# Change in Noise Evaluation Methodology for Air Tour Operations Over Grand Canyon National Park

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A99-1685

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** January 26, 1999
- **Citation:** 64 FR 3969

## Text

DEPARTMENT OF THE INTERIOR

National Park Service

Change in Noise Evaluation Methodology for Air Tour Operations
Over Grand Canyon National Park

AGENCY: National Park Service, Interior.

ACTION: Public notice.

-----------------------------------------------------------------------

SUMMARY: As part of its implementation actions to achieve the
objectives of Public Law 100-91 regarding the substantial restoration
of natural quiet at Grand Canyon National Park (GCNP), including
current rulemaking [and environmental assessment actions], the National
Park Service (NPS) is working cooperatively with the Federal Aviation
Administration (FAA) on further actions to aid that restoration as well
as planning for the development of a comprehensive noise management
plan for air tour operations over GCNP. NPS previously determined that
in order to substantially restore natural quiet to GCNP, at least 50
percent of the park must achieve ``natural quiet'' (i.e., no aircraft
audible) for 75 to 100 percent of the day. The reasonableness and
validity of this standard was upheld by the United States Court of
Appeals for the District of Columbia in 1998.
In previous environmental assessments related to GCNP

[[Page 3970]]

rulemaking since 1996, a single threshold of the average natural
ambient sound level plus 3 decibels was applied through the FAA
Integrated Noise Model to estimate the percent of time that air tour
aircraft would be noticeable under each action alternative. In light of
its experience and additional information, NPS is now refining its
methodology used to evaluate the achievement of its natural quiet
restoration standard.
Particularly, the NPS refinements contemplate a two-zone system for
evaluating achievement of the natural quiet standard. The zones reflect
more accurately the differences in geography, facilities development,
and regulatory restraints of specific geographic areas of GCNP and
allow noise thresholds to be tailored to the circumstances of each
zone. The refinements apply only to evaluation methodology; the
standard for substantial restoration of natural quiet remains
unchanged.
This notice seeks public comment on the refinements to NPS's
evaluation methodology, i.e., the two-zone system and the noise
thresholds to be applied to the zones. Additional matters concerning
the GCNP comprehensive noise management plan for air tour operations
will be addressed in subsequent public notices, including, but not
limited to, a model validation study and a noise monitoring strategy.

DATES: Comments must be received on or before March 20, 1999.

ADDRESSES: Comments may be delivered or mailed, in triplicate, to, the
National Park Service, attention: Tom Hale, National Park Service,
Grand Canyon Science Center, P.O. Box 129, Grand Canyon, Arizona 86023.

FOR FURTHER INFORMATION CONTACT: Tom Hale (520-556-7219).

