Airport and Air Traffic Control System

January 1982

NTIS order #PB82-207606

Library of Congress Catalog Card Number 82-600545

For sale by the Superintendent of Documents,U.S. Government Printing Office, Washington, D.C. 20402

Foreword

Air transportation is expected to continue growing during the next two decades. Indealing with this growth it will be important to ensure safety and minimize the costs ofthe system to the Government and airspace users. Large investments are now antici-pated in both airports and air traffic control systems, investments that require unusu-ally long leadtimes. For these reasons the House Committee on Appropriations has re-quested that OTA conduct an assessment of airport capacity and related air traffic con-trol issues.

This subject is, more than most, a moving target. There have been rapid changesin Federal Aviation Administration (FAA) plans in recent years, and these plans havebeen further complicated by airline deregulation and the aftermath of the ProfessionalAir Traffic Controllers Organization strike. These events affect future plans becausethey influence the rate of growth and where that growth will occur. There also con-tinue to be rapid and significant changes in the aviation, telecommunications, anddata-processing technologies on which the system relies. In addition, these plans arecoming before Congress during a period of increasing budgetary constraints.

This assessment is intended to provide a perspective on both airport developmentaid and FAA’s proposed air traffic control system modernization. In both areas thereare questions of how much improvement will be needed, how soon it will be needed,and how the funding of improvements will be allocated among airspace users.

Director

. . .Ill

Airport and Air Traffic Control Advisory Panel Members

Raymond L. Bisplinghoff, ChairmanVice President and Director of R&D, Tyco Laboratories

Jesse BorthwickExecutive DirectorNational Association of Noise Control Officials

Secor D. BrowneSecor D. Browne Associates, Inc.

Jack EndersPresidentThe Mitre Corp.

Matthew FinucaneAviation Consumer Action Project

William T. HardakerAssistant Vice President, Air Navigation/Traffic

ControlAir Transport Association

William Horn, Jr.National Business Aircraft Association, Inc.

Jack D. HowellAir Line Pilots Association, International

Alton G. Keel, Jr.Assistant Secretary of the Air ForceResearch, Development and Logistics

Clifton A. MooreGeneral ManagerDepartment of AirportsCity of Los Angeles

Thomas L. OnetoPlanning OfficerAircraft Owners and Pilots Association

Robert E. PoliPresidentProfessional Air Traffic Controllers Association

Gilbert F. QuinbyConsultant

Janet St. MarkPresidentSMS Associates

David S. StemplerAirline Passengers Association

Richard TaylorVice PresidentBoeing Commercial Airplane Co.

David ThomasGeneral Aviation Manufacturers Association

iv

Airport and Air Traffic Control System Project Staff

John Andelin, Assistant Director, OTAScience, Information, and Natural Resources Division

William Mills, Project Director

Marsha Fenn M. Karen Gamble Larry L. Jenney Paul B. Phelps Zalman Shaven

Contractors

Adib Kanafani, Institute of Transportation Studies, University of California at BerkeleyVincent Volpicelli, Port Authority of New York and New Jersey

Jerry D. WardRobert Simpson, Flight Transportation Laboratory, Massachusetts Institute of Technology

John Heritage, EditorR. Bryan Harrison

OTA Publishing Staff

John C. Holmes, Publishing Officer

John Bergling Kathie Boss Debra M. Datcher Joe Henson

Contents

Chapter

1. Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. Introduction and Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. The National Airspace System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Aviation Growth Scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S. Technology and the Future Evolution of the ATC System . . . . . . . . . . . . . . . . . . .

6. Airport Capacity Alternatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7. Policy Implications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page

3

9

25

45

67

101

125

ACRONYMS

AATF

ACARS

ACAS

ADAP

AERA

ANCLUC

ARINCARTCCARTS

ASRATAATARS

ATCATCRBS

BCAS

CDTI

CFCDABS

DARCDMEDODDOTDPIF&EFAA

FARFSSGAGPSICAO

IFR

Airport and Airways TrustFund, trust fund

ARINC /Communications Ad-dressing Reporting System

Airborne Collision AvoidanceSystem

Airport Development Aid Pro-gram

automated en route air trafficcontrol

airport noise comparability andland use

Aeronautical Radio, Inc.air route traffic control centerAutomated Radar Terminal

System, a computer-drivendisplay system used in ter-minal areas

airport surveillance radarAir Transport AssociationAutomatic Traffic Advisory

and Resolution Serviceair traffic controlAir Traffic Control Radar

Beacon SystemBeacon Collision Avoidance

Systemcockpit display of traffic infor-

mationcentral flow controlDiscrete Address Beacon Sys-

tem (Mode S)Direct Access Radar Channeldistance measuring equipmentDepartment of DefenseDepartment of Transportationdisposable personal incomefacilities and equipmentFederal Aviation Administra-

tionFederal Air Regulationflight service stationsgeneral aviationGlobal Positioning SystemInternational Civil Aviation

OrganizationInstrument Flight Rules

ILSINSITU

MLSMode S

NASCOM

NASNASPNOTAMsO&MOMB

PANCAP

PATCO

PIREPPMSPSRRCAG

RE&D

ROIRNAVSACDRS

SMSA

SSRTACAN

TCATCAS

TRACONTRBTri-Modal BCAS

VFRVOR

VORTAC

Instrument Landing Systeminertial navigation systemInternational Telecommunica-

tion UnionMicrowave Landing Systema digital data link system

(formerly DABS)National Airspace Communica-

tions SystemNational Airspace SystemNational Airport System PlanNotices to Airmenoperation and maintenanceOffice of Management and

Budgetpractical annual capacity of an

airportProfessional Air Traffic Con-

trollers Organization

Performance Measuring Systemprimary surveillance radarremote communication air-

groundresearch, engineering, and

developmentreturn on investmentarea navigationStandard Air Carrier Delay

Reporting SystemStandard Metropolitan Station

Areasecondary surveillance radarTactical Control and Naviga-

tion Systemterminal control areaTraffic Alert and Collision

Avoidance Systemterminal radar approach controlTransportation Research Boarda variation of the Beacon Col-

lision Avoidance SystemVisual Flight Rulesvery high frequency omnirange

transmittersA TACAN colocated with a

VOR station

. . .Vlll

Chapter 1

EXECUTIVE SUMMARY

Contents

Page

Aviation Growth Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Airport Capacity Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Air Traffic Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Funding Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Response to Future Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chapter 1

EXECUTIVE SUMMARY.

The National Airspace System includes about6,500 public-use airports connected by a net-work of air routes defined by navigational aids.Aircraft operating along these routes and in ter-minal areas near airports are monitored and con-trolled by a system of ground-based surveillanceand communications equipment—the air trafficcontrol (ATC) system—operated by the FederalAviation Administration (FAA).

In 1980, the 435 airports with FAA towershandled some 180,000 takeoffs and landings perday, or roughly 66 million per year, of which 74percent are general aviation flights and 4 percentare military. The remaining 22 percent of opera-tions are commercial flights (air carrier, com-muter, and air taxi) and are heavily concen-trated in a few large airports. The 66 top airportshandle 77 percent of commercial operations and88 percent of passenger enplanements; the 10largest handle 33 percent of operations and 47percent of passengers.

This concentration of air traffic at a few largehubs creates congestion and delay, which in turnincreases airline operating costs and, ultimately,the cost of air travel for the public. As air trafficand fuel prices increase, the cost of these delays

will be magnified. General aviation users of ma-jor hubs also feel the effects of delay in the formof access restrictions imposed during peak hoursto deal with airport congestion.

Concern about these problems, and about thefeasibility and cost of the proposed solutions,prompted the House Committee on Appropria-tions (Subcommittee on Transportation) to re-quest that OTA undertake an assessment of air-port and terminal area capacity and related ATCissues. The Senate Committee on Commerce,Science, and Transportation endorsed the re-quest of the House Committee on Appropria-tions, which directed OTA to concentrate onfour major topics:

● scenarios of future growth in air transporta-tion;

• alternative ways to increase airport and ter-minal area capacity;

● technological and economic alternatives tothe ATC system modifications proposed byFAA; and

• alternatives to the present ATC process.

OTA’s major findings are presented below.

AVIATION GROWTH SCENARIOS

FAA expects air traffic to increase consider-ably over the next 10 to 20 years, and with it thedemand for ATC services. Its plans for modern-izing and expanding the National Airspace Sys-tem are predicated on accommodating contin-ued rapid growth. A key assumption in FAA’sAviation Forecasts has been that there will be noconstraints on future growth and that new facil-ities and equipment will be deployed where andwhen needed to meet demand. FAA forecastshave consistently exceeded actual demand inthe past, however, with lo-year projections ofgrowth as much as 50 percent higher than ac-tually occurred. This raises questions about theusefulness of FAA forecasts as a basis for long-

term planning and about how quickly FAAneeds to proceed with capacity-related improve-ments in its 1982 National Airspace System Plan(NASP).

