ICAO Doc 9426 Part 3 Air Traffic Services Planning Manual 1984.pdf

AIR TRAFFIC SERVICES PLANNING MANUAL PART III FACILITIES REQUIRED BY ATS  AIR TRAFFIC SERVICES PLANNING MANUAL PART III SECTION 1. GROUND BASED NAVIGATION, SURVEILLANCE AND COMMUNICATIONS EQUIPMEN...

AIR TRAFFIC SERVICES PLANNING MANUAL PART III FACILITIES REQUIRED BY ATS  AIR TRAFFIC SERVICES PLANNING MANUAL PART III SECTION 1. GROUND BASED NAVIGATION, SURVEILLANCE AND COMMUNICATIONS EQUIPMENT  SECTION 1 GROUND BASED NAVIGATION, SURVEILLANCE AND COMMUNICATIONS EQUIPMENT Contents Page Chapter 1. General..................... 111-1-1-l 4.1.2 OMEGA...................... 111-1-4-l 4.1.3 LORAN-C..................... 111-l-4-3 1.1 Introduction......................... 111-1-1-l 4.2 Operational application............... III-144 1.2 Cost-benefit considerations............ 111-1-l-I 1.3 Types of equipment associated with ATC services...................... III-l-l-3 Chapter 5. Landing Systems............. 111-1-5-l Chapter 2. VOR/DME and TACAN...... 111-l-2-1 5.1 Functional requirements.............. 111-l-5-1 5.1.1 Instrument landing system....... 111-l-5-1 2.1 Functional requirements.............. 111-l-2-1 5.1.2 Microwave landing system....... 111-l-5-2 2.2 Operational application............... 111-l-2-2 5.2 Operational application............... 111-l-5-3 5.2.1 Instrument landing system....... 111-l-5-3 5.2.2 Microwave landing system....... 111-l-5-3 Chapter 3. Non-directional Radio Beacon. 111-13-l Appendix A. General procedures used in 3.1 Functional requirements.............. 111-l-3-1 the United States for the control of 3.2 Operational application............... 111-l-3-1 aircraft in ILS critical areas............. 111-l-5-4 Chapter 4. Long-range Radio Navigation Aids.................................. 111-14-l Chapter 6. VHF Direction Finder......... 111-1-6-l 4.1 Functional requirements.............. 111-1-4-l 6.1 Functional requirements.............. 111-l-6-1 4.1.l Genera1....................... 111-1-4-l 6.2 Operational application............... 111-l-6-1 III-l-(i)  Chapter 1 General 1.l INTRODUCTION catastrophes which could be expected to occur at that location (e.g. earthquake, landslide, flood, washout, etc.); provision of utilities including the required degree 1.1.1 To function properly, an air traffic control (ATC) of reliability; site access improvement as needed (e.g. system requires various items of equipment. Types and power lines and access roads); quantities of this equipment will vary with the properly d) preparation of equipment specifications - an equip- justified demands on the particular system. ment specification is prepared either as a functional specification or as a technical specification: 1.1.2 Equipment elements should generally be installed in 1) a functional specification describes the purpose the stages and in proportion to the increase in demand(s) equipment is expected to serve and the terms of imposed on the air traffic services (ATS). Such phasing has desired performance, i.e. operational needs, main- the advantage of reducing the immediate economic burden tainability, reliability, durability and useful life, etc. imposed on administrations by spreading system estab- It gives the potential supplier information on how, lishment or expansion costs over a longer time. It also or what equipment, he will need to produce in reduces the critical effect of time on personnel recruitment, order to satisfy the specified functional performance selection and training necessary for equipment installation, requirements; maintenance and operation. 2) a technical specification describes the detailed engineering (physical, mechanical, electronic) 1.1.3 In addition to the pure equipment costs, there are aspects of the components making up the equipment many “hidden” costs associated with the acquisition of in question; major items of ATC equipment. Hidden costs include e) contract negotiation; personnel salary and allowance costs associated with the 0 equipment inspection(s) before technical acceptance; preparatory work and the procurement, installation, is) installation; operation and maintenance of the equipment. It is there- h) systems evaluation (operational acceptance) including fore essential that relevant hidden costs be included in the flight inspection costs for aircraft and crew; preparation of initial budgetary estimates. 9 ancillary monitor equipment; 9 standby equipment and/or fail-safe or fail-soft 1.1.3.1 Activities, materials and other elements which are provisions; associated with hidden costs may include: k) spare parts inventory or suitable alternative(s) such as rapid, reliable replacement from a centralized source; a) site survey - selection of the best site for optimum 0 special tools required for maintenance of that operational benefit from the equipment, commensurate equipment; with ecological considerations and consistent with ml training for operations and maintenance personnel; budgetary limitations; n) manuals of the operation and maintenance of the b) site acquisition - rights to the property including equipment. protection against future neighbouring encroachments (e.g. growing trees, other structures or electronic inter- ference) which could adversely affect the performance of the equipment; rights to ensure appropriate site 1.2 COST-BENEFIT CONSIDERATIONS access throughout the predicted life of the equipment; 