SUPPLEMENTARY INFORMATION

Background

Section 3 of Public Law 100-91 (Overflights Act) states that noise
associated with aircraft overflights at Grand Canyon National Park
(GCNP) is causing a significant adverse effect on the natural quiet and
the experience of GCNP. The statute directed the Secretary of the
Interior (Secretary) to make recommendations to the Administrator of
the FAA for the development of a plan for management of air traffic in
the air space above GCNP for the purposes, among other matters, of
providing substantial restoration to the natural quiet and experience
of the park and protection of public health and safety from adverse
effects associated with aircraft overflight. The FAA is charged with
implementing these recommendations without change unless it determines
that they would adversely affect aviation safety.
A plan intended to achieve these purposes was established by FAA in
1988 with the adoption of Special Federal Aviation Regulation (SFAR)
No. 50-2. SFAR 50-2 established minimum altitudes, four flight free
zones, and special routes for commercial air-tour operators over the
park.
In 1994, as required by the Overflights Act, the Secretary
submitted to the Congress a report, developed by NPS, regarding
overflights over units of the national park system in general. The
``Report on the Effects of Aircraft Overflights on the National Park
System'' (Report), reviewed the effectiveness of SFAR 50-2 and offered
a new set of recommendations for further regulatory action by FAA. The
Report concluded that SFAR 50-2 had not succeeded in substantially
restoring natural quiet to GCNP noting, particularly, that the level of
commercial air-tour operations (and consequent aircraft noise) at GCNP
had increased since 1988 and was likely to continue to increase under
SFAR 50-2. The Report recommended simplification of the existing
commercial air-tour route structure, expansion of flight free zones,
phased implementation of quieter aircraft technology, consideration of
limits on aircraft operations or noise, and the imposition of temporal
curfews on commercial air-tour overflights.
In addition, the Report determined the threshold value for the
substantial restoration of natural quiet: 50% or more of the park must
achieve ``natural quiet'' (i.e., no aircraft audible) for 75-100
percent of the day. ``Natural quiet'' is a park resource defined as the
natural ambient sound conditions found in national park units. It
describes the natural sound conditions found in national parks when
people with normal hearing can perceive nothing but the sounds produced
by the natural and cultural components of the parks.
On April 22, 1996, in an Executive Memorandum, the President
required the Secretary of Transportation, in consultation with the
Secretary of the Interior and the National Park Service, to issue
regulations ``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 aviation
safety in accordance with the Overflights Act (Pub. L. 100-91).''
In response, on December 31, 1996, the FAA published a Final Rule
amending part 93 of Federal Aviation Regulations by adding a new
subpart (Subpart U) to codify the provisions of Special Federal
Aviation Regulation (SFAR) 50-2, Special Flight Rules in the Vicinity
of GCNP (61 FR No. 252, pages 69302-69333) modifying the dimensions of
the GCNP Special Flight Rules Area; establishing new and modifying
existing flight corridors and flight free zones; establishing reporting
requirements for commercial sightseeing companies operating in the
Special Flight Rules Area; restricting flights in Zuni and Dragon
Corridors during certain time periods (curfews); and limiting the
number of aircraft that can be used for commercial sightseeing
operations in the GCNP Special Flight Rules Area (cap). Subsequently,
it became necessary to delay implementation of several of the rule's
provisions to continue consultation with Indian tribes on routes and
address problems with the cap on sightseeing operations. As a result,
the reporting requirements, curfews, and cap on aircraft numbers are in
effect, but modification of the Special Flight Rules Area and the
flight free zones will not be completed until decisions on air tour
routes can be finalized.
In addition, on December 31, 1996, FAA published a notice of a
proposed rulemaking regarding additional noise limitations for aircraft
operations in the vicinity of GCNP (61 FR No. 252, pages 69334-69355).
Then, on December 31, 1996, FAA issued proposed air-tour routes for
GCNP (61 FR No. 252, pages 69356-69357). These latter actions have not
been finalized. The FAA has initiated other actions since that time,
notably delaying implementation of certain sections of the final rule
to allow the FAA and the Department of Interior to consider comments
and suggestions to improve the proposed route structure. Complete
background information on these and other actions taken by the FAA may
be found in the Federal Register Vol. 63, No. 234, pages 67544-67546.
The preamble to Subpart U, in addition to discussing the need for
the rule, states that FAA and NPS are committed to the development of a
noise management plan for GCNP related to air tour operations. This
plan is intended to provide for a more adaptive management approach,
full resolution of all monitoring and modeling issues, additional
public input, and the provision of improved incentives to invest in
noise efficient aircraft. The GCNP noise management plan is intended to
ensure development of a flexible and adaptive approach to noise
mitigation and management, and,

[[Page 3971]]

among other matters, will address validation and documentation of the
most effective way(s) to monitor and model aircraft noise in GCNP.