Most other aviation forecasts generally sup-port FAA’s projections, but some do not. This isnot surprising in light of the uncertainty aboutthe factors that may affect future traffic growth.The Air Transport Association and a major aer-ospace firm have suggested that the U.S. airlineindustry may already be approaching its maturesize, which would mean that air carrier opera-tions may level off or even decline by the end ofthe century. Airline deregulation has destabil-

3

4 ● Airport and Air Traffic Control System

.

ized market structure and airline profitability,leading to questions about the ability of the in-dustry to finance badly needed new equipment.There are questions about the future price andavailability of aviation fuel and about the long-term impacts of the Professional Air TrafficControllers Organization walkout.

There is also uncertainty about the future dis-tribution of operations among user groups andamong airports. FAA expects general aviationusers to account for 75 percent of the increase indemand, but there are large uncertainties aboutthe continued growth of the general aviation

fleet. One such uncertainty is the future priceand availability of the aviation gasoline used bysmall personal aircraft. As for air carriers, mar-ket forces and the restrictions imposed followingthe strike have already resulted in a redistribu-tion of operations away from congested hubs tosecond-tier airports that have excess capacity.This new trend, in combination with improvedfacilities for general aviation traffic at relieverairports, could make it possible to accommodatesome increases in aggregated operations withinexisting system capacity.

AIRPORT CAPACITY ALTERNATIVES

At any given airport, delay occurs when de-mand for terminal airspace or runways ap-proaches the capacity to handle aircraft safely.Some delay is normal and inevitable, especiallyduring peak traffic hours or when capacity isreduced because of adverse weather. At somemajor airports, however, the level of demand isnow such that delay is chronic and severe. Thesedelays inconvenience passengers, increase airlineoperating costs, and waste over a hundred mil-lion gallons of fuel each year.

One way to deal with delay is to increase thecapacity of hub areas, either by adding runwaysto an existing airport or by building a new air-port to relieve other, overcrowded airports.Large amounts of land are required, however,and there are strong community objections toairport noise. These factors have made majorairport construction and expansion rare in thepast decade. In addition, building new runwaysor airports requires years of planning (and, insome cases, litigation) before it can be imple-mented. At some airports, however, indepen-dent “stub” runways for propeller aircraft couldincrease effective capacity and minimize land-use and noise problems.

A more immediate way to alleviate delay is tomanage traffic so that demand fits within ex-isting capacity. This could be done througheconomic measures, such as differential pricingschemes to help divert traffic from peak to off-peak hours, or perhaps from congested to under-utilized airports. Administrative measures, suchas hourly quotas or user restrictions, could in-duce a similar reallocation of demand.

Improved ATC technology could also helpease airport congestion. Automated terminal-area metering and spacing, to smooth and ex-pedite the flow of traffic, and the MicrowaveLanding System, to permit more flexible use ofcrowded airspace close to the airport, might per-mit existing capacity to accommodate more op-erations. The magnitude of the potential benefitsvaries widely with local conditions, runwayconfiguration, and traffic mix.

There is no single “best” way to increase capa-city or reduce delay. A variety of measures—economic, administrative, and technological—will be needed and the optimum solution for anygiven airport will be determined largely by localconditions.

Ch. 1—Executive Summary ● 5

AIR TRAFFIC

FAA is planning a program of technologicalimprovements intended to enable the NationalAirspace System to handle a higher volume oftraffic with increased efficiency and safety. Thisnew technology will replace present equipment—some of which has been in use for over 40years—with a modern integrated system thatwill be more reliable and productive. Thisshould allow new or improved forms of serviceto be offered to airspace users. Operating costsshould be lower than with the current generationof ATC equipment, but there would also be ma-jor capital cost requirements. Many of these im-provements can be implemented during the next10 years, but the full modernization programwill not be completed until the late 1990’s.

Two technologies are at the heart of the newgeneration of ATC: 1) advanced computers; and2) a two-way digital data link between aircraftand the ground. Advanced high-speed comput-ers and new software will permit the ATC sys-tem to improve the overall management of traf-fic flow, as well as to formulate tactical measuresthat will ensure conflict-free, expeditious, andfuel-efficient flight paths for individual aircraft.Replacement computers will be installed first inen route ATC centers, then in terminal areas,and finally in a central flow control facility thatwill manage air traffic on a national basis. In ad-dition to safety and capacity benefits, these com-puters will permit a level of automation in ATCthat will greatly reduce the workforce needed tohandle future traffic loads.

The improved data link between aircraft andground facilities will permit a rapid and exten-sive exchange of information and instructionswithout relying exclusively on voice radio forcommunication—for example, transmittal ofclearances and weather information. FAA alsoproposes to use this data link as the basis for theTraffic Alert and Collision Avoidance System(TCAS) which will provide aircraft with anindependent, airborne supplement to ground-based separation assurance.

In terminal areas, the use of the MicrowaveLanding System (MLS) will provide more precise

CONTROL

and reliable guidance for landing in adverseweather conditions. In combination with pro-cedural changes, MLS could also lead to moreefficient use of airport capacity because it allowsaircraft to follow any of several curving or seg-mented approach paths to the runway, therebyeasing some of the constraint imposed by thepresent Instrument Landing System (ILS), whichprovides only straight-line guidance along asingle path.

In general, OTA finds that the ATC systemimprovements proposed by FAA are technolog-ically feasible and desirable with respect to safe-ty, capacity, and productivity, although thereare alternatives that might be equally effective.In most of the programs reviewed, detailed costand benefit information is not yet available,making it difficult to judge the cost effectivenessof the FAA proposals in relation to the possiblealternatives. For the same reason, it is not yetfully clear whether the overall benefits will ex-ceed the capital expenditures needed to effect theimprovements, how the benefits will be distrib-uted among user groups, and how system costwill be allocated. Further information will beneeded on implementation plans and specificcosts and benefits throughout the Congress’ con-sideration of the FAA’s 1982 National AirspaceSystem Plan.

Funding Issues

Based on information available at the end of1981, OTA estimates that the costs of airportdevelopment grants-in-aid, modernization ofATC facilities and equipment, and related re-search and development could average roughly$1.5 billion per year over the next 10 years,about 50 percent higher than the level of recentyears. Congress has several options to providefunding for these programs. One would be tocover these expenditures by general fund ap-propriations. This option, while it would affordthe Congress continuing close control of FAAprograms through the annual appropriationsprocess, might not provide the assured continu-ity of funding needed for undertaking a 10-yearprogram of the scope envisioned by FAA.

6 ● Airport and Air Traffic Control System

Alternative options involve reestablishing, inone form or another, the Airport and AirwaysTrust Fund which expired in October 1980. Pos-sible approaches to reinstituting the trust fundinclude: 1) a user tax structure and tax rates simi-lar to those that existed before; 2) higher user taxrates—raised either uniformly or selectively bytype of user; or 3) a different scheme of taxationthat would levy fees in proportion to benefitsreceived or costs imposed by each type of air-space user.

All of these options are controversial, and thesearch for a solution is complicated by manylong-standing issues about the equity of user

charges and the appropriate distribution of trustfund revenues. Other issues that could emerge inthe debate are how to use the present uncom-mitted balance in the trust fund (amounting toabout $3 billion) and whether to use trust fundmoneys to help meet operating and maintenancecosts. In the past, trust fund allocations derivedfrom user fees have covered only about 15 per-cent of these costs, and many feel that usersshould pay a larger share of them. Others arguethat trust fund moneys should be reserved ex-clusively for capital improvements and R&D ex-penses,

RESPONSE TO FUTURE GROWTH

Basically, there are three forms of action thatcan be taken to affect growth: regulatory, eco-nomic, and technological. Regulatory actions in-clude measures imposed by the Government thatwould restrict the use of airspace or the availa-bility of ATC services according to user class ortypes of activity. Economic measures are thosethat would affect the cost of using the airspaceor that would allow the market forces of com-petitive pricing to determine access to facilitiesand services that are in high demand. Techno-logical responses include not only improvedforms of ground-based and avionic equipment

to increase the efficiency of airspace use, butalso increases in airport capacity through theconstruction of new or improved landing facili-ties. All three approaches are likely to be used;the issue is not which to adopt, but what combi-nation and with what relative emphasis. Ulti-mately, the measures adopted to deal withgrowth will reflect a more fundamental policydecision: is growth to be accommodated wher-ever and whenever it occurs; or is it to be man-aged and directed so as to make the most effec-tive use of existing resources, with the costs fair-ly borne by the beneficiaries.

