and reasonable justification for the definitions it
chose. See NPS Report at 60, 78, 182. Moreover, notwith-
standing the FAA's legal position that it need not offer
anything in addition, the Final Rule further elaborated on
that explanation. See Final Rule, 61 Fed. Reg. at 69,305-10.
Most of that explanation has already been discussed at sever-
al places above. The Park Service noted that under the
statute it was required to make a recommendation that would
provide for "substantial" restoration of the natural quiet, and
it concluded that a reasonable definition of "substantial" was
one that restored natural quiet in at least half the park for
most (75%) of the day. NPS Report at 182. The agency also
reasonably read the statute's requirement that "natural"
quiet be restored, to mean it should look to an increment
above the ambient, natural sounds of the Park. See id. at 60.
Finally, the agency reasonably chose to measure that incre-
ment based on the smallest sound "an attentive listener"
could hear, because that measure could be easily "related to
visitor reactions to the sound of aircraft overflights," id., and
because that measure best protected the experience of the

back-country users, see Final Rule at 69,309-10; NPS Report
at 13.

The Coalition further contends that, in formulating its rule,
the FAA failed to take into consideration "the two policy
goals to be accommodated in the Overflights Act--'the sub-
stantial restoration of the natural quiet and experience of the
park' ... and maintenance of viable air tourism in the
GCNP." Coalition Br. at 14. But it is not by chance that the
Coalition could put only the first of those goals in quotation
marks. The second--maintenance of viable air tourism--is
not mentioned in the Overflights Act. For evidence of this
"goal," the Coalition is forced to look to a colloquy on the
Senate floor between Senators Matsunaga and McCain. But
again, even if we were to accord weight to a floor colloquy,
the colloquy the Coalition has chosen shows only that "it was
not our intent to eliminate the so-called air tour industry."
133 Cong. Rec. at S10800 (emphasis added). All the Senators
agreed to was that "when the essential values for which the
park was created can accommodate such use, air tours are
perfectly appropriate." Id. (emphasis added). And Senator
McCain further noted that "when it comes to a choice be-
tween the interests of our park system and those who profit
from it, without a doubt, the interests of the land must come
first." Id. at S10799.

But this argument is again beside the point. Contrary to
the Coalition's suggestion, the FAA did consider the impact
its regulation would have on the air tour industry. As the
FAA explained, "[t]he primary policy reason for adopting this
rule, is that it is the best compromise the FAA has been able
to formulate to achieve the mandate of [the Overflights Act]
and maintain a viable air tour industry serving GCNP."
Final Rule, 61 Fed. Reg. at 69,328. Hence, whether it was
required to do so or not, the Park Service did in fact consider
the interests the Coalition represents.12

__________
12 We also reject the Coalition's suggestion that the President's
Earth Day memorandum, directing the agencies to complete their
rulemaking by the end of 1996 and to achieve the substantial
restoration of natural quiet by 2008, renders the FAA's decision

The Coalition also contends that the agencies failed to
explain what the Coalition calls a "departure" from their prior
course. In 1987 the Park Service recommended, and in 1988
the FAA adopted, SFAR 50-2, the first rule promulgated
under the Overflights Act. That rule created air tour exclu-
sion zones covering 45% of the Park. See Special Flight
Rules in the Vicinity of Grand Canyon National Park, 53 Fed.
Reg. 20,264 (1988); see also Proposed Final Rule, 61 Fed.
Reg. at 40,124. The Coalition notes that this led to a
dramatic reduction in visitor complaints, as measured by
visitor surveys. It argues that given this improvement under
the old rule, the agency should have, but did not, explain why
a new rule--which would expand flight-free zones to 87% of
the Park--was necessary.

We reject this argument for two reasons. First, the char-
acterization of the FAA's 1996 Final Rule as a "departure" is
somewhat of an overstatement, since the 1988 rule initially
was set to expire in 1992. See 53 Fed. Reg. at 20,264.
Hence, we cannot say that the 1988 rule expressed the
government's final position on how to achieve the substantial
restoration of the natural quiet; the Park Service did not
adopt a final definition of that phrase until its 1994 Report to
Congress.

