NPC Editor's Note: This document is under construction. Some figures in Chapters 9 and 10 are not in place.

 

REPORT TO CONGRESS

 

REPORT ON EFFECTS OF AIRCRAFT OVERFLIGHTS

ON THE NATIONAL PARK SYSTEM

 

 

 

PREPARED PURSUANT TO PUBLIC LAW 100-91,

THE NATIONAL PARKS OVERFLIGHTS ACT OF 1987

 

  

NATIONAL PARK SERVICE

September 12, 1994

 

 

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ACKNOWLEDGEMENTS

 

This Report to Congress provides the U.S. Department of Interior, National Response to Public Law l00-91, the National Parks Overflights Act of 1987. The information presented herein represents the combined efforts of many scientists, specialists, and park managers and staff. In particular, the National Park Service would like to acknowledge the contribution of the following:

 

The Department Of Interior - Department of Transportation Interagency Working Group

 Ms. Jackie Lowey, Ms. Barbara West, Mr. Joseph Canny, Mr. John Reynolds, Mr. Dale McDaniel, Mr. Destry Jarvis, Mr. Hal Becker, and Dr. Wes Henry

 

Grand Canyon National Park

 Superintendents Boyd Evison and Robert Arnberger and Staff, especially Mr. Mike Ebersole and Ms. Linda Mazzu.

 

The National Park Service, Denver Service Center

Mr. Rick Ernenwein and Mr. Elmer Hernandez

 

Research Contractors and Subcontractors

Harris Miller Miller & Hanson Inc.: Mr. Nicholas P. Miller and Staff

BBN Systems and Technologies: Dr. Sanford Fidell and Staff

 HBRS, Inc.: Dr. Robert Baumgartner and Dr. Cary McDonald

Sterna Fuscata, Inc.: Mr. Douglas Gladwin and Ms. Alexie McKechnie

Research Triangle Institute: Dr. Ronaldo Iachan

 

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The Eloquent Sounds of Silence

 

Everyone of us knows the sensation of going up, on retreat, to a high place and feeling ourselves so lifted up that we can hardly imagine the circumstances of our usual lives, or all the things that make us fret. In such a place, in such a state, we start to recite the standard litany: that silence is sunshine, where company is clouds; that silence is rapture, where company is doubt; that silence is golden, where company is brass.

But silence is not so easily won. And before we race off to go prospecting in those hills, we might usefully recall that fool's gold is much more common and that gold has to be panned for, dug out from other substances. "All profound things and emotions of things are preceded and attended by Silence," wrote Herman Melville, one of the loftiest and most eloquent of souls. Working himself up to an ever more thunderous cry of affirmation, he went on. "Silence is the general consecration of the universe. Silence is the invisible laying on of the Divine Pontiffs hands upon the world. Silence is the only Voice of our God." For Melville, though, silence finally meant darkness and hopelessness and self-annihilation. Devastated by the silence that greeted his heartfelt novels, he retired into a public silence from which he did not emerge for more than 30 years. Then, just before his death, he came forth with his final utterance-the luminous tale of Billy Budd--and showed that silence is only as worthy as what we can bring back from it.

We have to earn silence, then, to work for it: to make it not an absence but a presence; not emptiness but repletion. Silence is something more than just a pause; it is that enchanted place where space is cleared and time is stayed and the horizon itself expands. In silence, we often say, we can hear ourselves think; but what is ruler to say is that in silence we can hear ourselves not think, and so sink below our selves into a place far deeper than mere thought allows. In silence, we might better say, we can hear someone else think.

Or simply breathe. For silence is responsiveness, and in silence we can listen to something behind the clamor of the world. "A man who loves God, necessarily loves silence," wrote Thomas Merton, who was, as a Trappist, a connoisseur, a caretaker of silences. It is no coincidence that places of worship are places of silence; if idleness is the devil's playground, silence may be the angels'. It is no surprise that silence is an anagram of license. And it is only right that Quakers all but worship silence, for it is the place where everyone finds his God, however he may express it. Silence is an ecumenical state, beyond the doctrines and divisions created by the mind. If everyone has a spiritual story to tell of his life, everyone has a spiritual silence to preserve.