Chapter 2

INTRODUCTION ANDOVERVIEW

Contents

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Trends and Forecasts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .The Airport Capacity Problem. ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .The ATC Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .The Committee Request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .OTA’s Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Technological Improvements. ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Control Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Freedom of Airspace Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Automation and Controller Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Funding and Cost Allocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LIST OF FIGURES

‘99

1112141414151616181920

Figure No. Page1. Profile of U.S. Airports, 1980. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102. FAA Budget and Funding Sources, 1971-80. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Chapter 2

INTRODUCTION AND OVERVIEW

BACKGROUND

The National Airspace System (NAS) includesabout 6,500 public-use airports serving nearly allcities and small communities in the UnitedStates. Connecting these airports is a network ofair routes, defined by navigational aids, thatchanneI the flow of traffic. Flight along theseroutes, as well as operations in the terminalareas surrounding airports, is monitored andcontrolled by a system of ground-based surveil-lance equipment and communication links—theair traffic control (ATC) system.

With two exceptions (Washington NationalAirport and Dunes International Airport), * U.S.airports used by commercial flights are ownedand operated by local, regional, or State author-ities. Many general aviation (GA) aircraft alsouse these commercial air carrier airports, butmost are served by smaller public airports andby roughly 10,000 privately owned fields. Theair route system and the ATC system are oper-ated by the Federal Aviation Administration

*Washington National and Dunes International are owned bythe Federal Government and operated by the FAA.

(FAA), which has responsibility for assuring thesafe and expeditious movement of aircraft inU.S. airspace and contiguous areas. FAA is alsoresponsible for coordinating the use of airspaceshared by military and civil aviation.

In all, the NAS accommodates about 180,000operations (takeoffs and landings) per day at air-ports with FAA control towers, or roughly 66million per year. Of these, 22 percent are com-mercial flights (scheduled air carrier, commuter,and air taxi), 74 percent are general aviation,and 4 percent are military. Most of the commer-cial operations are concentrated at the top 66airports, which account for over 77 percent ofcommercial operations and 88 percent of passen-ger enplanements. Within this group, airlinetraffic is even more highly concentrated at a fewmajor hubs. As shown in figure 1, the 10 largesthubs handle 33 percent of all operations and 47percent of all passengers.l

‘FAA Statistical Handbook of Aviation, Calendar Year 1980(Washington, D. C.: Federal Aviation Administration, 1981),passim.

TRENDS AND FORECASTS

The use of NAS, as measured by aircraft oper-ations at airports with FAA towers, has grownat an annual rate of about 4 percent in recentyears, due almost entirely to the rapid growth ofthe GA sector.2 FAA expects the rate of growthto slow to about 3 percent per year in the nextdecade, but this would still mean that the con-gestion now experienced at the 5 or 10 largestairports may spread to 10 or 15 additional air-ports by the year 2000. This growth would alsolead to substantial increases in the workload ofthe ATC system. FAA workload forecasts in-dicate that there may be both capacity* and

—‘FAA Aviation Forecasts, Fiscal Years 1981-1992 (Washington,

D. C.: Federal Aviation Administration, 1980), passim.*In a general sense, capacity refers to the number of aircraft that

can be safely accommodated in a given period of time. Airport ca-

safety problems arising from the growth in de-mand for ATC services, problems that will notbe confined to major airports or commercialoperations. Projections show the demand forATC services by GA users could increase by asmuch as 70 percent over the next 10 years.

The accuracy of these forecasts depends onfactors that are difficult to predict reliably, Forexample, the growth in aviation is extremely

pacity is defined as the maximum number of aircraft operations(takeoffs and landings) that can be accommodated in a given peri-od of time on a given runway (or set of runways) under prevailingconditions of wind and weather and in conformance with estab-lished procedures for maintaining safe separation of aircraft. Simi-larly, airspace capacity is defined as the maximum number offlights that can be allowed to pass through a volume of airspaceduring a given period of time without violating minimum separa-tion standards.

9

10 ● Airport and Air Traffic Control System

Figure 1.— Profile of U.S. Airports, 1980a

alncludes heliports, STOL ports, seaplane bases, and mllltary-cwll joint.use fields, excludes facllltles tn Puerlo RICO, Vlrgln Islands, and PaclflcTerritories.

SOURCE FAA Stat/s r/ca/ Handbook, 7980

sensitive to the state of the national economy.The price and availability of fuel could be a seri-ous constraint on all classes of aviation. Thelong-term effects of airline deregulation are un-certain but they could have an important influ-ence on the profitability and competitive struc-ture of the industry. Thus, while there is a con-sensus that air activity as a whole will continueto grow, it is not certain how much growth toexpect, where it will occur, or what strategiesshould be adopted to accommodate it. It doesseem clear, however, that growth of aviation,even at a rather slow rate, gives rise to concernabout future airport capacity, terminal area con-gestion, and the safety and efficiency of the ATCsystem.

Photo credit: Bill Osmun, Air Transport Association

A crowded terminal

Ch. 2—Introduction and Overview • 11

THE AIRPORT CAPACITY PROBLEM

Concentration of air traffic at a few largehubs, brought about by the economics of airtransportation and by the general increase in airtravel, creates congestion and delay. * The cut-back in scheduled flights following the air trafficcontrollers’ strike has caused the problem toabate temporarily, but congestion can be ex-pected to recur when operations return to nor-mal levels, and with it the associated problem ofsafely handling a growing volume of air traffic.Congestion results in delays that increase airlineoperating costs and, ultimately, the cost of airtravel for the public. If fuel prices increase, thecost of these delays will become magnified.Commuter airlines and air taxi services are evenmore vulnerable to delay costs than trunk air-lines, since they have a much smaller base ofpassengers across which to spread these costs.

*Delay occurs whenever aircraft must wait beyond the time theyare scheduled to use an airport or a sector of airspace. In practicalterms, delay is usually defined as occurring whenever some per-centage of aircraft must wait longer than a specified period of time,e.g., 80 percent of the aircraft must wait 4 minutes or longer. Con-gestion occurs as demand (the desired number of operational ap-proaches capacity. An increasing number of aircraft seeking to usean airport or an airspace sector at the same time causes queues tobuild up among aircraft awaiting clearance to proceed.

GA users of major hubs also feeldelay in the form of restrictionsbusy airports imposed during peakwith congestion.

the effects ofon access tohours to deal

Expanding airport capacity, either throughconstruction of new airports or enlargement ofexisting ones, is an obvious but far from easy so-lution. The availability of land for airport ex-pansion is severely limited in major metropoli-tan areas, and the cost of available land is oftenprohibitive. There is also rising communityresistance to airport expansion and constructionon the grounds of noise, surface congestion, andthe diversion of land from other desired pur-poses. Even where these obstacles could be over-come, increasing capacity by building a new air-port is at best a long-range solution—the lead-time from conception to beneficial use of a newairport is often a decade or more.

To deal with the problem of congestion in thenear term, and in a less capital-intensive way,two management approaches may be used. Oneis to shift some of the demand for use of the air-port from peak to off peak hours by administra-tively imposing quotas or by applying differen-

Photo credit: Neal Callahan

Congestion and delay

12 ● Airport and Air Traffic Control System

tial pricing for airport access according to thetime of day. This solution tends to work to theadvantage of major air carriers and against thecommuter and air taxi operators, and even moreheavily against GA users, who complain thatquotas or peak-hour pricing might effectivelypreclude them from using major airports at all.An alternative strategy is to divert some trafficto another airport—for example, from a largemetropolitan hub to GA reliever airports in thevicinity. In several cities the problem is not ageneral shortage of capacity but a dispropor-tionate demand at one airport, while excesscapacity exists at nearby airports that couldserve as satellites or relievers. The difficultyarises in determining who is to be diverted, sincefew potential users of reliever airports would

willingly accept diversion, especially if it im-poses inconvenience or extra cost. One way tomake diversion more attractive would be to im-prove the ground transportation links betweenhubs and reliever airports.

The intractability of the congestion problemand the difficulties of increasing airport capacityor making more efficient use of capacity throughmanagerial techniques have prompted somepeople to look to the ATC system for an alter-nate solution. Through procedural changes ortechnological improvements, the ATC systemmight be able to make more efficient use of theairspace in crowded terminal areas, thereby ex-pediting the flow of traffic to and from runways.