But second, and contrary to the Coalition's contention, the
government did explain why something more than the 1988
rule was necessary. The Park Service explained that al-
though under SFAR 50-2, 34% of the Park enjoyed substan-
tial restoration of natural quiet, without revisions to the
regulation the percentage would drop to less than 10% by the
year 2010. See NPS Report at 13. The Park Service noted

__________
suspect. The Coalition does not argue that the President's di-
rection itself violated any statutory rule, but rather that as a
consequence of the "haste" that it engendered, the FAA was unable
to offer a reasoned explanation for the Final Rule, and was other-
wise unable to satisfy the requirements of the APA. Because we
hold that the FAA's explanation for its Final Rule is reasonable,
and that the promulgation of the rule satisfied the APA, the
President's memorandum does not affect our analysis. See general-
ly Sierra Club v. Costle, 657 F.2d 298, 407-08 (D.C. Cir. 1981).

that "air tours have increased significantly over the Canyon"
in the years since the 1988 regulation, increasing from
120,180 in the year prior to the regulation to more than
187,000 in 1993, and that the number was expected to contin-
ue to increase still further. Id. "It is vital that this evalua-
tion of [SFAR 50-2] be understood in the context of the
predicted growth in the number of flights," the Park Service
said. Id. Accordingly, the Service found that "natural quiet
is not yet substantially restored," id. at 195, and 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. This is more than
sufficient explanation for the government's decision to revise
the 1988 rule.

Finally, the Coalition contends that the FAA failed to
respond to comments on the inadequacy of its analysis under
the Regulatory Flexibility Act, and failed to consider alterna-
tives to the rule it adopted. We reject both challenges as
factually inaccurate. The FAA did a lengthy analysis of the
economic impact of the proposed rule on small businesses, as
required by the Regulatory Flexibility Act, and responded to
comments submitted by the Small Business Administration
and other commenters. See Final Rule, 61 Fed. Reg. at
69,318-28. It also considered alternatives to the rule. The
Coalition claims that the FAA flatly rejected its obligations to
consider alternatives, stating that such consideration was
" 'beyond the scope of this analysis.' " Coalition Br. at 15
(quoting 61 Fed. Reg. at 69,327-28). But that quotes the
FAA too selectively. What the FAA said was that, "[t]o
recount all the alternatives that were considered would be
beyond the scope of this analysis." Final Rule, 61 Fed. Reg.
at 69,328 (emphasis added). The FAA made clear, however,
that it did consider alternatives, expressly listing seven that
were recommended and noting that "[m]any combinations of
all of these alternatives or recommendations were considered
in developing this rule." Id.; see also Environmental Assess-
ment at 2-1 to -14 (identifying and analyzing alternatives).
The FAA thus satisfied the requirements necessary to dem-
onstrate a rational decision-making process--that is, that it

respond to relevant comments and consider reasonable alter-
natives. See State Farm, 463 U.S. at 51; Professional Pilots
Fed'n, 118 F.3d at 763. The Coalition does not describe any
particular response as inadequate, nor does it point to any
alternative that the agency irrationally rejected--other than
the alternative of routing tours away from concentrations of
visitors which, as we noted above, the FAA reasonably could
reject.

C

The gravamen of Clark County's petition is that the FAA
promulgated its flight free zones too soon. The FAA should
not have done so, the County maintains, until it was also
ready to promulgate the associated flight corridors and tour
routes. Nor should the FAA have issued the flight free zones
until it had more adequately assessed their environmental
impact.

The County's first contention is that it was unreasonable
for the FAA to promulgate expanded flight free zones without
at the same time promulgating final routes, because that
made it impossible to assess the effect of the flight free zones
either on noise or on the viability of air tours. Without
defined routes, Clark County says, it is "forced to guess
where FAA might place routes amongst the almost infinite
options left by the flight free zones." County Br. at 19.
Underlying this dispute is the County's fear that the expand-
ed flight free zones appear to have the effect of closing the
lucrative Blue 1 route out of Las Vegas--the principal city in
the County--without providing a viable alternative.

We should note that, ordinarily, agencies have wide latitude
to attack a regulatory problem in phases and that a phased-
attack often has substantial benefits. See City of Las Vegas
v. Lujan, 891 F.2d 927, 935 (D.C. Cir. 1989); General Am.
Transp. Corp. v. ICC, 872 F.2d 1048, 1058 (D.C. Cir. 1989).
Indeed, at oral argument the Air Tour Coalition conceded
that it would benefit from an early resolution of the definition
of "substantial restoration," because that would enable it to
"negotiate" an acceptable route structure with the govern-

ment and the Trust. See Oral Arg. Tr. at 135-39; id. at 135-
36 (advising that "[t]here is a national negotiated rulemaking
that's currently pending" regarding air tours over other
national parks).

