REPORT OF THE NATIONAL COMMITTEE CLEAR AIR TURBULENCE TO THE FEDERAL COORDINATOR FOR METEOROLOGICAL SERVICES AND SUPPORTING RESEARCH DECEMBER 1966 U. S. DEPARTMENT OF COMMERCE \i Clear Air Turbulence is defined as "all turbulence in the free atmosphere of interest in aerospace operations that is not in or adjacent to visible convective activity (this includes turbulence found in cirrus clouds not in or adjacent to visible convective activity)". For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price 35 cents : ^ T °^Q ^ATES O* * U. S. DEPARTMENT OF COMMERCE John T. Connor, Secretary ENVIRONMENTAL SCIENCE SERVICES ADMINISTRATION Robert M. White, Administrator REPORT OF THE NATIONAL COMMITTEE FOR CLEAR AIR TURBULENCE TO THE FEDERAL COORDINATOR FOR METEOROLOGICAL SERVICES AND SUPPORTING RESEARCH DECEMBER 1966 FOREWORD On behalf of the National Committee for Clear Air Turbulence, may I express our genuine hope that this report will lead to an aggressive effort to overcome a most serious aerospace problem. JACK J. CATTON Major General, USAF Chairman, NCCAT PREFACE The Department of Defense is concerned with the level of coordination of the efforts of various governmental agencies in the area of Clear Air Turbulence (CAT ) . , . It is recommended that a special National CAT Committee be estab- lished under the Federal Coordinator for Meteorological Services and Support- ing Research. Specific terms of reference should be prepared by the committee itself, but the following areas of research and development should be included: airborne detection devices, forecasting, basic research and data collection. This recommendation, excerpted from a letter, dated 18 August 1965, was made by Dr. Harold Brown, now Secretary of the Air Force but then Director of Defense Research and Engineering, to Dr. J. Herbert Hollomon of the Depart- ment of Commerce in his capacity as chairman of the Federal Committee for Meteorological Services and Supporting Research. Dr. Hollomon, on behalf of the Federal Committee, concurred and the National Committee for Clear Air Turbulence was born on 18 February 1966. This report to the Federal Coordinator reflects the results of their investigation, with an appraisal of the needs and suggestions for future courses of action. The report is in two parts. The first embraces an introductory statement, an evaluation of the requirements and general recommendations. The second part deals with the technical aspects — specific recommendations relating to measurements and observations, remote detection, pilot/aircraft response, forecasting and dissemination. The committee, with Major General Jack J. Catton, (then) Director of Operational Requirements and Development Plans, Headquarters, USAF, of the Department of Defense as chairman, was assisted by an advisory panel of specialists in the field of Clear Air Turbulence. Digitized by the Internet Archive in 2012 with funding from LYRASIS Members and Sloan Foundation http://www.archive.org/details/reportofnationaOOunit Part Two Appendices CONTENTS Part One Pa s e I. Introduction 6 II. Conclusions 8 III. General Recommendations 9 IV. Evaluation of the Needs 10 V. Existing Programs and Deficiencies 12 VI. Priorities For Future Action 19 Specific Recommendations 22 A. Measurements and Observations 22 B. Forecasting 25 C. Dissemination 26 A. Correspondence Leading to Formation of NCCAT and Membership of NCCAT, Advisory Panel 27 B. Requirements Justification 36 C. Turbulence Criteria Table 43 D. R&D Projects Concerned with Clear Air Turbu- lence 44 PART ONE I. INTRODUCTION Turbulence has always been a factor for consideration in the operation of aircraft. Clear Air Turbulence (CAT) became a problem for consideration at least as far back as the introduction of the pressurized aircraft, and became a more critical problem with the introduction of large jet aircraft. Particular attention has been paid recently to clear air turbulence since there is less known about the cause of this phenomenon than turbulence produced by thunderstorms and squall lines. The weather services have directed their attention to methods of forecasting the occurrence of CAT and others have concentrated on improving pilot procedures and operational techniques in turbulence. Although turbulence, regardless of its cause, is a major problem in aircraft operations, turbulence in clear air is especially troublesome because unexpectedly it can exist without any visual evidence. The meteorological services know little about the cause of clear air turbulence and the forecasts are inadequate for operational purposes. Encounters with CAT became more numerous as operations of jet transports increased. Passengers and crew members were injured, aircraft structural components were damaged and aircraft have gone out of control with near disastrous results. In the late 1950's several major accidents in military aviation were directly or indirectly caused by CAT. By 1964 the situation was such that a major effort was deemed necessary by the United States to determine the cause of CAT, and work was started on the development of detection devices. Additionally, recent efforts to locate and avoid CAT areas have resulted in some improvements such that unexpected encounters, upsets, and structural damages have been considerably reduced. However, the turbulence problem, including CAT, still exists and is a major one for the military where flexibility of operations for mission accomplishment is much less than that of routine civil operations. In addition, the supersonic transport (SST), expected to be in operation in the 1970's, may be faced with turbulence in the clear air of the stratosphere, which can pose serious problems over some routes during certain seasons of the year. The committee reviewed the various agency programs which were directly or indirectly related to the CAT problem. These programs included those of a meteorological nature as well as those related to aircraft design and operation. It might seem that the development of remote detection and some sensing devices should be postponed until more research has been accomplished on the nature and physical parameters of CAT itself. However, this would result in the dilemma of needing such devices in order to more thoroughly investigate and measure the physical parameters of CAT and permit reliable avoidance. Con- sequently, it is entirely justifiable to encourage and support the trial and development of a number of possible sensors and detectors based upon different CAT detection principles, even though these principles are not yet proven. It appears that availability of CAT remote detection and avoidance systems is not likely in the near future. In view of this, the committee believed it necessary to review not only the meteorological programs but also those related to aircraft operations, i.e., pilot techniques, cockpit instrumentation, and pilot/ aircraft relationships in turbulence. The committee found no evidence of duplication of effort. However, there was a requirement for a national project, or other means, to facilitate and promote exchange and dissemination of scientific information concerning CAT and CAT projects among government and private agencies. There appeared to be a lack of full coordination of programs and accomplishments to solve specifically the CAT problem, and it was clear no agency was responsible for the solution of the total problem. Since CAT is common to all of aviation, the committee looked at the problem as a whole without regard for agency responsibility. In establishing an order of priority, the importance of the ultimate solution of the problem to aircraft operations was established without regard for the state-of-the-art. Airborne remote detection was considered of the highest importance. Although forecasting of CAT is improving, precise forecasting of the location and time of local patches of CAT, does not appear feasible, any more than the times and positions of individual small local thundershowers can be forecast with pinpoint accuracy. For this reason, an airborne device is needed to detect and locate CAT sufficiently ahead of the aircraft to permit either evasive action or preparation for penetration. If such a system could be developed, it would permit pilots to avoid areas of significant CAT in the same manner as they now avoid thunderstorm and squall line turbulence with the use of radar. Closely related to the importance of airborne remote detection is the require- ment for an accurate prediction of CAT areas so that plans to avoid them could be made during the pre-flight planning stage. The committee fully recognized the difficulty and time required to solve the detection and forecasting problems. It therefore considered other actions which would bring about significant improvements in operations and lessen the chance of unexpected CAT encounters. These included such things as improved criteria for identifying and reporting CAT, establishment of a national CAT forecasting facility, maintenance of a continuous CAT watch, the publication of climatological atlases showing seasonal and geographical areas of CAT, the review of aircraft design criteria, improvements in flight techniques in turbulent areas, aircraft flight instrumentation, and pilot/aircraft response in turbulence. II. CONCLUSIONS The Committee, after reviewing all agencies' requirements, programs and plans concludes that: 1. The solution of the CAT problem is in the national interest. 2. Although much work on CAT is underway within the military, civil gov- ernment, and industry, a coordinated national effort leading to a common solution has not been established. 3. The detection and prediction problems are far from solution. 4. Recognizing that the best way to cope with turbulence is to avoid it, the development of reliable remote detection devices is of greatest importance. 5. There is a need for a national CAT project to attack the problem on a broad front and direct the U. S. efforts to the end that detection and forecasting problems will be solved. 6. There is a need for a national CAT facility to serve as a focal point for the collection, processing, and dissemination of current CAT information, including the issuance of forecasts and warnings of significant CAT. 7. Aircraft design and operational flight test programs and the national CAT project should so far as practicable take mutual advantage of the products and flight programs of their respective activities. III. GENERAL RECOMMENDATIONS 1. That government agencies be encouraged to support work that will produce better fundamental knowledge of CAT. 2. That the following government agencies assume primary re- sponsibility for and coordination of government efforts in the areas indicated: (a) Department of Defense — measurements and observations, including remote detection; (b) Department of Commerce — forecasting; (c) National Aeronautics and Space Administration — pilot/ aircraft response; (d) Federal Aviation Agency — dissemination; and further that the Federal Coordina- tor for Meteorological Services and Supporting Research be responsible for overall coordination through an appropriate mechanism. 3. That a National CAT Data Collection project be established as the focal point for collecting, storing, and retrieving data re- quired for the solution of CAT detection and forecasting prob- lems. This effort will feature interagency operational task force efforts in CAT reconnaissance, measurements, and observations. It is further recommended that the Department of Defense be the executive agent for the operation of the National CAT Data Collection Project. 4. That, at an appropriate time(s), the Federal Committee for Meteorological Services and Supporting Research review the progress made toward solving the CAT problem and determine the need for further joint agency actions. Type A/C Civil Military 259 344 38.6% 51.3% IV. EVALUATION OF THE NEEDS The extent of CAT, in general, can be gauged from the reports received by the Weather Bureau of CAT incidents. During 1964 there were 8,507 pilot reports of CAT of all degrees as reported by all types of commercial and military aircraft. Of these, 671 were reports of moderate — or — greater intensity en- countered by turbine-powered aircraft. These CAT incidents were summarized as follows: Degree of Turbulence Unknown Moderate Severe Extreme 68 497 163 11 10.1% 74.1% 24.3% 1.6% While there were no doubt many additional encounters unreported, this gives a good general picture of the problem. The Committee evaluated the need for solutions to CAT-related problems by taking account of the effects of CAT on aircraft operations which are enumerated below. 1. Common to Civil and Mili- tary OnGrationS Clear air turbulence affects all U. S. aviation activities including Department of Defense and civil operations by creating: (a) A need to cancel missions or divert aircraft around aieas of CAT. (b) An increase in the number of required aircraft inspections due to loads encountered. (c) The potential for temporary loss of aircraft control and resultant injury to passengers and/or crew requiring compensation or medical treatment. (d) The potential for shortening the operational time available to the aircraft due to structural fatigue limitations. (e) The need for special aircrew training in turbulence flight. (f) A shortage of available airspace due to increased numbers of general aviation "baby jets" operating between 20,000 feet and 40,000 feet. 2. Unique Military Require- ments Military aircraft have been destroyed and numerous accidents and incidents have occurred as a result of encounters with clear air turbulence. CAT has affected peacetime and cold war operations and has a large potential for causing degradation of wartime activities. In addition to those listed above, CAT affects military operations by: (a) Creating a serious hazard to air-to-air refueling operations. (b) Reducing the amount of airspace available in which to conduct simulated combat missions. (c) Causing degradation of reconnaissance sensor and bombing accuracies by loss of the stability of the platform. The exact cost of CAT to DOD is difficult to gauge. Costs for aircraft lost and damages encountered in major mishaps have been estimated to total about $30,000,000 over the 3-year period 1963-1965. Costs of special aircraft inspec- tions because of CAT, minor repairs, minor injuries, and special training are not known. In addition, a dollar value cannot be placed on loss of skilled pilots/ crew, reduction of airspace available for simulated missions, or effects of lack of advance knowledge of location of CAT on actual combat missions. 