Wake Turbulence—An Obstacle to Increased Air Traffic Capacity

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Committee to Conduct an Independent Assessment of the Nation’s Wake Turbulence Research and Development Program Aeronautics and Space Engineering Board Division on Engineering and Physical Sciences

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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Gov- erning Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engi- neering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported by Contract No. NASW-03009 between the National Academy of Sciences and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this pub- lication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number-13: 978-0-309-11379-3 International Standard Book Number-10: 0-309-11379-2 Cover: Shown in this photograph by Steve Morris are the wake vortices gen- erated by a Boeing 767-3Y0/ER aircraft, operated by Virgin Nigeria, as seen on its approach to London Gatwick Airport. Copyright by AirTeamImages.com. Reprinted with permission. Cover design by Michael Dudzik of the National Academies Press. Available in limited supply from Aeronautics and Space Engineering Board, 500 Fifth Street, N.W., Washington, DC 20001, (202) 334-2858. Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, www.nap.edu. Copyright 2008 by the National Academy of Sciences. All rights reserved.

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal govern- ment on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the char- ter of the National Academy of Sciences, as a parallel organization of outstand- ing engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in pro- viding services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE TO CONDUCT AN INDEPENDENT ASSESSMENT OF THE NATION’S WAKE TURBULENCE RESEARCH AND DEVELOPMENT PROGRAM ANTHONY J. BRODERICK, Aviation Safety Consultant, Catlett, Virginia, Chair PAUL BEVILAQUA, Lockheed Martin Aeronautics Company JEFFREY CROUCH, The Boeing Company FREDERICK GREGORY, Lohfeld Consulting Group FAZLE HUSSAIN, University of Houston BILL F. JEFFERS, Independent Consultant, Newnan, Georgia DENNIS W. NEWTON, Independent Consultant, Kent, Washington DUNG PHU “CHI” NGUYEN, Research Triangle Institute J. DAVID POWELL, Stanford University (professor emeritus) ALFRED T. SPAIN, JetBlue Airways (retired), New Roads, Louisiana ROBERT P. STONE, United Airlines KAREN WILLCOX, Massachusetts Institute of Technology Staff KERRIE SMITH, Study Director SARAH CAPOTE, Program Associate HEATHER LOZOWSKI, Financial Associate MARCIA S. SMITH, Aeronautics and Space Engineering Board Director v

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AERONAUTICS AND SPACE ENGINEERING BOARD RAYMOND S. COLLADAY, Lockheed Martin Astronautics (retired), Golden, Colorado, Chair CHARLES F. BOLDEN, JR., Jack and Panther, LLC ANTHONY J. BRODERICK, Aviation Safety Consultant, Catlett, Virginia AMY BUHRIG, Boeing Commercial Airplanes Group PIERRE CHAO, Center for Strategic and International Studies INDERJIT CHOPRA, University of Maryland, College Park ROBERT L. CRIPPEN, Thiokol Propulsion (retired), Palm Beach Gardens, Florida DAVID GOLDSTON, Princeton University R. JOHN HANSMAN, Massachusetts Institute of Technology PRESTON HENNE, Gulfstream Aerospace Corporation JOHN M. KLINEBERG, Space Systems/Loral (retired), Redwood City, California RICHARD KOHRS, Independent Consultant, Dickinson, Texas ILAN KROO, Stanford University IVETT LEYVA, Air Force Research Laboratory, Edwards Air Force Base EDMOND SOLIDAY, United Airlines (retired), Valparaiso, Indiana Staff MARCIA S. SMITH, Director (from January 2007) GEORGE LEVIN, Director (through January 2007) vi

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Preface Demand for air transportation continues to increase rapidly and is projected to double or even triple by 2025. The present air transporta- tion system cannot accommodate such a large increase in demand and in many places is already stretched, resulting in frequent and lengthy delays. In the early part of this decade, government agencies and Congress recognized that continued incremental improvements would not provide the capacity needed in the coming decades; a different approach was required. Congress responded by enacting Public Law 108-176, Vision 100Century of Aviation Reauthorization Act. It included a framework to accomplish a major transformation of the nation’s air transportation system through the cooperation of the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA), the Department of Homeland Security (DHS), the Department of Transpor- tation (DOT), the Department of Commerce (principally the National Oceanic and Atmospheric Administration, NOAA), the Office of Science and Technology Policy (OSTP), and the Department of Defense (DOD). The resulting Joint Planning and Development Office (JPDO), which includes representation from all of those organizations, is working on a wide-ranging set of programs that aim to make major changes to the air transportation system. Called the Next Generation Air Transportation System, or “NextGen,” the system will have greater capacity to accom- modate the increased air traffic demand projected for around 2025. vii

