IFATCA The Controller - April/June 1968 by IFATCA

D 20418 F

I FATCA JOURNAL OF AIR TRAFFIC CONTROL

In this Issue Digital Radar PIDt &tracto• Fail-Safe M~P....,

s.,....._

Talldilg to

FRANKFUR T AM MA I N

A PRIL / J U NE 1968

VOLUME 7

Cjnl,._..

NO . 2

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•

New TELEFUNKEN precision approach radars improve landing safety Why? Range inc reased from 10 NM to 12 NM Indica tor sc reens enlarge d from 10 in. to 16 in . Separate screens for 4 and 12 NM range Modern ised antennas fo r con trol o f approaches to different runways In consequence landing fa cilities are greatly improved for poor visibility conditions In addition we supply: airways s urveillance radars ·te rmina l a rea radars· radar remo ting systems · data processing systems · data transmissi on systems

ALLGEME INE ELEKTRIC IT 'ATS-GESELLSCHAFT AEG -TEL EFUNKEN Export Departme nt · 79 Ulm (Donau)· E lisabe thenstraBe 3 · Ge rmany

An international capability in radar and specialised electronics products Plessey Rada r designs and manu factures an extensi ve range o f standard radar equipmen ts for specific func tions and also special radars for applications w here no standard eq uipment is suitable. Equally important is the contribution of Plessey Radar to the fi eld of display and data prese ntation, ranging from autonomous disp lay units to complex air traffic contro l centres. Advanced autom ation techniques, custom -bu ilt to speci fic requirements, tog ether with comprehensive communication s eq uipment are combined in sophisticated display systems fed w ith data from radar an d other sensors of varying types and manufacture. As part of its policy for the future, Plessey Radar is already heavily engaged in the field of space technology, with particular emphasis on satellite communications earth terminals.

路cal radars and Equi p m ents: Defence, A.T.C and M eteoro Iog1 . . 路 ment-satelhte radar systems - display and data handling equip communication ground stations. nt Activities: Research and development-project manageme -system design-installat ion - design studies. . . Id service 路 a nd spares-post design.. Servi ces: Tra .in .ing- fie 路 ent and services For fu ll detai ls of Plessey Radar equipm 'd 1 write to: Plessey Radar Li mite?, Addl eston;, ;ive.y~~ ;;9 S u rrey, England Tel: Weybndge 47282 e ex . Cabl es: Pl essrad Weybridge

~P~ L~E~S~S~E~Y_:R:.=A:...::.D~A--R_ _ A PLESSEY ELECTRONICS GROUP

~ PE(R) JGC

Marconi Touch-wire displays

Displ ays based on the Marconi Tabular Display, w hich provides direct alpha-numeric read-out from a computer, but with the added facility of touch-wires for instant communication with the computer

D ll

Marconi High-definition displays

Fi xed-coil radar displays that have the hig hest reso lution of any available. Suitabl e for P.P.I , Heig ht, Label-plan and Synthetic applications

Marconi Bright displays Marconi T ouch-wire displays provide fingertip access to a computer for instantaneous insertion and extract ion of information

Europe's largest manufacturer of air traffic control and defence radar systems

Displays em ploying Direct View Storage Tu bes for day light v iew ing w ith full faci liti es for Distance from -Threshold, P.P.I or Height路 finding applications

T he Marconi Company Limited, Radar Di vision, Marcon i House, Chelmsford, Essex, England

A N ' ENGLI SH ELECTRIC ' COM PANY

LTO/SSBI

The Marconi Myriad Computer is the most powerful tool available to Air Traffic Control today. Versatile - M yriad's sophistic ated interru pt faci lity and exce ptional hi gh speed make it idea l for Flight Pl an Processing or Radar Data Processing or both simultaneously. Economic- Myriad rental scheme saves high ca pita l outlay and enables economi c updating of eq ui pment. Smal l size saves space.

Software Service - Com plete programmes prepared - program me advice service - customers ' program mers trained - programme li brary. The new London Air Traffic Control Centre is to have a triplicated Marconi Myriad computer Flight Plan Processing system with instant access touch displays, which will mal<e it the most advanced centre in the world .

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IFATCA JOURNAL OF AIR TRAFFIC CONTROL

THE CONTROLLER Frankfurt am Main, April/June 1968

Volume 7 · No. 2

Publisher: International Federation of Air Traffic Controllers' Associations, 40 Pork House Gardens, East Twickenham, Middlesex, England. Officers of IFATCA: L. N. Tekstra, President; G . W. Monk, Executive Secretary; J. R. Campbell, First Vice President; Second Vice-President (post vacant) ; Hon. Secretary (post vacant) ; Bernhard ROthy, Treasurer; Walter Endlich, Editor. Editor: Walter H. Endlich, 3, rue Roosendoel, Bruxelles-Forest, Belgique Telephone: 456248 Publishing Company, Production and Advertising Sales Office: Verlag W. Kramdr & Co., 6 Frankfurt am Main N014, Bornheimer Landwehr 570, Phone 434325,492169, Postscheck Frankfurt (M) 11727. Rote Card Nr. 2. Printed by: W.Kromer&Co., 6 Frankfurt am Main NO 14, Bornheimer Landwehr 570 . Subscription Rote: OM 8,- per annum (in Germany). Contributors ore expressing their personal points of view and opinions, which must not necessarily coincide with those of the International Federation of Air Traffic Controllers' Associations (IFATCA). IFATCA does not assume responsibility for statements mode and opinions expressed, it does only accept responsibility for publishing these contributions. Contributions ore welcome as ore comments and criticism. No payment can be made for manuscripts submitted for publication in •The Controller·. The Editor reserves the. right to m.ake any editorial changes in manuscripts, whi~ he b~lieves will improve the material without oltermg the intended meaning.

CONTENTS Digital Radar Plot Extractors

. .. . . .. . . ... . ........ . . · · · · ·

by Dr. Heinz Ebert Written permission by the Editor is necessary for reprinting any part of this Journal.

Advertisers in this Issue: AEG-Telefunken (Inside Cover) . Wolfgang Assmonn Gmb.H (31) ; The Decca Nav igate; Co., Ltd. (Bo~k Cover); Ell1ott/Cossor (Inside Bock Cover} ; The Marconi Co., Ltd . (2, 3) ; N.V. Hollondse Signaolapparoten (13); N .V. Ph ilips ' Telecommunicatie lndustrie (32); Plessey Radar Ltd . (1); Se lenia S. p. A. (4) ; Solartron (6); Standard Elektrik Lorenz AG (21); Standard Radio & Telefon AB (?.3) .

IFATCA Addresses and Officers . ............ . .. .. . . . .

Fail-Safe Multi-Computer Systems in Air Traffic Control · · · · by H. Teiber

The Digital Simulator as a Tool for ATC Automatic Data Processing . . .. ... . .. . .... .. .. . · · · · · · · · · · · · · · · · · · · · ·

by F. J. Crewe New ATIS Equipment

.. . .. ... ... · · · · · · · · · · · · · · · · · · ·

News from IFATCA Member Associations . · · · · · · · · · · · · · · ·

..... . .... . ............... ...... . .

New Look at Amsterdam .. . . ...... .. .. . . . . . ...... . . .. .. .

Talking to Computers Picture Credit: AEG-Telefunken (8, 9, 10, 16, 18, 19, 20) ; The Merwin Co. Ltd . (27); The Solartron Electronic group Ltd . (26, 28, 29) ; Wolfgang Assmonn GmbH (32) .

by R. N. Harrison

This year, take a look

at Solartron's activities • • • 1n av1on1cs.

Start with our video maps. They're standard with the Royal Air Force and with the U.K. Board of Trade. And they've been chosen by civil and military author ities in twenty-four other countries. In less than t hree years we've sold over 130 systems.

Then take a look at our digital a ir traffic control simulators. They provide for one pilot/five aircraft operation where aircraft are under close control, a nd can provide higher r atios wh ere tra ffic is less dense or is flown strictly according to flight plan. After that you could move on to our analogue simula tors. They're for basic a nd refresher A.T.C. training. The R.A.F. alone h as thirteen of them at t he Central A.T.C. School. That's a £200,000 installation. And there are oth ers a ll over the world. Analogue simulators provide up to twenty-four targets and can either be locked to live radar or work in a wholly synthetic mode. They will match the parameters of a ny r a dar, can be coupled to a ny type of display, and will simulate S.S.R. Then there are our video recorders. They give you a direct video playback ofli ve radar

as part of a training programme on a simulator. But our interest in avionics doesn't stop even there. Solartron data logging, dynamic analysis and digita l t a pe equ ipment is being used for both the Con corde and the Black Arrow projects, a nd in the case of the Black Arrow we h ave a lso provided the digita l computer . So why not come to Farnborough and see the resear ch and production centre from which all our avionics systems come? You 'll enjoy t a lking to the experts.

@·l@=ii;t·]~i 2.· ·~<1 Th e Solartron Electronic Group Limited, Farnborough Hampshire England Telephone : 44433 A Schlumberger company.

Digital Radar Plot Extractors Translation from German

by Dr. Heinz Eben AEG-TELEFUNKEN Ulm/Donou

Basic Functions of Radar Plot Extractors Improved methods for air traffic control are increasingly based on the information gained by radar on the air traffic situation. Thus failsafe radar control becomes more and more important. This can be achieved primarily by a multiple coverage of the respective air space with the aid of an increased number of radar systems. In order to permit evaluation at centrally located places of the information supplied by these radar systems, it is necessary to build up a closely meshed network for the transmission of such information, enabling economic transfer of radar data even over great distances. An additional requirement resulting from this fact is to more and more equip major Air Traffic Control Centers with major digital computer systems facilitating or rendering it possible to process the high rate of information received. One of the important functions which must be assumed by computers is the organization of the presentation of the air traffic situation on displays designed along a new concept for control by computers, and on which both geographical and alphanumerical information is presented. If the air traffic presentation is to be continuously and automatically updated, the installations primarily used for determination of the air traffic situation, primary and secondary radar, must be directly connected to the computer system at the Control Center. Radar installations, however, h_a ve not originally been designed for such linkage, their s1gn?I~, therefore, must first be "digitized" and subjected !o d1g1tal pre-processing. This requires a sub-system serving as a connecting link between radar and computer. Upon closer investigation of the problems arising as a result of radar and computer linkage, it is noted that several important !nterm~~iate problems normally solved by the controller in addition to his other tasks must now be sol~ed automatically, viz. detection of the presence of valid targets, determination of target position, and tracking of target movements. The controller observing the r~da_r sc.reen performs all these tasks on the basis of the d1stribut10~ of the radar echoes displayed, discriminating between aircraft targets and clutter caused by ground and weather returns. For target detection he utilizes his experience, for target tracking his memory, and perhaps also a grease pencil or a "shrimp-boat". Ta.rget tracking on the basis of fed-in target position data 1s a task which can best be performed by a generalpurpose computer. It can, therefore, be accomplished additionally by the computer provided for general information processing.