10 3. Civil OpBfdtionS While there have been airline accidents and incidents attributable to CAT, many potentially serious situations have been avoided by effective use of pre- flight planning and in-flight actions. A result of the effects of CAT on civil operations, in addition to that listed as common, is the creation of a potential loss of revenue because of disgruntled passengers. According to a study made by the Flight Safety Foundation for NASA, in 1964 there was a total expense attributable to turbulence of: Injury 384,000 Diversions 16,000,000 Training 517,000 Information 989,000 Inspection 200,000 Total $18,090,000 This does not include loss of use of grounded aircraft, loss of employable time by injured occupants, and overhead involved in settling claims for injuries. General aviation jet aircraft number some 700 today and are being produced at a rate of approximately 20 per month in this country alone. The number of such U. S. aircraft operating in the 20,000-40,000 foot environment now exceed the approximately 600 large U. S. civil transports currently in operation. Significantly, these general aviation jets with 7-10 passengers require the same airspace in the ATC system as the large jet with 200 or more passengers on board and require approximately the same runway interval for landings and takeoffs. Also, the two- and three-engine transport jets are rapidly replacing large piston transports thereby further increasing the number of aircraft in the 20,000-40,000 foot environment. With more civil jets competing for airspace in the 20,000- 40,000 foot environment, which at times may be restricted vertically and horizontally because of reported or forecast CAT, the result could be severe economic penalties on the operators of the aircraft. A general lack of experience of the response characteristics of typical super- sonic transport configurations has focused attention to atmospheric turbulence effects on such airplanes. Among many overlapping areas of concern are: the turbulent structure of the atmosphere at altitudes where SST's will fly; the aerodynamic response of an SST configuration in all phases of its flight; the consequent structural response of the airplane; the resulting ride comfort; the effect on engine performance, especially with regard to unstarts; the effect on diffusion properties controlling the dispersion of air pollutants; and the possible effects on the sonic boom overpressure. 4. flirspaCc Utilization FAA is responsible for effective use of the airspace. The need to change altitude assignments and to re-route aircraft repeatedly in flight because of CAT is difficult due to the lack of information on CAT. Also, the hazard associated with aircraft wake turbulence slows the flow of traffic in many cases since the wake location on runways (even though temporary) cannot be definitely deter- mined. 11 V. EXISTING PROGRAMS AND DEFICIENCIES A. EXISTING PROGRAMS 1. Operational a. Observations and Meas- urements of CAT b. Remote Detection c. Pilot/Aircraft Response in Turbulence d. Forecasting e. Dissemination Present programs in the operational service to obtain data on CAT depend almost exclusively on subjective reports from pilots of routine commercial and military flights. Reports of CAT encounters are in the form of pilot reports (PIREPS) and the intensity of turbulence reported is based on an evaluation by the pilot. The intensity of the CAT encounters is based on subjective turbulence intensity criteria established several years ago and used as a standard guide for pilots and meteorologists (Appendix C ) . There are no current plans to introduce any new data collection techniques or procedures as part of the operational program in the immediate future. There are no operational systems as yet that provide objective remote detection of CAT, either airborne or ground-based. However, several approaches show promise. There are no governmental operational programs now underway that deal operationally with pilot/aircraft response in CAT as distinguished from other forms of turbulence. However, there are substantial efforts throughout govern- ment and industry that make use of operational experience of pilot reactions and aircraft characteristics in turbulence. CAT forecasts are prepared by both civil and military weather services. Both manual and computer techniques are employed in the preparation of the fore- casts which are valid for various periods up to 36 hours in advance. The fore- casts cover the area traversed by U. S. civil and military flights and, generally, extend up to altitudes of about 45,000 feet. CAT forecasts of a long-term nature (beyond 12 hours) are prepared in graphic form and issued at 6-hourly intervals. They are intended to assist pilots and operators in pre-flight planning. Shorter-period CAT forecasts (0 to 12 hours) are prepared in plain language and issued at 6-hourly intervals. Very-short-period CAT forecasts (0 to 4 hours) of moderate or greater tur- bulence are prepared in plain language on a non-scheduled basis as circumstances require. Within the next 18 months the operating services plan to establish a national CAT forecasting facility serving the 48 contiguous states. This service will also have the capability of maintaining a continuous CAT watch, producing more detailed forecasts with provisions for rapid updating and provide a national focal point for CAT data. CAT reports made by civil and military pilots are usually given to an FAA Air Route Traffic Control Center (ARTCC) via air-ground radio channels since most aircraft encountering CAT are operating on an IFR flight plan, therefore are in direct communications with an ARTCC. Occasionally FAA Flight Service Stations (FSS) and control towers receive CAT reports directly from pilots. 12 2. Research and Development a. Observations and Meas- urements of CAT Once CAT reports have been received by the FAA they are transmitted on the national Center B system, which gives distribution to all conterminous ARTC Centers. Delivery is made to the Flight Service Station (FSS) and Tower nearest the location of the reported CAT. At this FSS they are included in a PIREP summary which is distributed to all FSS's within 200 miles and to one or more Flight Advisory Weather Service (FAWS) and ARTC Centers via Area B service. The appropriate FAWS Center then includes the PIREP in a summary for distribution on Service A. Airborne pilots obtain CAT PIREPS by requests to FSS's or ARTCC's over the standard air-ground frequencies or by listening to the continuous or scheduled broadcasts over the navigational aids. CAT forecasts of a long-term nature (beyond 12 hours), prepared in graphic form, are disseminated over Weather Bureau and Air Force weather facsimile circuits to aviation forecast offices and briefing facilities, including a limited, but increasing, number of FAA facilities. Non-government users obtain this information by obtaining connections to the appropriate facsimile circuit. These forecasts are intended to assist the pilot in his pre-flight planning. Shorter-period CAT forecasts (0 to 12 hours), prepared in plain language, are disseminated over the aviation weather teletypewriter circuits to briefing offices. Very-short-period forecasts (0 to 4 hours) of CAT of moderate or greater intensity, prepared in the form of an alert or warning, are disseminated in the same manner as the to 12 hour forecasts, and in addition, an alert is broadcast over air-ground frequencies immediately upon receipt by FAA facilities and at frequent intervals. ARTCC's, on their initiative, are required to deliver CAT reports to aircraft under their control which might be affected by the CAT. FSS's, on their initiative, are required to deliver CAT forecasts of moderate or greater intensity to aircraft under their control which might be affected by the CAT. Pre-flight pilots may obtain CAT reports and forecasts by visiting or tele- phoning an FSS or WBAS. There are 51 Research and Development projects which apply to observations and measurements of CAT (data collection). These projects are listed in Appendix D and have been divided into four sub-categories: Directly applicable to CAT (Table D-l). General atmospheric data measurements ( Table D-2 ) . Development of instruments and techniques (Table D-3). Basic research (Table D^f). (1) The fourteen R&D projects listed in Table D-l are directly related to one or more of the stated requirements for data collection. Most of these projects are related to the requirement for preparing forecasts and warnings. One project is also related to the requirement for pre- paring upper-air climatology of CAT. Four of the projects are also re- lated to the requirements for aircraft design, aircraft response, and the measuring and recording of CAT encounters. 13 (2) The sixteen R&D projects listed in Table D-2 concern general atmos- pheric data measurements. Although these projects are not specifically related to CAT, they are considered to be of such a nature that the re- sults should be useful in solving CAT problems. Several of these proj- ects will also serve in meeting the requirement for preparing CAT climatology. (3) The twelve R&D projects listed in Table D-3 have to do with instrumen- tal and technique development. Although they are not directed specifi- cally to CAT problems, they are considered to have useful applications in solving interrelated problems of CAT. The projects include wind sensing techniques, aircraft weather measuring equipment, gust load measuring techniques and instrumentation, and atmospheric scattering techniques. (4) The nine R&D projects listed in Table D-4 apply to basic research con- cerned with developing an understanding of the physical processes in the atmosphere which are related to turbulent motion. b. Remote Detection Thirteen R&D projects, as listed in Table D-5, are specifically directed towards the development of techniques for CAT detection. These projects respond to re- quirements for both airborne and ground-based CAT remote detection systems and include most of the known techniques which offer the most hope for a practical CAT detection system. Some projects listed in Table D-l are also related to the remote detection re- quirements, specifically those having to do with temperature gradient recorders, electric field anomalies, and ozone. All of these projects respond to the require- ment for both airborne and ground-based CAT detection systems. Most of these projects employ ground-based equipment in the present developmental studies, but are eventually aimed toward airborne use. All the projects listed in Table D— I (Basic Research) are important in the understanding of CAT phenomena which is necessary for the successful develop- ment of a practical CAT detection capability. It is recognized that a considerable number of private firms in the aerospace, electronic, optical and airline industries are conducting in-house studies and developments aimed at the solution of the CAT problem, including the develop- ment of remote detection devices. The portion of this development which is not government supported did not come under the purview of this study and report. The same is true of efforts and developments in other nations. A brief resume of the present government-sponsored R&D efforts include the following type systems: ( 1 ) Temperature One project is obtaining data on the correlation of temperature changes and turbulence occurrences. If this relationship proves valid it will then be necessary to sense the temperature changes far enough in advance of the aircraft to give the pilot time to take action. At the same time, one project is studying techniques for remote temperature sensing through micro-wave and infrared techniques. (2) Electric Field Three separate projects are studying the atmospheric electrical field varia- tions, and their relation to turbulence. 14 c. Pilot/Aircraft in Turbulence Response d. Forecasting One project is studying the existence and detection of low frequency electrostatic return signatures in known turbulence areas. (3) Radar Two projects are studying the use of radar in its possible relation to tur- bulence. These are being used with large high powered ground-based radar equipment to investigate angels and the electro-magnetic backscatter from regions of perturbed refractivity. (4) Lasers Four separate projects are investigating the use of optical laser systems. Most of this effort at the present involves ground-based equipment. (5) Ozone Two projects are concerned with the distribution of ozone, particularly the penetrations of ozone into the upper troposphere and its use as a tur- bulence detector. ( 6 ) Optical Two projects are investigating the use of passive optical returns and their use as turbulence detectors. One project is studying possible variations in ultraviolet; another project is concerned with a "cross beam correlation" experiment designed to remotely sense wind speeds and turbulence properties in the atmosphere. (7) Others One project is a study of general atmospheric variables, which might prove useful in CAT detection. The nine R&D projects listed in Table D-6 are concerned specifically with pilot/aircraft response in turbulence. One of the projects is directed toward recording pilot reactions during penetration of severe atmospheric turbulence during routine airline operations. This information should provide a valuable link in comparing pilot reactions measured under actual stress levels in flight to pilot reactions measured under simulated flight conditions. Aircraft response to turbulence will be catalogued in three other programs where specific vehicles are to be instrumented to record pertinent data for structural analysis of turbulence effects. An aircraft will also be instrumented to demonstrate techniques to alleviate gust and maneuvering mode induced oscillations of the structure. Sweptwing encounters with turbulence and B-70 flights to date confirm the need to improve attitude presentation, altimeter accuracy, vertical speed and air speed information, particularly for the SST pilot. Research programs are planned to provide command information to the pilot which will prescribe the proper velocity and attitude as target information during flight in turbulence. Several of the projects listed in Table D-l will also supply data to describe the turbulence