But events have largely overtaken this dispute. Although
the FAA did not originally make clear whether it would stay
the implementation of the flight free zones until it issued the
final corridors and route structure, thereafter the FAA repre-
sented to this court that it would extend the effective date of
the flight free zones until that time. See id. at 97; see also
FAA Supp. Br. at 11 (filed after oral argument, making same
representation). Since then, the agency has formally extend-
ed the effective date to January 31, 1999. See Special Flight
Rules in the Vicinity of Grand Canyon National Park, 62 Fed.
Reg. 66,248, 66,248 (1997). Accordingly, whatever its merits,
Clark County's contention that it was irrational for the agen-
cy to implement flight free zones until it issued final corridors
and routes is now moot.

On the other hand, the County's underlying concern, that
the flight free zones will have a negative impact on Las
Vegas-based flights, is not moot. But it is also not yet ripe.
We follow a two-pronged test in determining whether a
challenge to a final rule is ripe for review. First, we consider
the "fitness of the issues for judicial decision." This involves
an inquiry into "whether the court or agency would benefit
from postponing review until the policy in question has suffi-
ciently crystallized." Florida Power & Light Co. v. EPA, 145
F.3d 1414, 1421 (D.C. Cir. 1998) (internal quotations omitted).
"The court's interests in avoiding unnecessary adjudication
and in deciding issues in a concrete setting militate in favor of
postponing review if, for example, the court finds that resolu-
tion of the dispute is likely to prove unnecessary or that the
court's deliberations might benefit from letting the question
arise in some more concrete form." Id. (internal quotations
omitted). Second, if a challenged decision is not "fit" for
review, we must consider whether postponing review will
cause the petitioner "hardship." Id.

In light of the fact that the FAA is still working on
corridors and routes, the County's challenge to the flight free
zones is not fit for review at this time. As the County's own
argument makes clear, neither it nor we can assess whether
the flight free zones will hurt the County, or how much they
will do so, until we know which new routes and corridors
through the flight free zones the FAA will authorize. "The
effects of the Final Rule," the County correctly notes, "de-
pend on where FAA places flight tracks for air tour opera-
tions...." County Br. at 18. Waiting until those new routes
and corridors are issued may make "resolution of the dispute
... unnecessary." Florida Power, 145 F.3d at 1421, because
they may accommodate the Las Vegas flights that are the
County's principal concern. At a minimum we will "benefit
from letting the question arise in [a] concrete form." Id.
Moreover, given the FAA's stay of the flight free zones
pending promulgation of new routes and corridors--which
permits the Blue 1 route to continue to operate in the
interim--the County will not suffer hardship as a result of the
postponement. Accordingly, this challenge by the County is
not currently ripe for review.

The same is true of the County's contention that the FAA
violated the National Environmental Policy Act (NEPA), 42
U.S.C. s 4321 et seq., by concluding in its Environmental
Assessment that the Final Rule would have no significant
environmental impact. See Environmental Assessment (J.A.
151-52).13 The County contends that if the effect of the Final

__________
13 Based on that Assessment, the agency determined that the
Final Rule warranted a "finding of no significant impact." See
Final Rule, 61 Fed. Reg. at 69,318. If correct, this finding means
that the FAA was not obligated under NEPA to prepare an
environmental impact statement. See 40 C.F.R. ss 1501.4, 1508.13
(1997); see also Public Citizen v. National Highway Traffic Safety
Admin., 848 F.2d 256, 265-68 (D.C. Cir. 1988); Sierra Club v.
United States Dep't of Transp., 753 F.2d 120, 126 (D.C. Cir. 1985).

Rule is to close Blue 1 without providing a viable alternative,
it would cause significant environmental effects by shifting
tourists from air to ground transportation. Without consider-
ing the legal merits of this argument, it is clear that we
cannot evaluate it factually without knowing whether the final
list of routes and corridors will leave air tour operators
without a viable alternative.14

D

The Hualapai Tribe also makes what amounts to an argu-
ment that the FAA issued its Final Rule too soon, because it
failed to consider first whether the establishment of the
expanded flight free zones would push aircraft noise off the
Park and onto the Hualapai Reservation. The consequences
of such a shift, the Tribe contends, would be harm to the
Tribe's traditional cultural properties, sacred sites, ongoing
religious and cultural practices, natural resources, and eco-
nomic development. In the Tribe's view, the FAA's failure to
consider these consequences, and to consult with the Tribe
about them, violated the National Historic Preservation Act,
16 U.S.C. s 470 et seq., NEPA, the APA, and the United
States' trust obligation to the Tribe.