 

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So it is that we might almost say silence is the tribute we pay to holiness; we slip off words when we enter a sacred space, just as we slip off shoes. A "moment of silence" is the highest honor we can pay someone; it is the point at which the mind stops and something else takes over (words run out when feelings rush in). A "vow of silence" is for holy men the highest devotional act. We hold our breath, we hold our words; we suspend our chattering selves and let ourselves “fall silent," and fall into the highest place of all.

It often seems that the world is getting noisier these days: in Japan, which may be a model of our future, cars and buses have voices, doors and elevators speak. The answering machine talks to us, and for us, somewhere above the din of the TV; the walkman preserves a public silence but ensures that we need never--in the bathtub, on a mountaintop, even at our desks--be without the clangor of the world. White noise becomes the aural equivalent of the clash of images, the nonstop blast of fragments that increasingly agitates our minds. As Ben Okri, the young Nigerian novelist, puts it, "When chaos is the god of an era, clamorous music is the deity's chief instrument."

There is, of course, a place for noise, as there is for daily lives. There is a place for roofing, for the shouting exultation of a baseball game, for hymns and spoken prayers, for orchestras and cries of pleasure. Silence, like all the best things, is best appreciated in its absence: if noise is the signature tune of the world, silence is the music of the other world, the closest thing we know to the harmony of the spheres. But the greatest charm of noise is when it ceases. In silence, suddenly, it seems as if all the windows of the world are thrown open and everything is as clear as on a morning after the rain. Silence, ideally hums. It charges the air. In Tibet, where the silence has a tragic cause, it is still quickened by the fluttering of prayer flags, the tolling of temple bells, the roar of wind across the plains, the memory of chant.

Silence, then, could be said to be the ultimate province of trust: it is the place where we trust ourselves to be alone; where we trust others to understand the things we do not say; where we trust a higher harmony to assert itself. We all know how treacherous are words, and how often we use them to paper over embarrassment, or emptiness, or fear of the larger spaces that silence brings. "Words, words, words" commit us to positions we do not really hold, the imperatives of chatter; words are what we use for lies, false promises and gossip. We babble with strangers; with intimates we can be silent. We "make conversation" when we are alone, or with those so close to us that we can afford to be alone with them.

In love, we are speechless; in awe, we say, words fail us. - Pico Iyer

 

Copyright 1993 Time Inc. Reprinted with permission.

 

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TABLE OF CONTENTS

 