THE ATC PROBLEM

The task of controlling air traffic in congestedterminal areas is greatly complicated when traf-fic consists of a mixture of large and small,piston and jet aircraft. Arriving and departingtraffic, which is descending and climbing alongvarious paths and at different speeds to andfrom en route altitudes, may consist of a com-bination of IFR and VFR traffic. * This trafficmixture is inherently difficult to manage. Effi-ciency dictates that aircraft be moved to andfrom - the runway as expeditiously as possibleand that gaps in traffic be kept to a minimum.Safety, on the other hand, requires a regulartraffic pattern to prevent conflicts, and aminimum safe separation distance to preventfast aircraft from overtaking slower ones. Airturbulence in the form of wake vortices,**which are more severe behind heavier aircraft,requires even greater separation between aircraftthan would be needed if all were a uniform size.The overall result is that ATC procedures neces-sary to assure safety and to manage the work-load also contribute to delays in terminal areas.

—.—“Aircraft operating under Instrument Flight Rules (IFR) and Vis-

ual Flight Rules (VFR).**Eddies and turbulence, generated in the flow of air over wings

and fuselage, can upset the stability of following aircraft. Wakevortices, which are invisible, cannot now be accurately detected,and their movement and duration cannot be reliably predicted.

Technological improvements to the ATC sys-tem could help make fuller use of the physicalcapacity of the airport and reduce controllerworkload. Among these improvements are newsurveillance, communication, navigation, anddata processing equipment that could enhancethe controllers’ ability to separate and directtraffic. The Discrete Address Beacon System(previously know as DABS and now designatedas Mode S) is a new generation of radar equip-ment that permits aircraft to be interrogated in-dividually for information about identity, posi-tion, and altitude. Mode S also provides a two-way data link that could reduce dependence onthe present voice radio channels and provide amuch more rapid and extensive exchange of in-formation between air and ground. Variousforms of proposed airborne systems to detectand avoid potential collisions would provide asupplement to present separation assurancetechniques and reduce some of the controller’sburden in handling a high volume of traffic. Itmay also be possible to provide computer analy-sis of flight plans in advance that would helpresolve conflicts in terminal areas, expedite traf-fic flow, and permit more direct and fuel-savingrouting from origin to destination. Another pro-posed improvement is the addition of specialcockpit displays that would provide a picture of

Ch. 2—Introduction and Overview • 13

traffic in terminal areas and thereby permitpilots to cooperate more effectively with thecontroller or to assume some of the controller’spresent responsibility for separation assuranceand determining flight path in terminal areas.Finally, the Microwave Landing System (MLS)would not only improve the ability to land inconditions of severely reduced visibility, butalso permit multiple or curving approach pathsto the runway instead of the single-file, straight-en approach required with the present Instru-ment Landing System (ILS). In the longer term,proposed new ATC technology might replacethe present system of ground-based radar andradio navigation and surveillance capabilities.

These proposed improvements, if adopted,would require very large investments over thenext two decades. These investments would be

made by the Federal Government, but some ofthe funds could be provided by taxes on airspaceusers, who might also have to purchase newavionics equipment to supplement or replacewhat they already have. Managing the transi-tion to a new generation of ATC would also re-quire careful attention, both to assure continuityof service and to avoid the penalties of excessivecost or unexpected delay. It therefore seemsespecially important to select an evolutionarypath that does not foreclose options prematurelyand does allow flexibility in the choice betweencompeting technologies.

These prospective ATC improvements raiseimportant issues for airspace users. If the re-quired new avionics systems become mandatoryfor access to terminal areas or for general use ofcontrolled airspace, some GA, small commuter,

Photo credit: Federal Aviation Administration

Air controller and screen

14 • Airport and Air Traffic Control System

and air taxi operators may find the cost pro- of the present system as possible. Some possiblehibitive. New civil aviation requirements may improvements might ultimately have to be re-not be entirely compatible with the missions or jected, despite of their potential for increasingcapabilities of military aircraft that share the capacity or enhancing safety, because of the costairspace. There will probably be pressure to pro- to users or infringement of the right of access tolong the transition period and to retain as much the airspace.

THE COMMITTEE REQUEST

Concerns about these problems and about Specifically, the Committee on Appropria-te feasibility and cost of proposed solutions tions requested that OTA make an independentprompted the House Committee on Appropria- assessment in four major areas:tions, - Subcommittee on Transportation, to re- ●quest that OTA undertake an assessment of air-port and terminal area capacity and related ATC ●issues. Subsequently, the Senate Committee onCommerce, Science, and Transportation also ex- ●pressed interest in these issues and endorsed therequest of the House Committee on Appropria-tions. ●

scenarios of future growth in air transporta-tion;alternative ways to increase airport and ter-minal area capacity;technological and economic alternatives tothe ATC system modifications proposed byFAA; andalternatives to the present ATC process.

OTA’s APPROACH

This assessment considers the growth of airtransportation over the remainder of this cen-tury. Particular attention is given to large hubairports, where most of the congestion and delayis expected to occur. For the ATC system, the as-sessment focuses on improvements that wouldaffect the safety and capacity of terminal air-space, but developments in other parts of theATC system (en route and flight informationservices) are also considered, Effects of thesechanges on airspace users (commercial opera-tors, passengers, general aviation, and the mili-tary services) are also examined. Policy optionsand alternative development plans are identifiedand analyzed.

The results of this assessment are presented inthe following five chapters:

Chapter 3. Description of the functions, or-ganization, and operation of NAS with em-phasis on ATC.

Chapter 4. Analysis of possible long-rangetrends in air activity and the effect theymight have on technical, investment, andmanagement decisions.

Chapter 5. Examination of prospective newtechnologies and organizational alterna-tives for the ATC system.

Chapter 6. Analysis of various ways to in-crease airport capacity and their advantagesand disadvantages.

Chapter 7. Discussion of the policy implica-tions that arise from alternative approachesto increasing airport capacity and improv-ing the ATC system.

ISSUES

Expanding, improving, and maintaining the of the Federal Government from the earliestnational system of airways, airports, and air days of aviation. There have been undeniabletraffic control has been an important objective benefits to airspace users and the general public

Ch. 2—Introducflon and Overview • 15——.———

from the greater speed and regularity of airtransportation and from the remarkable recordof safety that has been achieved over the years.The rationale for Federal involvement in the de-velopment and operation of NAS has tradition-ally rested on two grounds: 1) promotion andregulation of interstate and foreign commerce;and 2) enhancement of the capability for na-tional defense. It has been argued on bothgrounds that the Federal Government must takean active role to coordinate the developmentand to manage the operation of the system. Thesystem that has evolved under Federal sponsor-ship and direction is not without its flaws,however, and some observers believe that futuredevelopment should be directed along linesother than those of the past. Many of their con-cerns are embodied in the summary of majorissues which follows; these issues will be treatedin greater detail in subsequent chapters of thereport.

Growth

There is basic agreement among aviation ex-perts that civil aviation in the United States willcontinue to grow, thereby increasing the overalldemand for airport use and ATC services. Thereis considerably less agreement about the rate ofgrowth, the distribution among airspace users,the demands on various types of facilities andthe kinds of services that will be required. As aresult, there are sharp disputes about how to ac-commodate this growth or to influence the formand direction it may take.

FAA’s projections have led it to conclude thatsevere capacity restrictions will manifest them-selves in terminal areas and some parts of the enroute system and that perhaps as many as 20 air-ports may be saturated by 2000. To accommo-date this expected growth, the FAA proposes theaddition of new airport capacity and ATC facil-ities designed to handle higher traffic volumes.However, past FAA forecasts have consistentlyprojected higher rates of growth than have ac-tually materialized, casting doubt on the currentFAA forecasts and the expected demand forATC services through the remainder of this cen-tury. Some observers see trends already devel-oping in a different way. They argue that recent

changes such as airline deregulation, the growthof commuter service, sharp rises in fuel cost, andslower economic growth will either dampengrowth or cause it to develop in a patternsignificantly different from that of the past. Forexample, one suggestion is that in an unregu-lated environment, market forces will cause aredistribution of traffic as users find that delaycosts outweigh the benefits of operating at con-gested hub airports.