For target detection and determination of the target coordinates, however, it is preferable to utilize a system specifically designed for these purposes, and assuming the function of a connecting link between radar and computer. This system is called "Radar Plot Extractor".

Principle and Technical Function of Radar Plot Extractors Automatic Target Detection Technique Basic Principles In principle, automatic target detection is subject to the same difficulties as human target detection . These difficulties are a result of the specific characteristics of radar signals:

1. Due to the decrease of the return pulse power by the 4th power of range, the return signals are always weak and subject to considerable noise interference . 2. Returns from the earth 's surface, rain clouds etc., in short called "clutter returns", frequently make it very difficult to detect and process aircraft target returns (valid targets). Generally it can be said that a reasonable target detection in the case of a primary radar of great range coverage would hardly be feasible if the target would furnish but a single return pulse as the antenna beam is passing over the target. For this reason, radar systems are designed in such a way that an aircraft target is subjected to several hits, normally 10 to 20. Target detection is then based on the detection of a correlated pulse train reflected by the target, the individual pulses of the pulse train having the same range values. Noise pulses, however, are more or less uncorrelated and have different range values. By the addition of several target returns on the d_isplay screen or in the observer's eye, respectively, the valid target is distinguished from a single noise return. Thus target detection is the result of an " integration" over several individual returns Foi; automatic target detection, the human capabilitie~ are replaced by circuits having simi.lar capabilities of integration . The process of target detection may be broken down into two steps:

1. Return signal detection . 2.

Return signal correlation ( = integration) .

TARGET HIT

NOISE HIT

-~-w-v"'-1.......~-lil/J-\jJ\J~~------++-~-\/\Jl- THRESHOLD :

I I I

Figure l

D 0

QUANTIZED HITS

Principle of hit detection

Return Signal Detection Return signal detection settles the question whether a received return pulse can be declared a target pulse or s:mply a pulse generated due to noise. This is accomplished in a threshold circuit having a bivalent threshold criterion (Fig. 1): if the amplitude of the return pulse exceeds a pre:;et threshold voltage, a digital "I" is declared for that pulse. If it does not exceed this threshold, it is rejected, resulting in a digital "O". Once a digital "I" has been

1st THRESHOLD

QUANTIZER

decleared for a return pulse, it is definitely declared a target return, even if it might result from an occasionally occurring noise spike (Fig. 1). This means that the effectiveness of target detection greatly depends on the absolute value of this threshold: if the threshold setting is low, all target pulses are detected, but the probability of noise pulses exceeding the low threshold increases. If the threshold setting is high, it will not be exceeded by many noise pulses, but target pulses of low amplitude may be lost. In practice, the threshold is adjusted so that the number of noise spikes occasionally exceeding the threshold is still great compared with the number of actual target pulses. Since the chosen threshold setting must be strictly maintained for the sake of uniform system operation, an automatic threshold adjusting circuit is used, adjusting the threshold in accordance with any changes of the noise level. The value to which the threshold is set is the mean value of the number of noise pulses exceeding the first threshold; this mean value is determined by the circuitry denoted noise meter (NM) in the block diagram (Fig. 2). The threshold circuit denoted "l st threshold" is followed by the "quantizer" declaring a "O" or "I", respectively. The pulses leaving the quantizer are stored in memory Ml from where they are supplied to a circuit denoted "2nd threshold" for target detection.

DIGITAL MEMORY

2nd THRESHOLD =SLIDING WINDOW

BUFFER MEMORY

DETECTOR R

SWD

NM NOISE METER Figure 2

Automatic target detection system -

block diagram

Return Signal Correlation (=Target Detection) Now target detection is performed in such a way that the quantized return pulses received within one antenna beamwidth are examined as to their correlation, and their number is compared with a second threshold criterion, the "2nd threshold". This is accomplished by a circuit called "sliding window detector" (SWD) in accordance with its method of operation. Figure 3 illustrates the method of operation of the sliding window detector: a target is assumed at a range of 58.25 NM, and the antenna beam pattern passes over this target. Within this pattern, the target is to be hit by a total of 9 radar periods. Period P1 supplies a return pulse which, after exceeding the frrst threshold, is written as a "!" into the first location of a register consisting of 9 memory locations. Then the entire contents of the register is shifted by one location, thus automatically erasing the contents of the 9th location; the frrst location into which the "I" of period P, has just been

TARGET INFORMATION

written becomes free since the "I" has been transferred to the second location. Period P2 of the antenna beam supplies a return pulse not exceeding the frrst threshold. A "O" is written into the sliding window; again, the content is shifted by one location. In the third through sixth periods, ''l''s are written into the sliding window; this means that by this time the target has supplied 5 quantized return pulses. This number 5 out of a total of 9 possible hits is now defined as the criterion for exceeding a second threshold, the target detection threshold. If the number of hits coming from a target attains this minimum value during one antenna sweep, start-of-target is declared. When the antenna continues to rotate, the target is getting out of the beam. If the sliding window contents falls below a certain value, "end-of-target" is declared. (In the above example, "end-of-target" is declared if the value decreases to 4 hits.} Depending on the resolution and range of the radar, approximately 500 to 1000 sliding windows will be required in range direction in order to permit optimum target detection within the radar's range. The radar range

may then be assumed to be subdivided into range increments, each sliding window corresponding to a certain range value. The range of coverage of one range increment is determined in accordance with the radar pulse duration; normally it will amount to 2 to 4 microseconds. In practice, the shift register and the second threshold circuit of the SWD are installed but once and operated on a time multiplexing principle. A ferrite core memory stores the information of all sliding windows and makes available the information of the sliding window required at a given moment. The number of sliding window locations depends on the maximum number of hits per one antenna sweep. Generally this number amounts to between 9 and 20 and can be computed from the antenna beamwidth, the rotation speed and the pulse repetition frequency. Together with the associated azimuth and range values, the "start-of-target" and "end-of-target" information furnished by the sliding window is fed to the buffer memory M2 (Fig. 2), where they are stored until further processing takes place. Whereas the first threshold is operating with analogue quantities, the second threshold is operating by counting the available return pulses and comparing their number with a given value, thus providing an "m out of k" criterion. For this reason, the process of target detection is also called "binary integration".

Detection of SSR Targets The principle of automatic target detection discussed above can also be utilized for SSR targets. The information supplied by an SSR decoder and obtained by detection of bracket pulse pairs is processed in an SW detector.

Processing of Detected Targets Basically, the process of automatic target detection is completed when the PR and SSR azimuth and range data of detected targets have been fed to a memory. For operational reasons, it is necessary to complete the plot extractor by provisions for further processing of detected targets. A remarkable result of automatic target detection which can be exploited operationally is the substantial reduction of the data flow originally coming from the radar system. This finds its expression in the fact that 2 to 3 telephone lines will be sufficient for transmission of the detected targets e. g. to the control center located at some distance, while a bandwidth of approximately 10 MHz is required for transmission of the PR and SSR raw video. This makes it possible to materialize the above network for the exchange of radar information over great distances without exceeding a reasonable cost level. In some instances, radar plot extractors are used if only for the reason that thus the

RANGE---

START-OF-TAR S:T

lst

RADAR PERIOD Figure 3

Principles of sliding window detector

problem of radar data transmission can be solved in a technically simple way. For the transmission of information via telephone cables, several additional provisions are required in the plot extractor: a) buffer memory for converting the statistical data flow into a continuous one; b) circuits for assembling the target information into socalled target messages; c) provisions for digital data transmission through telephone lines ("modem"). In the interest of a data flow reduction, it is furthermore useful to assemble the PR and SSR replies of the same target aircraft into one target message. For purposes of monitoring the overall system, defined test targets can be inserted automatically, and their correct processing can be checked continuously. Malfunctions can also be reported and switchover to the standby unit be initiated. This short discussion gives only a general outline of the possible and necessary requirements for processing detected targets which must be met by a plot extractor. For the solution of this and other problems, a so-called process computer is used which can be universally programmed. The respective tasks are then determined by a program specifically established for this computer. Utilization of such a computer for the target processing portion of a digital detector permits a high degree of flexibility with respect to the operational requirements. By program changes it will be possible at any time to make us of the experience gained during operation, and to comply with particular needs.

- - - - - - - - PLOT DETECTOR

Block Diagram of a Combined PR/SSR Plot Extractor Figure 4 is a block diagram of a combined PR/SSR plot extractor equipped with a process computer: The group denoted "plot detector" accommodates the circuits for target detection, one separate processing channel each being provided for PR and SSR targets. Since the antennas of both radar systems are mechanically or electronically linked, a commong timing unit is sufficient for the generation of digital azimuth and range information. If a start-of-target or end-of-target is declared, the associated azimuth and range data are sent to the computer by transfer circuit. In addition to these data, the received code information is connected through to the computer if the start-of-target of an SSR target has been declared. One of the computer tasks is then to determine the center-oftarget from the azimuth values for start-of-target and endof-target. Additional tasks are i. a. the previously mentioned correlation of PR and SSR replies from the same target, buffering of the position coordinates of the detected targets and their associated additional data, organization of data transmission and performance of test functions. The units shown in the block diagram are duplicated in the plot extractor systems utilized in actual operation; this means that immediate switch-over to a complete standby portion is possible if a malfunction occurs. By this measure and the almost exclusive use of integrated circuits for the individual circuitries it is possible, despite the great number of functions to be exerted, to attain such a high degree of reliability that a practically failure-free operation can be ensured.