LIST OF TABLES

v

LIST OF FIGURES

vi

CHAPTER 1 - INTRODUCTION

1.1

1.1 Background

1.1

1.2 Public Law 100-91 and this Report

1.3

1.3 Organization of the Report

1.3

1.3.1 The Nature and Scope of Overflight Problems

1.3

1.3.2 Effects of Overflights on Natural Quiet

1.5

1.3.3 Effects on Cultural and Historical Resources, Sacred Sites and Ceremonies

1.5

1.3.4 Effects on Wildlife

1.5

1.3.5 Effects of Overflights on Visitors

1.5

1.3.6 Aircraft Overflights and Safety

1.5

1.3.7 Values Associated with Aircraft Overflights

1.6

1.3.8 Restoration of Natural Quiet

1.6

1.3.9 Conclusions, Issues and Recommendations

1.6

1.3.10 Availability of NPS Studies

1.6

CHAPTER 2 - NATURE AND SCOPE OF OVERFLIGHT PROBLEMS IN THE NATIONAL PARK SYSTEM

2.1

2.1 Survey of Park Managers

2.2

2.1.1 Number of Parks Affected

2.2

2.1.2 Types of Aircraft Overflights

2.3

2.1.3 Types of Impacts

2.3

2.1.4 Estimated Numbers of Overflights

2.6

2.1.5 Superintendents' Judgments of Overflight Problems

2.9

2.2 Estimates of Overflight Exposure

2.13

2.3 Sound Measurement Results

2.14

2.4 Summary

2.19

CHAPTER 3 - EFFECTS OF OVERFLIGHTS ON NATURAL QUIET

3.1

3.1 How Important is Natural Quiet?

3.1

3.1.1 Importance to the Congress

3.1

3.1.2 Importance of Natural Quiet to the National Park Service

3.3

3.1.3 Importance of Natural Quiet to Park Managers

3.4

3.1.4 Importance of Natural Quiet to Park Visitors

3.5

3.2 What is Natural Quiet?

3.5

3.2.1 Qualitative Assessment of Natural Quiet

3.7

3.2.2 Quantitative Assessment of Natural Quiet

3.7

3.3 What Are the Characteristics of Natural Quiet?

3.8

3.4 Why is it Difficult to Preserve Natural Quiet?

3.11

3.5 Aircraft Overflight Effects on Natural Quiet

3.13

3.6 Summary

3.14

CHAPTER 4 - EFFECTS ON CULTURAL AND HISTORIC RESOURCES, SACRED SITES, AND CEREMONIES

4.1

4.1 Extent of Concern by Park Management and Visitors

4.2

4.1.1 Park Management Assessment

4.2

4.1.2 Visitor Assessment

4.5

4.2 Acoustic Impact on Cultural and Historical Resources

4.7

4.3 Vibration Impact on Cultural and Historical resources

4.9

4.3.1 How Structures Respond

4.9

4.3.2 Types of Aircraft Noise That Can Excite Structural Response

4.10

4.3.3 Damage Potential

4.12

4.3.4 Mitigation

4.15

4.4 Summary

4.15

CHAPTER 5 - EFFECTS OF OVERFLIGHTS ON WILDLIFE

5.1

5.1 Introduction

5.1

5.2 Physiological Responses to Aircraft Overflights

5.2

5.3 Behavioral Responses to Aircraft Overflights

5.3

5.4 Indirect Effects of Disturbance from Overflights, and Consequences for Animals

5.4

5.4.1 Accidental Injury

5.12

5.4.2 Reproductive Losses

5.12

5.4.3 Energy Losses

5.14

5.4.4 Habitat Avoidance and Abandonment

5.15

5.4.5 Potential Bird Strike Hazards

5.16

5.5 Factors that Influence Animal Responses to Aircraft

5.16

5.5.1 How Animals Perceive the Aircraft Stimulus

5.16

5.5.2 Aircraft Sound and Animal Hearing

5.17

5.5.3 Increased Tolerance to Overflights

5.17

5.6 Biotic Factors that Influence Animal Responses to Aircraft

5.18

5.7 Problems with Detecting Long-Term Effects of Aircraft Disturbance

5.19

5.8 Overflight Impacts on Endangered Species

5.22

5.9 Overflight Impacts on National Park Animals

5.23

5.10 Development of Impact Criteria

5.25

5.11 Summary

5.26

CHAPTER 6 - EFFECTS OF OVERFLIGHTS ON VISITOR ENJOYMENT

6.1

6.1 Introduction

6.1

6.2 The System-Wide Impacts of Overflights on Visitors

6.2

6.2.1 Importance of Natural Quiet

6.3

6.2.2 Impacts Produced by Hearing and Seeing Aircraft

6.4

6.2.3 Impacts Among Different User Groups Produced by Hearing Aircraft

6.6

6.3 Impacts at Specific Parks and at Specific Sites

6.6

6.3.1 Impacts at Specific Parks

6.8

6.3.2 Impacts at Specific Sites

6.16

6.4 Identification, Analysis and Mitigation of Impacts

6.20

6.4.1 Identification

6.20

6.4.2 Analysis and Mitigation

6.22

6.4.3 Limitations

6.24

6.5 Summary

6.24

CHAPTER 7 - AIRCRAFT OVERFLIGHTS AND SAFETY

7.1

7.1 Concerns of Park Management

7.1

7.2 Concerns of Park Visitors

7.5

7.3 Outdoor Recreation Community Concerns

7.7

7.4 Temporary Flight Restriction (TFR) Problems

7.7

7.5 Summary

7.8

CHAPTER 8 - VALUES ASSOCIATED WITH AIRCRAFT OVERFLIGHTS

