XXXX 2001

DEPARTMENT OF TRANSPORTATION                    

Federal Aviation Administration

14 CFR Part 93

[Docket No. XXXX; Amendment No. 93-  ]

Noise Limitations for Aircraft Operations in the Vicinity of Grand
Canyon National Park

AGENCY:	Federal Aviation Administration (FAA), DOT.

ACTION:	Supplemental notice of proposed rulemaking.

____________________________________________________________

SUMMARY:  This supplemental proposal amends the notice of proposed
rulemaking (NPRM) published on December 31, 1996 (61 FR 69334; Notice
96-15) which proposed to establish noise efficiency limitations for
certain aircraft operations in the vicinity of Grand Canyon National
Park (GCNP).  The NPRM is being re-examined because Congress passed
legislation that directed the FAA to Specifically, the FAA has
reexamined the December 1996 proposal in light of the direction provided
in Section 804, Quiet Aircraft Technology for Grand Canyon, of the
Wendell H. Ford Aviation Investment and Reform Act for the 21st Century
(Pub. L. 106-181).  Under the mandate, the Administrator shall designate
reasonably achievable requirements for quiet technology in commercial
air tour aircraft at GCNP.  This SNPRM proposes standards for quiet
technology that are reasonably achievable.  fixed-wing and helicopter
aircraft necessary for such aircraft to be considered as employing quiet
aircraft technology for purposes of this section.  The proposed quiet
technology designations require air tour aircraft to be categorized
according to each aircraft's noise efficiency.  The eventual goal is The
standards for quiet technology proposed in this SNPRM will be used to
assist the National Park Service (NPS) in achievingachieve its statutory
mandate mandate imposed by Public Law 100-91 to provide for the
substantial restoration of natural quiet and experience in the GCNP. 
This proposed rulemaking is related to and consistent with other
rulemaking actions being implemented by the FAA concerning the GCNP. 
The SNPRM also serves to disposes of the comments that had beenwere
received in response to the December 1996 NPRM.

	This SNPRM drops the three noise efficiency categories that were
proposed in the December 1996.  This SNPRM only proposes to designate as
quiet technology those aircraft complying with what was formerly
described as Category C.  This SNPRM does not include any incentive
flight corridors through the park as proposed in December 1996 nor does
it propose any phase-out of air tour aircraft that do not satisfy the
quiet technology designation.  The SNPRM does not propose to implement
the provision of the National Air Tour Management Act of 2000 that would
permit a lifting of the cap on commercial sightseeing air tour
operations in the Park.  The implementation of incentive flight
corridors and cap removal for quiet technology aircraft will be the
subject of future rulemaking as the FAA, in consultation with the NPS,
works with an advisory group composed of representatives of general
aviation, commercial air tour operations, environmental concerns, and
Indian Tribes.

DATES:  Comments must be received on or before <fill in date>.

ADDRESSES:  Address your comments to the Docket Management System, U.S.
Department of Transportation, Room PL401, 400 Seventh Street, SW.,
Washington, DC 20590-0001.  You must identify Docket Number
FAA-2001-XXXX at the beginning of your comments.

	You may also submit comments through the Internet to
http://dms.dot.gov.  You may also review the entire public docket for
this SNPRM at that same site.

 	You may also review the public docket in person in the Docket Office
between 9 9 a.m. and 5 5 p.m., Monday through Friday, except Federal
holidays.  The Docket Office is on the plaza level.

FOR FURTHER INFORMATION CONTACT:  Mr. Thomas L. Connor, AEE-100, Federal
Aviation Administration, 800 Independence Avenue, S.W., Washington, DC
20591; Telephone: (202) 267-8933.

SUPPLEMENTARY INFORMATION:

Comments Invited

	The FAA invites interested persons to participate in this rulemaking by
submitting written comments, data, or views.  We also invite comments
relating to the economic, environmental, energy, or federalism impacts
that might result from adopting the proposals in this document.  The
most helpful comments reference a specific portion of the proposal,
explain the reason for any recommended change, and include supporting
data.  We ask that you send us two copies of written comments.

	Interested persons are invited to participate in this proposed
rulemaking by submitting such written data, views, or arguments, as they
may desire. Comments relating to the environmental, energy, federalism,
or economic impact that may result from adopting the proposals in this
notice are also invited. Comments that provide the factual basis
supporting the views and suggestions presented are particularly helpful
in developing reasoned regulatory decisions. Communications should
identify the regulatory docket number and be submitted in triplicate to
the above-specified address. 	We will file in the docket all comments we
receive, as well as a report summarizing each substantive public contact
with FAA personnel concerning this proposed rulemaking.All
communications and a report summarizing any substantive public contact
with FAA personnel on this rulemaking will be filed in the docket.  The
docket is available for public inspection both before and after the
closing date for receiving comments.  Before taking any final action on
this proposal, the Administratorwe will consider all comments made on or
before the closing date for comments, and the proposal may be changed in
light of the comments received.

	If you want the FAA to  The FAA will acknowledge receipt of a your
comments if the commenteron this proposal, includes with your comments a
selfpre-addressed, stamped postcard on which the docket number
appearswith the comment.  The postcard should be marked ‘‘Comments
to No. XXXXX.’’ When the FAA receives the comment, the postcard will
be dated, time stamped, and returned to the commenter.We will stamp the
date on the postcard and mail it to you.

Availability of the SNPRM

	You can get an electronic copy using the Internet by taking the
following steps:

	(1)	Go to the search function of the Department of Transportation's
electronic Docket Management System (DMS) web page
(http://dms.dot.gov/search).

	(2)	On the search page type in the last four digits of the Docket
number shown at the beginning of this notice.  Click on "search."

	(3)	On the next page, which contains the Docket summary information for
the Docket you selected, click on the document number for the item you
wish to view.

	You can also get an electronic copy using the Internet through the
Office of Rulemaking’s web page at http://www.faa.gov/avr/armhome.htm
or the Federal Register's web page at
http://www.access.gpo.gov/su_docs/aces/aces140.html.

	You can also get a copy by submitting a request to the Federal Aviation
Administration, Office of Rulemaking, ARM-1, 800 Independence Avenue
SW., Washington, DC  20591, or by calling (202) 267-9680.  Make sure to
identify the docket number, notice number or amendment number of this
rulemaking.

	Any person may obtain a copy of this SNPRM by submitting a request to
the Federal Aviation Administration, Office of Rulemaking, 800
Independence Avenue SW., Washington, DC 20591, or by calling (202)
267–9677. Communications must identify the notice number of this
SNPRM. Persons interested in being placed on a mailing list for future
FAA NPRM’s should request a copy of Advisory Circular No. 11–2A,
Notice of Proposed Rulemaking Distribution System, which describes
application procedures. An electronic copy of this document may be
downloaded using a modem and suitable communications software from the
FAA regulations section of the Fedworld electronic bulletin board
service (telephone: 703–321–3339) or the Federal Register’s
electronic bulletin board service (telephone: 202–512– 1661).
Internet users may reach the FAA’s web page at http://www.faa.gov or
the Federal Register’s web page at http://www.access.gpo.gov/suldocs
for access to recently published rulemaking documents.

History

	Table 1 provides a timeline of events related to the effort to
designate quiet technology requirements for air tour operations in Grand
Canyon National Park (GCNP).  These events are described in this and
succeeding sections.

	Beginning in the summer of 1986, the FAA initiated regulatory action to
address increasing air traffic over GCNP.  On March 26, 1987, the FAA
issued Special Federal Aviation Regulation (SFAR) No. 50 (subsequently
amended on June 15, 1987; 52 FR 22734) establishing flight regulations
in the vicinity of the Grand CanyonGCNP.  The purpose of the SFAR was to
reduce the risk of midair collision, reduce the risk of terrain contact
accidents below the rim level, and reduce the impact of aircraft noise
on the park environment.

Table 1. Timeline of Events related to the Designation of Quiet
Technology for Air Tour Operations in GCNP (Part 1 of 2)

Year	Month	Event

1987	March/June	The FAA publishes SFAR No. 50 to establish special
flight regulations in vicinity of GCNP (52 FR 22734)

	August	Congress enacts National Parks Overflights Act (Pub. L. 100-91)

	December	The DOI transmits "Grand Canyon Aircraft Management
Recommendation" to the FAA

1988	May/June	The FAA publishes SFAR No. 50-2 to revise flight
procedures in GCNP airspace (53 FR 20264)

1994	March	The FAA and the NPS jointly issue ANPRM seeking public
comment on quiet technology and incentives (59 FR 12740)

	September	The DOI submits to Congress "Report on Effects of Aircraft
Overflights on the National Park Systems”

1995	June	The FAA extends SFAR No. 50-2 until June 15, 1997
(60 FR 31608)

	July	The DOI report to Congress is published.

1996	April	The President publishes a memorandum directing the
substantial restoration of natural quiet in GCNP

	July	The FAA publishes NPRM (Notice 96-11) to amend 14 CFR part 93 to
codify SFAR No. 50-2 (61 FR 40120)

	December	The FAA publishes final rule to codify SFAR 50-2 into a new
subpart U of 14 CFR part 93 (61 FR 69302)

	December	The FAA publishes NPRM (Notice 96-15) on noise limitations for
air tour operations in GCNP (61 FR 69334)

	December	The FAA publishes notice of availability of proposed
commercial air tour routes (61 FR 69356)

1997	February	The FAA delays the effective date of 14 CFR sections
93.301, 93.305, and 93.307 and reinstates portions of SFAR No 50-2
(62 FR 8862)

	May	The FAA publishes NPRM (Notice 97-6) to establish Bright Angel
incentive corridor and the National Canyon corridor for air tour routes
(62 FR 26902)

	October	The FAA publishes clarification of its reevaluation of the
economic and environmental impacts of the final rule published on
12/31/96 (62 FR 58898)

	December	The FAA further delays the effective date of 14 CFR sections
93.301, 93.305, and 93.307 and reinstates portions of SFAR No 50-2 
(62 FR 66248)

1998	July	The FAA withdraws the National Canyon corridor proposal
(63 FR 38232)

	July	The FAA also withdraws Notice 97-6, which proposed two quiet
technology incentive corridors (63 FR 38233)

	December	The FAA delays the effective date of 14 CFR sections 93.301,
93.305, and 93.307 and reinstates portions of SFAR No 50-2
(63 FR 67544)

1999	January	The NPS publishes a notice of agency policy, "Evaluation
Methodology for Air Tour Operations Over Grand Canyon National Park"
(64 FR 3969)

	February	The FAA delays the effective of 14 CFR sections 93.301,
93.305, and 93.307 and reinstates portions of SFAR No 50-2
(64 FR 5152)

	July	The FAA published an NPRM (Notice 99-11) to modify the dimensions
of the GCNP SFRA (64 FR 37296)

	July	The FAA also published NPRM (Notice 99-12) to limit the number of
commercial air tours conducted in GCNP (64 FR 37304)

	July	The NPS evaluation methodology becomes effective (64 FR 38006)



Table 1. Timeline of Events related to the Designation of Quiet
Technology for Air Tour Operations in GCNP (Part 2 of 2)

Year	Month	Activity

2000	February	The FAA delays the effective of 14 CFR sections 93.301,
93.305, and 93.307 and reinstates portions of SFAR No 50-2
(65 FR 5395)

	April	The FAA publishes the commercial air tour limitations final rule
(65 FR 17708)

	April	The FAA publishes the airspace modification final rule
(65 FR 17736)

	April	Congress enacts the National Parks Air Tour Management Act of
2000 (Pub. L. 106-181, Title VIII)

	May	The commercial air tour limitations final rule becomes effective
(14 CFR §§ 93.315, 93.317, 93.319, 93.321, 93.323, and 93.325)

	November	The FAA delays the effective date of the airspace modification
final rule (65 FR 69846)

2001	January	The FAA delays the effective date of the airspace
modification final rule (66 FR 1002)

	March	The FAA and the NPS jointly issue a notice establishing the NPOAG
(66 FR 14429)

	March	The FAA delays the effective date of the airspace modification
final rule (66 FR 16582)

	April	The airspace modifications final rule becomes effective (14 CFR
§§ 93.301, 93.305, 93.307, and 93.309)

	June	The FAA and the NPS announce the NPOAG membership (66 FR 32974)



ANPRM	Advanced Notice of Proposed Rulemaking

CFR	Code of Federal Regulations

FR	Federal Register

NPOAG	National Parks Overflights Advisory Group

NPRM	Notice of Proposed Rulemaking

SFAR	Special Federal Aviation Regulation

In August 1987, Congress enacted Public Law (Pub. L.) 100-91, commonly
known as the National Parks Overflights Act (or the Overflights Act). 
The Overflights Act stated, in part, that noise associated with aircraft
overflights at GCNP was 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.”