GA is the sector of aviation where growth hasbeen the most rapid and where there is most seri-ous concern about accommodating future de-mand. Twenty years ago, GA accounted foronly a small fraction of instrument operations;today it represents slightly over half of all instru-ment operations at FAA facilities, and mostforecast; show GA demand for ATC services in-creasing at rates far higher than those of com-mercial air carriers. Measures to restrict GAactivity at major hubs or to divert it to relieverairports or offpeak hours are certain to be con-troversial. GA users feel that reservations, quo-tas, or differential pricing schemes, would un-fairly deny them access to and use of the air-space system. On the other hand, some believethat GA flights into congested terminal areasshould be limited because they typically carryvery few passengers and so provide less publicbenefit than commercial aviation per operationor per unit of airspace use.

At a more general level, the prospects of traf-fic growth and capacity limitations raise theissue of strategic response to accommodatingfuture demand. In the past, the approach hasbeen essentially to accommodate demand wher-ever and whenever it occurred, i.e., the aim hasbeen to foster growth in civil aviation. Somequestion whether this approach is still desirable,arguing that demand and the growth of air activ-ity should be managed and directed in ways tomake the most productive use of airspace andthe most efficient use of existing facilities.

Basically, there are three forms of action thatcan be taken to influence growth: regulatory,economic, and technological. Regulatory ac-tions include measures imposed by the Govern-ment that would control the use of the airspaceor the availability of ATC services according to

16 ● Airport and Air Traffic Control System

user class or types of activity. Economic meas-ures are those that would affect the cost or priceof using the airspace or that would allow marketcompetition to determine access to facilities andservices that are in high demand. Technologicalresponses include not only improved forms ofground-based and avionic equipment to increasethe efficiency of airspace use, but also increasesin airport capacity through construction of newor improved landing facilities. All three ap-proaches are likely to be used, and the issue isnot which to adopt but what combination andwith what relative emphasis. Ultimately, thechoice of measures will reflect a more fundamen-tal strategic decision about how to meet increas-ing demand. Chapter 4 presents a further discus-sion of future growth, and chapters 5 and 6 ex-amine the various responses to growth.

Technological Improvements

The many technological improvements of theATC system being contemplated by FAA fallinto four classes:

● navigation and guidance systems;● surveillance;● communication; and● process improvements.

These potential improvements have three majorcharacteristics: 1) most are technologicallysophisticated and require further developmentand testing before they can be operationallydeployed; 2) they will entail very large expendi-tures by the Federal Government to put them inplace and— in most cases—additional costs toairspace users who will have to equip their air-craft with special avionics; and 3) many yearswill be required for full deployment.

There are several controversial aspects ofthese technologies. First, there are purelytechnical and engineering questions that need tobe answered: will these new systems work as in-tended, what are their advantages and disadvan-tages compared to existing technology, and howcan their development be managed so that op-tions are not foreclosed prematurely? As deci-sions are made and implementation proceeds, itwill be necessary to coordinate the programcarefully in order to provide an orderly transi-

tion and to avoid the costs that could result fromdelay or unexpected technical setbacks.

Beyond these technical and managerial mat-ters, there are more fundamental questionsabout the role of FAA in planning and carryingout technological programs of this nature. Con-gress, for example, has questioned FAA’s pro-posed handling of the program for moderniza-tion of its en route computer system, as haveother members of the aviation community. Theyare concerned that FAA is not consulting ade-quately with specific user groups and not takingadvantage of relevant expertise available outsidethe aviation community. Some of them foresee atime when air traffic may have to be curtailedsimply because the technology to handle in-creased traffic with an acceptable level of safetyhas not been properly planned, developed, anddeployed.

On the other side, there are those who defendFAA’s general strategy for ATC modernizationand approve the way in which particular techno-logical programs are being handled. They arguethat deployment must proceed at a cautious paceboth because of the enormous uncertainties thatmust be overcome and because there must becontinuity of operations throughout the transi-tion. In their view, the potential consequences ofabrupt changes or premature decisions are moreserious and, in the long run, more harmful toaviation than temporary curtailments that mayhave to be imposed while technological dif-ficulties are being resolved.

Chapters examines some of the technologicalissues surrounding proposed system improve-ments, and chapter 7 addresses strategy andpolicy options for managing the transition.

Control Philosophy

Perhaps the most fundamental issue underly-ing the proposed improvements in the ATC sys-tem is that of control philosophy—the principlesthat should govern the future operation of thesystem. The philosophy of the present systemfor controlling IFR traffic is embodied in threeoperational characteristics: the system is primar-ily ground-based, highly centralized, and placesgreat emphasis on standardized (i.e., predict-

Ch. 2—lntroduction and Overview • 17

able) behavior by airspace users. In contrast,VFR traffic has little contact with the ATC sys-tem, except with flight service stations and con-trol towers at airports, and operates much as itdid in the early days of aviation, even though itshares airspace with IFR traffic in some in-stances.

As ATC technology evolved the locus of deci-sionmaking under IFR began to shift from thecockpit to the ground. Routes were determinedby the placement of ground-based navigationaids; surveillance was accomplished by reportsto ground centers and later by search radar; andobservers in airport towers began to direct air-craft in landing and takeoff patterns. As the den-sity of air traffic increased, ground-based ATCpersonnel began to take more and more controlover the altitude, route, and speed to be flown.To some extent this transfer of responsibilitywas the inevitable consequence of the technol-ogy employed, but organizational reasons alsodictated ground-based control. Decisions con-cerning not the movement of individual aircraftbut the pattern of traffic as a whole can best bemade by a single person who is in a position toobserve all flights operating throughout avolume of airspace over a span of time. Coor-dination and direction of several aircraft re-quired that a single individual have authorityover others—a role that the pilot of a single air-craft could not be expected to assume or thatother pilots would accept.

Ground basing implies concentration of con-trol at relatively few locations, and the trend hasbeen for centralization to increase over time.Again, the reasons are both technological andorganizational: centralization is organizationallyadvantageous because it consolidates functional-ly similar activities and allows technical speciali-zation, both of which lead to greater efficiencyand reliability of operation. For example, enroute traffic in continental U.S. airspace is nowcontrolled from 20 regional centers (ARTCCs,and proposed ATC system improvements wouldlead to even further consolidation, with en routeand terminal control eventually merging into asingle type of facility. A similar trend towardcentralization can be observed in FAA’s plans toconsolidate flight service station activities at

about 60 sites, compared to the present disper-sion at over 300 locations.

Perhaps the best example of the trend towardcentralization is the growing importance of theCentral Flow Control (CFC) facility at FAAheadquarters in Washington, D. C., which actsas a nerve center for the entire airspace system.With the aid of computers, CFC reviews the na-tional weather picture and anticipated aircraftoperations for the coming day and determinesthe incidence and cost (extra fuel consumed) ofdelays that could occur because of weather andair traffic demand. This results in a daily opera-tional master plan that smooths demand amongairports and allows delays to be taken on theground at the point of departure rather than inholding patterns at the destination. The value ofthis capability was demonstrated when capacityquotas were imposed as a consequence of theAugust 1981 air traffic controllers’ strike. CFCallowed a national airspace utilization plan to bedeveloped, with detailed instructions to airportsand en route centers on how to manage trafficand minimize the adverse effects of the capacityrestrictions,

A system characteristic that accompaniesground-based centralization of control authorityis standardization of performance. FAA operat-ing procedures specify the behavior of pilots andcontrollers in every circumstance, which in-creases the reliability of system operation byreducing uncertainty and by routinizing nearlyevery form of air-ground transaction. Safety isthe prime motivating factor, but capacity and ef-ficiency are also highly important considera-tions. Controller workload is reduced when therange of possibilities they have to deal with islimited, and this in turn permits a given volumeof traffic to be handled with less stress or, alter-nately, an increase in the number of aircraft eachcontroller can safely handle. Either way, the effi-ciency of the ATC system (measured in terms ofhourly throughput or controller productivity) isincreased, with a corresponding reduction insystem operating cost.

Despite the advantages of ground-basing, cen-tralization, and standardization, there are com-plaints about the control philosophy of the pre-

18 • Airport and Air Traffic Control System

sent system. Pilots complain that a ground-based system detracts from their control overthe conduct of the flight. Centralization mayalso be a problem if, by concentrating controlfacilities or flight services, the personnel on theground are less able to provide particularized in-structions or to take action based on localizedknowledge of flight conditions. Standardization,by definition, limits the flexibility of responseand the freedom to pursue individual or specialcourses of action.