- - - - - - - - - t - - T A R G E T INFORMATIC'N PROCESS COMPUTER

PD VIDEO

t - - o - - - - t lst THRESHOLD

OUAITIZER

MEMORY SWD FDA PA

TARGET RUGE AZIMUTH

FUICTIDIS PR TARGET INFORMATION

TARGET mm PRDCESSllG TARGET MESSAGE ORGAHIZATIOI OVERFLOW COlfTROl

PRF

1--------<>-AZ

RAa6E AZIMUTH TIME TEST TARGETS

i------+-----+--+--------

DATA TRANSMISSIOâ&#x20AC;˘ ORGAMIZATIOI FIXED PARAMETER CONTROL

----Ii

I i

MODEM 1 TARGETTAUSFER INFORMATIOI FOR DATA TRAHSMISSIQI COKMECTllll OFTELEPHlllE LINES

~---+-----+--+--------i TEST COMTROL

TIMIA6 UlllT MODE Ml MEMORY SSR DECODER

SWD FOR SSA

SSA TARGET INFORMATIOll

SSA VIDEO SSR CODE llFORMATIOD

RADAR Figure ,\

Combin ed PR SSR plo t ex l rnclo r block diagram

PLOT EXTRACTOR

DATA TRANSMISSION

The International Federation of Air Traffic Controllers Associations Addresses and Officers AUSTRIA

FRANCE

Verband Osterreichischer Flugverkehrsleiter A 1300, Wien Flughafen, Austria

French Air Traffic Control Association Association Professionnelle de la Circulation Aerienne

President Vice-President Secretary Deputy Secretary Treasurer

A. Nagy

B. P. 206

H. Kihr F. Apflauer W. Seidl W. Chrystoph

Paris Orly Airport 94 France

BELGIUM Belgian Guild of Air Traffic Controllers Airport Brussels National Zaventem 1, Belgium President Vice-President Secretary Secretary General Treasurer Editor

A. Maziers M. van der Straate C. Scheers A. Davister H. Campsteyn J. Meulenbergs

CANADA Canadian Air Traffic Control Association 56, Sparks Street Room 305 Ottawa 4, Canada President Vice-President Managing Director Treasurer Chairman IFATCA Comm.

J. D. Lyon J.C. Conway L. R. Mattern A. Cockrem R.Roy

DENMARK Danish Air Traffic Controllers Association Copenhagen Airport - Kastrup Denmark Chairman Vice-Chairman Secretary Treasurer Member of the Board

V. Frederiksen Aa. Jaenicke E. Christiansen P. Breddam M. Jensen

President First Vice-President Second Vice-President General Secretary Treasurer Deputy Secretary Deputy Treasurer IFATCA Liaison Officer

Francis Zammith J.M. Lefranc M. Pinon J. Lesueur J. Bocard R. Philipeau M. Imbert R. Philippeau

GERMANY German Air Traffic Controllers Association Verband Deutscher Flugleiter e. V. 3 Hannover-Flughafen, Germany Postlagernd Chairman Vice-Chairman Vice-Chairman Vice-Chairman Secretary Treasurer Editor

W. Kassebohm H. Guddat E. van Bismarck H. W. Kremer H.J. Klinke K. Piotrowski L. Goebbels

GREECE Air Traffic Controllers Association of Greece Ekatis Street 24 Athens 808, Greece President Vice-President General Secretary Treasurer

N. Gones E. Petroulias E. Karagianides C. Theodoropoulus

I CELANO Air Traffic Control Association of Iceland Reykjavik Airport, Iceland Chairman Secretary Treasurer

G. Olafsson S. Trampe D. Helgason

IRAN FINLAND Association of Finnish Air Traffic Control Officers Suomen Lennonjohtajien Yhdistys r. y. Air Traffic Control Helsinki Lento Finland Chairman Vice-Chairman Secretary Treasurer Deputy

Iranian Air Traffic Controllers Association Mehrobad International Airport Teheran, Iran Secretary General

E. A. Rahimpour

IRELAND Fred. Lehto Vaine Pitkanen Heikki Nevaste Aimo Happonen Viljo Suhonen

Irish Air Traffic Control Officers Association ATS Shannon Ireland President Vice-President

D. J. Egl1ngton P. J. O'Herlihy

Gen. Secretary Treasurer IFATCA Liaison

J. Kerin T. Lane J. Grey

IS RAEL Air Traffic Controllers Association of Israel

P. 0 . B. 33 Lod Airport, Israel Chairman Vice-Chairman Treasurer

Jacob Wachtel W. Katz E. Medina

ITALY Associazione Nazionale Assistenti e Controllori della Civil Navigazione Aerea Italia Via Cola di Rienzo 28 Rome, Italy Senator P. Caleffi President L. Mercuri Secretary

LUXEMBOURG Luxembourg Guild of Air Traffic Controllers Luxembourg Airport President Secretary Treasurer

Alfred Feltes Andre Klein J.P. Kimmes

NETHERLANDS Netherland Guild of Air Traffic Controllers Postbox 7590 Schiphol Airport Central, Netherlands President Secretary Treasurer Member, Publicity Member, I FATCA-affairs

Lufttraflkkledelsens Forening Box 135 Lysaker, Norway

Chairman Secretary

J. D. Monin T. Roulin

UNITED KINGDOM Guild of Air Traffic Control Officers 14, South Street Park Lane London W 1, England Master Executive Secretary Treasurer

P. D. S. Mealing W. Rimmer E. Bradshaw

URUGUAY Asociac;:i6n de Controladores Aeropuerto Nacional de Carrasco Tor re de Control Montevideo, Uruguay U. Pallares J. Beder M. Puchkoff

Asociacion Nacional de Tecnicos en Transito Aereo Venezuela Avenida Andres Bello, Local 7 8129 Caracas, Venezuela President Seer. General Seer. Public Rei. Seer. Organisation Seer. Documentation Seer. Finance Seer. Cultur & Prop. Seer. Social Affairs Vocal Vocal

Manuel A. Rivera P. V. Alvarez. Jimenez L. E. Meza L. S. Michellangely A. Sequera B. Luis R. Dominguez G. 0. Partidas M. R. Ravelo S. E. Castro Mata M. Bracho

F. Oie K. Christiansen P. W . Pedersen A . Torres

RHODESIA Rhodesian Air Traffic Control Association Private Bag 2, Salisbury Airport Rhodesia

Swiss Air Traffic Controllers Association V. P. R. S., P. 0. Box 34 CH 1215, Geneva Airport, Switzerland

VENEZUELA

E.Meachen C. Latham

L. Berkenstam A. Karlahag C. A. Starkman G. Atterholm

SWITZERLAND

P. Kalff T. M. van Gaalen B. H. van Ommen

NORWAY

President Secretary Treosurer

Chairman Secretary Treasurer I FAT CA Representative

Chairman Secretary Treasurer

Air Traffic Control Association Dept. of Civil Aviation, 8th Floor, Dept. Bldgs. Stout Street Wellington, New Zealand

Chairman Vice-Chairman Secretary Treasurer

Swedish Air Traffic Controllers Association Fack 22 Sistuna, Sweden

J. van Londen F. M. J. Mente

NEW ZEALAND

President Secretary

SWEDEN

C. W . Drake C. P. Flavell W . Vandewaal

YUGOSLAVIA Jugoslovensko Udruzenje Kontrolora Letenja Direkcija Za Civilnu Vazdusnu Plovidbu Novi Beograd Lenjinov Bulevar 2 Yugoslavia President Vice-President Secretary Treasurer Member

A. Stef anovic Z. Veres D. Zivkovic D. Zivkovic B. Budimirovic

AIR TBA.FFIC CONTROL DATA PROCESSING 路SYSTEMS rnow largely . being 路realised in /

,/ / /

/ /

/ / /

/ /

/ / / /

/ . / / /

/ / / /

/ /

With SM R-124, Signaal 's highspeed micro-min realtime general purpose co mputer in corpo rated in your AT C data processing system you w ill have at your d isposal a highly mod ern processor. Signaal's experience accompanies all elements of ATC system s, for example the m icro-min d igit al display sub system for radar v id eo , syn th et ic dynamic and electronic tabu lar data di splay. Signaal also produces prima ry and secondary radar video extractors. Signaa l's syst em covers the entire range - hardware and software. S IGNAA L radar, weapon control, data handling and air traffic control systems.

N.V. HOLLANDSE SIGNAALAPPARATEN, HENGELO, THE NETHERLANDS

Fail-Safe Multi-Computer Systems in Air Traffic Control Translation from German by H. Teiber AEG - TELEFUNKEN Konstanz

Introduction The major importance attained by digital data processing within the last few years, and likely to be maintained in future, too, is mainly based on the many-faceted application of digital computing systems in almost every field of economical and technical activity. The expedient and advantageous use of these computing systems is especially enhanced by the capability of digital computers to accomplish rapidly and economically routine tasks such as accounting in financial systems, to solve complicated technical and scientific problems within relatively short periods of time as well as to control processes in real-time operation. In the freld of air traffic control, too, digital computers can be used for a variety of functions. The general trend is to free the controller, as far as possible, from routine tasks in order to entrust him with essential coordinating and supervising functions. In addition, complex problems are posed by the ever increasing air traffic and the high speed of aircraft to be expected in future. Such problems, as for instance, examination of conflict situations, cannot be solved within the frequently very brief periods of time available for their solution with due consideration of the numerous determining criteria except by means of automatic computers. Unlike in many other applications where the reliability of_ a compu~ing system is not of overriding importance, this feature is vital in air traffic control. The failure of a digital computer forming an integral part of an air traffic systems entails a great danger to th e h uman b eings 路 an d to materials. Moreover, the tasks presented in such a system must . be tackled virtually with no d e Iay, 路1. e. 路in rea I . time operation, and must not be interrupted at all, or for ve_ry short periods. of time only. Occurence of long-drawn failures can result in a loss of significant and unretrievable information. Hence it is clear that, especially as regards handling of real time processes, the development of computer technique is not exclusively oriented towards high speed and performance capability, but that the trend is more and more towards the design of especially fail-safe computing systems. The reliability problem of an electronic system is, however, not solely of financial and technical nature and it cannot be coped with satisfactorily by simply allocating cidequate resources for its solution, since endeavours to achieve highest computer reliability are subject to certain technological limitations.