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viii PREFACE The Global Positioning System (GPS) constellation of some two dozen satellites provides remarkably accurate positioning and timing capability, far better than that provided by existing radar surveillance and ground- based navigation systems. Since determination of aircraft spacing en route and for approach and landing is affected by inaccuracies inherent in existing systems, one goal of NextGen involves taking advantage of GPS to enable aircraft to fly more closely spaced without diminishing safety. Developments in avionics, surveillance, navigation, and landing tech- niques based in whole or in part on GPS have, in the last 10 years or so, demonstrated that this is indeed possible. The use of GPS can practically and safely permit much closer flying. Unfortunately, the accuracy of GPS does not solve the problem of wake turbulence. As an inevitable product of lift, an aircraft wing gener- ates a wake in its trail. The heavier an aircraft is, the stronger its wake; the greater an aircraft’s wingspan, the longer a wake will persist. This wake can be a safety hazard when smaller aircraft follow relatively larger aircraft too closely—a few accidents have demonstrated this fact clearly. In the early 1970s, the B747 was introduceda much larger aircraft by far than the B707 and other similar aircraft of the time. To address the wake turbulence problem, the FAA introduced separation standards based on aircraft size. These standards have since been modified somewhat, but the principle remains: Aircraft are designated small, large, or heavy1 based on their maximum takeoff weights. A heavy aircraft must be followed no more closely than 4 miles by another heavy aircraft, no more closely than 5 miles by a large aircraft, and no more closely than 6 miles by a small aircraft if the following aircraft is at the same altitude or less than 1,000 feet below. However, these standards are quite conservative. For example, the 4-mile spacing between a heavy aircraft and a large aircraft applies equally to large aircraft weighing between 50,000 and 250,000 lb, and the heavy aircraft can weigh anywhere from 255,000 lb to over 900,000 lb (the heaviest B747 in service). The new A380, weighing in at 1.2 million pounds, has been given larger spacing requirements by the International Civil Aviation Organization. Recognizing the potential obstacle to capacity growth presented by the wake vortex hazard and that little had changed in establishing these standards in over three decades, in the 2005 National Aeronautics and Space Administration Authorization Act (P.L. 109-155) Congress directed NASA to contract with the National Research Council (NRC) to conduct a study of the issue. NASA and the NRC developed a statement of task 1The International Civil Aviation Organization (ICAO) standards, used in Europe, use slightly different categories: light, medium, and heavy.

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ix PREFACE that included three steps. First, in the context of addressing the air traffic capacity issue, the study was to identify wake vortex research challenges, suggest a plan for accomplishing them, and recommend responsible agen- cies. Second, the study was to identify ongoing U.S. government research, including gaps and how to address them to best contribute to improved air traffic capacity. Finally, that review was to be expanded to include non- U.S. government research as well as research and information exchange partnerships, recommending any changes deemed necessary. The Committee to Conduct an Independent Assessment of the Nation’s Wake Turbulence Research and Development Program found that the wake vortex problem does present a real impediment to increased air traffic capacity, something reflected in most of the documentation that has been drafted to date by the JPDO. Most aircraft can clear a runway in less than 1 minute from touchdown to turnoff. However, wake vortex sepa- ration standards require a separation of 2 minutes or more, leaving the runway used only half as much as it might be. The need to address wake vortex limitations is clearly articulated throughout the NextGen plan- ning documents, the concept of operations document, and the research presentations reviewed by the committee. However, although the need to address wake vortex issues is clearly acknowledged, the research required to provide the required solutions is not yet under way. While European agencies are conducting research on a wide variety of wake vortex issues, there is little such work ongoing in the United States. In part, this is the result of reductions in aeronautics research funding. Recent aeronautics research funding reductions applied to the NASA budget have resulted in a realignment and reprioritization of NASA’s research work. Prior to the cuts, NASA and the FAA pursued a partner- ship of research programs. The FAA focused on near-term operational issues. NASA provided the technical support that the FAA lacked and also sponsored and conducted more fundamental, long-term research. At pres- ent, NASA’s budget can no longer support the FAA’s short-term activities, nor is much funding available for long-term fundamental research. The committee saw gaps in the technical research effort in terms of technical support to the FAA’s ongoing, relatively near-term research that promises capacity improvement, in long-range, higher-risk but potentially high- payoff research work, and in the modeling needed to advance funda- mental understanding of wake behavior. The committee also noted that in many cases, small-scale weather can actually dominate vortex spacing considerations. Favorable winds may transport the wake out of the flight path of following aircraft. Unfavorable winds may transport a wake into the flight path of an aircraft on a parallel course. Understanding what measurements are needed to take advantage of these short-term weather