8.1

8.1 Values Associated with Administrative Use of Aircraft

8.1

8.2 Values Associated with Aerial Tourism

8.2

8.2.1 Tour Passenger Survey Results

8.4

8.2.2 Are Air Tour Passengers Park Visitors?

8.8

8.3 Value of Overflights to Local Economies

8.12

8.4 Values and Impacts of Aerial Filming

8.12

8.5 Summary

8.13

CHAPTER 9 - RESTORATION OF NATURAL QUIET

9.1

9.1 Report on Section 2 Requirements

9.1

9.1.1 Yosemite National Park

9.1

9.1.2 Haleakala National Park

9.2

9.2 Report on Section 3 Requirements: Grand Canyon National Park

9.3

9.2.1 Defining a Substantial Restoration of Natural Quiet

9.3

9.2.2 Special Federal Aviation Regulations 50-2

9.3

9.2.3 Evaluation of Restoration Efforts (SFAR 50-2)

9.5

9.2.4. Summary of Section 3 Requirements

9.19

9.3 What are the Opportunities for Solutions?

9.19

9.3.1 Realistic Expectations

9.20

9.3.2 Realistic Opportunities

9.20

9.3.3 Environment Needed for Effective Comprehensive Solutions

9.2 .1

9.4 Summary

9.23

CHAPTER 10 - CONCLUSIONS AND RECOMMENDATIONS

10.1

10.1 Conclusions

10.1

10.2 Airspace Management Issues: The NPS Perspective

10.4

10.2.1 The FAA and The NPS: Learning How to Work Together

10.5

10.2.2 Military Airspace / Park Use Issues: Prospects for Change

10.5

10.3 NPS Recommendations to Congress

10.8

10.3.1 Recommendation 1: Develop Airspace / Park Use Issue Resolution Processes

10.8

10.3.2 Recommendation 2: Establish and Maintain Agency Points of Contact

10.8

10.3.3 Recommendation 3: Use the Full Range of Methods and Tools for Problem Solving

10.8

10.3.4 Recommendation 4: FAA to Address High Priority NPS Airspace / Park Use Issues

10.10

10.3.4.1 NPS Managerial Priorities

10.10

10.3.4.2 NPS Priorities for Protection of Natural Quiet

10. 11

10.3.4.3 NPS Priorities for Resolution of Safety Concerns

10.11

10.3.4.4 NPS Priorities for Problem Solving with Department of Defense

10.11

10.3.5 Recommendation 5: Develop FAA Operational Rule Triggered by NPS

10.12

10.3.6 Recommendation 6: Develop FAA Rule to Facilitate Preservation of Natural Quiet

10.12

10.3.7 Recommendation 7: Develop a Movie Waiver Policy

10.14

10.3.8 Recommendation 8: Develop an Interagency Airspace Coordination Guide/Training

10.14

10.3.9 Recommendation 9: Seek Continued Improvements in Safety and Interagency Planning Related to Airspace Management

10.14

10.3.10 Recommendation 10: Improve SFAR 50-2 to Effect and Maintain the Substantial Restoration of Natural Quiet at Grand Canyon National Park

10.15

10.3.10.1 GCNP Airspace Structure Recommendations

10.16

10.3.10.2 Aircraft Equipment Recommendations

10.20

10.3.10.3 Aircraft Operations Recommendations

10.20

10.3.10.4 Flights Outside the SFRA

10.21

10.3.10.5 Miscellaneous Recommendations

10.21

10.3.10.6 Modeling the NPS Recommendation for GCNP

10.22

10.3.10.7 Summary of GCNP Recommendation

10.23

Epilogue

10.23

 

LIST OF REFERENCES

R.1

i - iv

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LIST OF TABLES

Table 1.1

Questions Pose by P.L. 100-91

1.4

Table 2.1

National Parks whose Managers are Very to Extremely Concerned about Aircraft Overflights

2.12

Table 5.1

General responses by specific animal species to aircraft overflights

5.5

Table 6.1

Importance of Natural Quiet and Natural Scenery as Reasons for Park Visit

6.3

Table 6.2

Numbers of Visitors who Reported Hearing or Seeing Aircraft

6.4

Table 6.3

Impacts that Resulted from Hearing Aircraft

6.5

Table 6.4

Annoyance that Resulted from Seeing Aircraft

6.5

Table 6.5

Reported Exposure and Impact from Hearing Aircraft at Visitors Survey Parks

6.8

Table 6.6

Visitor Survey Parks with More than 10,000 Visitors Impacted by Overflights During Survey

6.13

Table 6.7

Dose-Response Data Collection Study Areas

6.17

Table 7.1

Parks Where Safety is Perceived as a Serious, or Very Serious Problem

7.3

Table 7.2

Visitor Safety Concerns Reported to Park Management During FY 1992

7.4

Table 9.1

Grand Canyon National Park Management Objectives

9.6

Table 9.2

Percent of Time Aircraft were Audible Under Flight-Free Zones

9.9

Table 9.3

Percent of Time Aircraft were Audible Under Flight Corridors

9.10

v

 