In order to better understand these interrelations, let us first examine in detail the causes of malfunctioning of computing systems and elucidate the problem of availability in the light of data components used in a TR4 computer and the pertinent mean times between failure. Furthermore, the following exposition will show that it is possible to eliminate to a large extent the adverse effects of defective components by means of modifying the computer structure.

Reliability As in any electronic device, failures occuring in a computing system are mainly caused by defective components such as transistors, diodes, resistors, and capacitors as well as by faults in connecting elements such as printed circuits, soldered connections, and plug and socket connectors. In addition, failures of computing systems may also be attributable to error-affected programs. However, this will not be taken into account, since errors of this kind can be eliminated to a large extent during an exhaustive test and trial phase. A component is defective if its electrical characteristics are no longer within the specified tolerances. If this state becomes permanent, it is referred to as a permanent failure of the component. Among the causes of such failures are aging processes, material and manufacturing defects, etc. In evaluating such failures, however, it is understood that the computing system is operating under the specified environmental conditions regarding temperature and humidity ranges. By applying preventive maintenance measures, i. e. by operating the computer under stringent conditions, for instance, with an increased clock frequency, marginal components operating close to their tolerance limits can be traced and replaced. More often than not, permanent failures of components or connecting elements within the computer can be rapidly detected, and subsequently cleared, by means of various built-in testing facilities such as the modulo-three check unit. Independent of currently running application programs, these facilities are continously checking the major computer units, such as the storage unit, and the control unit, for their proper functioning. Unlike the permanent failures, there are also sporadic faults, which can contribute to failures in computing

systems. The characteristic features of such faults are that they tend to occur only for very brief periods of time, sometimes no longer than the duration of a switching transient within the computer, and that they can appear at random intervals. These variations of electrical behaviour of components are due to the already mentioned aging processes, to material and manufacturing deficiencies as well as to addional short-time external influences such as fluctuations in temperature of the component environment or the other external interferences. The probability of sporadic errors can be greatly reduced, but not completely ruled out, by means of appropriately dimensioning the electrical circuits. Special checks performed in the computer and built-in program test routines ensure that sporadic errors are detected and adverse effects on processing avoided by means of repetitive runs of the program section concerned. Many years of experience gained by component manufacturers as well as continuous improvement of production processes and testing procedures now assure that electronic components have an extremely long lifetime. This lifetime is determined on the basic of statistical methods, and the values obtained must be regarded as statistical mean values. Fig. 1 shows some typical lifetimes of electronic components used in digital computing systems and, for comparison purposes, the corresponding lifetime of electron valves.

Mean Lifetime

Electronic Components

Hours

Years

Transistors Diodes Resistors Capacitors Electron valves

approx. 10,000,000 approx. 100 ,OOO ,OOO approx. 50,000,000 approx. 70,000,000 approx. 10,000

approx. 1,140 approx. 11,400 approx. 5,700 approx. 8,000 1.1 approx.

Figure 1

Typical lifetime of electronic components

However, as will be shown below, a quantitative evaluation of computer system availability must also take into account the number of components used in such a system. Components

Number of Units

Transistors Diodes Resistors Capacitors Plug-in cards Soldered joints Plug and socket connectors Ferrite cores

approx. approx. approx. approx. approx. approx. approx. approx.

15,000 100,000 60,000 16,000 1,200 600,000 45,000 1,500,000

Figure 2 Components of

TR 4 digital computer without peripheral equipment

Fig. 2 sh~w.s a survey of all essential electronic components of a d1g1tal computer, including connecting elements which also may c?use failures. A TR4 computer, installed at the Frankfurt Airport, and used to assist in the performance of various air traffic control functions, is chosen to demonstrate our case. This computer, excluding the peri-

pheral equipment, consists of approximately 2,300,000 individual elements which must all be taken into account when tracing faults. Let it be assumed that a computing system like the TR4 computer (cf. Fig. 2) contains 15,000 transistors. To obtain the trouble-free time between the failure of two transistors, the mean transistor life-time of 10,000,000 hours (cf. Fig. 1) must be divided by the number of components used, which amounts to 15,000 in this example. This calculation yields the mean time interval between two failures which in our examples is approximately 670 hours. This means that, on the average, a failure of the computing system caused by a defective transistor is to be expected about every 670 hours. If all other components of a computing system are likewise taken into account, one may easily realize that the system availability is bound to fall below the value of 670 hours. But in addition to the number of individual components built into a computer, the number of correctly effected switching operations is also significant. The clock frequency of the TR4 computer is 2 MHz which means that 2,000,000 pulses per second are delivered by the clock pulse generator. Each of these pulses involves at least 50 switching operations, e. g. setting or clearing of a flip-flop in the central processor. Thus, the total number of switching operations in the computer is 100,000,000 per second. These figures illustrate the extremely high requirements which must be met by a component in order to ensure, even over longer periods of time, the proper execution of the requisite number of switching operations in a computer. In summarizing it may be pointed out that, due to the large number of components used in a computer and the fact that the lifetime of these components is not infinite, and on account of the high internal processing speed, i. e. the immense number of switching operations per second, it is basically impossible to prevent failures in computers, just like in all other electronic devices. However, the application of computers in air traffic control requires, as already mentioned, permanent availability of the computing system. In the computing systern described so far, this stringent requirement can eventually be achieved through further development of manufacturing processes and improvement of component reliability, e. g. by means of using integrated elements, but it cannot be met completely. Taking into account that component failures cannot be avoided, the obvious alternative is to find a new system configuration which will provide the required extra high degree of availability. The first step in this direction is the coupling of two systems. For some time, this dual-system approach has advantageously been used in many electronic configurations of current air traffic control systems. Examples may be found in the doubling of transmitters and receivers in radiotelephone systems as well as in radar system applications. In a dual-computer system the same tasks can be handled by two computers simultaneously, one being "operational_", the other on "standby". Upon failure of the operational system, its functions are taken over by the standby system.

Dual-Computer System In pursuance of the endeavours of the Bunde~an~talt for Flugsicherung at Frankfurt to introduce outomat1on into air traffic control, a duol-computer system for a first phase 15

of automation has been designed and insta ll ed at the Frankfurt Airport in cooperation with AEG-TELEFUNKEN. The supervisor programs requi red for the system have also been developed. These, in cooperation with the pertinent application programs, provide for the operational use of the data processing system in a ir tra ffic control. The functions to be performed by the system are printing of flight prog ress strips and processing of NOTAMs. Following the installation of the system in spring 1968, a trial phase of several months has commenced and is still under way. Upon completion of the tria l phase, the data processing system wil l be placed at the diposal of the ATC authority for operational use.

System Configuration The system configuration and the connection between all input and output stations are indicated in Fig. ·3. The central processing system con sists of two TR4 computers connected by a coupling unit. The coupling unit provides for close in te rco nnection of the two computers so as to ensure that the internal processing state con be communicated at any time to ei ther of the two computers. For the input of programs or for reading in of program modifications and ex pan sions respectively, magnetic tape uni ts and paper tape units are provided. The req uired da ta exch ange between the computers and the operators is accompl ished via two control teletypewriters. Fo r each of the two compute rs, a disk store is provided os bocking sto re. Mutual data exchange between the two

- · - -- -·- . ,! ACC Hannover

~ans

flight

stand-by -system dis k storage2

compute rs and the tw o disk stores is feasible. This double access facil ity substantially en hances the availab ility of the ove ra ll system, since upon fa ilure of d isk store I and computer II , d isk s tore II and computer I can still be comb ined to fo rm a workable system. Apart from this, however, this kind of cross connection perm its on especially advantageous data exchange between the two computers v ia the disk stores. The resu lt is that data transfer from one computer to the othe r can be effected via tw o commun ication paths, namely v ia the coupling units and via the disk stores. Thus, should the coupling unit, wh ich is not dup li cated, fail, its funct io n can be assumed by the disk stores. Furthermore, the large capacity of such an external store compris ing a total of 1,080,000 words of 60 bits each with the short overag e access time of 24 msec enta il s a considerable re lief of the interna l fe rrite core s tore of the computer, wh ich results in an especially economical exploitation of the ce ntral processors. As far as the two a ir traffic control functions mentioned above a re concerned, th e disk stores ore mai nly used to store t he ex tens ive NOTAM information as we ll as those flight p lans which ore not immediately processed. In this connection it must be pointed out thot it is intended to use the d isk stores on ly in a second stage which presumably will commence at the end o f 1968. Up to this date the functions of the disk stores wi ll be perform ed by magnetic tape units. The need fo r real-time p rocess ing of flight prog ress strip~ and NOTAMs and the resultant temporary accumu-

lation of a hig h volume of information require a high degree of spe ed and safe ty in the exchange of da ta be-

opera ting system

a pprooch contlol F1ankfurt

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tween the central processor and the 1/0-equipment. This requirement is met by means of a teletype multiplexer which, via two 1/0-channels, is connected to each of the two computers. One of the two 110-channels is used exclusively for data input, so that data transmission is not impeded by other operations and data can be passed on for further processing in the computer without delay. In the dote system installed at Frankfurt, up to 40 teletype lines of 75 bauds and one highspeed line of 600 bauds can be linked to the teletype multiplexer. This 600-baud line provides for the connection of the dual-computer system to a main teletype message exchange which is also installed at the Frankfurt Airport. This connection permits the input into the data processing system of teletype messages, in particular flight plans and NOTAMs, originated by the ATC units connected to the Aeronautical Fixed Telecommunication Network. As may be seen in Fig. 3, the overall system configuration is to a large extent symmetrical; the individual units which are available in pairs are completely identical. Hence, neither of the two systems exhibits any distinctive features. The symmetrical set-up ensures an especially advantageous coupling of the individual units. However, since the implementation of a computer-controlled cross connection would involve a rather high degree of design and program complexity, it is more expedient to do without an automatic control of the cross connection between the two basic units I and II and the two computers (cf. Fig. 3). This decision was governed i. a. by economical considerations in respect of the intended use of the dual-computer system. However, if required, such a cross connection can rapidly and safely be established by manual patching at the central switch cabinet. In addition to the advantages inherent in the symmetrical organisation mentioned above, the proposed configuration permits the design of simple and logically arranged supervisor programs. Supervisor Programs The supervisor programs are designed to perform the following functions: control of data exchange between the two computers and of the input/output operations of the teletypewriters, checking for proper functioning of the individual units incorporated in the overall system, initiation of switch-over action in the event of a failure of the computing system in operation, and arrangement for the restart of a newly repaired unit within the overall system. As illustrated by Fig. 3, the input of telex messages into the operating computer is effected via teletype lines, teletype connecting units, the switch-over units and the basis teletype unit. Subsequently, these data are input via the connecting unit into the stand-by computer as well. Once the t~on~fer operation is duly completed, the appropriate appl1cat1on programs are called up in both computers. These programs are batch-processed in such a manner that the processing of the next botch is not commenced by one computer before both have signalled completion of the same batch. Thus, it is assured that the two computers ore operating in synchronism, i. e. that they are operating on the some batch. As soon as the processed results are available, they are transmitted by the operating computer to the appropriate output stations, while the standby computer stores these output data until proper completion of the output operation is signalled by the operating computer.