Section 3 of the Overflights Act required the Department of the Interior
(DOI) to submit to the FAA recommendations to protect resources in the
Grand CanyonGCNP from adverse impacts associated with aircraft
overflights.  The law mandated that the recommendations:  (1) provide
for substantial restoration of the natural quiet and experience of the
park and protection of public health and safety from adverse effects
associated with aircraft overflight, (2) with limited exceptions,
prohibit the flight of aircraft below the rim of the canyon, and (3)
designate flight-free zones except for purposes of administration and
emergency operations.

In December 1987, the DOI transmitted its “Grand Canyon Aircraft
Management Recommendation” to the FAA.  The Overflights Act required
the FAA to prepare and issue a final plan for the management of air
traffic above the Grand CanyonGCNP, implementing the recommendations of
the DOI without change unless the FAA determined that executing the
recommendations would adversely affect aviation safety.

On May 27, 1988, the FAA issued SFAR No. 50-2 revising the procedures
for operation of aircraft in the airspace above the Grand CanyonGCNP (53
FR 20264).  SFAR No. 50-2 established a Special Flight Rules Area (SFRA)
from the surface to 14,499 feet above mean sea level (MSL) in the area
of the Grand CanyonGCNP.  The SFAR prohibited flight below a certain
altitude in each of five sectors of this area, with certain exceptions. 
The SFAR established four flight-free zones from the surface to 14,499
feet MSL covering large areas of the park.  The SFAR provided for
special routes for commercial sightseeing operators.  These operators
are required to conduct sightseeing operations under either part 121 or
part 135 of Title 14 of the Code of Federal Regulations (CFR) as
specified in their operations specifications.  Finally, the SFAR
SFAR 50-2 contained certain terrain avoidance and communications
requirements for flights in the area.

In March 1994, the two agencies jointly issued an advance notice of
proposed rulemaking (ANPRM) seeking public comment on policy
recommendations addressing the effects of aircraft overflights on
national parks, including GCNP (59 FR 12740).  The recommendations
presented for comment included:  (1) voluntary measures, (2) altitude
restrictions, (3) flight-free periods, (4) flight-free zones, (5)
allocation of noise equivalencies, and (6) incentives to encourage use
of quiet aircraft technology.  In response to the ANPRM, the FAA
received 644 comments that specifically addressed GCNP.  

A second major provision of section 3 of the Overflights Act required
the DOI to submit a report to Congress discussing whether SFAR No. 50
“has succeeded in substantially restoring the natural quiet in the
park; and such other matters, including possible revisions in the plan,
as may be of interest.”  The report was to include comments by the FAA
“regarding the effect of the plan's implementation on aircraft
safety.”  The Overflights Act mandated a number of studies related to
the effect of overflights on parks.

On September 12, 1994, the DOI submitted its final report and
recommendations to Congress.  This report “Report on Effects of
Aircraft Overflights on the National Park System,” was published in
July 1995.  The report recommended numerous revisions to SFAR No. 50-2
in order to substantially restore natural quiet in GCNP.  Recommendation
No. 10, “Improve SFAR 50-2 to Effect and Maintain the Substantial
Restoration of Natural Quiet at Grand Canyon National Park,” is of
particular interest to this rulemaking.  This recommendation
incorporated the following general concepts:  (1) simplification of the
commercial sightseeing route structure, (2) expansion of flight-free
zones, (3) accommodation of the forecast growth in the air tour
industry, (4) phased-in use of quieter aircraft technology, (5) temporal
restrictions (“flight-free” time periods), (6) use of the full range
of methods and tools for problem solving, and (7) institution of changes
in approaches to park management, including the establishment of an
acoustic monitoring program by the NPS in coordination with the FAA.  On
June 15, 1995, the FAA published a final rule that extended the
provisions of SFAR No. 50-2 to June 15, 1997 (60 FR 31608).  This action
allowed the FAA sufficient time to review the NPS recommendations and to
initiate and complete appropriate rulemaking action.

President's Memorandum

	The President, on April 22, 1996, issued a Memorandum for the Heads of
Executive Departments and Agencies to address the significant impacts on
visitor experience in national parks.  Specifically, the President
directed the Secretary of Transportation to issue proposed regulations
for the Grand Canyon National Park that would appropriately limit
sightseeing aircraft to reduce the noise immediately and to further
restore natural quiet, as defined by the Secretary of the Interior,
while maintaining aviation safety in accordance with the Overflights
Act.  

On July 31, 1996 the FAA published an NPRM (61 FR 40120; Notice 96-11)
to reduce the impact of aircraft noise on GCNP and to assist the NPS in
achieving its statutory mandate imposed by the Overflights Act to
provide for the substantial restoration of natural quiet and experience
in GCNP.  A final rule was issued on December 31, 1996 (61 FR 69302) to
amend 14 CFR part 93 with a new subpart U (Sections 93.301 to 93.317). 
The amendment adopted the following:  (1) modification of the dimensions
of the GCNP SFRA, (2) establishment of new flight-free zones and flight
corridors, as well as modification of existing flight-free zones and
flight corridors, (3) establishment of flight-free periods (curfews) in
the Dragon and Zuni Point Corridors, and (4) establishment of reporting
requirements for commercial sightseeing companies operating in the SFRA.
 In addition, the FAA sought comments on a number of questions and
alternatives regarding curfews and caps, as well as on the issue of
quiet aircraft technology.  This final rule also placed a temporary
limit on the number of aircraft that could be used for commercial
sightseeing operations in the GCNP SFRA.  These provisions were to
become effective on May 1, 1997.  Only the reporting requirements, and
aircraft cap were actually implemented.  Implementation of the remaining
provisions had been delayed.

Additionally, on December 31, 1996, the FAA published an NPRM on Noise
Limitations for Aircraft Operations in the Vicinity of Grand Canyon
National Park (61 FR 69334; Notice 96-15), and a Notice of
Availability of Proposed Commercial Air Tour Routes in the Federal
Register (61 FR 69356).  These two documents were part of an overall
strategy to reduce further the impact of aircraft noise on the park
environment and to assist the NPS in achieving its statutory mandate
imposed by the Overflights Act.

1996 Proposal for Quiet Technology Designation

In the 1996 NPRM, Noise Limitations for Aircraft Operations in the
Vicinity of Grand Canyon National Park, FAA proposed to establish noise
limitations for certain aircraft operating in the vicinity of GCNP.  The
proposed aircraft noise limitations rule generally would have required
air tour aircraft to be categorized according to each aircraft’s noise
efficiency.   The 1996 proposal had three parts: (1) incentive flight
corridor through the National Canyon, (2) categorize aircraft by noise
efficiency, and (3) removal of the aircraft cap for the most noise
efficient aircraft.  

The first part was to provide incentives for the use of quieter aircraft
within the GCNP.  The proposed rule would have implemented incentives
for conversion to the most noise efficient category of air tour
aircraft.  The NPRM also provided an incentive route for the use of
noise efficient aircraft within the GCNP by establishing the National
Canyon Corridor, a route within the newly expanded Toroweap/Shinumo
Flight-free Zone.

The second part was to establish additional aircraft noise limitations
to further reduce the impact of aircraft noise on the GCNP environment. 
The NPRM proposed to divide air tour aircraft into three categories
according to their level of noise efficiency, as measured by the
relationship between the certificated noise level of the aircraft and
the number of passenger seats on the typical configuration of that
aircraft type.  The noise efficiency concept not only has had much in
common with the FAA’s historic approach to aircraft noise standards
but also supported the theme that the use of quieter, larger aircraft
would provide a two-fold benefit.  The replacement of a tour aircraft
with a larger, more noise efficient aircraft would both reduce the noise
of each operation and reduce the number of air tour operations while
still accommodating the same number of passengers.  This theme is in
accord with the FAA’s general policy of using cumulative aircraft
noise as an appropriate measure of potential impacts accounting for the
number of flights and intensity of their noise.  The FAA began to
explore a noise efficiency approach as an incentive for operators to
utilize aircraft equipped with the best available noise abatement
technology in the GCNP.  Additionally, the NPRM would have phased-out
the use of the least noise efficient aircraft.  The NPRM defined the
three categories of noise efficiency as, Category A, the least noise
efficient; Category B, more noise efficient than Category A; and,
Category C, the most noise efficient.

The third element was to minimize or eliminate the impact of the
aircraft cap on operators using the quietest aircraft in the GCNP by
lifting the immediate temporary cap placed on the number of aircraft
permitted to be used for commercial sightseeing operations in the GCNP
for Category C air tour aircraft, the most noise efficient aircraft. 
The intended goal of the 1996 NPRM requirements was to reduce the impact
of air tour aircraft noise in the GCNP and to assist the NPS in
achieving the statutory mandate to provide for the substantial
restoration of natural quiet and experience in the GCNP.

	The FAA’s findings and recommendations were presented in full detail
in the publication of the NPRM.  Following the publication of the NPRM,
as well as a number of other related rulemakings at the end of December
1996, the FAA and NPS jointly agreed that the best approach to
substantially restore natural quiet in GCNP was to devote their
resources to the development of those final rules that addressed
critical near-term needs.  Thus, priority was given to the promulgation
of final rules on changes to the airspace over GCNP and establishment of
operational operations limitations for air tour flights.  The agencies
delayed work on the final rule for noise limitations until the airspace
and operations limitation final rules were promulgated.  They once again
began workingfocused on the quiet technology rulemaking immediately
following publication of the final rulesas soon as the airspace and
operations limitation final rules were published in April 2000.

Related Federal Rulemaking and Policies since 1996

On Feb. ruary 26, 1997, the FAA published a final rule (62 FR 8862) that
amended the effective date of modifications to the GCNP SFRA that were
codified in an earlier final rule published on December 31, 1996.  This
action delayed the effective date for 14 CFR Sections 93.301, 93.305,
and 93.307 of the final rule and reinstated portions of and amended the
expiration date of SFAR No. 50–2.  

On May 15, 1997, the FAA published an NPRM (62 FR 26902; Notice 97-6),
which proposed to amend two of the Flight-Free Zones within the GCNP by
establishing two corridors through the Flight-free Zones.  The first
corridor through the Bright Angel Flight-free Zone would have been an
incentive corridor to be used only by the most noise efficient aircraft.
 The second corridor in the Toroweap/Shinumo Flight-free Zone through
the National Canyon area would create a marketable air tour route in the
central section of the Park while addressing some concerns of the Native
Americans.  

On October 31, 1997, the FAA published a notice of clarification (62 FR
58898) to set forth its reevaluation of the economic and environmental
impacts associated with the Special Flight Rules in the Vicinity of
Grand Canyon National Park (GCNP) Final Rule, published on December 31,
1996.  After implementation of certain provisions of the final rule, the
FAA discovered that it had underestimated the number of commercial air
tour aircraft operating in GCNP in 1995.  The FAA reevaluated the
economic and environmental analyses completed for the final rule in
light of this new information.  The FAA determined that the changes were
not of such magnitude as to affect the Agency’s position on the
implementation of the final rule.

On July 15, 1998, the FAA published a supplemental amendment (63 FR
38232) to the NPRM Notice 96-15 published on December 31, 1996, which
proposed to establish noise limitations for certain aircraft operating
in the vicinity of GCNP.  Specifically, the FAA removed two sections
from the 1996 NPRM that proposed to establish a corridor in the
Toroweap/Shinumo Flight-free Zone through the National Canyon area as an
incentive route for quiet technology aircraft.  The FAA, in consultation
with the NPS, removed these two sections from the NPRM because the
agencies determined not to proceed with an air tour route in the
vicinity of National Canyon and instead were considering alternatives to
this route.  Comments submitted by the air tour operators, the
environmentalists, and the Native Americans led the 2 two agencies to
conclude that the National Canyon air tour route was not a viable
option.  The supplemental amendment did not affect any other provisions
contained in the 1996 NPRM.  At the same time, the FAA withdrew NPRM
Notice 97-6, which had proposed 2 quiet technology incentive corridors
in the Park (63 FR 38233).

On January 26, 1999, the NPS published a public notice of agency policy,
“Evaluation Methodology for Air Tour Operations Over Grand Canyon
National Park” (64 FR 3969).  The intent of the notice was to solicit
comments on refinements to NPS’ noise evaluation (i.e., impact
assessment) methodology for air tour operations over GCNP. 
Specifically, the refinements contemplated a two-zone system for
assessing impacts related to substantial restoration of natural quiet at
GCNP.  In Zone One, which would encompass about one-third of the
Park’s area, the threshold of noticeability previously used in noise
modeling for environmental analyses related to GCNP air tours would
continue to be used (i.e., the average A-weighted natural ambient level
plus 3 decibels).  In Zone Two, which would encompass about two-thirds
of the Park’s area, the threshold for the onset of impact would be
audibility (i.e., the level at which aircraft can begin to be heard by
people with normal hearing, determined to be 8 decibels below the
average A-weighted natural ambient level at GCNP).  Because the noise
model used to assess air tour overflight noise in the park is based upon
A-weighted data, the adjustments of +3 and –8 dB are the respective
conversion factors related to the thresholds of noticeability and
audibility in terms of the noise frequency on the one-third octave band.
 This noise assessment methodology became effective on July 14, 1999 (64
FR 38006).