We find these arguments unripe for consideration for the
same reason we found the County's arguments unripe. Until
we know what routes the air tours will take, we simply cannot
assess whether, or how much, they will affect the Reserva-
tion. Holding off that assessment until the routes are con-
crete may make our resolution of the dispute unnecessary.
See FAA Br. at 39 ("The FAA has committed to ensuring that
any new routes that are located above the Hualapai Reserva-

__________
14 In light of this resolution, we do not consider whether Clark
County would have standing under NEPA based on its assertion
that, because the FAA's action will cause tourists to travel to the
Park by ground rather than by air, the County will be injured by an
increase in vehicular emissions within the County. See generally
Florida Audobon Soc'y v. Bentson, 94 F.3d 658, 665 (D.C. Cir. 1996)
(en banc).

tion avoid historic, cultural and religious sites."); id at 45
("The final routes may well meet many of the Tribe's antici-
pated [environmental] concerns."). Such a postponement
surely will facilitate any review that is necessary. And since
the flight free zones have been stayed in the interim, post-
ponement will not injure the Tribe.15

The FAA also has represented that it will continue to
consult with the Tribe regarding the location of routes, and to
evaluate the noise impact of different routes on the Tribe,
during the period prior to issuance of final routes. See Final
Rule, 61 Fed. Reg. at 69,306-07; see also FAA Br. at 38-39,
45, 46. Accordingly, if it has not done so already, the FAA
still has time to satisfy any consultative obligations it may
have before a final plan is implemented.16

The Tribe does not seriously dispute these conclusions. It
"recognizes that if the FAA completely removes all routes
from tribal lands, it will not be impacted." Hualapai Reply
Br. at 6. But it forthrightly states that it filed its current

__________
15 The same analysis applies to the Tribe's allegation that
overflights that "directly and substantially impair the use of" reser-
vation lands would constitute an unlawful taking of those lands.
Until the routes and corridors are established, it is not possible to
tell whether there will be overflights that impair the Tribe's use of
its lands. And as long as the FAA continues to stay the effective
date of the flight free zones, such overflights will not occur.

16 In its brief, the Tribe contended that under its trust obli-
gations, the United States was required, but failed, to consult with
it on a government-to-government basis while developing the Final
Rule. The FAA, however, cited considerable evidence that consul-
tations have occurred. See, e.g., Final Rule, 61 Fed. Reg. at 69,305-
07 (outlining consultations with Indian tribes); Environmental As-
sessment at 4-19 to -21, 4-23 (outlining meetings with Hualapai and
other tribes to review impact on historical sites and socio-economic
interests of tribes). At oral argument, the Tribe reformulated its
argument, conceding that there had been consultations, but con-
tending that they had not been meaningful. See Oral Arg. Tr. at
50-51.

petition because it feared that if had it waited until the FAA
promulgated the routes, it would have missed the deadline for
petitioning for review of the 1996 rule and hence be foreclos-
ed from obtaining review. This was a perfectly appropriate
reason for filing the petition. See Eagle-Picher Indus., Inc.
v. EPA, 759 F.2d 905, 909 (D.C. Cir. 1985). But "our finding
of unripeness gives petitioners the needed assurance" that
they will not be foreclosed from judicial review when the
appropriate time comes. Public Citizen v. NRC, 940 F.2d
679, 683 (D.C. Cir. 1991). This is because a "time limitation
on petitions for judicial review ... can run only against
challenges ripe for review." Baltimore Gas & Elec. Co., 672
F.2d 146, 149 (D.C. Cir. 1982). When the corridors and
routes finally are promulgated, the Tribe and the other
petitioners will be able to raise issues that specifically arise
from the interrelationship between the flight free zones and
those routes and corridors.

III

We now turn to the arguments of the Grand Canyon Trust,
which attack the FAA's Final Rule from the opposite side--
not as constituting too much, too soon; but as being too little,
too late. The Trust has little quarrel with the individual
elements of the Final Rule--the flight free zones, curfews,
aircraft caps or reporting requirements. But it argues that
they are not enough to achieve Congress' goal, and that the
agency has delayed action for far too long. The Final Rule is
too little, the Trust contends, because the government's defi-
nition of substantial restoration does not restore as much
natural quiet as the statute requires. The Final Rule is too
late, the Trust charges, because a rule that will not achieve
substantial restoration until the year 2008 is inconsistent with
the statutory goal.