On occurence of a fault during the output operation which necessitates a switch-over, all output messages stored in the standby computer are output. This may lead to repetition of some of the output data, but precludes the loss of information in case of failure. As already explained, data input into both computers does not take place simultaneously. This means that, whenever a fault occurs during input of a message which causes a subsequent switch-over, the input operation must be repeated. An appropriate signal to the input station concerned is originated by the standby computer. Although repetition of the input operation could be avoided if simultaneous data input into both computers hod been envisaged, the above input method hos been chosen for this particular application of the dual-computer system, because it involves less technical effort which in turn does not only result in economic advantages, but also reduces the probability of failures in the overall system. The proper execution of the above processes is controlled by the supervisor programs. In addition to these primary coordinating functions, a significant task of these programs consists in checking the individual units of the overall system for their proper functioning. This is necessary, because none of the single units in operational use except the two computers can be considered active units, and are therefore unable to check themselves. Continuous checking for proper functioning of the single units in the system, i. e. of units which ore not duplicated, such as teletype connecting units, teletype lines, teletypewriters, is a major prerequisite to rapid detection of faults and initiation of remedial measures. The underlying principle of all these checking operations is that fixed and predetermined time criteria must be adhered to during data exchange between the two computers on the one hand and the computer and the peripheral equipment on the other. For instance, data are exchanged between the two computers at intervals of 1/6 sec. If no operational data are presented for transmission during this period, a certain routine message is transmitted. In consequence, if the standby computer does not receive any data or a routine message from the operating computer for a period exceeding 1/6 sec, this will be interpreted as malfunctioning, and as a result switch-over action will be initiated by the standby computer, and indications for the operators as to the corrective actions to be token will be output via the control typewriter. For the proper execution of input and output operations numerous checking procedures have been provided. Espe~ially the basic teletype unit, the connecting .units, and the teletypewriters need to be monitored. Checking of the basic teletype units during data transmission is also accomplished on the basis of time criteria, the adherence ~o which is monitored by the computer. A negative result will provoke .instantaneous countermeasure s by the computer, . such as switch-over to the standby computer and printout · · d'1ca f ion s for the on the control typewriter of appropriate in operator. . The connecting units and the teletypewriters .can expediently be checked by means of an automati.c reply feature incorporated in the teletype machine. This reply · feature consists o f a transm1·tt e1· which ' on request of the compu t er, t rans m 'its a characteristic . identification . . . for. each to start 1 'ng operation / this 1dentif1cation as · mac h .ine. p rior . well as the addresses of the connecting units to which the teletype machines are attached, are stored in the corn-

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Figure 4 Legend:

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144 1 E EDDF 200 KT FL 80 DF3 Bl GMH B 1 EDDL E2 60 R

• •

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type of message (night pion); C, D 1, E, E 2 -

identification chorocters; ~ ringin g signal (end of message)

puter. Th us a comparative check within the computer is possible and any faults can easi ly be located, and the necessary indications be given to the operator, enabling rapid fault removal. In addition to this computer-controlled test o peration, teletype ope ra tors may initiate such feed-back tests by inputting a specia l letter combina t ion. Thus, an additional checking facility is p rov ided to w hich, if need be, recourse can be token between the program -controlled " reply " checks performed at short interval s on all connected teletype machines. Another important f unction of the supervisor programs is to ensure the res tart of individual units after fault removal or after servicing. For this p urpose, the restart proced ure must be indicated to t he computer via the contro l typewriter. All necessary arra ngements will then be made by the computer, e. g. output will be interrupted for the short period of resta rt in order to preven t loss of any significant data or repetit ion of output of previo us output data during the intercon nection process. Subseq uent ly, the unit newly incorporated in to the system, e. g. the standby computer, is loaded by the opera t ing computer with oil data

required for its operatio n, so that the some information leve l is again attained by both units. The forego ing discuss ion clearly shows that t he supervisor programs allow for adequate and re l iab le checking of the prope r functioning o f all individual uni ts of the syste m, w hich are of opera tional importance. They provi de for prompt error detection and, if requi red, for switchover to the standby syste m. Thus, the superv isor programs ensure o high deg ree of availability of the dual-computer system and a re, therefore, an essentia l p re requ isi te to t he operationa l a pp li ca ti on o f such equipment in air traffic control. Application Programs

Although the supervisor programs ore conceived so as to be larg ely independent of th e respective appl ica tion programs, the organisation of input data must conform to certain format req uirements. In the pa rt icular case of flight progress strip p ri nting, the input messages are formatted as illustrated in Fig. 4. After input into the compu ter, the supervisor programs check this message for completen ess and unambiguous-

___________________________________________ • • • • • • • • • 18

UPPER WIND FORC FIR EDDF VALID FOR 140700 TO 14 1500

230/ 030

240/ 050

250/050

300/060

240/ 050

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0658

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• • • • • • • •

Fig ure 5 Structu re of a wind message The wind message shown here (message prefix) is valid for the Frankfurt FIR between 7.00 o . m. and 3.00 p. m. It indicates the wind direction, e. g. 230 (degrees), end the wind speed, e . g. 030 {knots) for the 4 sectors A, B, C, D. These two indicat ions per sector o re mode for

FLSO, FLlOO, Fll 40, e nd Fll80. After proper input into the computer, a n acknowledge ment wi th a stotement of ti me, e. g. 0658 (h, min), is printed out on the input moch ine

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ness. If the res ult o f th e check is positive, furthe r p rocessing of the messoge wi ll be acco mp lished by the appropri ate ap p l ica tion p rogram. If the checki ng crite ria a re not co mplied w i th, the messo ge wi ll be o utput at the input sta tio n concern ed , su pp l emen ted by on error in dicati o n such as " M essage fau lty, repeat input". The cen tral com puter assembles t he requ ired da ta for flig ht progr ess st~ips relati ng to the di ffere nt reporting poi nts o n the basis of computer-stor ed infor mation which co ntai ns a description of the a irways structure a nd r eporting po ints wi thin t he co ntro l a rea. Fu rther more, the process ing of flig ht prog ress strip dote takes accou nt of the wind condi tions in the co ntro l a rea. Wind d irection and speed are inserted by telepri nters into the data p rocessor

in the form o f appropriate messoges which agai.n mu st conform to a specified format w hich is shown in Fig. 5. . The reporting po ints for which the flight prog ress strips a re prin ted a re co mb ined in so-called output sectors; each secto r is associ ated w i th one output machine. Fig. 6 shows a set of fl ight p rogress strips for a certain outp~t sector. In NOTAM processing, the messages amv1~g via the A FTN ar e transferred to the computer, sorted in accorda nce wit h certain criteria, and stored. I f required, these data can be called down. Fig. 7 shows a call-down .re~uest (in put message) and the computer response to this input (ou tpu t message). Again , the inpu t message mu st have a particular format; format complian ce is checked by the supervisor prog rams.

NOTAl\I-request

________

--------------"":--------------------------------_:-,_-._-

• •

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• • • • • • • • •

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13.02.68/ 1059

F I R : E9BR AERODROME INFORMATION EBAW ANTWERP 2/018/66

CRANE 54M GND 322DEG TRUE FROM ARP 1375M FROM THR 12.

2/021/67

CRANE ERECTED, HGT 30M GND, 315DEG TRUE 775M FROM ARP, NOT MARKED.

2/029/67

RWY 15/33 U/S.

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RWY 12/30 USABLE WIDTH 25M SOUTHERN PART AVBL ONLY·

• • • • • • • • • •

Figure 7 Input and output message in NOTAM processing

:\OTAl\l Because of the large capacity of the TR4 computer, it is possible to perform further automatic ATC functions in addition to the two functions described above (e. g. the presentation, in synthetic form, of the air traffic situation at controller consoles). Therefore, when developing the logic of the supervisor programs, appropriate precautions were taken by incorporating in their design a high degree of flexibility, which will permit the assignment of additional tasks to the dual-computer system.

Triple-Computer System In pursuance of the plans of the Bundesanstalt fi.ir Flugsicherung, to introduce automation into ATC, a single TR4computer was installed at the Frankfurt Airport in 1963, and used in a subsequent trial phase to aid in the performance of various A TC tasks. As early as the beginning of 1965, computer-controlled printing of flight progress strips in an operationally usable form was started. After the introduction into operation of the dual-computer system, the early single-computer system will be used for testing the automation of other ATC functions, such as the presentation in synthetic form of the air traffic situation at controller consoles. As this experimental system still incorporates all the equipment required for automatic processing of flight progress strips, this task could easily be re-assigned to this system should the dualcomputer system not be available for operational use. Such an event may occur when, on account of a required expansion, the dual-computer system must temporarily be put out of operation, or if new or modified sets of application programs need to be tested in cooperation with the supervisor programs. Therefore, a switch-over device has been provided by means of which it is possible to connect the different peripheral units of the two physically separated computing systems to each of the three TR4 computers.

This switch-over device ensures that even upon failure of several major peripheral units of the dual-computer system, these units can be replaced by the corresponding units of the experimental system. All requisite switching operations can be rapidly and reliably performed by changing the pertinent connecting cables at the main switching cabinet. The provision of this switch-over facility adds within certain limits substantially to the availability of the overall data processing system. In this context, it would seem appropriate to point out that, in addition to the technical serviceability of the units incorporated in a computing system, well trained maintenance staff and an efficient service organization are the essential features which condition the degree of system availability.