On July 9, 1999, the FAA published an NPRM to modify the dimensions of
the GCNP SFRA (64 FR 37296; Notice 99-11).  At the same time, the FAA
proposed a rulemaking (64 FR 37304; Notice 99-12) to limit the number of
commercial air tours that may be conducted in the GCNP SFRA and to
revise the reporting requirements for commercial air tours in the SFRA. 
A final rule was published on April 4, 2000 (65 FR 17708).  The final
rule enables the FAA and the NPS to limit and further assess the impact
of aircraft noise on the GCNP.  In addition, this rule adopts
non-substantive changes to 14 CFR part 93, subpart U to improve the
organization and clarity of the rule.  The rule temporarily limits
commercial air tours in the SFRA at the level reported to the FAA by the
operators for the year May 1, 1997–April 30, 1998 (the base year),
pending implementation of the comprehensive noise management plan. 
During the implementation of the commercial air tour limitation, the FAA
and the NPS will collect further information regarding commercial SFRA
operations and aircraft noise in the GCNP.  The NPS and the FAA will use
the information collected during this time to determine whether the
“substantial restoration of natural quiet” had been achieved at the
GCNP.  In the event that the agencies determine that the statutory goal
is not met through the various noise mitigation techniques adopted, the
FAA and NPS will need to take further steps to achieve the substantial
restoration of natural quiet.  This could mean that the commercial air
tour limitation will become permanent and/or that commercial air tours
will be further limited.  The commercial air tour limitation replaces
the current aircraft cap set forth in § 93.316(b).

On April 4, 2000, the FAA also published a final rule (65 FR 17736)
modifying the airspace in the SFRA.  This rule went into effect on April
19, 2001.  

The National Parks Air Tours Management Act of 2000

The National Parks Air Tour Management Act of 2000 (the Air Tour Act)
was enacted on April 5, 2000, as Title VIII of Public Law 106–181
(Pub. L. 106–181).  The Air Tour Act applies to ‘‘commercial air
tour operations’’ occurring over a unit of the national park system
or tribal lands within or abutting a national park.   Section 804 of the
Air Tour Act states that within 12 months after the date of its
enactment (April 5, 2000), the Administrator shall designate reasonably
achievable requirements for fixed-wing and helicopter aircraft necessary
for such aircraft to be considered as employing quiet aircraft
technology for purposes of this section.  If the Administrator
determines that it is not possible to make such designation before April
5, 2001, the Administrator shall transmit to Congress a report on the
reasons for not meeting such time period and the expected date of such
designation.  Additionally, Congress mandated that once such a
designation had been made, those commercial air tour operators who
employ quiet aircraft technology shall not be subject to the operational
flight allocations at Grand Canyon National Park, "...provided that the
cumulative impact of such operations does not increase noise at Grand
Canyon."   Finally, the Air Tour Act also directsed that "...the
Administrator shall establish, by rule, routes or corridors for
commercial air tour operations...by fixed-wing or helicopter aircraft
that employ quiet aircraft technology..." at Grand Canyon National Park,
"...provided that such routes or corridors can be located in areas that
will not negatively impact the substantial restoration of natural quiet,
tribal lands, or safety."

National Parks Overflights Advisory Group (NPOAG)

	On March 12, 2001, the NPS and FAA in accordance with the Air Tour Act,
invited persons interested in participating on the NPOAG to send a
letter to the FAA by April 2, 2001 (66 FR 14429).  The NPOAG membership
was announced on June 19, 2001 (66 FR 32974).

In accordance with the Air Tour Act, the advisory group will provide
advice, information, and recommendations to the Administrator and the
Director—

(1) On the implementation of this title [the Air Tour Act] and the
amendments made by this title;

(2) On commonly accepted quiet aircraft technology for use in commercial
air tour operations over a national park or tribal lands, which will
receive preferential treatment in a given air tour management plan;

(3) On other measures that might be taken to accommodate the interests
of visitors to national parks; and

(4) At the request of the Administrator and the Director, safety,
environmental, and other issues related to commercial air tour
operations over a national park or tribal lands.

	The Air Tour Act also requires FAA to consult with the advisory group
and the NPS on the establishment of routes or corridors for commercial
air tour operations by fixed-wing and helicopter aircraft that employ
quiet aircraft technology for--

(1) tours of the Grand Canyon originating in Clark County, Nevada; and

(2) `local loop' tours originating at the Grand Canyon National Park
Airport, in Tusayan, Arizona.

GCNP Aircraft Noise Model Validation Study

The noise modeling used in all of the GCNP environmental documents to
date, remains the best science currently available and produces results
consistent with available data.  However, as noise modeling is a
constantly evolving technology, both agencies are committed to making
appropriate adjustments to the approaches and methodologies as new
knowledge or science becomes available.  In 1999, the NPS and the FAA
jointly funded a noise model validation study to determine the degree of
accuracy and precision of existing computer models.  This study compares
the existing candidate models of for assessing air tour noise exposure
with noise measurements taken in GCNP.  The ongoing noise model
validation effort is part of the FAA and NPS commitment to work
cooperatively to meet the mandated goal of a substantial restoration of
natural quiet in GCNP.  The final results of this project, when they
become available, could have an effect on both the determination of
substantial restoration of natural quiet already achieved and in the
evaluation of alternative means of implementing quiet technology.  

The candidate models being validated are:

The FAA’s Integrated Noise Model, which has been modified to address
air tour aircraft noise exposure in GCNP and is referred to as the GCNP
Integrated Noise Model (GCINM).

The NPS’s National Park Service Overflight Decision Support System
(NODSS) designed and programmed specifically for park applications where
audibility, significant changes in terrain elevation, and shielding due
to terrain must be addressed.

NOISEMAP Simulation Model (NMSIM) developed by the US Air Force and the
National Aeronautics and Space Administration (NASA) to simulate
aircraft single event noise levels.

As part of the Noise Model Validation Study efforts, the agencies
jointly formed the Technical Review Committee (TRC) to review and
comment on various technical issues that may arise related to the
measurement, quantification and analysis of soundscapes.  The TRC is
composed of 8 acoustics and statistical experts from academia, private
companies, and government agencies.  

Environmental Review 

	In accordance with FAA Order 1050.1D, Appendix 4, Paragraph 4.j, the
FAA has determined that this proposed rulemaking is categorically
excluded from environmental review.  The proposed rulemaking establishes
quiet technology designations for air tour aircraft operating in GCNP. 
It does not impose a phase-out or any alteration of any air tour
operator’s fleet of aircraft.  In addition, the proposed rulemaking
does not lift the operations limitation, alter any flight corridors
through the Park, or make any change to the SFRA.  Finally, the FAA
notes that this proposed rulemaking has no impact on substantial
restoration of natural quiet at GCNP and environmental and economic
impacts will depend upon other future incentives yet to be defined. 
Accordingly, this proposed rulemaking will not individually or
cumulatively have a significant effect on the human environment.  

	The FAA has determined that this proposal does not instigate any
adverse environmental effects, which would require the preparation an
environmental assessment (EA) for this rulemaking effort to assure
conformance with the National Environmental Policy Act of 1969 (NEPA). 
As directed by the Air Tour Act, this proposal does not “relieve or
diminish-- (1) the statutory mandate imposed upon the Secretary of the
Interior and the Administrator of the Federal Aviation Administration
under Public Law 100-91 (16 U.S.C. 1a-1 note) to achieve the substantial
restoration of the natural quiet and experience at the Grand Canyon
National Park.”  The reasoning behind the FAA determination include: 

The proposal simply establishes quiet technology designations for air
tour aircraft operating in the Park.  It does not impose a phaseout or
any alteration of any air tour operator’s fleet of aircraft.

The proposal does not lift the operational cap, alter any flight
corridors through the Park, or make any change to the SFRA.

	As the eventual goal of this proposed rulemaking is the substantial
restoration of natural quiet in the GCNP, the FAA has conducted some
analyses to assess potential progress towards the goal.  The FAA
analysis included the use of the GCINM and with data input from the
preferred alternative operational scenario found in the February 2000
Final Supplemental Environmental Assessment.  The analysis found that by
replacing the entire current fleet of air tour aircraft that do not meet
the quiet technology designation with equipment meeting the designation,
almost 58% of the park area would achieve substantial restoration of
natural quiet on an average annual day.  By comparison, the mixed fleet
used for the calculations in the 2000 assessment achieved about 44%
substantial restoration for an annual average day.  This estimate
provides a relative measure of the gains that might be achieved with the
one-for-one conversion to quiet technology aircraft.  

Consultation with Affected Indian Tribes

	Six Native American communities represented by eight separate tribal
governments have ancestral ties to the Grand Canyon.  Three of these
communities have reservations that border the GCNP, the Navajo Nation to
the east, and the Havasupai and Hualapai Tribes to the south.  The
Department of Transportation (DOT), FAA, DOI, NPS, Advisory Council on
Historic Preservation (ACHP), Bureau of Indian Affairs (BIA), and
Arizona State Historic Preservation Officer (SHPO) have consulted with
these tribes, on a government-to-government basis,The Department of
Transportation (DOT) and the DOI have consulted with these tribes, on a
government-to-government basis, according to the provisions of the NEPA,
the National Historic Preservation Act (NHPA), and the Council on
Environmental Quality (CEQ) regulations and other applicable laws and
Executive Orders.  

	In accordance with Section 106 of the NHPA, the FAA issued a
Determination of No Adverse Effect to the Traditional Cultural
Properties (TCPs) for all of the tribes and/or nations, except the
Hualapai Tribe, for the April 2000 rulemaking actions associated with
the SFRA in the vicinity of the GCNP.  As to the Hualapai Tribe, the FAA
along with the NPS, the Advisory Council on Historic Preservation, the
Hualapai Tribal Historic Preservation Officer (THPO) and the Hualapai
Department of Cultural Resources signed a Programmatic Agreement on
January 24, 2000 related to Section 106 compliance and their TCPs.As to
the Hualapai Tribe, the FAA along with the NPS, the Advisory Council on
Historic Preservation and the Hualapai Department of Cultural Resources
signed a Programmatic Agreement on January 24, 2000 related to Section
106 compliance and their TCPs.  

	Due to new safety concerns raised by the Air Tour Operators related to
the proposed route and airspace modifications on the East End of the
SFRA, only those modifications from west of the Dragon Corridor were
implemented on April 19, 2001.  In accordance with Section 106 of the
NHPA, if significant modifications are proposed for the East End
commercial air tour routes and airspace related to address the new
safety concerns, raised are proposed for the East End, consultation with
the Navajo Nation and the other interested Native American tribes,
specifically the Hopi Tribe and Pueblo of Zuni will be
re-initiatednotified.  

Public Input

	The FAA has reexamined the December 1996 proposal in light of the
direction provided in Section 804 of the Air Tour Act.  Under the
mandate, the Administrator shall designate reasonably achievable
requirements for fixed-wing and helicopter aircraft necessary for such
aircraft to be considered as employing quiet aircraft technology for
purposes of this section.  The proposed quiet technology designations
require air tour aircraft to be categorized according to each aircraft's
noise efficiency.  The eventual goal is to assist the National Park
Service (NPS) in achieving its statutory mandate imposed by Public Law
100-91 to provide for the substantial restoration of natural quiet and
experience in the GCNP.  This proposed rulemaking is related to and
consistent with other rulemaking actions being implemented by the FAA
concerning the GCNP.

	In addition, the SNPRM does not propose to implement the provision of
the National Parks Air Tour Management Act of 2000 that would permit a
lifting of the cap on commercial sightseeing air tour operations in the
Park.  The implementation of any quiet technology incentive flight
corridors and the removal of operations limitation for quiet technology
aircraft will be the subject of future rulemaking as the FAA, in
consultation with the NPS, works with an advisory group composed of
representatives of general aviation, commercial air tour operations,
environmental concerns, and Indian Tribes.  

	The SNPRM also serves to disposes of the comments that had beenwere
received in response to the December 1996 NPRM (61 FR 69334).  The 1996
NPRM proposed to establish noise limitations for certain aircraft
operated in the vicinity of Grand Canyon National Park.  The 1996
proposal had three parts: (1) incentive flight corridor through the
National Canyon, (2) categorize aircraft by noise efficiency, and (3)
removal of the aircraft cap for the most noise efficient aircraft.