Discussion

As part of its preparation for developing the GCNP air tour noise
management plan, the NPS has reexamined the current methodology for
evaluating the substantial restoration of natural quiet in GCNP.
As previously noted, the NPS determined in 1994 that the threshold
for substantially restoring natural quiet to GCNP required that 50% or
more of the park must achieve natural quiet (i.e., no audible
aircraft), for 75-100% of the day.
The methodology previously used to evaluate the achievement of the
substantial restoration of natural quiet under this standard treated
the entirety of GCNP as one area and applied a single noise threshold
to the entire area. The threshold used was the average natural ambient
(multiple levels based on vegetative cover from the best available
acoustic data set) plus 3 decibels, otherwise known as noticeability.
Noticeability is defined as the level at which visitors engaged in
activities other than contemplation of the national park are likely to
hear aircraft noise. This threshold was used in calculating the
percentage of the day and the percentage of GCNP that aircraft noise
would be noticeable. And the threshold was used irrespective of
differences in geography, development circumstances, or regulatory
restraints of particular areas of the park, and, irrespective of the
fact that it might be appropriate to apply different noise thresholds
to different parts of GCNP to reflect such differing circumstances.
Based on further review and the experience of NPS and FAA in
applying the current aircraft noise evaluation methodology, the NPS
believes the current methodology should be refined to take into account
the characteristics of specific areas of GCNP and to utilize different
noise thresholds where appropriate.
Particularly, NPS is refining the current evaluation methodology by
incorporating a two-zone geographic system with different noise
thresholds applicable to the circumstances of each of the two zones.
In this connection, NPS, acting for the Secretary, is charged with
the management of areas of the National Park System. It is the
responsibility of NPS to preserve park areas and to provide for their
enjoyment in a manner that will leave them unimpaired for the enjoyment
of future generations. Preserving and maintaining natural and cultural
``soundscapes'' in areas of the national park system is a component of
this responsibility. A concern for the achievement of the ``substantial
restoration of natural quiet'' in GCNP is analogous to concerns
regarding the preservation of wildlife, historic structures or
ecosystems that are significant features of parks. As part of its
mandate, the NPS seeks to make available the opportunity to experience
the natural features of park areas with as little evidence of human
activity, visible or audible, as possible.
All of the larger natural area parks are zoned by NPS for differing
uses and differing levels of resource protection based upon park
purpose and other mandates, and differing levels of development to
serve visitors. In general, a park's frontcountry has facilities,
roads, parking lots and commercial services to provide necessary and
appropriate visitor needs, while the backcountry, whether a wilderness
area or not, has only trails for use by visitors.
A similar planning methodology is now proposed to be adopted by NPS
with respect to the substantial restoration of ``natural quiet'' at
GCNP. Under this methodology for Grand Canyon, Zone One would be
composed of (1) the developed areas of GCNP as identified in GCNP's
1995 General Management Plan, encompassing, on the South Rim, the area
from approximately Desert View to Hermits Rest, and, on the North Rim,
the developed area on Bright Angel Point; (2) the Sanup Flight Free
Zone; and (3), the Marble Canyon Sector. Zone One comprises
approximately one-third of the area of GCNP.
The developed areas included in Zone One for this purpose are
generally those delineated as ``Developed Areas'' on the Management
Zones map in the 1995 GCNP General Management Plan. Exceptions include
(a) Tuweep and Phantom Ranch which are excluded from Zone One because
they are managed to more primitive standards than the other developed
areas; and (b) the North Rim paved roads because they are surrounded by
proposed wilderness areas and because the roads and utility corridors
are too narrow (approximately 600 feet) for practical noise and impact
modeling on the scales involved. Only the Bright Angel Point developed
area is included in Zone One on the North Rim. For Zone One on the
South Rim, the system of developed areas, roads, and utility corridors
is blocked into a single contiguous unit. This unit extends from the
rim to the southern boundary of GCNP and from Hermit's Rest to Desert
View.
The North and South Rim developed areas as described above are
included in Zone One in recognition of the greater amount of human
activity and consequent more limited expectations of natural quiet in
these areas as opposed to undeveloped areas of the park. The area west
Whitmore Rapid is included in Zone One because the relatively low
designated aircraft ceiling of the Sanup Flight-free Zone (7999 feet,
MSL), needed for safe transit of the area by general aviation, limits
the ability of the flight-free zone to provide acoustic protection to
this area.
The Marble Canyon Sector is included in Zone One because the
narrowness of Marble Canyon and the SFRA boundary effectively preclude
acoustic protection of the canyon floor and river area, and because it
is not feasible to establish a flight-free zone while still providing
for safe transit of the area by general aviation traffic.
Zone Two would encompass, in a large contiguous area in the center
of GCNP, approximately two-thirds of the park's area. The two zones are
shown on the map accompanying this notice.
Under this proposal, the noise threshold for Zone One is set at 3
decibels above the average natural ambient sound levels (A-weighted)
found to exist in these areas of the park as determined by previous
scientific acoustic measurement studies. This is the same as the single
standard used in previous evaluations (i.e., noticeability).
The threshold for Zone Two is proposed to be different because data
collected at GCNP indicates that technicians monitoring the sound
environment identified aircraft noise levels at levels significantly
below A-weighted natural ambient levels. These technicians, tested to
have normal hearing, were listening actively to note the source of
noise levels as the source changed over time, noting, for example,
whether the noise source was the natural ambient environment or one or
more of a variety of human sources such as aircraft or vehicles. The
level at which an attentive listener, such as these technicians, can
begin to hear a noise source is the only objective point from which the
amount of time the source is audible can be measured; it incorporates
the masking level natural ambient environment, including wind. Park
visitors, sitting quietly but actively seeking to experience the
natural quiet and solitude of the park, were key people that NPS
decision-makers had in mind concerning the phrase ``no aircraft
audible'' in the natural quiet standard. However, with a noise
threshold of 3