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x PREFACE fluctuations is key to permitting safe adjustments to wake vortex sepa- ration standards. To claim this potential capacity, research is needed to move this effort ahead now. The committee was fortunate to have as members knowledgeable vol- unteers, some retired, with experience in a broad range of disciplines, and representing a cross section of the academic, industrial, and government communities. The diversity of the group made for enthusiastic discussion and debate, which in turn facilitated getting the task done efficiently in only three meetings in Washington, D.C. The members’ unselfish efforts made the task do able, and the committee’s work was made much easier by the superb support provided by the National Academies’ staff, particu- larly Kerrie Smith, program officer, and Sarah Capote, program associate. Without their able assistance throughout the study, the committee would have been far less efficient and informed. Anthony J. Broderick, Chair Committee to Conduct an Independent Assessment of the Nation’s Wake Turbulence Research and Development Program

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Acknowledgments This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Report Review Committee of the National Research Council (NRC). The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and respon- siveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: Thomas Gerz, DLR, Preston Henne, Gulfstream, Ilan Kroo, Stanford University, Jack Olcott, General Aero Company, Inc., Turgut Sarpkaya, Naval Postgraduate School, and Roger Wall, FedEx. Although the reviewers listed above have provided many construc- tive comments and suggestions, they were not asked to endorse the con- clusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Louis Lanze- rotti, New Jersey Institute of Technology. Appointed by the NRC, he was xi

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xii ACKNOWLEDGMENTS responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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Contents SUMMARY 1 1 INTRODUCTION 15 Needs of NextGen, 15 Wake Hazards and Overview of Current Standards, 16 Wake Turbulence: A Long Pole for Capacity?, 19 Study Process, 21 Challenges, 22 References, 22 2 ORGANIZATIONAL CHALLENGES IN WAKE 24 TURBULENCE RESEARCH Get Organized, 24 Get the Community Talking, 27 3 TECHNICAL CHALLENGES IN WAKE 29 TURBULENCE RESEARCH Introduction, 29 Improved Spacing System Design, 30 Vortex Visualization: Cockpit and Controller, 34 Vortex Alleviation, 37 Weather Forecasting, 40 Wake Vortex Modeling, 41 Wake Vortex Measurement, 45 xiii

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xiv CONTENTS Safety Analysis and Hazard Boundaries, 48 Systems to Gather Data About Wake Events, 50 System-Level Study of Benefits, 54 References, 56 4 WAKE TURBULENCE PROGRAM PLAN 60 Prioritization of Challenges, 60 Periodic Assessment, 63 Roles, 65 5 FINDINGS AND RECOMMENDATIONS 66 APPENDIXES A Statement of Task 73 B Committee Biographies 75 C List of Speakers 81 D Acronyms and Abbreviations 83 E Sample Wake Encounter Reporting Form 85

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Tables and Figures TABLES S-1 Deliverables, 13 S-2 Evaluation Metrics, 14 1-1 IFR Separation Requirements for Arrival on the Same Runway, 17 1-2 Separation Distances Observed During Self-separation in VMC, 18 3-1 Milestones for Advanced Spacing System Design, 34 3-2 Milestones for Wake Vortex Visualization, 37 3-3 Milestones for Vortex Alleviation, 39 3-4 Milestones for Weather Forecasting, 41 3-5 Milestones for Wake Vortex Modeling, 44 3-6 Milestones for Wake Vortex Measurement, 47 3-7 Milestones for Safety Analysis and Hazard Boundaries, 50 3-8 Milestones for Systems to Gather Data About Wake Events, 54 3-9 Milestones for System-Level Study of Benefits, 56 4-1 Deliverables, 63 4-2 Evaluation Metrics, 64 FIGURES S-1 Recommended priority and level of effort for wake turbulence challenges, 12 4-1 Recommended priority and level of effort for wake turbulence challenges, 61 xv

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