A

The Trust argues that for four reasons, the Final Rule's
definition of substantial restoration of the natural quiet--that

50% of the Park achieve natural quiet for at least 75% of the
day--does not satisfy the Overflights Act.

First, the Trust contends that Congress intended more
than half of the Park to be free of aircraft noise 100% of the
time, a percentage the government's 75% figure will not
necessarily achieve in any area.17 But the statute does not
say that a substantial area of the Park must be quiet 100% of
the time. The statutory goal is simply the "substantial
restoration of the natural quiet," a phrase too broad and
ambiguous to read as "address[ing] th[is] precise question."
Chevron, 467 U.S. at 843. The Act does require the designa-
tion of "flight free zones," but even if the Final Rule permits
noise to leak into those zones,18 the statutory language still
requires only that the zones be "flight free," not "noise free."

Faced with the absence of support in the Act's language,
the Trust looks instead to the legislative history. But, like
the Air Tour Coalition, it is unable to point to anything other
than an isolated floor statement in support of its position.
Indeed, the irony is that the Trust points to the same floor
statement that the Coalition contends supports its opposite
view: Senator McCain's statement that the flight free zones
were intended to provide a location "where visitors can
experience the park essentially free from aircraft sound intru-
sions." 133 Cong. Rec. at S10799. Again putting to one side
the fact that this was the statement of a single Senator, a

__________
17 That is not to say there will be no such areas. There are a
number of back-country areas of the Park that experienced almost a
complete absence of aircraft sound even under the previous rule.
See NPS Report at 187-88; Environmental Assessment at 4-13 to
-15 (tables describing three locations at which aircraft are audible
for only 0-4 % of the day, and one where they are audible 0-9%).

18 The FAA found that because of the way aircraft sound
carries in the Canyon, it was able, for some part of the time, "to
fully penetrate to the center of every flight-free zone created by"
the previous rule. See Final Rule, 61 Fed. Reg. at 69,309. The
record does not disclose whether the same will result for the
expanded flight free zones created by the new rule.

location "essentially free from aircraft sound intrusions" is
not necessarily inconsistent with one that is quiet for at least
75% of the day and for 100% of the night (during which air
tours do not fly). That is particularly so in light of the
Senator's declaration, in the same statement, that "[t]his
measure ... resists the wide-spread impulse to micromanage,
by setting out a framework and leaving the real decisions up
to the agencies with the expertise to make them." Id.
Indeed, that declaration accords well with the Supreme
Court's suggestion in Chevron that where Congress leaves a
statutory term undefined, it makes an implicit "delegation of
authority to the agency to elucidate a specific provision of the
statute" through reasonable interpretation. 467 U.S. at 843-
44. We cannot say the FAA has exercised that delegated
power in an unreasonable way.

The Trust contends, second, that even if the statute does
not require the agency to create completely noise-free areas,
the Park Service definition still does not provide "substantial"
restoration. It argues that the "dictionary meaning" of "sub-
stantial" is "more than half." It then argues that a rule
requiring that 50% of the Park be quiet for 75% of the day, is
mathematically equivalent to one yielding a "restoration"
value of only 37.5%, because 50% x 75% = 37.5%. Neither
the statute nor the legislative history compels acceptance of
either part of this argument.

"Substantial" may well be defined as meaning "more than
half." See Webster's Third New International Dictionary
2280 (1993) ("being that specified to a large degree or in the
main") (4th meaning). But it also has a host of much vaguer
dictionary meanings, ranging from "not seeming or imagi-
nary," id. (1st meaning), to "considerable in amount," id. (2nd
meaning). See Victor v. Nebraska, 511 U.S. 1, 19 (1994)
("[O]n the one hand, 'substantial' means 'not seeming or
imaginary'; on the other, it means 'that specified to a large
degree.' "). Indeed, in the administrative law context, we
refer to "substantial" evidence as meaning "more than a
scintilla, but less than a preponderance." Burns v. Office of

Workers' Compensation Programs, 41 F.3d 1555, 1562 n.10
(D.C. Cir. 1994) (internal quotations and citation omitted). In
short, the term is simply too ambiguous to compel the "plain
meaning" claimed by the Trust, and more than sufficiently
elastic to support the agency's definition as reasonable.