Final Observation It can be foreseen today that the automation of further functions in an automated air traffic control system planned for the future will certainly pose more difficult and complex problems than the printing of flight progress strips and the processing of NOTAMs. However, in parallel with the growing complexity, the requirements with respect to performance capability and reliability will increase. Therefore, computer manufacturers have recently initiated developments which aim at computer structures designed to meet such extremely high requirements of the future. References Heidelauf, K., "Development of on universally usable display working position of air traffic control function", AGARD meeting at Munich, 1966. Guntsch, F. R., ·Mensch und Maschine in der Flugsicherung", Bild der Wissenschoft, Vol. 2, No. 8, 1965, pp. 642-653. Arnolds, R., "Automatisierung in der Flugsicherung", Elektronische Rechenanlagen, Vol. 7, No. 4, 1965, pp. 194-202.

p 390.468

Navigation, Air Traffic Control , Space Flight Standard Elektrik Lorenz AG has a long history of achievements in the f ield of radio navigation. As early as i n 1936, our engineers developed the fi rst V H F Omnid irectional Radio Range (VOR), whic h in 1959 was introduced as standard international rad io navigation aid. In the past 15 years, SEL supplied more than 200 VOR ins tallations to customers all over t he world. The SEL Dopple r VOR represents another essentia l ~ontribution to the safety of_ air traffic. It substantially improves medium range nav1gat1on : Using a wide-aperture antenna and operating on the Doppler principle this new navigational aid provides extremely accu rate cdurse info rmatio n which is not affected by reflections from natural obstacles and buildings. The signals supplied may

be used to control the automatic pi lot. A combination of DVOR and T ACAN known as DVORT AC, is now being field-tested by the Federal German Adm inistration of A i r Navi gation Safety (BFS). The test results so far obtained are very satisfactory. SEL - active 1n the whole field of telecommunications. Fo r further information, please write quoting No. WS 257 You are invited to visit our stand at the La ngenhagen Air Show between April 26th and May 5th, 1968, H all B; Stand 1204/1304. Standard Elektrik Lorenz AG Tra nsmiss ion and Navigation Di vision Hell muth-H irth- Stra13e 42 7 Stuttga rt-Zutfenhausen

The Digital Simulator as a Tool for ATC Automatic Data Processing by F. J. Crewe, Elliott-Automation Airspace Control Division

Introduction The digital radar simulator after many years of development is at last being widely recognised as an experimental and evaluation system for use in planning future ATC Data Processing Systems. For a long time, the training potential and the procedural and operational evaluation possibilities have been well known; to a lesser degree so have the analysis capabilities. At this point it is worth mentioning that most digital simulators which have been used in the procedural and operational evaluation role have carried out exercises where combinat:ons of traffic samples (present and future) have been related to present day and future procedures. Whilst such exercises are of paramount importance; when the results have been obtained and analysed little indication has been forthcoming lo suggest the area!; in which ATC aulomatic data processing should be employed.Where some indication has been forthcoming, it has been more by chance than by intention in the majority of cases; and even so, the indications given have been related to a limited set of conditions rather than the whole. It is fair to say that perhaps the reason for this is that the exercises have not been directed towards automation evaluation in the frrst place.

Programming Before pursuing the theme further, it is worthwhile mentioning programming of digital simulators. Our experience in the Airspace Control Division of Elliott-Automation has shown that in order to produce digital radar ATC simulators which meet the customer requirements a number of points which are directly related to programming stand out. They are: The simulator must be realistic and flexible and expansible. The simulator must be economic to run. Exercises must be simple to prepare. Recording and analysis must be available. To meel路 these requirements the programming team must have a comprehensive understanding of Air Traffic Control (Cvil and Military) and fully understand the problems posed therein. Given time and advice, a program or set of programs could be written by any competent programming team, but such programs would almost certainly not make full effective use of the computer neither would the price be competitive. Every consideration must be given to realism, flexibility and expansibility; this is particularly true where the simulator needs to simultaneously reproduce two or more different types of radar. Another area where the programm:ng team contribute to the success of a digital radar simulator is in the preparation phase. It is essential that exercise preparation is made simple and easy; that maximum use of the computer is made in order to reduce time consuming and ted:ous semi-repetitive work to o minimum. This particular feature, properly im-

plemented by the use of Exercise Translation programs, permits greater utilisation of the simulator (with a greatly reduced man/month preparation effort) than would otherwise be possible. Hence, the system meets both requirements; being economic to run and, exercises simple and expedient to prepare. Obviously, the results of exercises must be analysed if the system is to be used to obtain maximum benefit from the work that has been performed. Whilst analysis is helpful after training exercises have been run, analysis becomes of paramount importance after Airspace Configurations, Traffic Densities and "Automation" exercises have been carried out.

Evaluation Keeping in mind that above, it must be apparent that digital simulation systems lend themselves readily for use as "ATC Automation" evaluation tools. In this context, some of the following features of ATC Automation can be investigated and evaluated: a) Whether there is a basic need now for automation or not, or the point at which in time or traffic density, automation should be introduced. b) If a) shows there is a need, the essential area or areas will be indicated. c) Type of display techniques best applied in conjunction with a computer orientated A TC system. d) Rationalisation of display information and its distribution. e) The extent to which automation shou!d be applied [c.f. b) above]. f)

The type and processing power of the computer necessary. g) An outline of the programming requirements. h) The relationship between the controller and computer [c.f. c) and d) above]. i) Input/Output devices bearing in mind h) above.

Conclusion The above list is by no means comprehensive, but it serves to show the power of a properly designed and programmed modern digital simulator when intelligent use is made of its potential in the ATC Automation freld. In all aspecrs it is essential that exercise preparation along the lines of paragraph 5 above, is available. Under these circumstances the maximum utilisation of the system is possible and time between the planning of the exercise and subsequent analysis is greatly reduced; results are available in a shorter time than was hitherto possible, and ready to support further studies. Logically then, this powerful aspect of simulator application is of paramount importance and should be assessed by potential users when considering the purchase of a Digital Radar Simulator.

RADAR DATA EXTRACTION means: Digitizing of signals Selecting the radar information on preset criteri as Freed om from disturbances

requirement for : Narrow-Band real-time transmission Compatibility with data handling equipment involving : Auto-tracking Flight plan calculation Daylight digital display presentation Comprehensive symbol display

achievements: Insta llations of military and air traffic control centres in many places in Europe illustrate the flexibility of the SAT Rada r Data Handl ing System .

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New ATIS Equipment " It is r esolved that IFATCA recommends the implem entation of broadcast of r outi ne ATIS informolion ol oirports where o reduction in the load on AT C/ RT channe ls is de sirable. It is resolved that due to th e w ide imp lications of the present aeronautical information service Member Associations should initiate studies into this service with a view to formulating IFATCA pol icy on di ssem ination of information". These resolutions on Aeronautical Termina l Information Service were passed three years ago by the Fourth Annual IFATCA Conference in Vienna . After three years it is very encouraging to note that AT IS is being introduced on on eve r increasing basis. The above resolutions hove obviously also contributed to the further development of eq uipment suitable for the dissemination of Aeronautica l Termi nal Information.

Inside view of A 4 equipment

One of the latest d evelopments in th is fiel d is the Magnetic Disc Store, Type A 4, which is be ing produced by Wolfgang Assmonn GmbH, Bod Homburg, F.R.G. Some of the outstanding features of this equipment ore its modular construction , which provides for o variety of system configurations, full remote control, quick exchange of stored information, and high reliabi lity through the use of full y transistorized modular components in con j unction with a specia l recording head and reco rding medium princip le. The first equipments of this type are now being installed al German airports. After some months of daily routine service, we intend to publish a report on their performance in THE CONTROLLER. - r

News from IFATCA Member Associations The Danish Air Tra ffic Co ntro llers' Asso ci ation elected a new Boord of Officers:

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V. Frederiksen Ao. Janicke P. Breddom M. Jense n E. Christiansen

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J. van Londen F. M . J. Mente P. Kolff P. Ka lff T. M . van Gaalen B. H. van Ommen

The new address of th e Netherland s' Guild is:

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Vereniging "He! Nederlond se Lu chtverkee rsleidersgilde " The Netherlands' Gui ld of Air Tra ffic Contr ollers P. 0. Box 7590, Schiphol Airport Central The N etherlands.

Talking to Computers by R. N. Harrison, The Solartron Electronic Group Ltd.

Introduction The next few years will see the gradual introduction of ATC automation into operational service in all those countries where the density of traffic is sufficient to warrant it. In that time a number of problems now forseen will have to be solved. In addition, there will be a number of secondgeneration problems, some of these as difficult as those already tackled. Two areas of difficulty in automation are the controller/ computer relationship and fears about the reliability of the computer. However nowadays no one talks about reverting to manual control in the event of computer failure, and sophisticated hardware redundancy schemes have replaced the earlier concept of duplication, or triplication, of all computer equipment. The point has been reached where computer failure is not only a very small risk, but where any failure would be "soft", beginning with less essential services, allowing the controller to take action to restrict traffic. It follows therefore that the operational efficiency of the system, and its ability to deal with any situation, are dependant to a major degree on the compatability of the computer and controller. The problems here are not readily susceptible to mathematical analysis, the less so in view of the limited experimental data avail-

for the operator to sort out what he wants. It is important that as much of the selection as possible should be done within the computer, so that the final choice by the operator does not delay his actions in other respects. Secondly, the computer has no inherent ability to understand English, or any other language designed for communication between people. It can be made to accept instructions in English, but these require a particular form of words, inserted either directly by means of an electric typewriter, or indirectly through punched tape. In any case the use of ordinary language would slow down operations tremendously as the computer can perform some hundreds of operations in the time it takes to utter one syllable. It therefore follows that some type of keyboard will have to be used for inserting messages, either keys in the form of a tabulator keyboard, or touch wires on the face of a display. The problem of information coming out of the computer is a much simpler one. The computer can write data on an Electronic Data Display using English or any other human language. The only qualification is that the range of information and the manner in which it is set out has to be specified in the computer programme.

able. Fortunately the plans of a number of countries include the introduction of digital ATC simulation on a time scale which will allow it to come into service ahead of the introduction of extensive ATC automation. It is therefore possible to look at digital simulation not only as a means of training and evaluation, but as a means of examining the kind of interface required between a human being working in an ATC environment and a computer operating on his behalf. Understanding of the situation depends on two basic facts. Firstly the computer is a two-way machine. It takes in information and it produces new information calculated from the data it has been given. It can be instructed to produce information at a particular time, in relation to a particular event, or (in the case of a conflict for instance) where its calculations show thoi a warning is required. It can also provide a library serv;ce of untreated data, selecting this on the basis of a programme it has been given, or on request from the operator. The usual difficulty with computers is too much information rather than too little, so that it becomes necessary

The Electronic Data Display The electronic data display (EDD) is a cathode ray tube, g~nerally r~ctangular in shape, and having a phosphor with a persistence very much less than that of the conventiona I PPI. Associated with it is a symbol generator which produces letters and figures, and these are written on the face of the display at the place the computer determines. E~D.s are sometimes referred to as tabular displays, but this is onl~ a part of their function. It is possible to have a tab.ular display on one part of the EDD, leaving the remai~der fr.ee for information specially called for, informat10~ which the computer is programmed to display at a particular time or aircraft position, warning information, and readback information when an entry is being made by means of the keyboard . The writing rate is high, so the information appears as though it were being flashed on to the screen. With a minimum renewal rate of 16 2 h cycles per second - it is normally a sub-multiple of the mains frequency - the operator does not depend on afterglow to see the information which has been written. This means that the display can be used in any lighting short of direct sun light.