The prospective changes in ATC technologyare viewed with mixed feelings by airspace usersand air traffic controllers. Technology thatwould increase the level of automation could, onone hand, promote greater centralization andstandardization of control functions and couldlead to increases in safety, capacity, or efficien-cy, On the other, automation could serve to in-crease ground authority still further and toreduce the flexibility of the system in dealingwith nonroutine events. Technology like colli-sion avoidance systems or cockpit displays oftraffic information could give back to the pilotcritical information (and hence control respon-sibility) and might enhance the pilot’s ability tocooperate more effectively with the ground-based controller. At the moment, these devicesare thought of as backups in the event of con-troller or system error, but their prospective usealso raises the possibility of independent pilotactions that might contravene controller instruc-tions or disrupt the overall pattern of traffic.

Chapter S, which deals with these and otherforms of advanced aviation technology forground-based and airborne application, treatsthe issues that arise from prospective changes indistribution of control between the air and theground or from further centralization of ATCfunctions and services.

Freedom of Airspace Use

The rising demand for ATC services and theprospect of congestion at more and more majorairports are the basic stimuli for many of thetechnological improvements and proceduralchanges now being sought by the FAA. How-ever, the very measures that might ease capacity

problems or assure the safety of high-densityairspace are often controversial with some cate-gories of users because they are perceived as in-fringements on their freedom to use NAS. GAusers feel particularly threatened, but air carriersand commuter airline operators have also voicedconcern. The military services as well are waryof some new forms of ATC technology and theprocedures that may accompany their use be-cause they may interfere with military missionsor be incompatible with performance re-quirements for combat aircraft.

As the complexity of ATC technology has in-creased, so has the amount of equipment thatmust be carried on the aircraft and the amountof controlled airspace from which VFR flight isexcluded unless the aircraft is equipped with atransponder to allow identification and trackingby the ATC system. Restrictions on airport use,especially at large and medium hubs, have alsogrown more confining for VFR flights, and theairspace around many of the busiest airports isnow designated as a “terminal control area” inwhich all aircraft are subject to air traffic controland may operate only under rules and equip-ment requirements specified by FAA. GA, theprincipal user of the VFR system, finds itselfpressured in several ways. Uncontrolled airspaceis shrinking and may disappear altogether; it isbecoming increasingly difficult to use metropoli-tan airports because of equipment requirements;and the cost of equipping the aircraft with IFRavionics and acquiring an instrument rating areoften out of economic reach for the personal GApilot. Prospective technological improve-ments—such as the Traffic Alert and CollisionAvoidance System (TCAS), data link, or MLS—are viewed by many GA users as further restric-tions on their access to airports and airspace.Many of them feel that, while this new technol-ogy may be desirable or even necessary for aircarriers and larger business aircraft, it shouldnot be required of all GA users or made a pre-requisite for IFR services or access to commercialairports.

Commuter airline operators share some ofthese GA concerns. Virtually all commuter andair taxi operators are equipped for IFR operationand find their needs well served by the present

Ch. 2—Introduction and Overview ● 19—

ATC technology. They see little further advan-tage in new technology and are concerned aboutthe expense of having two sets of equipmentserving the same purpose—advanced avionicsneeded for a high-density terminal at one end ofthe flight and present-day equipment that maybe useful for many years to come at small com-munity airports. They are also concerned thatthe more advanced avionics might eventuallylead to more restrictive rules of operation or ac-cess to terminal areas. Thus, many commuterand air taxi operators would favor a dual-modesystem that allowed them to retain their presentIFR avionics even though more advanced formswere in use by other types of aircraft operators.

Military aviation operates under the civilATC system in all shared airspace and undermilitary control in areas restricted to militaryuse. In flying through civil airspace to and fromtraining areas, military aircraft must often fol-low circuitous routes or observe altitude andspeed restrictions that lengthen transit time. Themilitary services would prefer an arrangementthat allows more direct access to training areasand avoids operation in mixed airspace. Air car-riers have a different view: the most directroutes for trunk airlines are often blocked byrestricted military areas, and the air carriersargue for procedures that would allow them totraverse these areas in the interest of shorteningflight time and saving fuel.

Another issue has to do with new technologythat might be adopted for civil aviation, whichin most cases would be extra equipment for mili-tary aircraft. For combat aircraft, particularlyfighters, the space for avionics and antennas isoften at a premium. While careful coordinationof military and civil requirements can eliminatesome of these problems, certain basic incompati-bilities are likely to remain and to produce con-tinuing controversy.

The issues of freedom of airspace access anduse are discussed further in chapters in connec-tion with specific forms of new aviation technol-ogy.

Automation and Controller Functions

Despite the vast complex of ground-basedequipment and facilities for surveillance, com-munication, and data processing, ATC remainsa highly labor-intensive activity. FAA is keenlyaware of this and has sought for some time tofind ways to automate selected ATC functions.However, most of the automation that has beeninstituted so far has been to assist air traffic con-trollers rather than replace them. Decisionmak-ing and communication—two major elements ofcontroller workload—have not been automatedto any appreciable degree, and the ratio of con-troller work force to aircraft handled has re-mained relatively constant. In addition, thepresent method of backup to automated controlfunctions involves reversion to manual proce-dures used in the previous generation of ATCequipment; this method of assuring service inthe event of outages has tended to perpetuate theteam size and staffing patterns of the previousgeneration.

Plans for an advanced generation of ATC callfor automation of several manual controllerfunctions: conflict prediction and resolution,terminal area metering and spacing, flight planapproval and issue of clearances, and communi-cating routine control instructions to individualaircraft. Such forms of automation could lead tosubstantial increases in controller productivityand might eventually provide the basis for amore extensively automated system in whichmost routine control functions are carried out bycomputers, with the human controller acting inthe role of manager and overseer of machineoperation.

This path of evolution raises three importantgroups of issues. First, there are questions aboutthe feasibility and advisability of replacing thehuman controller to such an extent. ATC nowrelies heavily on judgment and awareness of thedynamics and subtleties of the air traffic situa-tion. Some observers doubt that all of thesecharacteristics could be dependably incorpo-rated into computer software in the foreseeable

20 . Airport and Air Traffic Control System

future. The proponents of automation arguethat much of the routine, repetitive, or predic-tive work of ATC is ideally suited to computers,and that an incremental approach to automationwill help solve many of the problems since eachnew step can build on successful previous ad-vances.

A second major set of issues is the reliabilityof automated systems and the backup methodsto be used when the inevitable equipmentfailures occur. Experience with the presentautomated ATC equipment indicates that com-puter failure rates are a cause for concern, andthe loss of computer-supplied data may meanthat ground personnel lose effective control oftraffic until manual backup procedures are in-stituted—a process that may take several min-utes to complete. Computer experts maintainthat equipment and software reliability can begreatly improved and that automated systemscan be designed to be more failure tolerant.These experts also contend that present ex-perience with manual procedures as backups tooutages of automated equipment indicates a fun-damental flaw in design philosophy because theproper backup to an automated system is notmanual operation, but another automated sys-tem. Critics of automation question the accept-ability of a system in which the human con-troller has no effective means of intervening indegraded states of operation.

A third issue is whether some of the respon-sibility that now resides with the ground-basedsystem ought not to be transferred to, or at leastshared with, the cockpit. A pilot in an aircraftequipped with an airborne collision avoidancesystem and a display of the immediately sur-rounding air traffic might be in a superior posi-tion to select the appropriate maneuver in caseof conflict; in effect, such an airborne systemwould create a mode of IFR operation similar tothe present VFR system. The chief disadvantageof this concept is that it could lead pilots to makea series of short-term tactical responses thatmight not be consistent with the overall schemeof managing traffic in congested airspace. In thiscase, the ground system would still have to actin the capacity of referee, and some contend that

it would be better to keep all control of individ-ual flight paths under one authority.

Chapter 5 contains a further examination ofthe issue of automation in connection with thediscussion of the proposed en route computer re-placement program and the mechanization ofthe Mode S data link and TCAS systems.

Funding and Cost Allocation

The expenditures that are likely to be requiredfor ATC system improvements over the comingyears could be considerably higher than those ofpast years. For the period 1971 to 1980, theamounts budgeted for facilities and equipment(F&E) and associated research, engineering, anddevelopment (RE&D) have averaged $397 mil-lion and $106 million respectively (in constant1980 dollars).3 Future improvements of the enroute and terminal area ATC system and relatedprograms for flight service station, navigation,and communication facility modernization maycall for spending at twice this annual level ormore. At the same time, operating and mainte-nance (O&M) costs are expected to rise, at leastuntil modern labor-saving equipment is installedand productivity gains begin to be realized.