environment for programming in simulators to study pilot/air- craft response. Detailed studies of pilot/aircraft response to turbulence of a severe nature will most certainly be carried out in simulators because of the risk involved in actual severe turbulence encounters. Table D-7 lists 10 R&D projects which are concerned with the analysis and forecasting of those conditions in the atmosphere which are related to CAT. 15 e. Dissemination B. DEFICIENCIES 1. Observations and Measure- ments of CAT 2. Remote Detection 3. Pilot/Aircraft Response in Turbulence However, in general, these projects are not specifically directed to the develop- ment of techniques for forecasting CAT. It should be noted that there are ongoing "projects", not identified here, within the operating forecast systems of the DOD, DOC and the air carriers which are of a support nature to the operating programs. These projects are concerned with modifying and improving existing CAT forecast programs in accordance with technical advancements. There are no R&D projects which relate directly to the problem of disseminat- ing CAT information. There are, of course, a number of projects, primarily by DOD, FAA and DOC, concerned with the general problem of disseminating, displaying and presenting all types of weather information. These projects have such broad applicability that they have not been included here. However, as in other areas, the results of these projects will undoubtedly have a fallout that will be of benefit to the dissemination of CAT information. CAT data obtained through PIREPS in the operational service are based on subjective evaluations by the pilot. These reports, although useful, offer little hope for operational improvements for the following reasons: a. The turbulence data from PIREPS are highly subjective and qualitative. b. The turbulence data from PIREPS are confined to scheduled commercial or routine military operations. Thus, most of the data are limited to the established routes and to altitudes below 40,000 feet. c. Outside of specially instrumented and planned research flights, data collection programs are not specifically designed to meet the Measurements and Observations requirements. d. Although the optimum density, frequency, and accuracy requirements of upper-air meteorological observations in relation to the CAT phenom- enon are not known, it is known that the density and frequency of upper- air meteorological observations are inadequate in relation to the scale of CAT phenomena in both time and space. Even with improved CAT forecasts, it will be necessary to supplement these forecasts with an adequate CAT detection capability for the penetration or avoidance of localized CAT cells. The substantial R&D effort directed toward CAT detection is essentially exploratory because little is known of the nature of the phenomena to be detected. As in the forecasting problem, it is vitally necessary to understand the CAT phenomena before any major success can be expected in the development of a detector. For example, the successful development of a laser detector could depend on the knowledge of the relationship between the concentration of partic- ulate matter and turbulence. Similar relationships need to be determined for the successful development of detection systems using other sensors. The de- velopment of a CAT detection capability is of extreme importance. The existing and planned pilot/aircraft response R&D programs should, if aggressively pursued, provide adequate and timely design information for aero- space vehicles of advanced design and permit development of piloting techniques 16 4. Forecasting a. Forecast Product b. Forecast Production Sys- tem and improved flight instruments to ensure proper control of aircraft in tur- bulence encounters. It is difficult to predict precisely from wind tunnel and design procedures all of the aerodynamics and control characteristics of aircraft of advanced design. Therefore, it is expected that each new design will be subjected to detailed simulator studies (when accurate aerodynamic characteristics become available through flight tests) to ensure proper response characteristics and pilot control techniques in severe turbulence. The display of aircraft attitude information should be clearly presented at all times and should have such prominence that the true attitude of the aircraft is unmistakable. Command target information should be provided the pilot which will prescribe the proper velocity and attitude required during flight in turbulence. Deficiencies in the CAT forecasts result primarily from the inability of the forecast system to predict the location and intensity of CAT in sufficient detail or with a degree of competence to permit operators to select routes and altitudes which will avoid areas of CAT with an acceptable degree of reliability. The longer-term CAT forecasts (beyond 4 hours) cover quite large volumes of the atmosphere. The airspace volume delineated by a CAT forecast box is generally on the order of 400 by 120 miles by 15,000 feet. This represents some 144,000 cubic miles of the atmosphere. Since there may be several of these boxes valid for the same time period over the contiguous 48 states, it is obvious that if these volumes were to be avoided during the season of maximum occur- rence, a very large portion of the airspace would be unuseable, resulting in an unnecessary curtailment of operations. In addition, scheduled CAT forecasts are rarely amended between times of issuance even though no CAT is reported in the expected areas. Although the shorter-period forecasts (less than 4 hours) are more accurate than the longer- term forecasts, the former "over-forecast" too often. Conversely, pilots are frequently faced with CAT encounters of moderate or greater intensity without forewarning. This causes discomfort and occasional injury to crew and pas- sengers, control problems, and hastens the structural fatigue of the airframe. It is concluded that CAT forecasts are too gross to be of much value for planning purposes and that the chance of encountering significant CAT is almost as great outside the forecast area as within it. The accuracy of CAT forecasts for periods beyond 4 hours should be such as to permit pre-flight plans to completely avoid encounters of severe or greater intensity CAT. The accuracy of short-period CAT forecasts (less than 4 hours) should be such as to provide sufficient advance notice of CAT existence to pilots to enable them to avoid the phenomenon or to adequately prepare for penetration. The deficiencies in the CAT forecast production system result primarily from the following: ( 1 ) The nature and cause of CAT is incompletely understood. (2) CAT reports are subjective, producing data which cannot be quantified. This precludes the establishment of a meaningful verification system. 241-384 O - 3 17 I 3 I CAT forecasts are prepared from analyses of the atmosphere based on a large-mesh grid which is too gross to identify the scale of motion involved in CAT. It is concluded that there must be a better understanding of the physical processes in the atmosphere which produce CAT. The present and planned research efforts in this area are inadequate. Significant improvement in CAT forecasting could be brought about within the present state-of-the-art if a con- certed effort were made to exploit all sources of available data and if a national facility devoting full time to the CAT problem were established. 3. IIISS6tTt!n3tl0n The dissemination deficiencies are related to the communications problem. There are no dedicated point-to-point, air-ground or air-ground-air channels available for the dissemination of CAT information. Forecasts and warnings, which include CAT reports, and other meteorological data such as hourly weather reports, winds aloft, etc., compete with each other on the fixed and mobile communications services. Delays are frequently encountered due to the saturation of the networks. The dissemination of information on the climatology of CAT in the free atmosphere is presently non-existent, except in a very limited form with restricted distribution. This information is not available on a routine basis as part of the operational services for use of the pilot or as ready reference for the operator or the forecaster. It is believed that existing and planned R&D projects concerned with the general problem of dissemination of weather information are adequate. How- ever, these projects should be pursued vigorously until results permit implemen- tation of improved communications and dissemination techniques and facilities which are vital to the timely dissemination of CAT information. 18 1. Detectors VI. PRIORITIES FOR FUTURE ACTION The establishment of an order of priority for future action was most difficult. Since CAT is common to all of aviation, both civil and military, the Committee looked at the problem as a whole without regard for agency responsibility. In establishing order of importance, the rule "first things first" was used without regard for state-of-the-art capability. The Committee carefully considered the operational needs relating to CAT and developed a tentative order of importance. Subsequently, representatives from the various airspace user organizations were invited to meet and review the list. Concurrence was reached on a set of priority operational needs and their order of importance as shown in the following list: 1. Detection — airborne and ground-based. 2. Improved forecasts. 3. Improved CAT reporting and alerting system. This includes improved criteria for identifying and reporting. 4. Aircraft design criteria, including flight techniques in turbulent areas and aircraft attitude instrumentation and other diagnostic readouts displayed in the cockpit. 5. Pilot/aircraft response in turbulence. 6. Flight manuals and/or publications on seasonal and geographical occur- rences of CAT. The priority list is based on the degree to which solutions to the operational needs alleviate problems imposed by CAT. It is important to point out that the priority list does not indicate the level of R&D effort to be placed on each item. Significant achievements toward alleviation of the problems of CAT are possible by providing the lower priority needs, using state-of-the-art techniques. The results of these efforts should also provide useful information for the develop- ment of improved forecasts and detection techniques. 3. Airbome An in- flight advance warning detector with a cockpit display will do more to solve the operational CAT problems than any other single thing. Therefore, the development of an airborne CAT detector is placed as the No. 1 priority. If a practical detection system could be developed for installation on aircraft, pilots would be able to avoid areas of significant CAT in the same manner as they now do in avoiding convective turbulence with the use of radar. With the higher speed aircraft, i.e., the SST, the importance of an airborne detector could become greater since CAT, made up of relatively smooth long wave lengths or motions, could induce structural responses of concern. A remote sensor of clear air turbulence must be capable of detecting turbulence in clear air irrespective of its location or how it was generated. It should also be capable of detecting turbulence in cirrus. D. GrOUnd-BdSed Falling in about the same category of importance is the need for a ground- based detection system to locate and identify CAT in time and space in the holding, approach and take-off areas of the terminals. Unexpected encounters in the terminal area can be very serious and under many circumstances the avoidance of significant CAT is mandatory. A ground-based CAT detection 19 2. Improved Forecasts 3. Improved CAT Reporting and Alerting system for the terminal area would also satisfy, in large part, the detection requirements for providing observations of CAT over the major air routes. The airborne and ground-based detection systems in Priority 1 would greatly improve operations where CAT is the consideration. There is a need for CAT forecasts for flight planning and airspace management. In fact, until reliable detectors are provided, forecasts will be the major tool for CAT avoidance. It is considered, therefore, that even slight improvements in the accuracy of CAT forecasts and warnings would bring about major improvements in flight operations. Recognizing the deficiencies in Priority 1 and Priority 2 and the slow improvements in the state-of-the-art in those two areas, the next most important requirement is a rapid response CAT reporting and alerting system on a world- wide basis. This would provide information on CAT encounters by aircraft for rapid dissemination to other aircraft and the use of these reports in issuing alerts for flight planning. Also, closely associated with this requirement is the need for improving and standardizing the language used in reporting CAT. Use of standard criteria in reporting CAT is an important adjunct to improving the reporting and alerting system. 4. Aircraft Design Criteria 5. Pilot/Aircraft Response in Turbulence 6. Flight Manuals and/or Pub- lications Every practical step should be taken to design aircraft to withstand CAT encounters regardless of the aforementioned requirements. Stresses to which aircraft should be designed should be evaluated and new or revised criteria established and the present ones reconfirmed. This includes work on DOD air- craft intended for low level operations. Closely related to this effort is the development of aircraft control techniques that would permit transit of turbu- lent areas in a manner that would not compromise the structural integrity of the vehicle. Pilot/Aircraft response in a turbulence environment varies widely depending on pilot experience and training and aircraft configuration, speed, wing loading, altitude, etc., and the environment itself. A better knowledge of pilot/aircraft response in turbulence is required together with advanced development of flight instruments which respond in consonance with the aircraft and the pilot. Information of a statistical nature which is contained as part of the flight manuals or publications giving the seasonal and geographical occurrences of CAT also fall in the list of priority items. This is a particularly important item in view of the rapid transition to the small jet in the general aviation field. These aircraft are used by individual and industrial executives for worldwide opera- tions and it is important that they have advance knowledge of potential areas of CAT. Conclusions The Committee fully recognized the difficulty in solving the detection and forecasting problems. There is no doubt that improvements can be brought about in the lesser priority areas. It is expected that work would go on simul- 20 taneously in all areas regardless of the priorities with a major effort in the detection and forecasting areas. The committee concludes that: 1. There is a major effort underway within the federal agencies and the commercial airline industry (operators and manufacturers) in the clear air turbulence area, but national coordination leading to a common solution has not been established. 