But even if "substantial" does mean "more than half," the
agency's definition of substantial restoration effectuates that
meaning by requiring that more than half of the Park be
silent more than half--indeed, more than three quarters--of
the time. The Trust's mathematical equation, while creative,
does not persuade us otherwise.19 There is no support in the
statute or legislative history for requiring that kind of numer-
ic calculation, nor for its unstated premise: that "substantial"
pertains to a combination of space and time, rather than to
each variable considered separately.

The Trust's third contention is that the agency's definition
of substantial restoration was infected by impermissible con-
sideration of the needs of the air tour industry, as was the
timetable the agency adopted for final achievement of sub-
stantial restoration. As we have noted above, the FAA did
consider the impact its regulation would have on the viability
of the air tour industry, explaining that "[t]he primary policy
reason for adopting this rule, is that it is the best compromise
the FAA has been able to formulate to achieve the mandate
of [the Overflights Act] and maintain a viable air tour indus-
try serving GCNP." Final Rule, 61 Fed. Reg. at 69,328. The

__________
19 Clark County has an equally imaginative mathematical reply.
The Final Rule, it points out, requires that 50% of the Park be quiet
75% of a 12-hour day--not 75% of a 24-hour day. When this is
combined with 100% silence during the 12-hour night, the correct
calculation is: (50% x 75%) + (50% x 100%), which results in a
"restoration" of 87.5%. See Clark County Intervenor Br. at 10-11.
This calculation may be a bit too creative. Because air tours have
never flown at night, it is hard to see how silence during that period
can be considered part of any "restoration." On the other hand, the
curfew, which extends the period of 100% silence beyond 12 hours,
may well raise the "combined" percentage above the Trust's calcula-
tion of 37.5%.

Trust argues not only that such considerations are not re-
quired--as the Air Coalition insists--but that they are not
even permitted.

We see nothing in the Overflights Act that forbids the
government from considering the impact of its regulations on
the air tour industry. Congress, after all, required "substan-
tial restoration of the natural quiet," not total restoration.
The statute's provisions for flight free zones and restrictions
on flight altitudes, see Overflights Act s 3(a)(1), and for a
plan to "manag[e] air traffic in the air space above the Grand
Canyon," id. s 3(a)(2), indicate that Congress contemplated
some overflights would continue. See also 133 Cong. Rec. at
S10799 (statement of Sen. McCain) ("I believe this bill will
enable the air tour industry to continue to thrive."). The
FAA's statement does not indicate that the agency considered
maintenance of a viable air tour industry in derogation of its
statutory responsibility to issue a plan that would provide for
substantial restoration of the natural quiet. To the contrary,
the agency said the Final Rule was a compromise that still
would "achieve the mandate" of the Act. Final Rule, 61 Fed.
Reg. at 69,328; see also id. ("It is the intent of the rule
adopted to permit the continuation of aerial viewing of the
canyon ... in a manner consistent with the stated purposes of
section 3 [of the Overflights Act] to substantially restore the
natural quiet of the Grand Canyon ....") (emphasis added).
As long as that is so, we do not find anything in the statute
that would bar the agency from considering this issue in the
course of promulgating its regulatory plan.20

Fourth, the Trust contends that the FAA inadequately
considered alternatives--or, better put, additions--to both

__________
20 We should note that the agency's concern for the tours was
at least as much for air tour passengers as for air tour operators.
See, e.g., Final Rule, 61 Fed. Reg. at 69,309 ("[V]iewing the canyon
from the air is a legitimate and valuable means of appreciating the
beauty of the Grand Canyon."); Proposed Final Rule, 61 Fed. Reg.
at 40,134 ("[C]ommercial sightseeing operators provide a valuable
public service by creating a unique way [for] all to view the Grand
Canyon and provide an effective means for elderly and handicapped
individuals to enjoy the park.").

the final and proposed rules. These primarily include a cap
not only on the number of aircraft but also on the number of
flights, and a more expedited conversion to quieter aircraft.
The Hualapai Tribe makes the same argument regarding the
flight cap, and Clark County makes a similar argument about
quieter aircraft--although the County regards quieter air-
craft as an alternative, rather than an addition, to the Final
Rule's expanded flight free zones. These complaints have
largely been mooted, or rendered unripe, by recent develop-
ments. The new data on the number of aircraft flying in the
Park has persuaded the FAA that in order to achieve sub-
stantial restoration it will have to reconsider implementing
both of these options. See FAA Letter at 2 (Nov. 12, 1997);
Oral Arg. Tr. at 82, 84-85. Since the FAA has committed
itself to reconsidering these options, now is not the time to
decide whether a failure to adopt them would be arbitrary or
capricious.