[[Page 3972]]

decibels above average natural ambient sound levels, the NPS learned
that such persons could potentially hear aircraft as much as 100% of
the time at levels lower than that threshold. The NPS considers this
standard to be inappropriate for the whole park.
The technicians identified aircraft noise at A-weighted levels of
8-12 decibels below the average A-weighted natural ambient sound
levels, depending upon aircraft type. Therefore, the threshold for Zone
Two is set at 8 decibels below the average ambient sound levels, a
threshold which reflects the point at which aviation noise can be heard
(i.e., audible) by ground visitors seeking to experience the natural
and cultural soundscapes of national parks.
The legislative history of Public Law 100-91 confirms that the
purpose of flight-free zones is to provide a location where visitors
can experience the park essentially free from aircraft sound
intrusions. The aerial extent of these zones will also be adequate to
ensure that sound from aircraft flying adjacent is not detectable from
most locations within the zones. It is within these flight-free zones
that substantial restoration of natural quiet is expected to be
achieved.
NPS considers that adoption of these changes to its noise
evaluation methodology for GCNP will result in more accurate and
realistic means to evaluate the substantial restoration of natural
quiet in GCNP consistent with the NPS Report to Congress. The Report
defined the substantial restoration of natural quiet using a noise
evaluation standard based upon the sound level at which a person with
normal hearing can hear aircraft noise.
The NPS and the FAA will use this refined methodology in future
evaluations of the substantial restoration of natural quiet at GCNP,
unless science or public planning processes provides better approaches.
These refinements of the evaluation methodology may make more
challenging the efforts to achieve the substantial restoration of
natural quiet in GCNP. However, the use of the two noise thresholds and
two geographic zones will better achieve the preservation of the GCNP
resources and visitor experiences the NPS is charged to protect.
Jaqueline Lowie,
Deputy Director.
[GRAPHIC] [TIFF OMITTED] TN26JA99.000

[FR Doc. 99-1685 Filed 1-25-99; 8:45 am]
BILLING CODE 4310-70-P

---

Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A99-1685. Public record. Not legal advice.