2. The detection problem is far from solved and a closely coordinated major effort of national scope is needed. Every technological approach of reasonable promise should be explored. 3. Research and development in the forecasting of CAT is largely confined to small efforts by operational units. Directed effort on a national basis is non-existent. Present forecasts are based on gross data derived from basic analyses produced for general forecasting. These are not adequate for CAT. 4. Priorities for CAT messages on standard communications facilities are too low. There is need for more emphasis on rapid handling of reports, fore- casts and warnings of CAT. particularly from the meteorological system to the pilot and operator, 5. The importance of the DOD actions in collection of CAT data for use in design of new aircraft (ALLCAT) is recognized and is considered essential. 21 PART TWO A. MEASUREMENTS AND OBSER- VATIONS 1. Observations and Measure- ments of CAT SPECIFIC RECOMMENDATIONS Observations and measurements ( data collection ) include those activities related to gathering information to be used in analyses related to improved weather forecasting, to define the structure of turbulence for use in aircraft design and operational procedures, to guide research on detection possibilities, etc. The data collection process, since it involves after-the-fact study of CAT, would not be expected, by itself, to solve user needs, but would provide the basis for ultimate solutions. a. The stated requirements are: b. The committee recom- mends: (1) Data for direct use of pilots and operators ( 2 ) Data for preparing forecasts and warnings (3) Data for preparing upper-air climatology of CAT (4) Data for sensing and recording CAT encounters ( 5 ) Data for basic research (6) Data for determining design criteria of new aircraft. These data requirements are fundamental to the development of an adequate understanding of the physical processes in the atmosphere which produce, main- tain, and dissipate turbulence cells. Such understanding is prerequisite to satisfactory detection, forecasting and reporting of CAT. This requires the acquisition of objective and quantitative data on CAT occurrences and asso- ciated meteorological variables under a closely coordinated interagency program which would attack the problem on a broad front. To do this a National CAT Data Collection Project is proposed to serve as the focal point for an operational task force effort. This project would require data gathering by specially instru- mented aircraft and other means within a specified area during three successive annual periods ( 30-60 days each ) of anticipated maximum CAT activity. Dur- ing these operational periods participating agencies would make maximum use of the National CAT Data Collection Project to acquire data and to test and evaluate detection and forecasting techniques. (1) That a National CAT Data Collection Project be established as the focal point for collecting, storing, and retrieving data re- quired for the solution of CAT tletection and forecasting prob- lems. This effort will feature annual interagency operational task force efforts in CAT reconnaissance, measurements, and observa- tions. It is further recommended that the Department of Defense be the executive agent for the operation of the National CAT Data Collection Project. (2) That the criteria for reporting turbulence (appendix c) be updated and standardized for uniform worldwide application. (3) That an aircraft turbulence measuring system be selected, in- stalled in a representative cross-section of types of aircraft, and implemented for daily operational use. To the greatest degree 22 possible, the instrumentation should provide the best available measure of turbulence intensity. (4) That developmental (and test) work on an airborne objective system be continued to provide a means to accurately identify, measure, and record in time and space the intensity of CAT encountered that can be related to all types of aircraft. Such work should include the development of techniques to provide a direct read-out of the intensity of CAT. (5) That a number of specific approaches be started or expanded simultaneously to obtain better data on actual turbulence patches and the associated meteorological phenomena such as, but not limited to: (a) Use of properly designed and adequately controlled constant- level balloons to obtain data on upper-level wind patterns. (b) Rawinsonde applications: (1) Investigation of the feasibility of new balloon systems, "thin film" electronics, sounding balloons without train, balloon systems with increased drag, etc., and of new radar systems for balloon tracking and delineation of the fine-scale structure of the upper-level winds. (2) Study of variations in the rate of ascent of the rawin- sonde balloon as related to turbulence in the free atmosphere. (3) Use of an accelerometer or other device attached to rawinsonde and/ or other balloons as a means of supplementing other data. (c) Use of weather satellite data on clouds and synoptic patterns as they may relate to CAT occurrences. (d) Use of temperature gradient measurements as related to occurrences of CAT. (e) Use of photo triangulation techniques to observe movement of tracers, including aircraft condensation trails, to obtain time variance information and extent of winds in regions frequented by CAT. 2 Remote Detection (^ That the DOD program of collection of CAT data for use in aircraft design (ALLCAT) be continued. Remote detection includes those activities which would provide the user with an immediate solution to his problems by identifying the existence of CAT to the degree necessary for any operating aircraft to take appropriate action. This 3. The StStet) requirements includes airborne, ground-based, and satellite-borne remote detection. The key «irg. point is that all activities related to detection will be directed at providing before-the-fact knowledge for the user. ( 1 ) An airborne detector to sense the presence of CAT in time to permit avoidance. 23 b. The committee recom- mends: ( 2 > Ground-based and/or satellite systems of detection of CAT at or near certain terminals or over other geographical areas. (3) Research and development of remote detection techniques. (1) That efforts continue in the development of both ground-based and airborne CAT remote detection systems. Work along present approaches should be continuetl and new concepts should be investigated to achieve at the earliest time possible a system (or systems) holding promise sufficient to warrant a major develop- mental effort. A successful CAT detection system is essential in meeting the requirements of the pilot, air traffic controller, and the forecaster. (2) That research and study be concentrated in the following areas: (a) Basic research on the nature and characteristics of turbu- lence patches, and the development of theoretical models of turbulence, aimed toward the development of remote detectors. (b) Studies of the relationship between the turbulence, patches and the atmospheric variables (physical and chemical) to be used in CAT remote detection systems. 3. Pilot/Aircraft Response in Turbulence Detailed data of the turbulence environment obtained under other phases of the Measurements and Observations program will be used in activities listed in this category to determine and analyze the response of pilots and aerospace vehicles of advanced design to various gust inputs. The objective here is to assure availability of adequate vehicle control and to develop piloting techniques, within reasonable physiological and psychological bounds, for use in the turbu- lence environment. a. The stated requirements are: b. The committee recom- mends: ( 1 ) Knowledge concerning the turbulence environment for use in studies of pilot/aircraft response. (2) Data on the effect of turbulence on adequacy of aircraft control; these data should be used in developing recommended pilot techniques for aircraft control in turbulence and included in new aircraft flight manuals. ( 3 ) Data to improve flight attitude instrument presentation for the pilot. (1) That the very substantial effort already made by federal agencies, manufacturers, and airlines concerning pilot reactions and air- craft characteristics in turbulence be continued to determine what is needed to ensure proper control of aircraft. (2) That work already being done by federal agencies, manufac- turers, and airlines to improve instrumentation (for indicating attitude, altitude, air speed, vertical speed, acceleration, etc.) in order to provide the pilot with adequate control cues for flight in turbulence, be continued. (3) That data becoming available from the National CAT Data Collection Project be incorporated in the efforts recommended in (1) and (2), above. 24 B. FORECASTING Forecasting includes those activities which will provide the aircraft operator with advance knowledge of the location and intensity of areas of CAT. Fore- casts normally are used as an aid in advance scheduling and routing of aircraft and for flight planning. Included in this category are the requirements of the forecast production system. 1. I he Sl3te0 requirements ( jj Improved CAT forecasts for periods beyond 12 hours in advance for long- 3T6: range pre-flight and systems planning. ' " (2) More precise CAT forecasts for periods from 4 to 12 hours in advance for specific flight planning. (3) More accurate short-period CAT forecasts, up to 4 hours in advance, for the purpose of alerting airborne pilots and briefing short-range flights. (4) CAT forecasts from the surface to 100,000 feet on a global basis to support military operations. D. ForeC3Sting ( 1 ) A better understanding of the physical processes in the atmosphere which produce CAT. (2) More frequent and more accurate quantitative measurements of CAT vol- umes and intensities. (3) Increased quality and quantity of meteorological data related to CAT. (4) The development of improved CAT forecasting techniques, both numerical and manual. (5) Timely distribution of all CAT related meteorological data to the forecast production and verification system. (6) A climatological atlas containing seasonal and geographical statistics of 2. The Committee reCOm- CAT occurrences by altitudes and routes. mends: ( 1 ) That a national CAT facility be established to serve as a focal point for the collection, processing, and dissemination of current CAT information, including the issuance of forecasts and warnings of significant CAT. This facility would (1) be staffed with qualified forecasters devoting full time to the CAT problem and maintaining a continuous CAT watch, (2) operate an alerting system consisting of updated forecasts and warnings which would provide a "how goes it" to the pilots and operators on a continuing basis, and (3) establish and operate a rigorous verification system which would include the operator's experience as part of the valuation. (2) That the density and frequency of rawinsonde observations in the United States be increased. (3) That a directed effort be instituted utilizing all sources of data to develop techniques that will improve the operational forecasting of CAT. (4) That a program be established for basic research into the atmos- pheric processes that produce CAT, for the purpose of developing forecasting techniques. 25 C. DISSEMINATION 1. The stated requirements are: 2. The Committee recom- mends: Dissemination includes those activities involved in the passing of observed and forecast information on CAT which is of direct use to aircraft in flight. Included is the reporting of CAT enroute from aircraft in flight, alerting of aircraft in flight to possible areas of CAT. and publication of CAT information in flight information manuals. ( 1 ) Distribution, on high priority basis, of forecasts and warnings of moderate or greater CAT. (2) Timely distribution of CAT reports. (Also required for forecasting.) (3) Publication of a climatological atlas containing seasonal and geographical statistics of CAT occurrences by altitudes and routes. ( Also required for forecasting. ) (1) That statistics be published on CAT occurrences based on the present knowledge of CAT and its causes, updated in the future as more and better data become available. (2) That significantly improved, rapid, timely, and effective com- munications be made available to airborne pilots and between them and the weather service to handle the exchange of significant CAT data. 26 APPENDIX A Original Correspondence that brought about the formation of the National Committee for Clear Air Turbulence, and the membership of the Committee and the Advisory Panel. 