B

Finally, we address the Trust's argument that the Final
Rule achieves a substantial restoration "too late," and its
request that we "(1) require the agencies within 60 days to
issue regulations that will immediately achieve the substan-
tial restoration of natural quiet ...; (2) direct that the
regulations ..., at a minimum, establish[ ] flight-free zones
sufficiently large that 50% of the Park is noise-free; and (3)
retain jurisdiction over this matter to ensure compliance...."
Trust Br. at 17-18 (emphasis in original). As an "interim
measure," the Trust asks us to order "an immediate cap of
40,000 annual air tour overflights." Id. at 18.

Although the APA gives courts the authority to "compel
agency action unlawfully withheld or unreasonably delayed,"
5 U.S.C. s 706(1); Telecommunications Research & Action
Ctr. v. FCC, 750 F.2d 70 (D.C. Cir. 1984) [hereinafter
"TRAC"], we are acutely aware of the limits of our institu-
tional competence in the highly technical area at issue in this
case. As a court we have no idea what the unintended
consequences of immediately imposing an expansion of the

flight free zones--which under the Final Rule already will
cover 87% of the Park--might be. In addition to air safety
concerns, it is possible that implementing such zones would
do no more than shift the flights and their noise from the
Park to the Hualapai Reservation. Nor do we know what the
consequences of ordering a cap on flights would be, or
whether there might be other regulations that could better do
the job. That, of course, is why such considerations normally
are the province of expert agencies rather than courts--and,
as noted above, the FAA currently is considering such op-
tions. Moreover, although the Trust's frustration with the
agencies' slow and faltering pace is understandable, we can-
not say it has made out a case for the immediate imposition of
so drastic a remedy.21

The language of the Overflights Act does manifest a con-
gressional concern with expeditious agency action. The Act
required the Secretary of the Interior to submit to the FAA
recommendations, providing for "substantial restoration of
the natural quiet and experience of the park," within 30 days
of its enactment. It required the FAA to issue a final plan

__________
21 When deciding whether to grant a petition for mandamus on
the ground of agency action unreasonably delayed, this court is
guided by the following criteria:

(1) the time agencies take to make decisions must be governed
by a rule of reason; (2) where Congress has provided a
timetable or other indication of the speed with which it expects
the agency to proceed in the enabling statute, that statutory
scheme may supply content for this rule of reason; (3) delays
that might be reasonable in the sphere of economic regulation
are less tolerable when human health and welfare are at stake;
(4) the court should consider the effect of expediting delayed
action on agency activities of a higher or competing priority;
(5) the court should also take into account the nature and
extent of the interests prejudiced by delay; and (6) the court
need not find any impropriety lurking behind agency lassitude
in order to hold that agency action is unreasonably delayed.

TRAC, 750 F.2d at 80 (D.C. Cir. 1984); see also Action on Smoking
& Health v. Dep't of Labor, 100 F.3d 991, 994 n.1 (D.C. Cir. 1996);
DiCola v. FDA, 77 F.3d 506, 509-10 (D.C. Cir. 1996).

not more than 90 days later. Overflights Act s 3(b)(1), (2).
Both agencies were late in carrying out these obligations.
The Act also required that within two years of its effective
date, the Secretary was to submit a report to Congress
discussing "whether the plan has succeeded in substantially
restoring the natural quiet in the park" and "such other
matters, including possible revisions in the plan, as may be
necessary." Id. s 3(b)(3). The Park Service was again late
in complying--this time by more than four years. It took
another two years--and an order from the President--for the
FAA to respond to the NPS Report and to issue the Final
Rule now before us. And, as we have noted above, it was not
until after it issued that rule that the FAA realized that some
of its key assumptions were grossly inaccurate, and that still
further modifications would be required to achieve Congress'
goal.

The statute's timing provisions do not, however, support
the Trust's contention that Congress "intended the job to be
done in 120 days." Trust Br. at 14. What Congress demand-
ed within 120 days was the issuance of a regulatory plan that
would achieve the goal of substantial restoration; it did not
direct that substantial restoration actually be in place on the
121st day. Indeed, the provision for a report, which was to
discuss whether the plan had succeeded and suggest revi-
sions, makes clear Congress contemplated that the agencies'
first plan might not succeed and might have to be revised--as
the agencies have done in the regulatory plan at issue here.