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How does the Operator "talk" to the Computer? In the accepted design of digital ATC simulators, the operator - in this case called the "pilot" - has a keyboard, and an EDD of the type described. A typical keyboard design is shown in Fig. l. This is called a multiple instruction keyboard because it contains a block of instruction keys which may be used either separately or sequentially as part of the same message. In addition it has an alphabetical keyboard similar to that of a typewriter, and a numerical keyboard consisting of the figures 0-9 arranged in a square with zero operated by a bar at the bottom . Not all the keys are used to the same extent. The least used are the alphabetical keys which are required only to enter the designators of reporting points or aerodromes, or, exceptionally, an alphabetical message for which the computer has been specially programmed. In addition to the keys so far mentioned, there is also provision for instructing the computer to cancel, enter or execute a message, for the acknowledgement of messages from the computer, and for the handing over and taking over of aircraft. The keyboard has been designed so that the "pilot" can act on the controller's instructions during the time that these are being given and acknowledged. A digital equipment simulates many more aircraft than most of the analogue equipments now in use . For economy of operation, each "pilot" is therefore required to handle several aircraft, and so that he will not be confused by receiving two instructions simultaneously from different controllers, it is arranged that all the aircraft handled by a single "pilot" are on the same R/T frequency. Effectively, this means that the " pilot" is handling the same number of aircraft as the controller. The computer knows that at any particular time certain aircraft are allocated to each "pilot's" desk. It is necessary however for a "pilot" to designate a particular aircraft out of those allocated, and for this purpose he has a key marked with a number associated with the aircraft on his EDD . On receipt of an instruction from the controller, he presses the appropriate aircraft key, and follows t~is with the instruction key and a numerical (or alphabetical) entry. For instance the clearance for Speedbird 123 to descend to flight level 100 would require operation of the appropriate aircraft key followed by the Required Flight Level key and the numerals one zero zero . As the keys are depressed, the message appears at the bottom of the. EDD. If t~is is the full extent of the controller 's instruction, the pilot now

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resses the EXECUTIVE key. If there is an additional clause in the instruction, the "pilot" presses the key at this stage. This clears th~ messa~e fr~m his keyboard, the instruction keys of which arE~ 11lu~mated when a message is being inserted, and make 1~ avail~ble for the insertion of the next part of the instruction. This could be a request to report passing FL 150. As t~e E~ECUTIV.E k:y has not yet been used, the aircraft ident1ficat1on key 1s ~till illuminated. The "pilot" now presses the Report Passing FL key followed by the numerals one five zero. The message at the bottom of his EDD reads: BA1~3 FllOO RP~L~50; After checking the message content on his EDD, the pilot now presses his EXECUTE key. The computer takes note of the instruction, and in the tabular part of the EDD a downward-pointing arrow appears immediately after the actual FL shown, and from the changing figures it can be seen that the aircraft has begun its descent. The airspeed will also be seen to change as the computer adjusts to the descent speed programmed for the particular aircraft type.

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From fig. 1 it w ill be seen that some of the keys allow the "pilot" to request informa t ion. Th ese con best be considered in rela tio n to the general display of informotion on the EDD.

More Details on the EDD Fig. 2o is a drawing sh owing the EDD layout, and th e sections into which it is div ided. Fig. 2b is a photograph of an actua l EDD showing the same information. The EDD is divided in to five sections. The first section is the tabu la r display providing standard information o n each of th e air cra ft under the particular "pilots" control. Th is informa tion is always up to dote and can be used by the "pilot " to answer most qu estions which may be put by the contro ller. When there is a varia t ion between the fl ig ht p lan and the a ctual fl ight path of the a ircraft, the foci is emphas ised by underlining the appropriate entry. For i nstance, an aircraft w hich has fl ight p lanned fo r FL 320 a nd hos been allotted FL280, w i ll have the figures two eigh t ze ro underlined in its entry. W hen an aircraft in this sect ion is in process of being hand ed over, the line r elating lo it w ill have a slow fli cker su perimposed upon it. When this aircraft is taken over, and is th erefore no longer th e responsib il ity of the " pil ot " who ha s been han d l ing it up to now, the entry wi l l b e de leted. When an aircraft

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The fourth secfion is where the keyboard entry is displayed for checking before being entered into the computer. It has already been described. The fifth section is a clock. In a simulator, the exercise time may be different from the actual time, and may vary during the course of the exercise if the exercise is frozen at any stage. The time shovm in this section is of course directly related to all times shown elsewhere on the EDD.

Digital Simulator Capabilities One of the characteristics of a digital simulator is that an aircraft can complete the flight in accordance with its flight plan without intervention on the part of the "pilot". The flight plan information is inserted by means of punch tape prior to and during the exercise. This is the same procedure as will be followed in automated ATC systems. The flight plan data is set out in a prescribed form, using an electric typewriter, and a tape is cut which is inserted into the computer either immediately, or at later stage prior to the departure of the flight. It is not necessary to insert the elapsed time for each leg as this can be calculated by the computer from the performance figures for the aircraft time and the forecast winds. The tape head which reads the tape when it is fed into the computer operates electronically, and there is virtually no wear on the tape. For exercises it is possible to use the same flight plan tapes over and over again. There is a parallel here between operation of the simulator and real life in that when flights take place day after day, the same tape can be used, the information being updated with the actual time of departure. As with the "pilot", it is equally important to limit the loading of the controller/computer interface to those items which cannot be fed into the computer outside the real time of flight operations.

In the simulator the flight plan tape can also be used for the printing of flight progress strips in the same way as is done in the Phase I SATCO system. The concept of programming is frequently a matter for owe rather than understanding. Teaching on digital computation tends to begin with the binary situation of two numbers zero and one, the choice between them being repeated tens of thousands of times in even the smallest computer. The progression from this to a programme requiring complex calculations about real objects is difficult to follow if taken step by step from the beginning. Fortunately it is not necessary to know this sort of detail any more than it is necessary to understand exactly how a watch works in order to be able to tell the time. When a computer is sold, many of its sub routines have already been established as part of the process of manufacture. The job of the programmer is to tell it about its environment, to instruct it in the calculations it must carry out, and to provide the permanent data for those calculations. He must also ensure that he can insert further data on a minute-to-minute basis, addressing it to the right part of the computer's store. At the same time he must arrange that the computer can provide information for the user in an intelligible form, either in relation to a time/ event scale, or in response to the user's request.

The Computer Programme When a computer forms port of a digital ATC simulator, the programme which is prepared has to cover the following aspects: a) ATC 0 per at ion The computer is required to process information so that it con calculate where an aircraft is or where it will be at a given time.

Figure 3 Pilot's desk showing relationship of keyboard and EDD . The desk is wide enough to be manned by two "pilotsw during changeover, and two foot-operated switches ore provided.

b) Rad a r a n d D F Presentation The computer must relate the position of an aircraft to the position of the radar head so that it can calculate where it will appear on the display and how it will appear having regard to its size and reflecting area and to the characteristics of the radar being simulated. The computer feeds this, together with data on the aircraft transponder setting, to an echo generator which does the job of providing the responses on the radar displays. In addition, the computer must provide information on the rotation rate, beamwidth and PRF of the radar, or radars being simulated. There is a similar need to provide information on DF sites and strobes if a DF System is in use. c) S it u at ion Includes information on aerodromes, reporting points, holding patterns, FIR boundaries, ILS approaches et cetera. This is used by the computer to calculate times and distances, and to compute manoeuvres such as flying to a particular reporting point or joining a localizer. d) Ai r craft 0 per at ion The operation of an aircraft can be defined in terms of climbing speed, cruising speed, rate of climb, rate of descent, TMA speed, normal rate of turn et cetera. If these parameters are stored in the computer memory for each aircraft type, it can draw upon them to calculate the performance of the aircraft without need for further instructions from the ,,pilot". e) Weather Con d it ions The computer needs to know the format in which it will be given information

on weather - i. e. areas, height bands et cetera. This forms part of its permanent (or basic) programme. The actual details of weather are fed in on a separate punched paper tape for each exercise or part of an exercise.

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I n put from Key boa r d This defines the function of each key in relation to the electrical input the computer will receive when a particular key is depressed.

h) Aircraft FI i g h t PI a n s This defines the proposed flight paths of the aircraft, together with the estimated time of departure. The information is updated by means of the "pilot's" keyboard or the electric typewriter when the actual time of departure is known. The permanent items of this programme ore recorded on a single paper tape . The information is fed into the computer and left there unless it is necessary to clear the memory to use the computer for another purpose. The temporary information is fed in, also on paper tape, on on ad hoe basis. Should it be necessary to change any of the permanent items, this can be done on a temporary basis by overwriting the previous information using the typewriter input. Alternatively, if the changes made are to be used in all subsequent exercises, the computer can be instructed to punch a new permanent tape. This is stored, and can be used to re-write the computer's memory should this have to be cleared at any time. Some of the items listed above - such as the radar and DF presentation - are exclusive to simulation . Others are

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Figu re 4 Equipment includ ed in a typical digital ATC simulator. Commun i ca lio ns are nol shown but m e p1路ovided b et we en th e co ntro ll er s a nd pilots ' des ks as w ell as b etween individual controll er s.

similar to those used in an operational programme. In the case of aircraft performance, it is of interest that the accuracy of the data supplied for simulation need not be as great as that required in real life. This is because in a simulator the aircraft is always where the computer says it is. In real life, slight deviations between actual and programmed performance could have a significant effect.