Since creation of the Airport and AirwaysTrust Fund in 1970, FAA has had two sources offunding. F&E, RE&D, and airport grants-in-aidhave been covered wholly by appropriationsfrom the trust fund. In addition, the trust fundhas covered about 15 percent of O&M expenses,although this proportion has varied consider-ably from year to year. The balance of O&Mcosts, about $1.9 billion per year (1980 dollars),and all other FAA budget items have been fromgeneral fund appropriations. Overall, trust fundoutlays have met about 40 percent of annualFAA expenses. The major source of revenue forthe trust fund has been a tax levied on domesticand international airline passengers (see fig. 2).

In October 1980, the Airport and Airways De-velopment Act expired, and Congress declinedto pass reauthorizing legislation. At that timethe trust fund had an uncommitted balance of

30TA calculations based on FAA budget data, 1971-80.

Ch. 2—Introduction and Overview • 21—————————— — .

Figure 2.— FAA Budget and Funding Sources, 1971-80

Generalfund

SOURCE: Off Ice of Technology Assessment, based on FAA budget data, 1971-80.

$2.9 billion, the equivalent of about 2 years’ ex-penditure at the then prevailing rate. Since thattime some of the user taxes contributing to thetrust fund have still been collected (but at re-duced rates of taxation), and these revenueshave been deposited partly in the General Fund

and partly in the Highway Trust Fund. If theserevenues are included and if authorizations fromthe trust fund during fiscal year 1981 are de-ducted, the uncommitted trust fund balancestood at roughly $3 billion at the beginning offiscal year 1982.

22 ● Airport and Air Traffic Control System

In considering sources of funding for futureairport and ATC system improvements, Con-gress will encounter three broad and long-stand-ing areas of controversy. In the absence of atrust fund or some other form of user charges tosupport capital improvement programs, theseparts of the FAA budget would have to befunded from general revenues, which is certainto raise the issue of whether civil aviation andthe airport and ATC system should be subsi-dized by the general public. The argument thatthe recipients of a service should pay the costsfor the Federal Government to provide that serv-ice (a position strongly supported by the presentadministration), holds that capital improve-ments of facilities and equipment and the O&Mcosts of running the airport and ATC systemshould be borne by airspace users through vari-ous specific taxes. On the other hand, it can beargued that civil aviation, like other modes oftransportation, provides a general benefit andtherefore deserves support with public moneys.Other modes of transportation receive subsidyfrom the Government, and some members of theaviation community contend that there is no jus-tification for singling out civil aviation for fullrecovery of capital and operating costs.

The resolution of this issue that has prevailedfor the past 10 years has been a combination ofspecial users taxes and General Fund financing,with the former going for capital expendituresand a small share of operating costs and the lat-ter for the balance of FAA costs. A perpetuationof this scheme, through reestablishment of theAirport and Airways Trust Fund, could embroilCongress in another issue—what is the “fair”amount to be paid by various user classes. Mostpeople concede that each user should pay rough-ly in proportion to the cost that they impose onthe system, but there is violent disagreementwithin the aviation community as to what thesecosts are and how they are to be reckoned. Costallocation studies conducted by the Departmentof Transportation and the FAA have generallyconcluded that, under the tax structure that ex-isted before October 1980, commercial aviation

paid nearly all (88 percent) of the cost of servicesprovided to them. On the other hand, generalaviation taxes returned at almost one quarter ofallocated costs.4 GA representatives have disa-greed strongly with these findings, arguing thatthere is a substantial public benefit of aviationthat has been undervalued in these cost alloca-tion studies and that GA is charged for facilitiesand services that are neither required nor usedby a major part of GA operators. Congress hasshown little inclination to alter the user chargestructure, and most of the proposed legislationto reestablish the trust fund would have little ef-fect on the distribution of user charges that ex-isted previously.

The third area of controversy concerns howthe collected levies should be applied to costs.By congressional action, the use of trust fundmoneys is restricted largely to capital expendi-tures and research and development activities,with some contribution toward operating ex-penditures. There are two major points at issue:1) how should expenditures for capital improve-ments be allocated between airports and ATCfacilities and equipment (and among airportsand ATC facilities used by various types of avia-tion); and 2) should the allocation be broadenedto cover a substantial part (or perhaps all) ofO&M costs.

Resolution of these issues will become espe-cially important when FAA presents its long-range plan for ATC system improvement. In-creased expenditures for facilities and equipmentand associated R&D will be called for, and oper-ating expenses will probably remain high. FAAwill be seeking a long-term commitment and anassured source of funding, but it will face strongopposition from segments of the aviation com-munity if paying for FAA’s programs and oper-ating costs entails an increase in user taxes or areallocation of the share to be borne by variousclasses of airspace users.

‘J. M. Rodgers, Financing the Airport gnd Air-way System; CostAllocation and Recovery, FAA-AVP-78-14 (Washington, D. C.:Federal Aviation Administration, November 1978).

Chapter 3

THE NATIONAL AIRSPACE SYSTEM

Photo credit U S Department of Transportafton

Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Airports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .International Airports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Domestic Air Carrier Airports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Commuter Airports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Reliever Airports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .General Aviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Air Traffic Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Landing Aids... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Flight Planning and Advisory Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Air Traffic Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

System Organization and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ATC Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ATC Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Airspace Users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

List of Tables

Tablel. Airports Included in National Airport System Plan, 1980 . . . . . . . . . . . . . . . . . . .2. U.S. Pilot Population, 1980 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. Summary of Aviation Activity, 1980 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

List of Figures

Figure3.4.5.6.7.8.

Airspace Structure . . . . . . . . .Typical Flight Service Station

. . .Communicat ionLinks. . . . . . . . . . . . . . . . . . . . . . : . . .

Air Route Traffic Control Center Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Connections of aTypical ARTCC With Other Facilities. . . . . . . . . . . . . . . . . . . . .ATC Activities for a Typical IFR Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ATC Facilities and Equipment at a Typical Large Airport . . . . . . . . . . . . . . . . . . .

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Chapter 3

THE NATIONAL AIRSPACE SYSTEM

The National Airspace System (NAS) is a see how the system operates and to identify fac-large and complex network of airports, airways, tors that may shape its future development. Forand air traffic control (ATC) facilities that exists explanatory purposes, it first considers the goalsto support the commercial, private, and military of the system and then describes the systemuse of aircraft in the United States. This chapter under three major headings: airports, air trafficexamines the major parts of the system, both to services, and airspace users.

GOALS

NAS is designed and operated to accomplishthree goals with respect to civil aviation:

1. safety of flight;2. expeditious movement of aircraft; and3. efficient operation.

These goals are related hierarchically, with safe-ty of flight the primary concern. The use of air-port facilities, the design and operation of theATC system, the flight rules and procedures em-ployed, and the conduct of operations are allguided by the principle that safety is the firstconsideration.

Without compromising safety, the secondgoal is to permit aircraft to move from origin todestination as promptly and with as little inter-ference as possible. This involves preventingconflicts between flights, avoiding delays at air-ports or en route, and eliminating inefficient orcircuitous flight paths. It also entails makingmaximum use of airport and airway capacity inorder to satisfy demand, so long as safety is notcompromised. If safety and capacity utilizationare in conflict, the Federal Aviation Adminstra-tion’s (FAA) operating rules require that the vol-ume of traffic using the system be reduced to alevel consistent with safety.

The third goal is to provide airport and ATCservices at low cost. This entails minimizing thecosts to users—not only monetary costs but alsothe penalties of delay, inconvenience, or unduerestriction. It also entails operating the system asefficiently as possible so as to reduce transactioncosts and to increase productivity, i.e., to han-

dle more aircraft or to provide better service tothose aircraft with a given combination of run-ways, controllers, and ATC facilities.

Whereas safety cannot be compromised in theinterest of cutting costs, capacity and cost maybe traded off for the sake of safety. The specialmeasures adopted to deal with disruption of thesystem as a result of the air traffic controllers’strike in August 1981 illustrate the hierarchal re-lationship of safety, capacity, and efficiency. Inorder to continue safe operation in the face ofwork force reductions, the number of aircraft al-lowed to use certain crowded airports and airways at peak demand hours was reduced to alevel that could be handled safely. These meas-ures reduced capacity (the number of aircraftthat the system could accommodate) and in-creased cost (delays, canceled flights, adherenceto quotas), but an effort was made to allow theremaining capacity to be used effectively andkeep costs within reasonable limits. For exam-ple, limits on the number of air carrier flightswere imposed only at the 22 busiest airports,and restrictions were later eased at those airportswhere more operations could be accommodated.Airlines were allowed to use larger aircraft so asto provide as much seat capacity as possible butwith fewer flights, and wherever possible flowcontrol procedures were employed to ensurethat aircraft were delayed on the ground ratherthan in flight, so as to minimize waste of fuel.Other restrictive measures were applied to cutback on general aviation (GA) flights. The mili-tary services voluntarily reduced flight oper-ations.