27 DIRECTOR OF DEFENSE RESEARCH AND ENGINEERING WASHINGTON, D.C. 20301 18 August 1965 Dr. J. Herbert Hollomon, Chairman Federal Committee for Meteorological Services and Supporting Research Department of Commerce Washington, D D Co Dear Herb: The Department of Defense is concerned with the level of coordination of the efforts of various governmental agencies in the area of Clear Air Turbulence (CAT) „ Activities in the area are currently underway within the Departments of the Air Force and Navy, FAA, NASA and the U. So Weather Bureau. The scope of these activities, including possible duplication of efforts and voids in the program, was discussed at an Air Force/FAA-sponsored meeting held April 26-27, 1965. The information presented clearly demonstrated the need for a more effective method of coordination on the national level. Since the work is not purely meteorological in nature, effective coordination is not now the responsibility of the Federal Coordinator for Meteorological Services and Supporting Research. However, that office would appear to be the most logical organization to have this responsibility since they are already responsible for coordination of the meteorological aspects. It is therefore recommended that a special National CAT Committee be established under the Federal Coordinator. Specific terms of reference should be prepared by the committee itself, but the following areas of research and development should be included: airborne detection devices, forecasting, basic research, and data collection. Sincerely, HAROLD BROWN NCCAT AGENDA 1/66 February 18, 1966 28 THE ASSISTANT SECRETARY OF COMMERCE WASHINGTON, D.C. 20230 August 31, 1965 Dr. Harold Brown Director of Defense Research and Engineering Department of Defense Washington, D„ C. 20301 Dear Dr. Brown: Reference your letter of August 18, 1965, I am also concerned with the level of coordination of the efforts of various governmental agencies in the area of Clear Air Turbulence. I agree that the Office of the Federal Coordinator for Meteoro- logical Services and Supporting Research is the logical organi- zation to have this responsibility even though it goes somewhat beyond the intent of Bureau of the Budget Circular A-62, which is the basis on which the office was established. Before undertaking the establishment of a National CAT Committee under the Federal Coordinator, I wish to inform the members of the Federal Committee of your recommendation to determine if there is any objection to this course. I will keep you advised of the progress of this matter. Sincerely yours, William W. Eaton for J. Herbert Hollomon OFCM DFMoore: Oc. 8/26/65 29 U.S. DEPARTMENT OF COMMERCE ENVIRONMENTAL SCIENCE SERVICES ADMINISTRATION WASHINGTON. D C 20235 OFFICE OF FEDERAL COORDINATOR FOR METEOROLOGICAL SERVICES AND SUPPORTING RESEARCH November 30, 1965 Dr. Chalmers W. Sherwin Deputy Director (Research and Technology) OSD DDR&E Department of Defense Washington, D. C. Dear Dr. Sherwin: As you know, the Federal Committee for Meteorological Services and Supporting Research endorsed, on November 12, 1965, the recommenda- tion of the Department of Defense to establish a National Committee for Clear Air Turbulence (CAT) that would report directly to the Federal Coordinator. Dr. Hollomon, as Chairman of the Federal Committee, suggested that the Department of Defense should chair this new committee and further suggested that Major General Jack J. Catton, Director of Operational Requirements and Development Plans, Headquarters, USAF, would be an excellent choice for this chairmanship in view of his interest and active participation in this problem area. I fully endorse the suggestions of Dr. Hollomon and would appreciate your inviting General Catton to be Chairman of the National Clear Air Turbulence Committee. I understand, informally, that this is acceptable to you and that you also plan to designate General Catton as the Department of Defense representative on this committee. I am addressing letters to the other members of the Federal Committee asking them, if interested, for appropriate high-level representation on this new committee. The Federal Committee also indicated that detailed coordination and planning activities deemed necessary by the National Clear Air Turbulence Committee could be accomplished within the existing committee structures under the Office of the Federal Coordinator; specifically, the Interdepartmental Committee for Applied Meteoro- logical Research and the Interdepartmental Committee for Meteoro- logical Services and their respective subcommittees. In addition, 30 I will invite the Chairman of the National Clear Air Turbulence Committee to call upon this office for further support, if desired, in the form of an Executive Secretary and other secretarial assist- ance . So that we can begin to make progress in this vital area, as soon as possible, may I have your answer by December 13, 1965, regarding the suggested Chairmanship of the new committee and the Department of Defense representation. Sincerely yours, /s/ Robert M. White Robert M. White Federal Coordinator for Meteorological Services and Supporting Research cc: Dr. J. Herbert Hollomon Chairman, Federal Committee for Meteorological Services and Supporting Research CEJ:pim 31 U.S. DEPARTMENT OF COMMERCE ENVIRONMENTAL SCIENCE SERVICES ADMINISTRATION WASHINGTON. D C 20235 OFFICE OF FEDERAL COORDINATOR FOR METEOROLOGICAL SERVICES AND SUPPORTING RESEARCH November 30, 1965 Addressees listed on Attachment Dear Sir As you know, the Federal Committee for Meteorological Services and Supporting Research endorsed, on November 12, 1965, the recommen- dation of the Department of Defense to establish a National Committee for Clear Air Turbulence (CAT) that would report directly to the Federal Coordinator. Dr. Hollomon, as Chairman of the Federal Committee, suggested that the Department of Defense should chair this new committee and further suggested that Major General Jack J. Catton, Director of Operational Requirements and Development Plans, Headquarters, USAF, would be an excellent choice for this chairmanship in view of his interest and active participation in this problem area. Dr. Sherwin has agreed with this suggestion and will ask General Catton to chair the committee and to serve as the Department of Defense representative as well. I would like to invite representation on this committee from those agencies having a sufficient interest in the clear air turbulence problem and would suggest that the committee be made up of personnel at the policy level. As indicated during the Federal Committee meeting, we plan to make full use of the existing ICMS and ICAMR structures for the detailed coordination and planning activities which will be required in support of this new committee. I would not expect the National Clear Air Turbulence Committee itself to meet more than twice a year after it has been initially constituted . So that we can begin to make progress in this vital area, as soon as possible, may I have your answer by December 23, 1965. Sincerely yours, /s/ Robert M. White Robert M. White Federal Coordinator for Meteorological 32 Services and Supporting Research ADDRESSEES Dr. Robert J. Anderson Chief, Bureau of State Services Public Health Service Department of Health, Education and Welfare Mr. Arvin 0. Basnight Associate Administrator for Programs Federal Aviation Agency Mr. Harry Perry Director of Coal Research Bureau of Mines Department of Interior Dr. H. A. Rodenhiser Deputy Administrator Agricultural Research Services Department of Agriculture Dr. Herman Pollack Office of International Scientific Affairs Department of State Dr. Homer E. Newell Associate Administrator for Space Science and Applications National Aeronautics and Space Administration Dr. Geoffrey Keller Division Director for Mathematical and Physical Sciences National Science Foundation Honorable William T. Davis, Jr. Assistant Secretary Department of Treasury Dr. George M. Kavanagh Deputy Assistant General Manager for Research and Development Atomic Energy Commission Dr. Robert M. White Administrator Environmental Science Services Administration Department of Commerce 33 NATIONAL COMMITTEE FOR CLEAR AIR TURBULENCE DEPARTMENT OF DEFENSE MEMBER: Major General Jack J. Catton, Chairman ALTERNATE: Dr. Rex C. Mack ATOMIC ENERGY COMMISSION OBSERVER: Mr. Joshua Z. Holland ALTERNATE: Mr. Eugene Bierly CIVIL AERONAUTICS BOARD OBSERVER: Mr. William L. Halnon ALTERNATE: Mr. Joseph C. Zacko, Jr. DEPARTMENT OF COMMERCE MEMBER: Mr. Newton A. Lieurance, Vice-Chairman ALTERNATE: Mr. Arthur C. Peterson FEDERAL AVIATION AGENCY MEMBER: Mr. Arvin 0. Basnight ALTERNATE: Mr. Clifford W. Walker NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MEMBER: Mr. Charles W. Harper ALTERNATE: Mr. William A. McGowan NATIONAL SCIENCE FOUNDATION MEMBER: Dr. Earl G. Droessler (Until June 30, 1966) MEMBER: Dr. Fred D. White (After June 30, 1966) DEPARTMENT OF STATE MEMBER: Mr. Herman Pollack ALTERNATE: Dr. J. Wallace Joyce SECRETARIAT Mr. David J. Eddleman, OFCM Mr. Frank A. Evangelista, OFCM 34 ADVISORY PANEL FOR THE COMMITTEE The National Committee for Clear Air Turbulence selected a panel of experts to: (1) Review the final draft of the NCCAT report to insure that all facets of the CAT problem have been considered and are adequately treated. (2) Advise on the scientific soundness of the report. (3) Recommend changes to the report, consulting the task project officers as required. (4) Present proposed changes to the NCCAT, with rationale for such changes and the consequences thereof. (5) Prepare a new draft of the report, as required, with assistance of representatives of member agencies and with the administrative assistance of the OFCM. Dr. Elmar R. Reiter, Chairman Professor of Atmospheric Science Colorado State University Mr. W. Boynton Beckwith Manager of Meteorology United Airlines Dr. Paul Rosenberg Director of Research Paul Rosenberg Associates Capt. Paul A. Soderlind Director of Flight Operations — Technical Northwest Airlines Dr. Holt Ashley Department of Aeronautics and Astronautics School of Engineering Massachusetts Institute of Technology 35 APPENDIX B A. Effect of Clear Air Turbulence on Operations 1. Department of Defense a. Routine Airlift Operations b. Air-to-Air Refueling Opera- tions c. Support Operations d. Strategic Operations REQUIREMENTS JUSTIFICATION Detailed justification for the requirements stated in the evaluation of the needs (Part One, Section IV) and the specific recommendations (Part Two). Military aircraft must be capable of operating under almost any condition that may occur, particularly under war or emergency conditions. During peacetime, avoidance of a CAT problem area is possible since there is considerable flexibility permitted in chang- ing courses. In wartime this may not be possible because of the confines of a War Operations Plan. During the winter 1965-1966, 27 B-52 aircraft were diverted around a forecasted area of severe CAT. The diversion route for some of these aircraft was rather close to the forecast area of severe turbulence, and two aircraft reported light to occasional moderate turbulence. During this same time, a C-130 aircraft entered the forecast area of severe CAT and reported severe CAT. The B-52 aircraft is rather sensitive to CAT, and pene- trations of severe turbulence areas are not authorized because of possible structural damage. The B-52 costs about 8 million dollars each and the 27 aircraft involved in the diversion, above, represent an investment of nearly one-quarter of a billion dollars. This does not include the inestimable value of the personnel involved. This case highlights the importance of CAT forecasting and the high stakes involved. Routine day-to-day operations have not been unduly affected by CAT. CAT has been encountered, but it has not been sufficiently severe to cause major damage to the aircraft although there have been cases where aircraft control has been lost for short periods of time and/or passengers or crew injured. Considerable discomfort has been created for Military Airlift Command passengers during unexpected encounters with CAT; but out- side of the interference with normal on-board activities, it has not seriously affected mission completion. CAT forecasts provided by the Air Weather Service have contributed greatly to the avoidance of significant CAT. It is expected that the higher altitudes to which transports will be flying in the future will increase the hazard presented by CAT. The greatest operational hazard to military aircraft due to CAT occurs during air-to-air refueling operations. CAT encountered while an aircraft is engaged to a tanker has caused structural, probe and probe receptacle damage, and could even cause engine failure due to fuel ingestion. The hazard is especially severe in the case of fighter aircraft on trans- oceanic and other operational missions. The successful completion of air-refueling is dependent upon a relatively stable fighter/tanker platform. Fighter aircraft and pilots could be lost if they were not able to take on required fuel loads. The undetected presence of CAT in refueling areas presents a serious problem and could preclude the successful completion of the mission. These refueling operations occur from the surface to over 35,000 feet. When moderate to severe, medium or low-level CAT is forecast, it is often necessary to cancel or divert the mission. When CAT is not forecast and is encountered there have been mission aborts. CAT has a most noticeable effect on the tactical airborne delivery role of the C-130 aircraft. On high-speed, low-level missions, severe or even moderate CAT could destroy an aircraft. Light to moderate CAT can be sufficient to preclude cargo drops and produce airsickness in paratroops. With the advent of advanced ways of de- termining aircraft location for air drops, a stable platform is desirable. The strategic task is dependent on adequate realistic peacetime training over simulated combat routes. It has become necessary, because of the number of operational aircraft destroyed or damaged by CAT, to change these routes when moderate or severe CAT is forecast. In addition, detailed instructions have been issued for planning flights and oper- 36 e. Reconnaissance Aircraft Op- erations f. Worldwide Operations ating in turbulence. Included are weather limitations for low-level operations, turbulence criteria for flight planning, advice on aircraft control when turbulence is encountered and cockpit "g" indications which govern withdrawal from a turbulent area. The effect of these instructions coupled with the information from the forecasting service is daily denial of certain air space to Strategic Air Command aircraft. Careful planning and coordination is required at wing command level, and it has been necessary to amend flight plans due to updated CAT forecasts. Similarly, during flight it has been necessary to adjust flight paths to avoid reported CAT. However, in spite of all these precautions, SAC has had accidents caused by unexpectedly entering CAT areas which were not forecast or were of greater intensity than forecast. Specialized reconnaissance operations which are generally conducted in the 25,000-30,000 foot envelope are affected by CAT. The presence of jet stream or CAT, results in con- siderable degradation of sensor accuracies. The aircraft control problems associated with clear air turbulence and jet streams prevent maintaining precise headings and altitudes which are necessary for accurate target location. The responsibility of the Department of Defense is worldwide and airlift and tactical aircraft may be required to operate in countries where there are little or no meteorological facilities. At these locations, it is impossible to obtain or to prepare dependable CAT forecasts. 