Simulator Specifications When digital simulator specifications are discussed, one of the important questions is the relationship between the

number of "pilots" and the number of aircraft to be simulated. Attempts to define the appropriate ratio for specific cases are still handicapped by sparseness of experimental information. We still have to define the limitations the keyboards and EDDs put on the human operator in carrying out other aspects of his job. The business of air traffic control is carried out in a real-time environment where the peaks of loading are largely outside the operator's control. The use of digital simulators will help to establish data on this point, including the mitigation of limitations by improvement in the design of input/output devices. They will also make it possible to provide practice for controllers, so that the handling of computer peripherals becomes a normal part of their job.

hew J!,o,o,k at Amsterdam At the end of February 1968, the Netherlands Department of Civil Aviation has put into operation its new Air Traffic Control Centre at Schiphol Airport, Amsterdam. In Spring 1967, Aerodrome Control already moved into the 150 ft high control tower, next to the new Airport terminal building. Now, nearly a year later, the Area Control Centre and Approach Control have taken residence in the modern ATC building, thus completing an operation of planning system design and equipment installation of many years. Approach Control and Area Control are co-located in one large ATC operations room which is situated immediately above the equipment r~om. In the latter room radars, radio transmitters and receivers direction finders and navigation beacons are remote co~trolled and monitored by the maintenance staff. This is also the heart of 1he internal and external voice communication networks closed circuit_ television system, signalling devices, displa; back-up equipment, secondary surveillance radar decoders, video map units, direction finder converters and switching and emergency power supply. The automatic telegraph exchange and the central computer complex are located in separate rooms, but all in the same building. This concentration makes it possible to monitor the beha'liour of oil essentiol equipment by a minimum of maintenonce slaff. Equipment in the ATC operations room is limiled to various types of displays and keyboards required by the controllers, all fitting into specially designed consoles. Many monufacturers, mostly Dutch, were involved in lhe production of this equipment. But the overall

design and installation supervision was in the hands of the Engineering section of the ATC and Telecom Division of the Dutch ATS authorities. Some sub-systems, for instance the highly complicated intercom-system, are completely own-design. Other sub-systems, such as the SATCO flight plan processing system, were produced completely under contract. In yet other cases, sub-systems were built by interfacing equipment of different manufacture: the radar display system allows the operator to choose either the long range or the medium range radar, to select SSR with one of these and to show bearings of direction finders on the scopes. No doubt, the Amsterdam Area Control Centre is one of the most modernly equipped centres in the world. Intercommunications between control positions have been automated to a great extent, electrical displays are used for data such as available runways, runways in use, occupied flight levels at holding positions. Weather and airfield information is available on a four-channel TV circuit. Controllers communicate with each other through an intercomsystem having facilities for both call-up and interrupt. Assistant controllers use a separate interphone network. Both intercom and interphone systems are linked to the operational ground-ground telephone exchange, the operators position of which is a special design based on thorough studies of human engineering and ergonomic specialists. The technical facilities are a challenge to the ATC staff to carry out ATC in only one way: ... the best! But the new centre does not only mean new equipment,

a spacious room and a carpet on the floor. At the some time the ATC system hos been re-organized operationally. This process hos been on its way for some years already, various trial s were carried out and improvements were introduced in small steps. Now the moment of proof hos come ... The main organizational change is a further sectorizot ion of the airspace and a more intimate creation of sector control teams with the facility to expand and decrease the number of sector teams as required. In the maximum configuration, the lower airspace will be controlled by five airways-sectors, converging into a TMA coordination-sector. Loter, the upper airspace will be controlled by a separate Eurocontrol sector within the some organization (this is a forerunner for the Eurocontrol Upper Area Control Centre at Moostricht). The control method is based on the principle of dividing up planning and executive functions, but at the some time planning and executive controllers and assistants will work together as control teams. Each airway control team is equipped with a computer driven automatic display for plan control, a radar display for executive control, stripprinters (producing radarstrips with clearance data) and a normal teleprinter for the sector assistant to make inputs of incoming traffic. In addition, printer outputs are mode of boundary estimates, to be passed by telephone ta the adjacent centre (this is a facility, which Amsterdam is anxious to link directly with adjacent centres). The TMA coordination sector is a planning secto r only and consequently, is not radar equipped. In addition to coordinating the clearances for overflying aircraft with the airways-sectors, thi s planning control ler is responsible for the initial planning of inbound traffic at the so call ed clearan ce limit positions. This is a computer-assisted planning of the seq uence of inbound traffic, th e executive control of which is carried out with the use of radar by approach control. The approach control unit ho s th e basic responsibility for all traffic in th e terminal control area Amsterdam. Th e computer provides APP wi th data of aircraft outbound from and inbound to each of the four airfields surroundin g Schiphol Airport when this traffi c is affecting the TMA. In addition to ACC and APP, also aerodrome control, the flight information office and the flight information centre have input/ output facilities with the SATCO computer system. Consequently, th e computer system serves as the central memory, calculating and data distributing ce ntre of the entire ATCC. Al so, th e military unit responsible for directing milita ry aircra f t in the Flight Information Region Amsterdam is provided with traffic information directly from computer. Facilities ore avai lable to connect the Airport Authority and Airline Services to this system in o rder to improve the provi sion of traffi c data to those concerned with the handl ing of aircraft, on the ground. The present environmen t, summarized above, is no reason to stop, interrupt or delay furth er p rogress and deve lopm ent. A co ntinuou s effort is required to keep up wi th the development of air traffic. This is we ll known to th e De portment of Ci v il Av iation : rece ntly on order w as placed for a new, very modern lon g range radar which i s to p loy on esse nti a l role in th e system of the seve nties. An ord er for a modern ATC training simulator is exp ected to be pl aced sho rtly, by use of which t he ATC tra ining scheme wi ll be brought into line w i th t he demands of a soph isti cated o per ationa l system.

Assmann COMMUNICATIONS RECORDERS AND AUTOMATIC ANNOUNCERS ARE AIDS FOR AIR TRAFFIC CONTROL CONTRIBUTING TO INCREASED SAFETY

Assmann AUTOMATIC - A 4 REMOTECONTROLLED FOR AT I S (AUTOMATIC TERMINAL INFORMATION SERVICE)

Wolfgang Assmann GmbH 6380 Bad Homburgv.d.Hohe lndu striestr. 5 (be i Frankfurt/M .) Westdeutsch land Tel. 6091, Te lex 04 15158 Cable AKUSTIK

J. S. 31

PHILIPS VHF GROUND-TO-AIR EQUIPMENT 50W VHF TRANSMITTER(l) Single-channel crystal-controlled type RZ 570, meets ICAO specifications. Frequency range 11 8-1 36 MHz or, on request 108-11 8 or 136-1 56 MHz. All transistorized but for the fi na l amplifier tube. Suitable for local and remote control. Built-in mains power supply.

lO W VHF TRANSMITTER(2) Surface and emergency equipment type RZ 560. Fully transistorized. Available for 24V DC battery supply or with 220V AC mains supply unit. 4 units or 3 units p lus power supply will fit imo o ne 19 in. rack.

STANDARD AIR-GROUND VHF RECEIVER (3) Modular-design single chan nel receiver type RO 980. Fully transistorized. Noise figure 6,5 dB. A squelch circuit is included. Special 19 in. mounting frame takes 4 receivers or 3 receivers plus 1 power suppl y unit. Power supply can feed a maximum of 5 receivers.

Other equipment available: 250 W VHF transmitters for area coverage, 2 kW transmitter for extended range.

PHILIPS

telecommunication for airports

PHILIPS TELECOMMUNICATIE INDUSTRIE - P.O. BOX 32 - HILVERSUM - THE NETHERLANDS

COS SOR '

~OR-ELLIOTT

The most flexible SSR system available providing full JCAO fac i li ties with 4096 codes in a l l modes.

INTO THE 70's

Active and Passive decoding avai lable at al l con trol positions

Maximum reliabil ity is ensured b y careful design and the use of advanced techniques

Prove n in operation

COSSOR ELECTRON I CS LI MITED . The Pinnacles, El izabeth Way. Harlow, Essex, England Te lephone: Harlow 26862 Telex : 81228

Al RS PA CE CO NTROL D IVIS I ON Elliott Bros. (Londo n) Ltd. Borehamwood, H erts .. England Telephone 路 01-953-2040 Telex 22777

I The answer to increasing air traffic confusion 1s an accurate. comprehensive. automatic and reliable Nav/ATC system incorporating a Data Link. Decca-Harco is the only system tl;iat can meet the nav1gat1on and ATC demands of both sub- and supersonic air traffic. And only Decca-Harco can provide the flex1b1l1ty and accuracy that permits close lateral separation of aircraft throughout the route structure At the control centre the Decca Data Link provides the controller with accurate displays of the identity. altitude and precise pos1t1on of all co-operating aircraft. using the common reference of a high accuracy. area coverage system The necessity for R/T communication 1s reduced by the use of two-way Alpha-Numeric messages and routine reports are eliminated. reducing the work load and increasing the reliability of the ATC system

On the flight- deck Decca Omnitrac-the world's most advanced l1ghtwe1ght d1g1tal computer-provides the pilot w ith undistorted pictorial presentation and automatic chart changing. Th e 'ghost beacon' fac1l1t y gives him bearing and distance to any point. Omnitrac also provides auto-pilot coupl in g and automatic altitude control which maintain respectively any required flight path and flight profile. The ETA meter indicates either time to destination or ETA.

It 1s only through an integrated system. operating from a common reference. such as Decca-Harco. that a great many aircra f t of different types flying at various speeds and altitudes can be ett1c1ently co-ordinated into a single d1sc1pl1ned traffic pattern.

DECCA-HARCO The comprehensive Nav/ATC system The Decca Navigator Company L1m1ted 路 London