	The first part of the 1996 proposal provided an incentive for the use
of noise efficient aircraft within the GCNP by establishing a National
Canyon Corridor within the newly expanded Toroweap/Shinumo Flight-free
Zone.  This SNPRM does not propose any incentive corridors.

	The second part of the 1996 proposal divided aircraft into three
categories according to their level of noise efficiency and proposed to
phase-out aircraft in the two least noise efficient categories
(Categories A and B).  Category A is the least noise efficient, Category
B is more noise efficient than Category A, and Category C is the most
noise efficient.  This SNPRM drops proposes to replace the three
categories and proposes to designate as quiet technology those aircraft
that comply with what was formerly described as Category C, the most
noise efficient category.  

	The third part of the 1996 proposal lifted the cap placed on the number
of aircraft permitted to be used for commercial sightseeing operations
in GCNP for the most noise efficient aircraft (Category C).  This SNPRM
does not include this part of the 1996 proposal as explained in a later
section of this notice.

	Interested persons were invited to participate in this the rulemaking
action by submitting written data, views, or argumentscomments.  The
comment period for the NPRM closed March 31, 1997.  The comment period
for the draft Environmental Assessment also closed on March 31, 1997. 
In response to the NPRM the FAA received 107 comments.  All comments
received were considered before issuing this SNPRM.  An analysis of the
comments is summarized below. 

	The comments presented in the subsections below were to the December
1996 NPRM.  As one of the purposes of this SNPRM is to dispose of the
1996 comments, the FAA responses take into account related Federal
actions since 1996.  Commenters include air tour operators and their
representatives, environmental groups, sightseeing organizations, Native
American tribes, pilots and pilot associations, and individuals.  Most
commenters do not support some or all aspects of the proposal. 
Generally, air tour operators who do not currently operate quiet
aircraft are against a phase-out of noisier aircraft as proposed in
1996; one Native American tribe is was against the 1996 proposal to
reintroduce a flight route through the National Canyon; while
environmental organizations argue that by itself the 1996 proposal would
not adequately restore the natural quiet to GCNP.

1.  General Comments on Proposal

	The FAA received a number of general comments on the NPRM, including
comments related to statutory issues, procedural complaints, and
environmental concerns.  Eagle Canyon Airlines (Eagle) (54), Vision Air
(Vision) (61), and King Airlines, Inc. (King) (56) state that the NPRM
failed to state the basis for the FAA's statutory authority for the
proposed rulemaking.  They state that the FAA cited the Overflights Act
as part of the statutory authority for the NPRM but that the final rule
(December 31, 1996) did not cite the Overflights Act as statutory
authority.

	These three commenters state that the Overflights Act gave the FAA the
legal authority to issue SFAR 50, but not to take further action beyond
that.  These commenters also state that the FAA's cited authority from
the FAA Act does not give the FAA authority to protect "environmental
values" or to promulgate a noise management plan.

	The Helicopter Association International (HAI) (63) states that the
proposals are arbitrary and capricious because unbiased data demonstrate
that natural quiet has been restored at GCNP and air tour aircraft
currently operating at GCNP are fully certificated by the FAA and in
compliance with all applicable FAA safety and operating regulations.

	The General Aviation Manufacturers Association (GAMA) (64) states that
the NPRM does not contain the necessary scientific data or
substantiation to prove that the proposal will accomplish its goal. 
GAMA believes that basing a rulemaking on a broad and indefinite range
of terms and objectives, such as "interference" or "annoyance" of
visitors and "substantial restoration of natural quiet," is subjective
and arbitrary.   GAMA fears that introducing noise limitations and
forced attrition for aircraft presently operating in the vicinity of
GCNP could be the beginning of a process that could progressively tear
down the entire U.S. aviation system.  GAMA believes that, if FAA's
strategy were applied to the vast holding of federal lands, federal
parks, state lands and state parks, it would severely impact the use of
general aviation aircraft and some commercial airliners as well. 

	Twin Otter (45) believes that quiet technology is the solution to the
problem of achieving substantial restoration of natural quiet to the
GCNP.  However, the alternative, caps, curfews and ever more limitations
on how air tours can be conducted, is totally unacceptable.

	Lake Mead Air (26, 53) suggests that protecting the park experience
from noise will be more effectively accomplished by routing traffic away
from the park visitors than by use of quiet technology and altitude.

	Clark County Department of Aviation and the Las Vegas Convention and
Visitors Authority (Clark County) (62) believe that the piecemeal nature
of the FAA's Grand Canyon rulemaking makes it impossible for the public
to meaningfully comment on the proposals.  Clark County suggests that
the FAA propose its entire Grand Canyon strategy -- flight-free zones,
tour routes, quiet aircraft requirements, and other measures -- as one
package, so that the public can assess the best overall program.

	The United States Air Tour Association (USATA) (60) states that all of
the various regulatory actions being implemented by the FAA should be
combined into a single rulemaking effort to ensure that all the relevant
issues are addressed as an integrated whole.

	Bell Helicopter Textron (91) and the Professional Helicopter Pilots
Association (85) believe that there are substantial issues in
controversy in this proposal, which should necessitate the use of
negotiated rulemaking by means of the Aviation Rulemaking Advisory
Committee (ARAC) process.

	The Sierra Club, Angeles and Grand Canyon Chapters (38, 75, 76),
opposes the permissive growth of the air tour industry in the GCNP.  The
level of flight operations should be reduced to the levels, which
existed in the Park in 1975.

	The Sierra Club, Grand Canyon Chapter, believes that the Noise
Limitations NPRM can be part of an acceptable plan, but would not by
itself substantially restore natural quiet at GCNP.  The proposal would
not bring GCNP into compliance with the Overflights Act, nor would it
bring the park into compliance with the management objectives of the
GCNP General Management Plan.  Furthermore, the proposal would not
implement the actions directed by President Clinton in his Earth Day
memorandum (April 1996).  The Overflights Act directs the FAA to
implement the recommendations of the NPS, revised only for safety.  The
FAA has ignored the law in this regard and continues to promote the air
tour industry.

FAA response

		The Overflights Act charged the FAA, in concert with the DOI, to enact
rulemaking and take what action is necessary to substantially restore
the natural quiet and experience of our national parks, and to protect
the public health and safety from adverse effects associated with
overflights.   This mandate imbued the FAA with the necessary authority
to carry out any measure recommended by the NPS that did not have safety
issues and was necessary to effect the substantial restoration of the
natural quiet and experience, which is an NPS designated “resource or
value” of the park, and to protect the public safety.  The practical
effect of this second requirement is the implementation of operational
rules for aircraft that facilitate the safe overflight of the Grand
CanyonGCNP.  In accordance with the Air Tour Act, the FAA has
established the NPOAG to provide advice and counsel on the
implementation of quiet aircraft technology at Grand CanyonGCNP.

	The FAA agencies acknowledges that the SNPRM on noise, alone, is
inadequate to accomplish its stated goal and mandate under the
Overflights Act.  It is for this reason that the FAA has adopted rules
to enhance flight free zones, modify the route structure, and limit the
number of air tours in GCNP.  

2.  Natural Quiet

	A number of commenters address the question of whether the proposals
would contribute to the substantial restoration of natural quiet in the
GCNP.  Grand Canyon Trust (Trust) (72) makes the following general
observations:

	(1) Whatever regulatory scheme is ultimately implemented, that scheme
must comply with the Overflights Act and that NPS, not the FAA, must
determine whether and when natural quiet is substantially restored.

	(2) The FAA must implement rules that immediately restore natural quiet
to the canyon.

	(3) The proposed rule must be substantially revised and strengthened
because it will permit an immediate degradation of natural quiet.

	(4) Any revisions will have to include an immediate conversion to the
quietest aircraft and a cap on the number of tour operators at well
below the 1987 level.

	The Sierra Club, Grand Canyon Chapter (76), states that the
detectability level (D'L) for defining natural quiet should be less than
5, rather than 17, which is used by NPS.  The higher criterion shows an
unrealistic prevalence of natural quiet.  Furthermore, the definition of
"substantial restoration of natural quiet" is flawed.  A more
appropriate definition would require natural quiet all of the time in
most of the park, and would require natural quiet most of the day in the
rest of the park.  Congress mandated action to restore natural quiet and
to reduce negative impact from aircraft.  The FAA and NPS policy of
ignoring the effects of all aircraft except tour aircraft is
inappropriate.

	HAI (63) states that banning some aircraft is not necessary to achieve
"restoration of natural quiet" in GCNP, even when natural quiet is
measured in the terms used by the NPS.  HAI points out that the FAA's
Draft Environmental Assessment (DEA), which accompanied the December
1996 NPRM, states that natural quiet at GCNP is within 1% of the NPS's
goals without the imposition of any aircraft ban.  HAI also believes
that, in estimating aircraft operational and performance data, the FAA
used inaccurate data and incorrect assumptions, thereby substantially
overestimating the sound generated by the aircraft used in tour
operations at GCNP.  HAI further states that the FAA substantially
underestimated the degree to which natural quiet has been restored under
SFAR 50-2, and that, if the impact of aircraft overflight sound is
measured in terms of visitor experience at GCNP, the data demonstrate
that natural quiet has been restored to the Park.  HAI believes that the
FAA's aircraft sound prediction model substantially underestimates
ground attenuation effects and that FAA estimates of ambient sound at
GCNP are unrealistically low.  

	Bell Helicopter Textron (91) states that the ambient noise projections
assigned to different areas of the Park are unrealistically low.  This
has the resultant effect of greatly overstating how long the aircraft's
sound is detectable.  Equally as damaging as this unrealistic projection
is the assumption that there is no lateral attenuation of aircraft sound
in the Grand Canyon.   Such false assumptions understate the substantial
restoration of natural quiet that currently exists in the GCNP.

	Clark County (62) comments that the FAA has provided no adequate basis
to demonstrate the reasonableness of the defined "natural quiet" goal. 
Further, the FAA's "time audible" metric does not reasonably measure
natural quiet.  Clark County also states that the models used to
estimate aircraft audibility have not been adequately explained and may
overstate the extent to which aircraft can be heard.

FAA Response: 

Since the issuance of the 1996 NPRM, the NPS published a public notice
of agency policy (64 FR 3969) titled Evaluation Methodology for Air Tour
Operations Over Grand Canyon National Park.  The policy refined the
NPS’ noise evaluation (i.e., impact assessment) methodology for air
tour operations over GCNP.  Specifically, the refinements included a
two-zone system for assessing impacts related to substantial restoration
of natural quiet at GCNP. 

The ongoing noise model validation effort is also part of the FAA and
NPS commitment to work cooperatively to meet the mandated goal of a
substantial restoration of natural quiet in GCNP.  The noise modeling
used in all of the GCNP environmental documents to date, remains is the
best science currently available.  However, as noise modeling is a
constantly evolving technology, both agencies are committed to making
appropriate adjustments to the approaches and methodologies as new
knowledge or science becomes available.

With regard to the ambient noise database and the lateral attenuation
calculation, the GCNP aircraft noise model validation project will
address these facets.  All existing evidence, including field
measurements, support both the choice of an ambient noise level data
file for the Park and the decision to suppress INM's lateral attenuation
algorithm for GCNP noise modeling.

3.  Native American Tribal Concerns 

	The Hualapai Tribe (52) states that it supports the use of quiet
technology and generally supports the NPRM with the following
exceptions:  (1) the FAA has failed to consult with the Hualapai Tribe
on a government-to-government basis as required by federal law, (2) the
multiple rulemakings published by the FAA on the GCNP make the comment
process more cumbersome, more expensive and obscures the cumulative
impact of the respective parts of the rulemakings, (3) there has been a
double standard with respect to testing noise impact since no
on-the-ground noise testing and modeling has been undertaken with
respect to the Hualapai Reservation, in collaboration with the Tribe,
(4) the FAA needs to look at alternatives to quiet technology such as
location of air tour routes and caps, (5) there need to be  "Tribal
Flight Free Zones" to protect cultural resources and practices, natural
resources, and tourism industry, as well as limitations on the number of
NPS flights over the Hualapai Reservation, (6) the FAA should delegate
to, or share with, the Hualapai Tribe oversight authority to make sure
that the quiet technology rules are being complied with over the
Reservation, and (7) there needs to be an exemption from quiet
technology requirements for tribal administrative flights, analogous to
the NPS exemption, to avoid burdening the Tribe's sovereign authority to
run its own government and administer its lands.

FAA Response:

The FAA has been consulting with the Hualapai in accordance with the
provisions of the President's April 24, 1994, memorandum on
Government-to-Government Consultation with Native American Tribes and
Section 106 of the NHPA.  The FAA has had numerous meetings with
representatives of the tribe’s natural resources and cultural
resources agencies since 1996.  Additionally, the Hualapai have been
part of the FAA and the NPS ongoing discussions with the other
individual tribes.  The Hualapai have also commented on several issues
that have been addressed in previous rulemaking and were a cooperating
agency on the February 2000 Final Supplemental Environmental Assessment.
 