2. Civil Operations The exposure of civil aircraft to CAT encounters has increased at about the same rate as the increase in the number of jet-powered aircraft engaged in air carrier, commercial and business flight operations. As a group, the air carriers are most affected because of their greater number of flights at altitudes above about 18,000 feet and their greater need to adhere to routes and schedules. All flight operators try to avoid significant turbulence for reasons of safety and because of discomfort to passengers and crew, accumulation of fatigue loading on aircraft struc- tures, the potential for excess ground time for inspection and repairs, possible injury to occupants, and possible loss of control or structural failure. Delays or diversions to avoid turbulence cost money. The money is well spent when significant turbulence existed and was effectively avoided. The money is poorly spent, however, when forecasts are inaccurate and result in unnecessary diversions and delay. The latter is too often the case. In spite of efforts to avoid significant turbulence, encounters do occur with resulting penalties in the form of injuries, airframe damage, repairs, ground time, and passenger dissatisfaction. Realization of the magnitude of these penalties may often be a factor in leading operators unwittingly to make ultra-conservative decisions. For example, in a situation where CAT is suspect, the forecaster knowing that he knows little about the mechanics of CAT and realizing the relative meagerness of the information with which he has to work, often forecasts what he believes to be a reasonable distribution in time and space of significant CAT; but which in reality is too extensive laterally or vertically, or both. On the basis of the forecast, the operator (pilot, or dispatcher and pilot) elects to divert and may add a reasonable margin for safety. The result is an excessive diversion. Long-haul flights, of course, have greater flexibility and can withstand diversions at less cost than medium- and short-haul flights. The average medical cost of an injury due to in-flight turbulence has been found to be about $1,156. This is based on a study of nearly 500 cases. In 1964 five U. S. air carriers reported 99 passenger injuries and three reported 42 crew injuries. * Costs for inspection and repairs due to turbulence have been estimated at five cents per air carrier flight; costs for dissemination of information on turbulence to guard against encounters have been estimated at 94 cents per flight; costs for diversions have been estimated at about $16 million for one year; and the overall cost per flight in 1964 has been roughly estimated at about $6.00 for 2,673,054 flights.* The above costs do not include loss of use of grounded aircraft, loss of employable time by injured occupants and overhead in settling claims. There are other intangible penalties such as disgruntled passengers and structural fatigue load accumulation. A general lack of experience of the response characteristics of typical supersonic trans- NASA CR-62028 of December 1965 by Flight Safety Foundation. 37 port configurations has focused attention on atmospheric turbulence effects on such aircraft. Among many overlapping areas of concern are included the turbulent structure of the atmosphere at altitudes where the SST will fly; the aerodynamic response of an SST configuration; the consequent structural response of the aircraft; the resulting ride com- fort; the effect on engine performance, especially with regard to unstarts; and the possible effects of focusing and maneuvering on the sonic boom overpressure signature. Both the Lockheed Company and the Boeing Company are aware of these problems and are working toward their solutions. The Air Force and NASA are also concerned and are aiding in the analyses and solutions. The major accomplishments in connection with the CAT problem are briefly sum- marized: the general theory has been well developed with regard to aircraft response to gusts; considerable effort has been made to define the structure of the atmosphere below 50,000 feet; and the USAF HICAT Program is in being. The latter, however, is not complete enough to provide an adequate picture of the atmospheric structure above 50,000 feet. Some records of XB-70 flights have been analyzed. SR-71 flight information consists of qualitative pilot reports. B-70 crew members report moderate turbulence in apparently the same temporal, geographical, and air mass locations where the SR-71 pilots report light turbulence. Similarly, B-58, T-38, and F-104 pilots flying chase on the B-70 report one increment less turbulence than do the B-70 pilots. B-70 pilots classified the turbulence effects as trace, light, moderate, heavy and severe. At the same time, the chase pilots re- ported light turbulence when B-70 crews reported moderate and so on. In contrast to frequent turbulence encounters in the B-70, SR-71 crews report that turbulence above 65.000 feet is very mild. These reports also define the most common region of turbulence to be between 40,000 and 60,000 feet at 1.5 to 2.6 Mach numbers. Speculation as to the differences between aircraft include such items as inadequate instrument information, excitation from sources such as the canard or from duct effects or from structural and aeroelastic effects. Analysis of both the Lockheed L-2000-7 and the Boeing 733-390 SST models show in- creased "g" force characteristics at the pilot's station and the tail of the aircraft as com- pared with that experienced in current jet aircraft. The analyses were based on such parametric variations as Mach number and aircraft gross weight. The more significant plans to resolve the CAT problem are: the USAF HICAT program is continuing to better define atmospheric characteristics above 50,000 feet; better instru- mentation, more detailed planning, more frequent testing and more intense analysis are being planned for future B-70 flights; existing B-70 and B-58 data are being reduced, analyzed and compared to resolve reasons for apparent differences in crew responses to turbulence; many agencies are working on all facets of the turbulence problem; and both Lockheed and Boeing are applying vigorous efforts in this area on a continuous updating basis. They are using the currently accepted model of the atmosphere but plan to make changes .as new information becomes available. In addition, analysis of records is being made to show the amount of time the B-70 has flown in turbulence related to ground track segments compared with weather data to correlate turbulence with cloud cover, jet stream action, etc.; NASA is performing power- spectral-density analysis of existing B-70 data to determine more adequately and ac- curately the actual "g" outputs of the aircraft; and plans are being made to install addi- tional turbulence-measuring instrumentation on the B-70. This instrumentation is antici- pated to be ready by January 1, 1967. Airspace Utilization Capabilities Required to Reduce or Eliminate the Effects of CAT on Operations 1. Measurements and Observa- tions a. Observations and Measure- ments of CAT FAA is responsible for effective use of the airspace. The need to change altitude or route of flight of aircraft because of CAT is frequently difficult because of the lack of information on CAT, and conflicting traffic. Quantitative and detailed data are needed on the horizontal and vertical extent and time duration of actual CAT volumes. Additional data are required on the spectral distribution of energy in CAT volumes. These data are not available at present. Data on CAT depend almost exclusively on subjective and highly qualitative reports from pilots of routine commercial and military nights. Even if aircrews are conscientious in reporting CAT, the value of these reports is degraded since there is no proper standard by which the crew can judge the intensity of CAT. Some improvement will be achieved through a revision of the present subjective reporting criteria. A greater improvement will be gained through the use of a lightweight turbulence indicator and recorder in each turbojet aircraft. This would facilitate more accurate re- porting and provide a record of turbulence encounters. An easy readout capability is essential. Turbulence measurements should record "g" loads, or a related factor and oscillatory acceleration encountered. These data can be interpreted in terms of effects on other aircraft. Detailed and quantitative data on actual turbulence volumes will require the use of specially instrumented research nights in programs designed for CAT data collection. These data are essential to furnish information which can be used by: (1) pilots for their own use and for dissemination to other pilots, air traffic controllers, and forecasters; (2) forecasters and researchers in development of forecast techniques, and the basic under- standing of CAT; (3) maintenance personnel to ensure airworthiness after serious CAT encounters, proof of turbulence (abuse) experienced by the aircraft (fatigue history) ; and (4) developers of remote detection systems. b. Remote Detection (1) Advance Warning of CAT Widespread areas of possible CAT occurrences and the usual limited areas of actual occurrences confirm the need for an airborne detector or detection system with the capa- bility to detect the presence of CAT in sufficient time to permit avoidance. One present concept is that such equipment should provide a presentation to the flight crew in a manner similar to weather radar. It should also provide a comparative measure of intensity to facilitate the selection of an alternate route. The equipment should include the capability to determine not only horizontal deviation alternates, but also vertical. In short, an air- borne detector or detection system is needed that will locate and indicate the turbulence intensity at least 4-5 minutes prior to penetration. Even this may often not provide sufficient time to permit situation evaluation, request for clearance change, receipt and execution of clearance change. A detector with a longer warning time would permit the aircraft to become more independent and responsible for CAT avoidance. (2) A Capability to Detect CAT at Terminals and Enroute from the Ground or by Satellite c. Pilot/Aircraft Response (1) A Better Understanding of the Response Rela- tionships of Pilot and Aircraft in Turbulence Turbulence detectors are needed to provide necessary information to pilots, controllers, and dispatchers routinely as a part of teletypewriter transmitted weather reports. Ground- based detectors are especially important in the terminal areas where traffic converges, the airspace is more restricted, and the pilot workload is correspondingly increased. Until satisfactory airborne turbulence detection capability is achieved it may prove necessary to employ ground-based detection systems enroute as well as at the terminal. This would be particularly true if a good detector system should be developed but be prohibitively large, heavy, or too costly for aircraft installation. Eventually a satellite de- tection system may prove practicable for both terminal and enroute. The pilot/aircraft response in a turbulence environment is not well known since the average turbojet pilot does not experience severe turbulence more than once in about 500 hours in flight, and it is obvious that he cannot be trained while actually in severe turbu- lence. This is something he has not been trained for; neither has he been flight-tested to prove competency. The size of a sweptwing transport requires a great amount of flexibility in order to relieve aerodynamic loads. A rigid structure of equal size would of necessity be so heavy that it would be impossible for satisfactory or efficient operation of the aircraft. When 39 an aircraft structure bends to relieve loads it tends to return to its original form provided the load is below the yield point of the structure. This elasticity results in "tuning fork actions" which manifest themselves in a fuselage frequency of about 4 cycles per second during the damping phase. Flight test measurements have shown that the amplitude at this frequency is greatest in the pilot compartment. Research has been conducted and is continuing in the study of human tolerance to cyclic frequencies. Present indications are that human tolerance is relatively low at the frequency of 4 cycles per second. The apparent physiological effect on the human being appears to be a reduction of the cyclic motor functions of spatial orientation and visibility perception. The normal ability of the pilot to interpret the aircraft motion through physio- logical sensation is upset and the scan of flight instruments tends to narrow to a single parameter; the most logical instrument to focus upon being the attitude indicator. (2) NeW Pilot Techniques Based on adequate data concerning turbulence and its effect on aircraft control, pilots may need more training and new techniques to minimize the effects of turbulence. For example, as a result of the transport upset problems in 1963-1964, it was learned that stabilizer trim, power changes and adherence to the proper speed in turbulence were extremely important. Recommended pilot techniques for aircraft control in turbulent air encounters should be included in new aircraft flight manuals. (3) Improved AirCrSft Design Knowledge of the degree of CAT intensity which may be encountered, the character and frequency of CAT in the stratosphere, and the transfer of this information into air- craft design criteria is required. Derived gust velocity information has been used for years in the design of aircraft and has been useful to relate the response of one aircraft to turbulence to that of another aircraft penetrating similar turbulence. Such a system for collecting data would be useful also for forecasters, researchers and operators (pilots) (4) Improved Flight Instru- ments The sweptwing transport initially was equipped with attitude instrumentation identical or similar to that used for years in straight-wing transports. The design requirements for this instrumentation considered the environment common to a transport aircraft as well as aircraft maneuverability. The range of attitude information in a transport aircraft was very limited since it was assumed that a transport aircraft's departure from the level reference was quite small as compared to a military fighter. Little or no intelligence was obtained from the instrument when the attitude progressed beyond 20° up or down. The range markings leading to these limits were difficult to see and gave a poor reference as to progressive movement either up or down. In extreme cases on some instruments no information at all could be obtained, hence giving the pilot no indication whether recovery was being effected or the angle was increasing. In severe turbulence the instruments and/or pilot would vibrate in such a manner that the instruments were unreadable. In the past two years measurable improvements have been made to existing aircraft attitude instruments in the nature of more pronounced range markings as well as addi- tional markings to show extremes not previously indicated. There also have been im- provements in the detection of instrument and energy source failures. Experience with turbulence encounters leaves no doubt that more accurate aircraft flight attitude instruments are needed. When pitch attitudes change, five cockpit indications respond, thus telling the pilot something about pitch attitude. 