25

26 • Airport and Air Traffic Control System—.—

The anticipated growth of air traffic and the capacity. Before turning to examination of thesedemand for ATC services over the next two dec- problems, however, it is first necessary to lookades poses several problems, and the need to at the major parts of the NAS and to considermaintain a dynamic balance among system goals the factors that could shape their course of re-motivates the search for improved methods of velopment.ATC and better utilization of airway and airport

AIRPORTS

Airports are the first major part of NAS. Theyare any place designed, equipped, or commonlyused for the landing and takeoff of aircraft. Thisdefinition covers a broad variety of sites: manyof the sites designated as airports by the FAA aremerely dirt strips or seaplane moorings nearopen water; at the opposite end of the spectrumare complex air terminals serving major metro-politan areas, like the 5,000-acre JFK Interna-tional Airport in New York. About 60 percent ofthe 15,000 U.S. airports are private or militaryfields and not available for public use. Of theroughly 6,500 civil airports open to the public,almost 90 percent are used exclusively by smallGA aircraft. The remaining 780 airports (about 5percent of all U.S. airports) are served either byscheduled air carriers or by commuter and airtaxi operators (see table 1).

FAA, in compliance with the Airport and Air-way Development Act of 1970, maintains a mas-ter list of airport development needs for the nextdecade. This compilation, which is periodicallyrevised, is known as the National Airport Sys-

tem Plan (NASP). It identifies categories of air-ports that are of Federal interest and that areeligible for Federal funds under the Airport De-velopment Aid Program (ADAP), and the Plan-ning Grant Program administered by FAA.NASP categorizes public use airports accordingto the type of aviation activity they accommo-date: international, domestic air carrier, com-muter, reliever, and general aviation. This doesnot imply that GA aircraft use only GA airports;in fact, there are GA operations at all categoriesof airports. Rather, the GA classification de-notes that such airports serve only GA and notother types of users.

International Airports

An international airport regularly serves aircarrier flights operating between the UnitedStates and foreign countries. International air-ports tend to be among the best equipped air-ports in terms of runways, landing aids, andATC facilities. In 1980 there were 76 such air-ports.

Table 1 .–Airports Included in National Airport System Plan, 1980a

Type of service Conventional Heliport Seaplane Total

Air carrierb . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 1 31 635Commuter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 — 6 145Reliever. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 — 155General aviation. . . . . . . . . . . . . . . . . . . . . . . . 2,198 4 22 2,224

Total NASP airports. . . . . . . . . . . . . . . . . . . 3,095 5 59 3,159Total public-use airports not in NASPc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,360

Total. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.519alncludes airports in Hawaii and Alaska.blnclude5 76 airports designated as ports of entrY.cEntirely general aviation.

SOURCE: Federal Aviation Administration, National A/rPort Sysfern Plan, 1980-89, 1980,

Ch. 3—The National Airspace System . 27

Domestic Air Carrier Airports

In 1980, NASP included 603 airports servedby domestic air carriers, a figure that includes allof the international airports described above butexcludes 1 heliport and 31 seaplane facilitiesserved by scheduled air carriers. These airportsare classified by FAA according to the size of thetraffic hub they serve, where a hub is definedas a Standard Metropolitan Statistical Area(SMSA) requiring air service. The hub classifica-tions are:

Percentage of totalHub classification: airline passengers *

Large (L) 1.00 or moreMedium (M) . 0.25 to 0.99Small (S) . . . . . . . . . . . . . . . . 0.05 to 0.24Nonhub (N) . . . . . . less than 0.05

*Passengers eplaned by domestic and foreign carriers at U S airports

A hub may have more than one air carrier air-port, and the 25 SMSAs presently designated aslarge hubs are served by a total of 38 air carrierairports. The distribution of aviation activity atdomestic air carrier airports is highly skewed,with progressively greater percentages of flightsand passengers concentrated at fewer and fewerairports. In 1980, for example, the 486 nonhubshandled only 3 percent of all passenger enplane-ments; the 76 small hubs handled 8 percent; the41 medium hubs handled 18 percent; and the 25large hubs handled 70 percent. To carry thispoint one step further, the top five air carrier air-ports (Chicago, Atlanta, Los Angeles, Denver,

Photo credit: Federal Aviation Administration

All filled up

Photo credit: Federal Aviation Administration

Room to grow

and Dallas/Fort Worth) handled about one-quarter of all passenger enplanements and one-fifth of all airline departures. This means that airtraffic congestion tends to center at a very smallfraction of airports; but because of the volumeof traffic handled at these airports, it affects alarge percentage of all aircraft and passengers.

Commuter Airports

Until the Airline Deregulation Act of 1978,many commuter and air taxi airlines were notcertificated as scheduled air carriers by the CivilAeronautics Board (CAB), and NASP classifiedairports served exclusively by commuter and airtaxi in a separate category. Since airline deregu-lation, the number of airports in this categoryhas fluctuated widely, showing sharp increasesin 1979 and 1980 as commuter airlines sought toopen up new markets and an almost equallysharp drop in 1981 as these markets failed tomaterialize. Commuter airports, typically lo-cated in small communities, handle a very lowvolume of traffic, 2,500 to 5,000 passenger en-planements per year. The major concern aboutthis category is not capacity but keeping the air-port in operation so as to provide essential airservice for the small communities in which theyare located.

Reliever Airports

Reliever airports are a special category of GAairport whose primary purpose is to reduce con-gestion at air carrier airports in large and medi-

28 ● Airport and Air Traffic Control System

urn hubs by providing GA users with alternativeoperational facilities and aircraft services ofroughly similar quality to those available at hubairports. The criteria for classification as a re-liever airport in NASP are 25,000 itinerant oper-ations or 35,000 local operations annually,either at present or within the last 2 years. Thereliever airport must also be situated in a SMSAwith a population of at least 500,000 or wherepassenger enplanements by scheduled airlinesare at least 250,000 annually. There were 155airports designated as relievers in the 1980-89NASP.

General Aviation

GA airports are either private use or publicuse, but only the latter are eligible for Federal

development or improvement funds underNASP. There were approximately 2,200 GApublic-use airports in the 1980 NASP. Capacityis usually not a concern except at the largest GAairports, such as Long Beach, Van Nuys, Teter-boro, or Opa-Locka, which may require im-provements similar to those contemplated atmajor hub airports. For most GA airports thechief concern is upgrading and extending airportfacilities and ATC services so as to accommo-date larger and more sophisticated aircraft andto allow operation under adverse conditions.These improvements are being sought both tosupport the expected growth of GA and to pro-vide facilities comparable to air carrier airports,thereby permitting diversion of some GA opera-tions from congested hubs.

AIR TRAFFIC SERVICES

The ATC system— the second major part ofthe National Airspace System—offers threebasic forms of service: navigation aid (includinglanding), flight planning and in-flight advisoryinformation, and air traffic control.

Navigation

Aid to navigation was the first service pro-vided to civil aviation by the Federal Govern-ment. At the end of World War I, the PostOffice undertook to set up a system of beaconsalong the original airmail routes to guide avia-tors at night and in times of poor visibility. By1927, this airway extended from New ‘fork toSan Francisco, with branches to other majorcities.

In the 1930’s, ground beacons for visual guid-ance were replaced by two types of low-fre-quency radio navigation aids—nondirectionalbeacons and four-course radio range stations.The nondirectional beacon emitted a continuoussignal that allowed the pilot to navigate, in amanner analogous to using a light ground bea-con, by homing on the signal with an airbornedirection finder. The radio range station was afurther improvement in that it emitted a direc-

tional signal, forming four beacons alined withrespect to the compass, each defining a course.Pilots listened to a radio receiver and followedthese radio beams from station to station alongthe route. The four-course radio range systemwas phased out beginning in 1950, after reachinga maximum deployment of 378 stations. Low-frequency nondirectional radio beacons are stillin limited use in the United States and wide-spread use in other parts of the world. *

The technology that supplanted the low-fre-quency four-course range as the basic navigationsystem for civil aviation was very high fre-quency omnirange (VOR) transmitters, whichwere first put in service in 1950. This system hadseveral advantages over low-frequency radio.VOR is less subject to interference and aberra-tions due to weather; it is omnidirectional, per-mitting the pilot to fly on any chosen radialrather than only the four courses possible withthe radio range station; and the addition of acockpit display freed the pilot from the need tolisten to radio signals continuously. The majordisadvant