Concerning the flight-free zones over the Hualapai Reservation, although
the Overflights Act does not expressly prohibit creation of flight free
zones over the reservation, the Congress instructed the FAA to accept
the recommendations of the NPS for substantially restoring natural quiet
in the GCNP, unless safety was at issue.  Moreover, with few exceptions,
the general policy of the United States is that the skies should be
generally open to aviation.  Further, the routes over the Hualapai have
developed under this general policy of open skies since the 1920s.  The
FAA began to document the de facto routes and established an SFAR in
1987.    In light of the broad Federal policy favoring open skies, the
FAA does not intend to create broad flight-free zones over the Hualapai
reservation.  Rather, the FAA can reduce effects of air tour operations
through a number of other means, including but not limited to the
introduction of quiet technology, the alignment and altitude of routes,
and the number and time of operations.  The FAA removed the National
Canyon route from the routes notice consideration, in July 1998, in
response to comments.

In accordance with Section 106 of the NHPA, the FAA issued a
Determination of No Adverse Effect to the Traditional Cultural
Properties (TCPs) for all of the tribes and/or nations, except the
Hualapai Tribe, for the rulemaking actions associated with the SFRA in
the vicinity of the GCNP.  As to the Hualapai Tribe, the FAA along with
the National Park ServiceNPS, the Advisory Council on Historic
Preservation, the Hualapai THPO, and the Hualapai Department of Cultural
Resources signed a Programmatic Agreement on January 24, 2000 related to
Section 106 compliance and their TCPs.  Concerning the flight-free zones
over the Hualapai Reservation, with few exceptions, the general policy
of the United States is that the skies should be generally open to
aviation.  The FAA removed the National Canyon route from the routes
notice consideration, in July 1998, in response to comments.

In response to the request for an exemption to conduct administrative
flights, the FAA reiterates that this and other rulemakings and affect
only flights satisfying the definition of a commercial air tour
operation contained in 14 CFR §93.303.  Moreover, this rule does not
phase-out aircraft that do not meet the designation as quiet technology.
 The FAA encourages the Hualapai, and other government agencies that use
public aircraft, to use quiet technology.

4.  Classification of Aircraft by Noise Characteristics

	A number of commenters address the issues related to classification
based on aircraft certification, as well as the 3 categories of aircraft
classification.  

	Lake Mead Air (26, 53) believes that the standard for quiet aircraft
should not be linked to the Aircraft Noise Certification provisions
prescribed in 14 CFR part 36, and listed in AC 36-1F, since it is
possible for aircraft to be reconfigured and flown differently than AC
36-1F.  The FAA should make sound measuring equipment available at Las
Vegas and Grand Canyon for determining actual flyover sound levels in
the tour "cruise configuration."  If Category A aircraft can be
retrofitted to Category B it should be encouraged since such a
conversion would be more easily implemented than direct conversion to
Category C.

	Clark County Department of Aviation and the Las Vegas Convention and
Visitors Authority (Clark County) (62) states that the NPRM will
unreasonably and arbitrarily burden air tour operators and the Las Vegas
tourist economy.  However if the FAA based its categorization of
aircraft on noise performance, rather than on certification, and
provided options for compliance flexibility, there would be
significantly less burden on tour operators, airborne visitors, and the
economy of the Las Vegas area.  Clark County states that it conducted a
study of actual ambient and aircraft noise in GCNP in an attempt to
validate FAA's methodology and found that using certification data, as a
basis does not accurately represent aircraft noise levels in the GCNP,
because it does not account for actual atmospheric and operational
conditions in the GCNP.  As a result, the FAA has placed aircraft in the
noisier A or B Categories that should belong in the B or C Categories. 
Clark County states that the NPRM provides no means for operators to
comply with the performance standards through the use of retrofitted
equipment, quiet operating procedures, or other enforceable steps to
reduce noise.  This is at odds with the Federal government's increasing
attempt to use performance standards and provide compliance flexibility
to reduce regulatory burden.

	An airline transport pilot (40) states that the noise propagation of a
propeller driven airplane is largely dependent on the design and speed
of its propeller.  Design and speed are responsible for a greater share
of the decibel level discernible in the hearing range than exhaust
output, wing shape, loading of the airplane, cowl and airframe
vibration, or accessory operation (e.g., flap extension, gear drag and
parasitic friction).  Since the design and speed factors affect all
aircraft operating in the Grand Canyon a simple change, for example,
operating a Cessna 207 at 2300 RPM instead of 2400 or 2500 RPM, can
affect whether an aircraft should be placed in one category or another,
if the categories are defined by noise values.  

	Lake Mead Air (26, 53) states that the decibel range for quiet Category
C helicopters starts at 80dB whereas the fixed wing threshold is 69dB. 
If 80 dB meets Category C standards for helicopters it should also meet
Category C standards for fixed wing.

	Eagle (54) states that its F27 aircraft would not be covered under the
NPRM.  Size (48 passenger), noise tests, and decibel adjustments do not
take the F27 into consideration.

	Professional Helicopter Pilots Association (85) states that the
existence of aircraft capable of achieving the lower sound levels is
still in the developmental stage such that only one manufacturer has any
such helicopters available which have the performance capability for air
tour operations.  As a result the NPRM is premature and should not be
implemented until technology improves.

	The Grand Canyon River Guides (GCRG) (50) state that helicopters, which
are generally accepted to be the most obnoxious of aircraft and carry
fewer people, should not fall into Category B, but should be put into
Category A.

	Twin Otter (45) states that it is appropriate to take into account both
the flyover sound level and aircraft passenger seating capacity in
establishing which models qualify as Category C aircraft because a
single Vistaliner replaces two flights with the nine passenger Cessna
402/Piper Chieftain, nearly three flights in the seven passenger Cessna
207 and four flights in the 4-5 passenger Bell Jetranger.

	Twin Otter adds that the Beechcraft C-99 and the Piper Chieftain could
be retrofitted with four bladed props, as have the Vistaliners, thus
converting them to Category C aircraft.

	Air Vegas (57) believes that its 15 Beechcraft C-99 aircraft should be
deemed Category C since it utilizes the same basic power plant, the
PT-6, as the Caravan and the Vistaliner, and has been modified for
sightseeing operations to include extra windows.  The average price for
these aircraft, configured to meet Air Vegas specifications, is in
excess of $1,300,000.  These aircraft are adequately available and have
proven to be cost effective.  Furthermore, the FAA studies, which placed
the Beechcraft C-99 into Category B, were based on max RPM level 2200
RPM.  If the RPM is reduced to 1900 (a reduction of 14%), there is an
equal reduction of 14% in the dB level of the propeller, thus 68.2 dB. 
Air Vegas operations specifications require pilots to maintain propeller
RPM at 1900 and with this power setting a Beechcraft C-99 is well below
the Category C cut off of 78 dB for a 15 passenger aircraft.  Air Vegas
believes there should be an incentive for decreasing the percent of time
audible for the aircraft.  Because of the higher speeds achievable by
the Beechcraft C-99, as compared to the Vistaliner, the C-99s have an
impact for less time.

	Scenic Airlines (74) states that the deHavilland DHC-6-300 Twin Otter
with quiet propellers and the Cessna 208 (A & B models) must be
classified as quiet aircraft technology (Category C).  Furthermore, in
developing Sound Exposure Level (SEL) dB limits, consideration must be
given to the speed of an aircraft.  Since disruption of natural quiet is
measured in terms of "Time of exposure" the faster of two aircraft with
the same dB output should be shown as the quieter.

	The Grand Canyon Trust (72) states that by defining the aircraft
categories in terms of sound exposure level per passenger seat, the FAA
obscures the fact that some Category C aircraft (e.g., the Vistaliner)
are noisier than some Category A or B aircraft.  The Trust further
states that unless a cap is established on the number of operations
Category C can fly, ultimately there will be no advantage to conversion
to certain Category C aircraft.  Therefore, the Trust's additional
comments assume that such a cap will be implemented.

	Clark County (62) states that the FAA should set default noise levels
and GCNP noise categories for the aircraft operating in GCNP using
methodologies that accurately reflect conditions in GCNP and should
validate the noise levels through field-testing.  If this were done,
some aircraft, such as the Beechcraft C-99 would actually meet Category
C standards.

	Eagle (54), King (56), and Vision (61) state that the FAA's formulation
of the aircraft categories in the NPRM is arbitrary and capricious for
the following reasons:

	(1) The FAA fails to justify its placement of the dividing line between
categories and has not consulted operators on this issue before
establishing the categories.

	(2) Use of part 36 test results is not appropriate (see discussion
under "Links to aircraft noise certification").

	(3) The proposed 4 decibel distinction between Category A and Category
C is inappropriate since it attempts to draw distinctions that cannot be
discerned by most humans.

	(4) Distinctions between categories fail to account for the effect of
speed on aircrafts' ”noiseprint.”

	(5) Tests that serve as a certification basis do not simulate actual
operating conditions.

	(6) Categories discriminate against propeller driven airplanes.

	(7) Proposed Category C could be met by only two types of existing
aircraft, one of which is unavailable while the other is prohibitively
expensive.

	Bell Helicopter Textron (91) states that the FAA's noise analysis
incorrectly assumed that there is no lateral attenuation of aircraft
sound.  The effect of this false assumption is great considering that if
the sound exposure levels attributed to aircraft were even 5 dB less,
then up to six additional aircraft would be in compliance with the
proposed Category C noise efficiency criteria.

FAA Response:

While this SNPRM drops replaces the three noise efficiency categories
proposed in the December 1996 NPRM, the currently proposed quiet
technology designation is based upon the same rationale and criteria. 
The FAA criteria for “reasonably achievable” quiet technology
requirements include what is technologically practicable, economically
reasonable, appropriate to the aircraft type design, and, in the final
analysis, environmentally beneficial.  The FAA also set forth the
followingthat as desired attributes for the quiet technology
designation, the designation should:

Is Be based on aircraft noise certification (14 CFR part 36)

Judges fixed- and rotary-wing aircraft on a common basis

Correlates with aircraft performance and operation at GCNP

Offers basis for incentives

Is Be manageable

Levels Noise levels obtained from aircraft noise certification represent
the highest quality of data available.  The flight tests are conducted
under controlled conditions with an FAA representative or designee in
attendance to witness the test setup and test activities.  Data obtained
during these flight tests are corrected to standard reference conditions
as prescribed in 14 CFR part 36.  The certification tests are designed
to acquire noise levels representing the noisiest flight configurations
for small propeller-driven airplanes and helicopters.  FAA believes that
this is appropriate for the GCNP situation as the certification flight
configurations are also the noisiest configurations that could be used
over the park.  Thus, the sightseeing aircraft can be judged equally,
fairly, and without the concern that the noise levels are undervalued.

The airport community has many years of experience using the
certificated noise levels.  FAA publishes these levels in Advisory
Circular (AC) 36-1, "Noise Levels for U.S. Certificated and Foreign
Aircraft."  The current version of this AC is 36-1F1G, dated June 5,
1992August 27, 1997.  These data have been used to establish use
restrictions, curfews, and noise budgets at some airports in the
country.  The certificated noise levels are not only available in the
advisory circulars, which are updated and published periodically, but
the levels are readily available to the aircraft owners from the
aircraft flight manuals (AFM).

Thus tThe quiet technology designation based on certificated noise
levels is proposed not only because of the long-standing precedent, but
it also because it eliminates the need for someone to make such
measurements in the field.  Years of experience with using data obtained
from airport noise monitoring systems have shown that noise levels
obtained under uncontrolled conditions are highly variable.  This
problem can only be overcome by obtaining very large samples of measured
data to reduce the statistically uncertainty.  Thus, FAA believes that a
quiet technology designation based on measured data taken at GCNP would
be economically unreasonable and susceptible to statistical error.

Unfortunately there is no single method applicable to all aircraft for
determining the certificated noise level.  Depending on date of
application for type certificate and whether the aircraft is a
helicopter or small propeller-driven airplane, the noise level could
have been obtained from one of 4 different tests.  With measurements
taken for different flight operations, at 3 different altitudes, and in
3 different units of noise, it is not possible to directly compare
certificated noise levels obtained for helicopters with those of small
propeller-driven airplanes.  As reported in the study, "Methodology to
Categorize the Noise Efficiency of Air Tour Aircraft in GCNP," FAA
developed a procedure for: (1) extrapolating from the controlled
conditions of a certification test to the operating conditions at GCNP
and (2) converting levels to a common noise unit, thus making it
possible to judge fixed- and rotary-wing aircraft on a common basis
under conditions that pertain to air tour operations over GCNP.  As a
result of the study, FAA found that it is possible to extrapolate from
the certification conditions applicable to helicopters and small
propeller-driven airplanes to produce a consistent set of noise levels
under conditions similar to those at GCNP.