1 These are: attitude indi- cator, airspeed indicator, altimeter, vertical speed indicator and load factor (seat-of-the- pants) changes. Of these, only the attitude indicator directly indicates pitch changes; the others do not and cannot indicate pitch. In gusts, the latter four instruments may give false indications to the pilot in one way or another if they are interpreted as indications of pitch; the degree to which the information is false depends, among other things, on the direction from which the gust comes. So many variables are involved that the pattern of false information is not repeatable and these cannot be learned. The fundamental problem here is using or being influenced by "pitch" indicators that do not indicate pitch. Therefore, the pilot may make PUSH control input when PULL is required. If reversed control inputs are made, loss of control in turbulence becomes a stronger possibility. The display of aircraft attitude should be clearly presented at all times and should have such prominence that the true attitude of the aircraft is unmistakable. The informa- 1 Northwest Airlines (NWA FSB No. 3-65) by Paul Soderlind. 40 2. Forecasting a. Better Understanding of the Physical Processes Which Produce CAT b. Meteorological Data Related to CAT c. New and Improved Fore- casting Techniques d. CAT Forecasts and Adviso- ries e. CAT Forecasts for Special Operations f. Better Use of Available In- formation 3. Dissemination a. Improved Systems Communications tion should be clearly presented and inclusive enough in both display and command to obviate the need for continuous scanning of the instrument panel. To accomplish this, the instruments and the pilot need improved damping. In this regard, command reference on any important instrument to achieve proper flight equilibrium is much easier for the pilot to fly and will assist him in maintaining a prescribed flight patch. The major constraint on improving CAT forecasts is the lack of a theoretical under- standing of the physical nature of turbulence. Basic research on the atmospheric processes producing CAT, including theoretical studies of turbulence, development of models and testing of theories, is required for a major improvement in the accuracy of CAT forecasts. Increased quality and quantity of meteorological data will improve the capability to forecast CAT. The high correlations found between vertical and/or horizontal wind shears and CAT occurrences suggest that the location, density, frequency and vertical resolution of rawinsonde reports should be critically evaluated in terms of CAT forecasting tech- niques. In addition, there is a need for a substantial decrease in the amount of time currently consumed in getting CAT-related meteorological data to the forecaster. Improved- forecasts require real- or near-real time data. Techniques are needed for short-term forecasts of CAT for operating purposes and longer term CAT forecasts for planning purposes. The best approach to technique develop- ment at the present time appears to be through the use of carefully detailed atmospheric analyses which do not smooth out the detailed information that is necessary to the pro- duction of better CAT forecasts. The requirement exists for improved routine forecasting of potential CAT areas to facilitate advance scheduling and routing of aircraft. Forecasts are required 24 hours in advance and should be updated every six hours. Potential CAT areas should be clearly defined in order to preclude both unwarranted interferences with aircraft operations and unnecessary aircraft re-routing. In addition, there is a requirement for non-routine ad- visories on CAT areas which would amend the routine CAT forecasts in those instances when the latter were found or believed to be in sufficient error to adversely affect op- erations. CAT forecasts are required covering an area from the surface to 100,000 feet on a global basis to support certain military operations. Such forecasts are the responsibility of the DOD and are often made on a special request basis within a period as short as two hours for some flights. These forecasts may be required to cover a time period in excess of 12 hours and must be time and altitude phased with the aircraft flight profile and flight plan and include specific locations, extents, and intensities of the expected CAT. The intensity should be in terms of a meteorological factor which is translatable to the effects of CAT upon each particular type of aircraft. A comprehensive CAT forecasting service is available in the Global Weather Central at Offutt AFB. This unit transmits CAT forecasts to every SAC unit operating within the North American Continent and its approaches. Additionally, a careful met watch of all turbulence reports and changing wind flow is maintained to ensure timely amendment of the forecast as required. Means need to be established so that an ESSA/WB and military exchange of available CAT information is in fact accomplished. It appears that consideration should be given to improving the apparent overlapping responsibilities of the National Meteorological Center at Suitland and the Flight Advisory Weather Service (FAWS). There is a need for a world-wide communications system which will permit a rapid 41 b. Civil-Military Exchange of CAT Information and effective exchange of CAT reports, forecasts and advisories among and between air- borne pilots, aircraft operators, air traffic controllers and meteorologists. Timeliness is of paramount importance in this system because, (1) the safety of aircraft in flight is in- volved, and (2) meteorologists require real- or near-real time data for forecast preparation. The CAT forecasting service currently operated by the DOD at Offutt AFB supports certain military operations with scheduled forecasts and a continuous CAT watch. The establishment of a centralized National CAT Facility, as recommended in this report, will not eliminate the requirement for this military CAT forecast facility since the latter will retain responsibility for certain military operations. Therefore, there is a need to establish procedures which will ensure the timely and effective exchange of available CAT informa- tion between the ESSA/WB centralized facility and the DOD facility. c. A CAT Climatological Atlas There is a need for a world-wide climatological atlas indicating CAT occurrences. It should be prepared from presently available data and updated periodically as more and better data permit. The atlas should indicate the temporal and spatial distribution of CAT occurrences as well as the accompanying meteorological conditions. As additional and better CAT reports and observations become available, refinements should be made within these three classifications. Pertinent extracts from this atlas should be published in appropriate flight publications, such as the IFR Supplement and the Airman's In- formation Manual. 42 APPENDIX C TURBULENCE CRITERIA TABLE AIRFRAME, OPERATIONAL, AND GUST ADJEC TIVAL CLASS AIRFRAME LIMITS 1 TRANSPORT AIRCRAFT OPERATIONAL CRITERIA 2 GUST CRITERIA Descriptive Air Speed Fluctuation Derived Gust Velocities-Ude 3 the order of: Light not specified A turbulent condition during which occupants may be re- quired to use seat belts, but objects in the aircraft re- main at rest. 5 to 15 knots 5 to 20 fps Moderate not specified A turbulent condition in which occupants require seat belts and occasionally are thrown against the belt. Un- secured objects in the air- craft move about. 15 to 25 knots 20 to 35 fps Severe not specified A turbulent condition in which the aircraft momen- tarily may be out of control. Occupants are thrown vio- lently against the belt and back into the seat. Objects not secured in the aircraft are tossed about. more than 25 knots 35 to 50 fps Extreme a. Positive and nega- tive gusts greater than 50 fps (Ude) 3 at Vc 4 between sea level and 20,000 ft for Transport Category Aircraft. b. Positive and nega- tive gusts greater than 30 fps (U e ) 3 at all speeds up to V for Normal Utility and Acrobatic Air- craft. A rarely encountered turbu- lent condition in which the aircraft is violently tossed about, and is practically im- possible to control. May cause structural damage. rapid fluctu- ations in ex- cess of 25 knots. more than 50 fps 5 Footnotes : 1. As derived from the Flight Loads section CAM 4b, Airplane Airworthiness, Transport Categories (May 1960); and CAM 3 Airplane Airworthiness: Normal, Utility, and Acrobatic Categories (Nov. 1959) of Civil Air Regulations. 2. Aircraft Turbulence Criteria developed by NACA Subcommittee on Meteorological Problems (May 1957). 3. Uc approximately equals 3/5 Ude. 4. Vc is the design cruising speed. 5. Special note by NASA, May 26, 1962 : "It might be well to note that the so-called design limit gust velocity of 50 fps could result in permanent set of an airplane structure, but does not neces- sarily imply loss of structural components. By implication, at least, a forecast of a general area of severe turbulence could require flight cancellation since the safety of civil aircraft is not know- ingly compromised. Although it is desirable for the meteorologist to have a standard set of defini- tions, he should also be provided with an understanding of the consequences of his forecast." Source: Exhibit III-B-20-7 Weather Bureau Manual 43 APPENDIX D R&D PROJECTS CONCERNED WITH CLEAR AIR TURBULENCE Detailed listing of R&D projects concerned with Clear Air Turbulence. Reference to these is made in Existing Programs and Deficiencies (Part One, Section V). This review covered a total of 227 R&D projects directly or indirectly related to the CAT problem in the areas of Data Collection, Detection, Pilot/Aircraft Response, and Forecasting. Screening reduced this to a list of 83 projects. This reduction was based in part on ground rules to include only projects directly or indirectly related to the "classical" CAT problem including turbulence associated with mountain waves. This eliminated a number of projects relating to turbulence associated with convective storms and low level convective and mechanical turbulence. In addition, projects were eliminated that were concerned with general R&D programs in the field of meteorology such as meteorological satellites, general circulation, and World Weather Watch studies. Although results from these studies will provide information that will be useful in seeking solutions to the CAT problem, it is believed that, for the purposes of this report, emphasis should be placed on those projects which are very clearly directed to the CAT problem and also to projects which, although not specifically directed to CAT, should produce results that will be clearly applicable to the specific CAT problem. The 83 R&D projects selected were placed in the categories of Data Collection, De- tection, Pilot/Aircraft Response, and Forecasting on the basis of a primary relationship but in many cases a project is related to more than one category. Similarly, the projects are often responsive to more than one of the requirements. REFERENCES 1. Rosenberg, Paul; Beard, M. Gould and Harrison, Henry T. : Clear Air Turbulence NASA CR-62028, December 1965. 2. ION-SAE Conference Proceedings: Clear Air Turbulence Meeting, Washington, D. C, February 23-24, 1966. 3. Reiter, Elmar R. ; The Fine-scale Structure of the Atmosphere, Colorado State Uni- versity, July 1965. 44 TABLE D-1 Existing and Planned R&D Programs DATA COLLECTION Directly Applicable to CAT Agency Project FAA Temperature Gradient Recorder — Determine the correlation between tempera- ture gradient and clear air turbulence as a basis for the development of a detector based on temperature changes. Commerce Clear Air Turbulence Data Collection and Analysis — Collection and analysis of routine PIREPS and special 5-day data collection programs (CAO). NASA Spectral Measurements of Clear Air Turbulence in Regions of Severe Gust Intensities at High Altitudes — Time histories and spectra of the three com- ponents of clear air turbulence in the tropopause, jet stream, mountain wave, gravity wave, etc. will be measured using an instrumented aircraft. Air Force Collection and Analysis of Flight Test Data Relating Low Frequency Electric Field Emissions to Clear Air Turbulence — Is concerned with determining the correlation of variations in the electric fields low frequency emissions with occurrence of CAT. Air Force Climatology of Clear Air Turbulence (CAT) — Will obtain data for use in preparing an atlas of CAT probability up to 100.000 feet for the entire world. Air Force Techniques to Investigate the Nature of Clear Air Turbulence — Intent is to develop a computer model to simulate the atmosphere for use in understanding CAT. Air Force Clear Air Turbulence — This project is to probe the atmospheric microstructure in regions of CAT in the upper troposphere and lower stratosphere. Measure- ments of Ozone will be emphasized. Air Force Medium Altitude Clear Air Turbulence Investigation (MED-CAT) — Will ob- tain data on CAT from 20,000 to 40,000 feet for use in providing aircraft/ vehicle structural design criteria and concepts. Air Force High Altitude Clear Air Turbulence (HICAT) — Will obtain data in CAT from 40,000 to 70,000 feet for use in verifying or correcting existing theories on the power spectral density of turbulence at these altitudes. Air Force High-High Altitude Clear Air Turbulence Investigation (HI-HI-CAT) — Will obtain data on CAT from 70,000 to 200,000 feet for use in verifying or cor- recting theories on the power spectral density of turbulence at these altitudes. Navy Clear Air Turbulence — Will gather data on the relationship between CAT and electric fields. Commerce Clear Air Turbulence — Study of variations in rawinsonde ascensional rate in relation to occurrences of turbulence. Commerce Clear Air Turbulence — Theoretical and Fine-scale Analysis — Detailed analyses of temperature and wind fields associated with turbulent zones and develop- ment of an index of CAT intensity. Air Force Clear Air Turbulence (CAT) — Will probe the atmospheric microstructure in regions of CAT in the upper troposphere and lower stratosphere with a U-2 aircraft. 