There is more force to the Trust's argument that, even if
Congress had no specific timetable in mind, it was unreason-
able for the FAA to wait ten years to issue a regulation
requiring substantial restoration, and then to issue one that
permits another ten years to pass before substantial restora-
tion is achieved. But although the FAA was tardy, it is
unfair to characterize it as doing nothing during those first
ten years. It issued SFAR 50-2, which went part of the way
toward restoration. As Congress directed, the government
then evaluated progress under that regulation, found it want-
ing, and eventually proposed the current rule. Although it
was undeniably slow in doing so, this is the first time any

party has challenged the agency's delay in court. That is not
to say, as the FAA implies, that this somehow estops the
Trust from complaining. But this is not a case where an
agency has been contumacious in ignoring court directions to
expedite decision-making.

Nor can we accept the Trust's argument that issuing a rule
that does not contemplate final achievement of Congress' goal
for ten years is inherently unreasonable. The issues involved
here are complex. It is clear from the record that achieving
substantial restoration will require a multitude of agency
actions, including the entry into service of quieter aircraft.
Nothing in the Trust's submissions demonstrate that this can
be achieved "immediately." Similarly, as we have noted
above, the interrelationship between the flight free zones and
the routes and corridors is complicated, as is the effect these
together will have on the surrounding land, including the
Hualapai Reservation.

Finally, we also note the Trust's complaint that even using
the Park Service's own definition, the Final Rule will not
achieve substantial restoration of natural quiet; and that the
FAA's latest reevaluation of the data indicates that not even
that rule plus the two proposed rules will achieve Congress'
goal. We agree that it would be arbitrary and capricious for
an agency simply to thumb its nose at Congress and say--
without any explanation--that it simply does not intend to
achieve a congressional goal on any timetable at all. Indeed,
counsel for the FAA conceded as much in oral argument.
Oral Arg. Tr. at 85-86, 89-90, 116.

But the FAA has not taken that course here. It has never
defended the Final Rule as the sole means for restoring the
natural quiet, but only as the first of three steps. Its
contemplation was that the three rules together would
achieve that goal by 2008. See Final Rule, 61 Fed. Reg. at
69,306; Noise Limitations Rule, 61 Fed. Reg. at 69,338. For
the same reason that we questioned the validity of Clark
County's contention that the FAA should have held up pro-
mulgation of the Final Rule until it had all three rules ready,
we reject the Trust's contention that the FAA must give birth

to all three today. See City of Las Vegas v. Lujan, 891 F.2d
at 935 (finding that "agencies have great discretion to treat a
problem partially" and holding that court will not strike down
agency action "if it were a first step toward a complete
solution"); General Am. Transp. Corp., 872 F.2d at 1058.

The FAA acknowledges that the new data on the number
of aircraft overflying the Park renders its original three-part
plan less effective than originally assumed. The FAA has
represented, however, that it still anticipates meeting the goal
of substantial restoration by 2008. See Oral Arg. Tr. at 82,
90. To do this, "[q]uiet aircraft technology will obviously
have to make up the gap in 2008, together with the route
structure." Id. at 82. The FAA also will consider using a
cap on the number of overflights. See FAA Letter at 2. The
FAA has assured this court that it still believes that "the
quiet technology rulemaking and the finalization of the air
tour routes, when completed, will result in attainment of the
statutory goal." FAA Supp. Br. at 4.

We will take the government at its word. See Orion
Communications Ltd. v. FCC, 131 F.3d 176, 182 (D.C. Cir.
1997). If the FAA does not issue additional regulations
reasonably promptly, or if those regulations do not appear
likely to achieve the statutory goal on a reasonable timetable,
the Trust may petition to compel agency action unlawfully
withheld or unreasonably delayed. But we are not at that
point yet, and hence can do no more than affirm the rule
currently before us.

IV

For the foregoing reasons, the petitions for review of the
Final Rule are denied. We note, however, that we have held
unripe those of petitioners' challenges that specifically arise
out of the interrelationship between the Final Rule's flight
free zones, and the still-uncertain flight corridors and routes.
Accordingly, those challenges may be raised again when the
corridors and routes finally are promulgated.22

__________
22 This reservation applies only to challenges specifically arising
out of the interrelationship between the zones and the routes and

_________
Note 22--Continued
corridors. It does not, for example, apply to a challenge to the
agency's interpretation of the statutory phrase, "substantial restora-
tion of the natural quiet," as we have found the present challenges
to that interpretation ripe and have upheld the agency's interpreta-
tion.