FAA finds that the noise efficiency concept, which was proposed in the
December 1996 NPRM and re-proposed in this SNPRM, albeit modified to
designate quiet technology, exhibits all of the desired attributes for
the quiet technology designation.  The concept is technically sound as
it takes into account aircraft design, flight configuration, acoustic
characteristics, productivity, and economic reasonableness.  As the
concept is based upon the certificated noise levels, the FAA is able to
judge the noise of the commercial sightseeing aircraft consistently,
fairly, and without the additional cost and technical problems found in
field monitoring.  In concert with related actions with respect to the
airspace and air tour operations, the quiet technology designation can
be an effective means toward achieve the substantially restoration
restoringof natural quiet at GCNP.

5.  Phase-Out of Less Noise Efficient Aircraft

	A number of commenters addressed the proposal to phase-out noisier
aircraft to further reduce noise impacts in GCNP.  As described in the
1996 NPRM, the less noise efficient aircraft would have been gradually
phased-out starting in the year 2000 with the phase-out of Category A
aircraft and continuing through to the end of 2008 at which point all
Category B aircraft would be phased-out and only Category C aircraft
would remain.  The phase-out would have limited future use of less noise
efficient aircraft in GCNP and would also have provided an incentive for
the use of the most noise efficient aircraft.

	Air Vegas (57) believes that from a business perspective there is no
reason for an interim conversion from Category A to Category B aircraft.
 Air Vegas supports the alternative proposal that the upgrade to
Category C should be the only choice for either new entrants or existing
operators.

	Air Vegas supports the use of incentives to encourage operators to
invest in the best available aircraft to reduce aircraft noise intrusion
and the number of flights in GCNP.  For the incentives to be of benefit
they must be available to any operator who wishes to invest in the
available technology.  The only two aircraft identified as quiet are the
Vistaliner and the Cessna Caravan.  By exclusive leasing contract the
Vistaliners are not available to any operators in the southwest area
other than Scenic and Grand Canyon Airlines.  The Cessna Caravan, a 9
seat aircraft, is not economically practicable since it costs in excess
of $1,000,000 when other 9 passenger aircraft sell for less than
$100,000.  

	Lake Mead Air (26, 53) states that the availability of used single
engine Category C aircraft is rare.  The only other aircraft listed as
fixed wing is the Raisback Conversion deHavilland Twin Otter, and the
supply is limited and the fleet is aged.

	Lake Mead Air says that conversion from Category A to Category B is
less burdensome than direct conversion to Category C.  It is possible
that simply changing propellers will convert Category A to Category B. 
Conversion of three Cessna 207 aircraft ($180,000 for 18-21 seats -
i.e., $10,000/seat) to two Cessna 208 Caravans ($2.4 million for 18
seats - i.e., $133,000/seat), for a net reduction of 5 dB, is not
sensible or cost effective.  Lake Mead Air (26, 53) believes that there
will be no noise-reduction effect of conversion to quiet aircraft.

	Lake Mead Air adds that for operators to pay the debt service on
"quieter aircraft" they may be forced to make more flights per day. 
Lake Mead points out that the Cessna T207, which seats 8 passengers,
generates the same decibels as the Vistaliner, which seats 19.  The
Vistaliner is deemed a noise efficient aircraft according to the NPRM
based on the noise per seat accounting.  However, to pay for the
Vistaliners the operators must make up to 5 or 6 round trip flights per
day.

	Papillon (55) states that conversion from Category A to Category B is
less burdensome since at the present time there is limited availability
of Category C aircraft.  With regard to helicopters the cost is higher
by approximately 20-30% for new Category C aircraft as compared with
purchasing Category B aircraft.  With used Category B helicopters
available the cost to convert to a new Category C aircraft is
approximately 125% higher compared to purchasing a used Category B. 
This commenter says that there are presently no used Category C aircraft
available for the helicopter industry.

	Papillon states that in some cases it would be sound business practice
to go directly from Category A to Category C to spread the acquisition
costs over more years.  The direct conversion from Category A to
Category C would accelerate the transition to greater quiet, since the
Category A aircraft have the loudest sound signature, however it would
prove to be a significant economic hardship on some operators and an
impossibility for others.  

	Papillon states that, once operators do acquire Category C aircraft, no
cap should apply, and they should be permitted to increase the number of
Category C aircraft in their fleet until such time as further expansion
would endanger aviation safety.  However, quiet technology would not
stop here since through further advancement in technology there is the
prospect of Category D and beyond.

	Eagle (54), King (56), and Vision (61) state that the NPRM
unnecessarily discourages the transfer of aircraft between operators or
other business combinations among air tour operators.

	Eagle states that the existence of new part 119 may make it most
efficient for an operator to split its operations between companies
based on aircraft size (e.g., > 9 passengers).  

	GAMA (64) objects to the proposal because it will force the near term
phase-out of 75% or more of the airplanes currently operating in the
vicinity of GCNP.  GAMA cites a NASA statement that a quantum leap in
technology is required to produce any measurable future noise reduction
and states that FAA is aware that it will be years before the necessary
research and development is completed and industry can begin to apply
new noise reduction technologies that will make measurable improvement
over today's technology.

	Scenic Airlines (74) agrees with the FAA recommendation that new
entrant operators be required to use Category C aircraft.  However,
current operators of Category A aircraft should not be forced to convert
directly to Category C aircraft.  They should be allowed to convert from
Category A to Category B to Category C.  Furthermore, operators should
only be permitted to convert from Category A to Category B aircraft if
the aircraft can be used for a minimum of five years, otherwise the
transition should be directly to Category C.

	GCRG (50) states that it would hasten the reduction of noise in the
GCNP if operators were required to convert from Category A directly to
Category C.  New entrants should not be allowed to start operations even
with Category C aircraft.  They should be required to buy existing
operations only.  Furthermore, the GCRG state that the temporary cap on
growth of the air tour industry should not be removed for Category C
aircraft, as this would negate the intended gains made by the conversion
to quieter aircraft.  Category C aircraft are not quiet.  Any changes in
the cap should be stayed until the comprehensive noise management plan
is completed.

	The Grand Canyon Trust (72) states that if the FAA decides to allow
Category B replacements, the FAA must, at a minimum, "retain its
proposal to phase-out an increment of 25 percent of Category B aircraft
every two years from 2002 to 2008...."

	The National Parks Conservation Association (NPCA) (65) believes
strongly that tour operators should be required to convert Category A
aircraft directly to Category C aircraft, rather than allowing the
interim substitution of Category B aircraft, because the FAA must do
whatever is necessary and safe to restore natural quiet.

	However, NPCA believes that the conversion to Category C aircraft may
constitute little or no progress toward reducing noise in the Grand
Canyon because, contrary to the premise of the NPRM, some Category C
aircraft, such as the Vistaliner, are in fact no more quiet than many
Category A or B aircraft.  NPCA states that the FAA obscures this point
by defining the categories in terms of sound exposure per passenger
seat.  To the ground visitor whose visit is disrupted by overflight
noise, the number of passengers a plane is carrying is irrelevant; it is
the absolute amount of noise generated by each flight and the number of
flights that matters.  

	The Sierra Club, Grand Canyon Chapter (76), recommends that the
transition to quieter aircraft should be accomplished in five years.

FAA Response:

This SNPRM only proposes to define quiet aircraft technology
designation.  The quiet technology designation is predicated on the
notion that the use of larger, relatively quieter aircraft (on a per
seat basis) is helpful in reaching the goal of substantial restoration
of natural quiet through a combination of reduction of noise at the
source and reduction in number of tour operations necessary to meet
demand.  Under the provisions of Section 804 of the Air Tour Act, all
incentives to replace current aircraft with those satisfying the
definition must be recommended by the NPOAG.  Thus, all proposals to
encourage the transition to quiet technology will be addressed in
subsequent FAA rulemaking in consultation with the NPS and the NPOAG. 
Upon promulgation of a quiet aircraft technology designation for GCNP,
the FAA, in consultation with the NPS and the NPOAG, will address the
implementation of quiet technology in the Park.  A phaseout is one of
the options that will be addressed.  

As described in the section “Environmental Review,” the FAA has done
some preliminary calculations and found that almost 58% of the park area
would achieve substantial restoration of natural quiet on an average
annual day if all the air tour operations met the quiet technology
designation.  This compares to 44% substantial restoration level
calculated in the final supplemental environmental assessment (SEA)
accompanying the final rules issued on April 4, 2000 (65 FR 17708 and
65 FR 17736).  The 58% estimate assumes that the current non-quiet
technology in the Grand Canyon air tour fleet would be replaced
one-for-one with quiet technology aircraft.  Any judgment on this
initial finding must be tempered with the knowledge that the ongoing
model validation effort could reveal the need to re-calibrate the noise
model if it is over representing the amount of substantial restoration
achieved.

The assumption of an airplane-for-airplane replacement, used in the
above analysis, will need to be addressed in any implementation of the
quiet technology designation.  The quiet technology designation is
predicated on the notion that the use of larger, relatively quieter
aircraft (on a per seat basis) achieves the goal of substantial
restoration of natural quiet through a combination of reduction of noise
at the source and reduction in number of tour operations necessary to
meet demand.  Thus, any implementation of the quiet technology
designation should include a mechanism to achieve the two-fold benefit
described in the previous sentence.  The assumption of the average
annual day, also used in the above analysis, has been the subject of
continuing debate and will require further consideration when it comes
time to assess the rulemaking proposal.  The NPS and some commenters to
the earlier GCNP environmental assessments have expressed concerns that
the average annual day is not the most appropriate measure to assess
aircraft noise impact on the Park.  With the highly seasonal use
patterns in GCNP, some parties believe substantial restoration of
natural quiet should be present any day of the year, thus peak day
rather than average annual day is the more appropriate measure. 

6.  Removal of Temporary Cap

	A number of commenters addressed the proposal to remove the cap on air
tour aircraft for all Category C aircraft.  This change was proposed as
an incentive for conversion to noise efficient aircraft.  

	NPCA (65) believes that the cap on the number of tour aircraft should
not be lifted and that operators should be allowed only a one-to-one
replacement of Category A with Category C aircraft.  Further, to be
effective in restoring natural quiet, the cap must be imposed on tour
flights, rather than on the number of tour aircraft; otherwise,
operators will conduct more flights and extend the tour season, thereby
destroying the natural quiet throughout the year.  Finally, to restore
natural quiet to the 1987 level, the number of operations should be
reduced.  By using Category C aircraft that carry more passengers, it
would be possible to reduce the number of operations, while still
increasing the number of passengers.

	The Havasupai Tribe (71) opposes the proposal to lift the cap on
Category C aircraft.  Lifting the cap would only permit more aircraft to
fly over the Reservation.  According to the Tribe, "the largest
operators at the Grand Canyon have either converted to quiet technology
or are in the process of converting" and thus lifting the cap in the
future would not create an incentive since the conversion has already
begun or taken place.  The air tours over the GCNP have nearly doubled
in the ten years ending in 1996 and without the temporary cap on all
aircraft it will only continue to grow.  Not only will the noise impact,
but also the visual impact, on the reservation will be greater without
the cap.  The Tribe agrees with the statement in the DEA that "the
visual impact of air traffic on the scenic vistas of GCNP and over
cultural areas, including sacred sites and historic sites, in the GCNP
and surrounding lands is of concern."  

	Grand Canyon Trust (72) states that the cap on the number of aircraft
should not be lifted.  At most, operators should be allowed a one-to-one
replacement of Category A with Category C aircraft.  Since Category C
aircraft are not necessarily quieter than the aircraft they are
replacing (noise efficiency is a function of per seat and not per
aircraft) operators should not be allowed a greater number of Category C
aircraft than the number of "noisier aircraft" they are replacing. 
Furthermore, any caps must be applied to the number of flights and not
the number of aircraft.

	The Sierra Club, Angeles Chapter (38, 75) opposes the proposal to lift
the caps on Category C aircraft.  The Sierra Club believes that at a
minimum the cap on fleet size should remain in effect until the
completion of the comprehensive noise management plan, however, it would
be more appropriate to apply the cap to the number of flights, rather
than the number of aircraft.  Along with the proposed caps the Sierra
Club supports the curfews and recommends that additional curfews be
proposed to create flight-free season(s) or period(s).

	The Sierra Club, Grand Canyon Chapter (76), recommends a permanent cap
on the number of all air tour flights.  There is no reason to allow one
interest--the air tour industry--continued growth while all other
activities have reasonable limits.  Initially the number of operations
should be capped at the 1996 level.  By 2008 the number of operations
should be reduced to the level of 1987, and by 2018 they should be
reduced to the number of operations prevailing in 1975.