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LIST OF FIGURES

Figure 2.1

Extent of Aircraft Overflight Problems in the National Park System

2.4

Figure 2.2

Locations of the 98 Park Units with Identified Aircraft Overflight Problems

2.4

Figure 2.3

Types of Aircraft Overflying National Parks as Identified by Managers

2.5

Figure 2.4

Park Manager Judgments of Types of Impacts Produced by Aircraft Overflights

2.5

Figure 2.5

Reported Number of Overflights per Week by Aircraft Type for All Parks

2.5

Figure 2.6

Reported Number of Overflights per Week Reduce by Four Parks

2.5

Figure 2.7

Distribution of Overflights per Day for All Aircraft Combined

2.7

Figure 2.8

Distribution of Overflights per Day for Military Aircraft

2.8

Figure 2.9

Distribution of Overflights per Day for Sightseeing Aircraft

2.8

Figure 2.10

Distribution of Overflights per Day for Commercial Aircraft

2.8

Figure 2.11

Distribution of Overflights per Day for General Aviation Aircraft

2.8

Figure 2.12

Managers’ Rating of Ten Potential Problems in Their Parks

2.10

Figure 2.13

Managers’ Rating of Sound-Related Problems in Their Parks

2.10

Figure 2.14

Managers’ Reported Degree of Overall Concern about Overflights

2.11

Figure 2.15

Managers’ Rating of Most Bothersome Aspects of Overflights

2.11

Figure 2.16

Managers’ Rating of Overflight Impacts on Visitors' Enjoyment

2.11

Figure 2.17

Sound Measurement Results Acquired in Eight National Parks

2.16

Figure 2.18

Acoustic Profile Data from Grand Canyon National Park

2.18

Figure 2.19

Acoustic Profile Data from Haleakala and Hawaii Volcanoes National Parks

2.20

Figure 3.1

Importance to Management of Various Opportunities

3.6

Figure 3.2

Management Perspective on Interference with Opportunities

3.6

Figure 3.3

Management Reports of Aircraft Impact on Park Resources

3.6

Figure 3.4

Grand Canyon Visitor Reports of Aircraft Impact on Park Resources

3.6

Figure 3.5

Sound Level Ranges Between Park and Non-Park Settings

3.9

Figure 3.6

Measured Ambient Sound Levels Along Colorado River in Grand Canyon National Park

3.10

Figure 3.7

Measured Ambient Sound Levels Along the Canyon Rim in Grand Canyon National Park

3.10

Figure 3.8

Measured Ambient Sound Levels in Hawaii Volcanoes and Haleakala National Parks

3.1

Figure 3.9

Protrusion of Aircraft Noise Above the Ambient in Various Settings

3.12

Figure 4.1

Management Rating of Importance of Providing Historical and Cultural Opportunities

4.4

Figure 4.2

Management Rating of Aircraft Interference With Historical and Cultural Significance of Park

4.4

Figure 4.3

Visitor Ratings at Eight "Cultural" Parks of Aircraft Interference With Historical and Cultural Significance of Park

4.6

Figure 4.4

Percent of Visitors Reporting Interference with History or Culture at Specific Parks

4.6

Figure 4.5

Representative Time History of a Sonic Boom "N-wave" Pressure Pulse

4.1.1

Figure 4.6

Helicopter "Blade Slap" Sound Wave Impinging on a Historical Site

4.13

Figure 4.7

Helicopter "Thickness" Noise Radiating to a Cultural Resource

4.13

Figure 5.1

Animal Responses to Low-Altitude Aircraft Overflights

5.20

Figure 5.2

External Factors that Influence Animal Responses to Overflights

5.21

Figure 6.1

Impacts of Hearing Aircraft Among Different Visitors-Groups

6.7

Figure 6.2

Percent of Visitors Hearing Aircraft and Annoyed by Aircraft at Visitors Survey Parks

6.11

Figure 6.3

Percent of Visitors Hearing Aircraft and Annoyed by Aircraft at Five Specific Sites

6.11

Figure 6.4

Numbers of Visitors Hearing Aircraft and Annoyed by Aircraft at Visitors Survey Parks

6.12

Figure 6.5

Comparison of NPS Management Rankings with Percent of Visitors Hearing Aircraft

6.14

Figure 6.6

Comparison of NPS Management Rankings with Percent of Visitors Annoyed

6.14

Figure 6.7

Comparison of NPS Management Rankings with Number of Visitors Annoyed

6.15

Figure 6.8

Dose-Response Curve for Visitor Annoyance vs. Percent of Time Aircraft are Heard

6.18

Figure 6.9

Dose-Response Curve for Visitor Annoyance vs. Hourly Equivalent Sound Level

6.18

Figure 6.10

Dose-Response Curves for Estimating Impacts at Sites Preserving Visitor Enjoyment