45 TABLE D-2 Existing and Planned R&D Programs DATA COLLECTION General Atmospheric Data Measurement Agency Project Commerce Three-Dimensional Global Climatology — Determination of the static and dy- namic structure of the atmosphere to as great height as possible. NASA Wind Statistics for Vehicle Launch Area — Statistical or climatological wind data will be obtained for launch areas to provide information to make space launch decisions and design calculations. NASA Smoke Trail Wind Measurement — Wind profile measurements will be obtained from photographic measurement (between 6,000 and 70,000 feet) of a visible trail left by a vertical rising rocket. Army Research in Atmospheric Sciences Subtask: Wind Shear Climatology — Intent is to collect wind shear data and then to compile a climatology of wind shear in various geographical locations, particularly at missile launch sites. Army Research Atmospheric Sciences: Subtask: Missile Climatological Research — Intent is to determine the impact of atmospheric influences on missile struc- ture and flight performance. Navy Naval Met. Ballistic Density — Purpose is to obtain data for use in updating the Navy Aerological Ballistic Manual. Air Force Oscillatory Winds in the Upper Stratosphere and Mesosphere — Will obtain data on radar and wavelike motions observed from 30 to 60 km. Air Force Meso-scale Variability and Special Features in the Troposphere — Will analyze 250 army AN/LMD-1 soundings to determine geometry and intensity of polar jet as part of a program to determine time and space variations of meteoro- logical phenomena and to prepare a humidity atlas. Air Force Supplemental Atmospheres — Provide for analysis of available upper-air sound- ing data to prepare tables that will depict vertical profiles of various param- eters by locations and time of the year. Air Force Methods of Presenting Climatology of Fine-scale Winds — Is intended to ob- tain and analyze wind details in a series of ROSE soundings and prepare a climatology. Air Force Mesospheric Time and Space Variability from Met-rocket Network Data — Will analyze previously obtained data and wind profiles at 30 to 60 km. NSF Lower Atmosphere-Ionosphere Coupling — Investigation of correlation between such phenomena in the lower atmosphere as atmospheric turbulence and atmospheric density waves in the lee of mountains and the ionosphere. NSF The Lower Atmosphere Using Scattering of Microwaves — Examination of the relationships between atmospheric processes (including turbulence) and transhorizon tropospheric scatter propagation of UHF radio waves. NSF Distribution of Ozone in the Atmosphere — Collection and summarization of ozone data, particularly at high latitudes with respect to seasonal, annual, and geographical distribution and the relation of ozone distribution to anomalous stratospheric circulation patterns. Commerce Jet Streams and Mountain Effects on Weather — Study of satellite cloud pic- tures in mountainous regions in relation to jet streams and how they are modified by orographic features. Commerce Feasibility Study and Detailed Investigation of Jet Stream Cirrus and its Re- lationship to Aircraft — Detailed investigation of the jet stream cirrus and its relation to CAT. 46 TABLE D-3 Existing and Planned R&D Programs DATA COLLECTION Development of Instruments and Techniques Agency Project FA A Experimental Testing of Aircraft Weather Measuring Equipment — Experi- mental testing for the development of an economically feasible automatic instrumental sensing of weather elements and telemetering system for op- erational use on commercial aircraft. Commerce SCOMO Balloon Design and Development — To conduct feasibility studies and support to climatological developments for a sounding balloon system. NASA High Resolution Wind Shear Measurements — The FPS-19 radar/spherical balloon technique is being refined. NASA Development of Fast-Rising High-Resolution Balloon Wind Sensors — Increase the fidelity of response of balloon-type wind sensors to the small-scale wind fluctuations. NASA Atmospheric Scattering Techniques — Develop an electronic technique for measuring meteorological variables by scattering of a laser beam. NASA Improved Meteorological Data for Flight Research Programs — Investigate possible data improvement from detailed wind soundings using radar-tracked super pressure balloons. NASA Standardization of Turbulence Intensity Measurements — Develop and verify a simple means of quantitatively determining the turbulence intensity from aircraft. NASA Development of Improved Gust-Measuring Equipment — Develop package to measure three gust velocity components of atmospheric motions over range of wave lengths to 50,000 feet. Army Wind Shear Probe — Prepare to test and improve a wind shear probe. Air Force Establishment of Gust Design Procedures for Aircraft Based on Power Spec- tral Density Techniques — Will outline and develop gust aircraft design ap- proaches based on power spectral techniques. Air Force Turbulence Measuring Equipment for Weather Reconnaissance Aircraft — Will develop, test, and evaluate an objective turbulence measuring system. The output will be in values of turbulence intensity levels which are independent of aircraft speed and type. For data transmission these values will be coded into established descriptive terms. Air Force Turbulence Above 100,000 feet — An investigation to determine the existence of random turbulence between 100,000 and 200,000 feet. 47 TABLE D-4 Existing and Planned R&D Programs DATA COLLECTION Basic Research Agency Project Commerce Airfloiv over Topographic Barriers — Study of how non-linear influences modify classical linear solutions of the problems of airflow over mountains. AEC Studies of Planetary transport processes in the stratosphere by analysis of available meteorological data and tracer measurements. AEC Studies of the structure, dynamics, synoptic conditions and frequency-intensity distribution of extrusions of stratospheric air into the troposphere and related phenomena. AEC Theoretical Study of turbulence dynamics and turbulent diffusion phenomena in the upper troposphere and lower stratosphere on a planetary scale. NSF Hydrodynamic Stability and the Transition to Turbulence — Laboratory studies in the transition from laminar to turbulent flow. NSF Hydrodynamics of a Liquid-Liquid Interface — Experimental and theoretical studies in interfacial stability, stresses, mixing and turbulent diffusion for miscible fluids. NSF Isotropic Turbulence — Experimental laboratory studies into the statistical properties of isotropic turbulence. Atmospheric Turbulence — Theoretical investigation of the basic nature of turbulent motion and associated phenomena in the atmosphere by means of mathematical models. Air Force Study of Turbulence and its Onset — This is an attempt to obtain an insight into the structures of turbulent fields. The approach will be statistical. Agency FAA Air Force NASA NASA NASA NASA Air Force Navy Navy Air Force Air Force Navy Air Force TABLE D-5 Existing and Planned R&D Programs Detection Project Remote Air Temperature Sensing — Development of remotely sensing tempera- ture gradients with microwave and infrared radiometric techniques to meet the requirement of an airborne detection system for CAT. Special Techniques in Radar Meteorology — A special 3-year program intended to determine the feasibility of using ultra-sensitive multi-wavelength ground- based radars for detecting and analyzing clear air perturbations in atmospheric refractivity as they relate to CAT. Will also assist in defining the fine-scale structures of the atmosphere and phenomena such as angels, turbulent areas, temperature inversions, etc. Related to the program using ultra-sensitive radars. An investigation of radar "angel" phenomena, and development of VISTAR Doppler radar. Techniques Studies for Detection of Clear Air Turbulence — Determine the physical characteristics of clear air turbulence phenomena and investigate means by which it can be detected using microwaves. Detection of Clear Air Turbulence — Passive optical techniques to detect turbu- lence are being considered. Laser Studies — Laboratory continuous wave length laser is being studied in relation to the clear air turbulence detection problem. Clear Air Turbulence Detection — Airborne ruby pulse laser is being investi- gated as to a feasible means of detecting CAT. New Concepts in Indirect Probing — Will study and develop advanced methods of measuring meteorological phenomena from reconnaissance aircraft. Clear Air Turbulence — An investigation of turbulence in the clear air around thunderstorms using a laser, an accelerometer, a temperature probe installed in an aircraft. Environmental Measuring Equipment — To develop and evaluate an airborne star scintillation detector for investigation of a potential relationship between CAT and star scintillation. Remote Detection Techniques — To develop remote detection techniques and equipment for the measurement of meteorological parameters from aircraft. Sub-centimeter Low Noise Amplification — Will investigate low noise constant loss amplification for sub-centimeter electromagnetic waves for possible ap- plication to studies of air turbulence. Airborne Ultra-Violet Photo-Reconnaissance — Will investigate the potential of airborne ultra-violet photo-reconnaissance for CAT detection. Intended to determine the use of PPI laser (optical radar) to detect CAT. Laser Doppler Radar for CAT Detection — Will investigate laser-doppler tech- niques for detecting CAT. 49 TABLE D-6 Existing and Planned R&D Programs DATA COLLECTION Pilot/ Aircraft Response Agency Project Air Force Wind Profiles for Aerospace Vehicle Launching — To develop a simplified method of presenting statistics of wind profiles. NASA Development and Flight Utilization of a General Purpose Airborne Simulator (GPAS) — A Jet Star airplane has been modified to provide capability to simulate in flight stability and control characteristics of a variety of airplanes under various flight conditions. NASA Interaction of Pilot Control, Structural and Aircraft Dynamics Due to Pene- tration of Turbulent Air — A study of the effects of atmospheric turbulence on piloting of aircraft through the use of piloted simulators and analytical techniques. NASA Flight Investigation of Handling Qualities in Rough Air — Determine the most desirable airplane handling qualities for safe flight in rough air. FAA Jet Pilot Reactions During Flight in Severe Atmospheric Turbulence — Deter- mination of pilot reaction characteristics upon encountering atmospheric tur- bulence while piloting jet transport sweptwing aircraft. Data will be equally valuable in CAT encounters. Air Force F-lll Category I Flight Test Program — During these tests accelerometers will be used to measure turbulence through which the aircraft may fly. Air Force C-135 Interim Flight Loads Program — A C-135 will be equipped with a VGH meter and recorder. Data obtained will be analyzed to determine effect of turbulence data on aircraft structure. Air Force C-141 Interim Flight Loads Program — A C-141 will be equipped with a VGH meter and recorder. Data obtained will be analyzed to determine effect of turbulence data on aircraft structure. Air Force Load Alleviation and Structural Mode Stabilization — A B-52 instrumented with a gust boom and accelerometer will be used to demonstrate techniques to alleviate gust and maneuvering mode oscillations. 50 TABLE D-7 Existing and Planned R&D Programs Forecasting Agency Project Commerce Objective Weather Analysis — Improved objective techniques for automatic analysis of wind, temperature, moisture, pressure, etc. at various meteorological surfaces. Commerce Enroute {Feather Prediction Techniques — Development of computer techniques for analysis and prediction of weather elements required for enroute aviation operations. Commerce Satellite Data Applications to Weather Analysis and Forecasting — To increase the utilization of meteorological satellite observations in weather analysis and forecasting. FA A Enroute Weather Analysis and Prediction — Development of objective tech- niques for diagnostic analysis and forecasting of horizontal and vertical dis- tributions of flight weather, especially hazardous weather in accordance with the requirements of the National Airspace System. Navy Operational Research into Structure of Jet Stream — Under this program the USN will conduct operational research into jet stream areas and develop forecast techniques for wind variations around the jet, CAT in relation to the jet and temperatures in and around the jet. Air Force Stratosphere Analysis — Objective is to develop techniques for making detailed analyses of the fields of wind and temperature in three dimensions in the stratosphere. Air Force Circulation Dynamics — Objective is to deduce the mechanics responsible for observed changes in the stratosphere circulation and subsequently develop models and techniques for forecasting stratosphere winds and temperatures. Air Force Stratosphere Research — Will develop models and techniques to specify and forecast the three-dimensional wind and temperature fields in the stratosphere. Air Force Stratospheric Analysis of Wind, Temperature, and Density — Intended to im- prove objective analysis of wind, temperature, and density in the region above 100 mbs. Air Force Analysis and Prediction of Wind in the Zone of the Jet Stream — Intended to improve the analysis and prediction of the layer of maximum wind for USAF operations. 51 U. S. GOVERNMENT PRINTING OFFICE : 1966 O - 241-384 PENN STATE UNIVERSITY LIBRARIES Milium