	Scenic Airlines (74) agrees with the proposal to remove the cap on
Category C aircraft.  The comprehensive noise management plan should
address any future restrictions on number of aircraft.

FAA Response: 

Since the 1996 NPRM, the FAA has issued a final rule that replaced the
cap on the number of air tour aircraft with a capan operations
limitation on the annual number of commercial air tour operations in the
GCNP SFRA (65 FR 17708).  As documented in the February 2000 Final SEA
accompanying the commercial air tour limitation final rule, only 44% of
the Park (on an annual average day) achieves substantial restoration of
natural quiet upon implementation of the air tour limitations and
changes to routes and airspace adopted in April 2000.  The FAA has
evaluated whether the designation of quiet technology requirements,
contained in this SNPRM, will enable the FAA to relieve commercial air
tour operators from the present commercial air tour operations
limitations.  More specifically, the FAA conducted studies to determine
the extent to which use of quiet technology aircraft could possibly
enable air tour operators to increase operations without increasing
cumulative noise levels at Grand Canyon National ParkGCNP pursuant to
section 804 of the Air Tour Act.

The FAA test was conducted by assessing the sensitivity of the
25% TA12hr contour to increases in quiet technology aircraft operations
using the GCINM.  The 25% TA12hr contour has been the measure used in
the environmental assessments associated with all GCNP SFRA rulemaking
to assess progress towards the goal of substantial restoration of
natural quiet.  The particular GCNP air tour scenario chosen for this
test was the preferred alternative of the February 2000 Ffinal SEA that
accompanied the April 2000 final rules (65 FR 17708 and
65 FR 17736).  Two separate runs of the GCINM were performed; fixed
wing aircraft operations on Zuni Reverse and helicopter operations on
the Green 1 loop.  The analysis found that adding less than 4 annual
fixed wing operations or 3 annual helicopter operations would increase
the 25% TA12hr contour area by 0.01 sq. mi.  FAA chose a hundredth of a
square mile as the threshold of significance because contour areas in
the GCNP EA documents have been reported to that significant digit.

The above result supports the FAA’s preliminary finding that operators
using aircraft that meet the quiet technology designation operating
without operations limitation will likely cumulatively increase noise in
the GCNP.  not enable Given that a condition of relief from the
operations limitation is that the cumulative impact of such operations
does not increase noise at GCNP, the FAA would likely be unable to
relieve these operators from the commercial air tour operations
limitations.  This analysis suggests that the operational cap can only
be lifted through a mechanism in which an air tour operator replaces a
current fleet not meeting the quiet technology designation with quiet
technology aircraft by some replacement ratio that reduces aircraft
noise exposure towards the goal.  That is, the reduction in noise gained
through the conversion to quiet technology aircraft might allow for a
limited number of additional operations of the quiet technology aircraft
should this reduction exceed the amount needed to reach the goal of
substantial restoration of natural quiet.  Such a mechanism must ensure
fair and equitable treatment of current and future operators under the
condition that the cumulative effect of any change in the operations
must not increase noise in the Park.   Thus, rRemoval of the operational
operations limitation will be addressed in subsequent FAA rulemaking in
consultation with the NPS and the NPOAG as directed by the Air Tour Act.

7.  Other or Alternative Incentives

	A number of commenters responded to the FAA's request for comments
regarding alternative or additional incentives for operators to convert
to noise efficient technology.

	Lake Mead Air (26, 53) states that with the conversion to "quieter
aircraft" several companies will not be able to meet the standard and
will sell or close.  Other incentives for quiet aircraft technology
should be considered such as tax credits or subsidies, for example the
FAA could pay the air tour operators not to fly Category A aircraft,
similar to soil banks.  Furthermore, more noise efficient aircraft
should be phased phased-in rather than phasing phasing-out the less
noise efficient aircraft.

	Twin Otter (45) states that it is an oversight that the FAA has not
provided for a quiet aircraft corridor in the eastern section of the
canyon.  Twin Otter then comments on routes proposed in 1996 that are no
longer part of this rulemaking.

	Twin Otter recommends the following additional incentives for Category
C aircraft:  (1) lift the aircraft cap immediately on the number of
Category C aircraft that may be operated, (2) eliminate the curfew for
Category C aircraft, and if this is not possible, then permit Category C
aircraft to operate one hour before and one hour later than curfew hours
for conventional aircraft (official sunrise at GCNP is two hours earlier
than the curfew permits for most of the summer), (3) roll back the
overflights fee for Category C aircraft as an additional incentive, and
(4) require helicopters to fly at the highest possible altitude in the
Zuni Corridor so that fixed wing aircraft can conduct tours at a lower
altitude and establish the lowest fixed wing tours in the Zuni for
Category C qualifying aircraft.

	Grand Canyon Airlines (GCA) (46) supports the concept of the proposed
amendment to part 93.  GCA also believes that the FAA needs to provide
quiet aircraft incentive routes in the eastern region.  Category B
helicopters are permitted to operate at the lowest possible altitude in
the eastern region and they are even encouraged to fly in the most
sensitive Dragon Corridor with the lowest altitudes and shortest direct
routes.  This makes the fixed wing Category C air tours less attractive
than the noisier Category B helicopters in this region.  To correct this
disparity the Category C aircraft should be given the lowest possible
routes in the eastern region.  GCA makes the following recommendations: 
(1) provide a Category C incentive route over the existing Black 1
route, (2) minimize advantages to Category B helicopter routes by
creating new Category C routes that provide superior tour features, (3)
waive overflight fees to Category C aircraft, and (4) eliminate caps and
curfews on Category C aircraft.

	Papillon (55) also supports the time frame for transition to quiet
technology and the guidelines for qualifying aircraft as quiet
technology, but recommends 35 dB as the threshold of substantial natural
quiet for the GCNP.  Further incentives for quiet technology should be
implemented for Category C aircraft only:  (1) eliminate the GCNP
overflight fee, (2) create route across the North Rim (through the
Bright Angel Flight-free Zone), (3) permit Category C aircraft to use
alternate routes that may enter flight-free zones to show specific
landmarks, (4) establish new curfews of one hour after sunrise and one
hour before sunset, and (5) restore the two-way helicopter loop in the
Zuni Corridor.

	An individual commenter (68) states that more incentives need to be
utilized to help air tour operators convert to quiet technology.  This
commenter suggests the following incentives:  (1) waiving overflight
fees and park admission fees for passengers, (2) offering and approving
low-cost government loans and tax credits, and (3) establishing new
quality view corridors through which only Category C aircraft could fly
at lower altitudes.

	Scenic Airlines (74) states that while 75% of the passengers it flew in
1996 were flown in Category C aircraft about one half of its air tour
fleet are Category A aircraft.  While Scenic would like to convert these
Category A to Category C it must be provided with incentives, in the
form of privileges that operators and passengers can value, before it
would voluntarily do so.  Operators have only invested in Category C
aircraft in the past based on the promise by the NPS that they will be
rewarded in the future.  If no such rewards materialize there will be a
disincentive to convert to Category Cs in the future.  

	Scenic states that the following Category C incentives should be
provided:  (1) a route through the northern portion of the expanded
Bright Angel Flight-free Zone using the existing Black 1A and Green 1A
(SFAR 50-2), (2) a route along the current Brown 3 (SFAR 50-2) departure
which goes through the north-west corner of the Toroweap Flight-free
Zone, (3) waiver of curfews in Dragon and Zuni corridors to extend the
hours of operation to Daylight hours, (4) waiver of overflight fees, (5)
investment tax credits, and (6) low cost government loans.

	AirStar Helicopters, Inc. (84) states that the following incentives for
transition to noise efficient aircraft should be considered: low cost
loans, overflight fee rebates or investment tax credits.  AirStar also
states that it has already begun the transition to quiet technology.

	The Grand Canyon Trust (72) proposes the use of Dragon and Zuni
Corridors as quiet aircraft incentives routes for Category C aircraft
only.

FAA Response:

This SNPRM only proposes to define quiet aircraft technology
designation.  Under the provisions of Section 804 of the Air Tour Act,
all incentives to replace current aircraft with those satisfying the
definition must be recommended by the NPOAG.  Thus, all proposals to
encourage the transition to quiet technology will be addressed in
subsequent FAA rulemaking in consultation with the NPS and the NPOAG. 
Under the conditions established in Section 804, the NPOAG will provide
advice and recommendations on, among other things, the establishments of
routes and corridors for the operation of quiet technology aircraft for
tours originating in Clark County, Nevada and for “local loop” tours
originating at the GCNP Airport in Tusayan, Arizona.

8.  Draft Environmental Assessment (DEA) 

	Some commenters addressed their concerns regarding the draft
environmental assessment that accompanied the December 1996 NPRM.  For
example, several commenters raise concern over compliance with NEPA and
the NHPA.  The Hualapai Tribe (35) states that the DOT must assess
socio-cultural impacts of the regulation under NEPA and potential
impacts to integrity of cultural resources under NHPA.

	Region IX of the U.S. Environmental Protection Agency (EPA) (70)
encourages the FAA and NPS to undertake all reasonable efforts to ensure
that environmental concerns expressed by the Native American tribes
potentially affected by the proposed action are fully reflected in the
Final Environmental Assessment (FEA).  The EPA also criticizes the FAA
for considering only two alternatives in the DEA -- no action and the
proposed action.  The EPA believes that, in terms of substantially
restoring natural quiet of GCNP, an earlier phase-out date for Category
A and B aircraft would be a more environmentally preferable alternative
that the FAA should consider in the FEA.

	The Havasupai Tribe (71) states that the conclusions of the DEA are
either disingenuously misleading or false.  While the Reservation is
within the SFRA, the Reservation is deleted from the analysis area
depicted in the DEA.  Therefore the conclusion about "substantial
improvement" and "continued improvement" in natural quiet do not apply
to the Reservation or to the entire SFRA.  

	The Havasupai Tribe states that the DEA is inadequate and grossly
deficient under NEPA and should be rewritten and distributed again for
public comment.  Furthermore, with respect to the proposal to lift the
temporary cap on Category C aircraft the DEA does not discuss whether
more noise would be created by one overflight of a Category A aircraft,
as compared with 3, 5, or 10 overflights of Category C aircraft. 
According to the Tribe, an impact statement must "set forth sufficient
information for the general public to make an informed evaluation, . . .
and for the decision-maker to 'consider fully the environmental factors
involved and to make a reasoned decision after balancing the risks of
harm to the environment against the benefits to be derived from the
proposed action.'"  

	Clark County (62) comments that the DEA narrowly construes the purpose
and need of this rulemaking to include only the reduction of aircraft
noise and improperly ignores the important Congressional goals of
ensuring the value of air tours and the safety of aircraft in GCNP. 
Also, despite correctly identifying its duty to rigorously review
alternatives, the FAA failed to comply by limiting its review to only
two alternatives.  The FAA should also have considered alterations in
the flight-free zones or tour routes, the use of retrofit equipment to
meet the quiet aircraft standards, the use of limitations on aircraft
operating parameters to reduce noise, the use of lower altitudes, or
other steps to minimize non-natural noise in GCNP.

	The American Helicopter Society (AHS) Acoustics Technical Committee
(48) comments that current FAA modeling has demonstrated that the No
Action Alternative has effectively achieved the goal of restoration of
the natural quiet because the results show a deficiency of less than 1
percent, a statistically insignificant amount.  Further, the goal would
be reached by the year 2000 with the elimination of all Category A
aircraft alone, so phase-outs of Category B aircraft are not needed. 
AHS suggests alternatives that the FAA should consider, such as careful
scheduling of air tour flights to achieve overlapping audibility or
allowing helicopters to fly below the rim and take advantage of the
acoustic shielding provided by canyon features.

	The Grand Canyon Air Tour Council (Council) (77) states that it is
difficult to comment on the DEA for the following reasons:

	(1) The FAA has not yet determined whether a finding of no significant
impact will be issued or an environmental impact statement will be
required.

	(2) The comprehensive noise management plan is yet to be developed.

	(3) Meanings of "natural quiet" and "substantial restoration of the
natural quiet" have not been resolved.

	(4) Full consultation with tribal governments cannot have occurred
since at least one tribe has initiated legal proceedings.

FAA Response:

In accordance with FAA Order 1050.1D, the FAA has determined that this
proposed rulemaking is categorically excluded from environmental review
under section 102(2)(C) of the National Environmental Policy Act of 1969
(NEPA).  The proposed rule is categorically excluded under FAA Order
1050.1D, Appendix 4, Paragraph 4.j, which covers regulations
“excluding those which if implemented may cause a significant impact
on the human environment.”  Unlike the DEA completed with the 1996
NPRM, this proposed rulemaking simply establishes quiet technology
designations for air tour aircraft operating in GCNP.  It does not
impose a phaseout or any alteration of any air tour operator’s fleet
of aircraft.  In addition, the proposed rulemaking does not lift the
operations limitation, alter any flight corridors through the Park, or
make any change to the SFRA.  Finally, the FAA notes that this proposed
rulemaking alone has no impact on substantial restoration of natural
quiet at GCNP and environmental and economic impacts will depend upon
other future incentives yet to be defined.  Accordingly, this proposed
rulemaking will not individually or cumulatively have a significant
effect on the human environment.  