6.21

Figure 6. 11

Dose-Response Curves for Estimating Impacts at Sites Preserving Natural Quiet

6.21

Figure 6.12

Dose-Response Curves for Analysis of Airspace at Sites Preserving Visitor Enjoyment

6.23

Figure 6.13

Dose-Response Curves for Analysis of Airspace at Sites Preserving Natural Quiet

6.23

Figure 7.1

Manager Assessment of Visitor and Staff Safety

7.2

Figure 7.2

Perceptions Managers Have About Visitor and Staff Concerns for Safety

7.2

Figure 7.3

Reported Aircraft Crashes in 91 NPS Units Suring the Past Five Years

7.6

Figure 7.4

Visitor Assessment of Decreased Feelings of Safety Due to Aircraft Operations

7.6

Figure 7.5

Visitor Assessment of Increased Feelings of Safety From Aircraft Overflights

7.6

Figure 8.1

Most Prevalent Uses of Aircraft by NPS Park Management

8.3

Figure 8.2

Annual Helicopter Flight Hours Flown by NPS Park Management

8.3

Figure 8.3

Annual Fixed Wing Flight Hours Flown by NPS Park Management

8.3

Figure 8.4

Relative Visitation Access Modes for Grand Canyon and Hawaiian Parks

8.3

Figure 8.5

Passenger Reports of Air Tour Enjoyment

8.5

Figure 8.6

Passenger Reports of Increased Appreciation of Park from Air Tours

8.5

Figure 8.7

Passenger Willingness to Recommend Air Tours to Others

8.5

Figure 8.8

Percentage of First Time Passengers on Air Tours

8.5

Figure 8.9

Passengers' Primary Reasons for Taking Air Tours

8.6

Figure 8.10

Importance of Time Constraints as a Reason For Taking Air Tour

8.6

Figure 8.11

Importance of Unique Perspective as a Reason For Taking Air Tour

8.7

Figure 8.12

Importance of Health Limitations as a Reason For Taking Air Tour

8.7

Figure 8.13

Passengers' Plans for Touring Park on the Ground As Well

8.7

Figure 8.14

Passenger Reports of Importance of Air Tour to Overall Enjoyment of the Park

8.9

Figure 8.15

Passenger Reports of Importance of Ground Tour to Overall Enjoyment of the Park

8.9

Figure 8.16

Passengers' Assessment of Disruptive Impact of Air Tours to Ground Visitors

8.10

Figure 8.17

Passengers' Assessment of Whether Air Tour Benefits Outweigh Impacts on the Ground

8.10

Figure 9.1

Grand Canyon National Park Special Flight Rules Area

9.4

Figure 9.2

Grand Canyon National Park Acoustic Monitoring Sites

9.8

Figure 9.3

Visitor Reports of Reasons for Visiting the Canyon

9.12

Figure 9.4

Visitor Reports of the Most Important Reasons

9.12

Figure 9.5

Visitor Reports of Hearing Aircraft

9.15

Figure 9.6

Visitor Reports of Impacts

9.15

Figure 9.7

Inappropriateness of Overflights

9. 15

Figure 9.8

Visitor View of Park Overflight Policy

9.16

Figure 9.9

Visitor Support for Overflight Limits

9.16

Figure 9.10

Computer Modeled Natural Quiet Restoration -- 1989 Tour Operations

9.17

Figure 9.11

Computer Modeled Natural Quiet Restoration -- 2010 Tour Operations

9.18

Figure 9.12

Observer-Based Audibility Contours Comparing Quiet and Other Aircraft

9.22

Figure 10.1

Recommended Special Flight Rules Area: NPS Proposal For Flight Free Zones and Corridors

10.17

Figure 10.2

Substantial Restoration of Natural Quiet-- Year 2010: The Result of the NPS Recommendation .

10.24

Figure 10.3

Percent of GCNP in Natural Quiet (100%) If NPS Recommendation Adopted

10.25

Figure 10.4

Percent of Park Where Natural Quiet Substantially Restored: A Comparison Between NPS Recommendation and No Action

10.26

vi - vii

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