The FAA has determined that the action proposed in this SNPRM does not
require environmental assessment.  The FAA has determined that this
proposal does not instigate any adverse environmental effects, which
would require the preparation an environmental assessment (EA) for this
rulemaking effort to assure conformance with NEPA.  As directed by the
Air Tour Act, this proposal does not “relieve or diminish-- (1) the
statutory mandate imposed upon the Secretary of the Interior and the
Administrator of the Federal Aviation Administration under Public Law
100-91 (16 U.S.C. 1a-1 note) to achieve the substantial restoration of
the natural quiet and experience at the Grand Canyon National Park.” 
The reasoning behind the FAA determination include: 

The proposal simply establishes quiet technology designations for air
tour aircraft operating in the Park.  It does not impose a phaseout or
any alteration of any air tour operator’s fleet of aircraft.

The proposal does not lift the operational cap, alter any flight
corridors through the Park, or make any change to the SFRA.

ECONOMIC SUMMARY

	Proposed changes to Federal regulations must undergo several economic
analyses.  First, Executive Order 12866 directs that each Federal agency
shall propose or adopt a regulation only upon a reasoned determination
that the benefits of the intended regulation justify its costs.  Second,
the Regulatory Flexibility Act of 1980 requires agencies to analyze the
economic impact of regulatory changes on small entities.  Third, the
Trade Agreements Act (19 U.S.C. section 2531-2533) prohibits agencies
from setting standards that create unnecessary obstacles to the foreign
commerce of the United States.  In developing U.S. standards, this Trade
Act requires agencies to consider international standards and, where
appropriate, that they be the basis of U.S. standards.  And fourth, the
Unfunded Mandates Reform Act of 1995 requires agencies to prepare a
written assessment of the costs, benefits and other effects of proposed
or final rules that include a Federal mandate likely to result in the
expenditure by State, local or tribal governments, in the aggregate, or
by the private sector, of $100 million or more, in any one year
(adjusted for inflation.)   

	However, for regulations with an expected minimal impact the
above-specified analyses are not required.  The Department of
Transportation Order DOT 2100.5 prescribes policies and procedures for
simplification, analysis, and review of regulations.  If it is
determined that the expected impact is so minimal that the proposal does
not warrant a full Evaluation, a statement to that effect and the basis
for it is included in proposed regulation.  Since this SNPRM serves only
to refine the quiet technology definition applied to air tour aircraft
operating in GCNP developed in the 1996 NPRM and removes all compliance
requirements proposed in that NPRM, the expected outcome is to have a
minimal impact.

	The SNPRM retains the “noise efficiency” concept defined by the
relationship between the certificated noise level of an aircraft and the
number of passenger seats on the typical configuration of that aircraft
type as initially proposed in the 1996 NPRM.  However, the three
principal rulemaking elements of 61 FR 69334 have been eliminated.  The
SNPRM drops replaces the three noise efficiency categories that were
proposed in the December 1996 NPRM and proposes to temporarily continue
to rely on the designation of quiet technology aircraft, those that were
formerly described as Category C.  Furthermore, the SNPRM does not
propose any phase-out of air tour aircraft that do not comply with the
Category C quiet technology designation.  Nor does it include any
incentive flight corridors through the park as proposed in December
1996.  Finally, as noted above, the SNPRM does not lift the cap
operations limitation on commercial air tour operations conducted in the
Park that has replaced the 1996 aircraft cap for those aircraft meeting
the Category C noise efficiency standard.  

	Therefore, this SNPRM is essentially a definition of quiet technology
and has negligible economic impact on the operators of GCNP air tours. 
The FAA seeks public comment before moving to future FAA rulemaking in
consultation with the NPS.  Future rulemaking would be coordinated with
an advisory group composed of representatives of general aviation,
commercial air tour operations, environmental concerns, and Native
American interests.

Regulatory Flexibility determination

	The Regulatory Flexibility Act of 1980 (RFA) establishes “as a
principle of regulatory issuance that agencies shall endeavor,
consistent with the objective of the rule and of applicable statutes, to
fit regulatory and informational requirements to the scale of the
business, organizations, and governmental jurisdictions subject to
regulation.”  To achieve that principle, the RFA requires agencies to
solicit and consider flexible regulatory proposals and to explain the
rationale for their actions.  The RFA covers a wide-range of small
entities, including small businesses, not-for-profit organizations and
small governmental jurisdictions.

	Agencies must perform a review to determine whether a proposed or final
rule will have a significant economic impact on a substantial number of
small entities.  If the determination is that it will, the agency must
prepare a regulatory flexibility analysis as described in the RFA.

	However, if an agency determines that a proposed or final rule is not
expected to have a significant economic impact on a substantial number
of small entities, section 605(b) of the RFA provides that the head of
the agency may so certify and a regulatory flexibility analysis is not
required.  The certification must include a statement providing the
factual basis for this determination, and the reasoning should be clear.

	This action merely defines quiet technology but does not impose any
requirements.  Therefore, the FAA does not expect this rule to impose
any cost on small entities.  Consequently, the FAA certifies that the
rule will not have a significant economic impact on a substantial number
of small air tour operators.

International Trade Impact Analysis 

The Trade Agreement Act of 1979 prohibits Federal agencies from engaging
in any standards or related activities that create unnecessary obstacles
to the foreign commerce of the United States.  Legitimate domestic
objectives, such as safety, are not considered unnecessary obstacles. 
The statute also requires consideration of international standards and
where appropriate, that they be the basis for U.S. standards. 

In accordance with the above statute, the FAA has assessed the potential
effect of this final rule to be minimal and therefore has determined
that this rule will not result in an impact on international trade by
companies doing business in or with the United States.

Unfunded Mandates Reform Act

The Unfunded Mandates Reform Act of 1995 (the Act), enacted as Pub. L.
104-4 on March 22, 1995, is intended, among other things, to curb the
practice of imposing unfunded Federal mandates on State, local, and
tribal governments.  Title II of the Act requires each Federal agency to
prepare a written statement assessing the effects of any Federal mandate
in a proposed or final agency rule that may result in a $100 million or
more expenditure (adjusted annually for inflation) in any one year by
State, local, and tribal governments, in the aggregate, or by the
private sector; such a mandate is deemed to be a “significant
regulatory action.” 

This final rule does not contain such a mandate.  Therefore, the
requirements of Title II of the Unfunded Mandates Reform Act of 1995 do
not apply. 

Federalism Implications

	The regulations herein would not have substantial direct effects on the
states, on the relationship between the national government and the
states, or on the distribution of power and responsibilities among the
various levels of government.  Therefore, in accordance with Executive
Order 12866, it is determined that this rule does not have sufficient
federalism implications to warrant the preparation of a Federalism
Assessment.

Paperwork Reduction Act

	In accordance with the Paperwork Reduction Act of 1995 (Pub. L.
104-13), there are no requirements for information collection associated
with the SNPRM. 

List of Subjects in 14 CFR Part 93

14 CFR Part 93

	Air traffic control, Airports, Navigation (Air), Reporting and record
keeping requirements.

Adoption ofThe Amendments

	AccordinglyFor reasons set forth above, the Federal Aviation
Administration amends 14 CFR part 93, in chapter I of Title 14, Code of
Federal Regulations, as follows:

PART 93--SPECIAL AIR TRAFFIC RULES AND AIRPORT TRAFFIC PATTERNS

	1.  The authority citation for part 93 continues to read as follows:

	Authority:  49 U.S.C. 106(g), 40103, 40106, 40109, 40113, 44502, 44514,
44701, 44719, 46301.

	2.  Section 93.303 is revised to add the definition to read as follows:

§ 93.303 Definitions.

* * *

	(d) Quiet technology aircraft means an aircraft that is subject to
§93.301 and has been shown to comply with the noise limit specified in
appendix A of this part.

*	*	*

	3.  Appendix A is added to read as follows:

Appendix A - GCNP Aircraft Quiet Technology Designation

	This appendix contains procedures for determining the quiet technology
status for each aircraft subject to §93.301 determined during the noise
certification process as prescribed under part 36 of this chapter. 
Where no certificated noise level is available, the Administrator may
approve an alternative measurement procedure.

1.	Aircraft Noise Limit for Quiet Technology

	A.  For helicopters with a flyover noise level obtained in accordance
with the measurement procedures prescribed in Appendix H of 14 CFR part
36, the limit is 80 dB for helicopters having 2 or fewer passenger
seats, increasing at 3 decibels per doubling of the number of passenger
seats for helicopters having 3 or more passenger seats.  The limit at
number of passenger seats of 3 or more can be calculated by the formula:

EPNL(H)  = 80 +10log(# PAX seats/2) dB

	B.  For helicopters with a flyover noise level obtained in accordance
with the measurement procedures prescribed in Appendix J of 14 CFR part
36, the limit is 77 dB for helicopters having 2 or fewer passenger
seats, increasing at 3 decibels per doubling of the number of passenger
seats for helicopters having 3 or more passenger seats.  The limit at
number of passenger seats of 3 or more can be calculated by the formula:

SEL(J)  = 77 +10log(# PAX seats/2) dB

	C.  For propeller-driven airplanes with a measured flyover noise level
obtained in accordance with the measurement procedures prescribed in
Appendix F of 14 CFR part 36 without the performance correction defined
in Sec. F35.201(c), the limit is 69 dB for airplanes having 2 or fewer
passenger seats, increasing at 3 decibels per doubling of the number of
passenger seats for airplanes having 3 or more passenger seats.  The
limit at number of passenger seats of 3 or more can be calculated by the
formula:

LAmax(F)  = 69 +10log(# PAX seats/2) dB

	D.  In the event that a flyover noise level is not available in
accordance with Appendix F of 14 CFR part 36, the noise limit for
propeller-driven airplanes with a takeoff noise level obtained in
accordance with the measurement procedures prescribed in Appendix G is
74 dB for airplanes having 2 or fewer passenger seats, increasing at 3
decibels per doubling of the number of passenger seats for airplanes
having 3 or more passenger seats.  The limit at number of passenger
seats of 3 or more can be calculated by the formula:

LAmax(G)  = 74 +10log(# PAX seats/2) dB

	Issued in Washington, DC on

 The provisions of SFAR No. 50-2 have been extended numerous times
(62 FR 8862; 62 FR 66248; 63 FR 67544; 64 FR 5152; 65 FR 5395)
with the last extension in January 2001 (66 FR 1002).

 The effective date for 14 CFR Sections 93.301, 93.305, and 93.307 was
delayed by subsequent amendments (62 FR 66248; 63 FR 67544;
64 FR 5152; 65 FR 5395; 65 FR 69846; 66 FR 1002) until finally
becoming effective on April 19, 2001.

 The effective date for the airspace modification rule was delayed by
subsequent amendments (65 FR 69846; 66 FR 1002; 66 FR 16582) until
finally becoming effective on April 19, 2001.

 The candidate models being validated are:

The FAA’s Integrated Noise Model, which has been modified to address
air tour aircraft noise exposure in GCNP and is referred to as the GCNP
Integrated Noise Model (GCINM).

The NPS’s National Park Service Overflight Decision Support System
(NODSS) designed and programmed specifically for park applications to
consider audibility, significant changes in terrain elevation, and
shielding due to terrain.

NOISEMAP Simulation Model (NMSIM) developed by the US Air Force and the
National Aeronautics and Space Administration (NASA) to simulate
aircraft single event noise levels.

 The time above (TA) metric provides the duration that aircraft related
noise exceed specified sound threshold.  For assessment of aircraft
noise in GCNP, the %TA12h represents the percentage of time aircraft are
audible during the 12-hour daytime period of primary visitor activity. 
The 25 %TA12h contour (the area where aircraft are audible greater 25%
of the time) measures the extent that the criterion for substantial
restoration of natural quiet is met.  When the 25 %TA12h contour for a
particular alternative occupies less than half of the area of GCNP then
that alternative has achieved substantial restoration of natural quiet
at the Park.

 Sierra Club v. Army Corps of Engineers, 701 F.2d 1011, 1029 (2d Cir.
1983).

This is a working DRAFT only.  It is not a final proposal, and may or
may not become a final proposal.

DRAFT 7		revised:   SAVEDATE  \* MERGEFORMAT  09/28/2001 7:15
AM09/26/2001 8:14 AM 

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