4 site preparation - foundations, clearing, etc., and shelter for the equipment and the maintenance 1.2.1 When considering the acquisition of expensive personnel against the meteorological conditions equipment, the use of cost-benefit methodology may be common to the location; similar protection against desirable to help in determining budget justification for III-I-I-I III-l-l-2 Air Traffic Services Plannina Manual new equipment. The cost-benefit method described in the 1.2.2.4 Where an efficiency improvement is expected by following paragraphs lists some of the elements which the use of more direct routings, the time saved per aircraft, should be considered in this respect. The method has been multiplied by the aircraft cost per unit of time, multiplied used successfully but the elements listed here are neither all- by the anticipated number of such flights over the lifetime inclusive nor does each of them merit inclusion in the of the equipment under consideration provides the equation in every case. Pre-operation costs have, to a large “efficiency” benefit. measure, been listed in 1.1.3.1 above. When added to the pre-operation cost outlay, the equipment price as agreed in 1.2.2.5 Where the additional equipment permits a the contract with the supplier, plus the anticipated reduction of ATC delays because of the following, the continuing operations and maintenance costs (personnel reductions are considered as time savings and computed as remuneration, utilities, etc.) give the total “cost” portion in 1.2.2.4 as an efficiency benefit: of the equation. If these estimated costs are within the budgetary limitations, then the “benefit” portion of the a) the use of lower landing minima (thus avoiding holding equation should be developed. or a diversion to an alternate aerodrome); or b) the use of lower departure minima; or 1.2.2 Benefits derived from additional ATC equipment c) the use of reduced separation and a resulting higher rate may be categorized by any one of the following: increased of arrivals and/or departures; or productivity, efficiency, safety and/or environmental d) the implementation of an improved ATS route structure improvements. As is done for the costs, the benefits are (e.g. parallel routes). normally determined for the life cycle of the equipment. 1.2.2.6 Where the reductions in operating time obtained in accordance with the provisions in 1.2.2.4 and 1.2.2.5 1.2.2.1 Productivity can be measured in terms of how above relate to commercial operators, the average number many more operations are expected to be handled with the of business travellers per affected flight and the economic improvement than without it. From this, one derives how value of such travellers’ time should be available from the many controllers expected to be leaving the service do not operators concerned. These factors are then treated as need to be replaced, or how many additional controllers described in 1.2.2.4. The result is added to the “benefit” need not be hired to satisfy increased demands on ATS. column. Cost-saving or cost-avoidance is then quantified by multiplying the cost per controller times the number of 1.2.2.7 It is difficult to quantify “safety”, since it is controllers not replaced or not hired (due to the new equip- virtually impossible to agree on the material value of a ment). Calculated for the equipment life, this is the benefit human life. However, an approximation for the safety for this element. benefit may be obtained by assessing the probable reduction in aircraft accidents attributable to the new 1.2.2.2 Productivity in the control environment may also equipment. This is then multiplied by the probable number be obtained by the elimination or reduction of non-control of fatalities (based on historical data) and this, in turn, is tasks which nonetheless contribute to the system, e.g. multiplied by a reasonable (national) assessed value for a automatic instead of manual preparation of flight progress life (insurance companies may be a logical source for such strips. The remuneration costs for the personnel whose a value). This total is then extrapolated for the life cycle of functions will then be eliminated or substantially reduced the equipment in question and the end product represents are then added to the benefit column of the equation. the “safety” benefit value. 1.2.2.3 Productivity related to replacement of main- 1.2.2.8 Environmental improvement cannot be easily tenance personnel and/or to additional equipment is quantified in economic terms; however, a reasonable measured by its predicted maintenance time (number of broad-based assessment is possible. A review of the scheduled and non-scheduled outages over a fixed period properties on the ground which are overflown with existing of time, multiplied by the average time per outage). The arrangements and its comparison with those overflown as time so obtained is then compared with actual maintenance a result of new routings, made possible through the new time as experienced with the equipment which is intended equipment, would provide a basis for such an assessment. to be replaced or supplemented. Where this comparison is Demographic comparisons of the two areas could then be in favour of the new or additional equipment the differ- made with special reference to numbers of people, hos- ential is multiplied by the maintenance personnel remuner- pitals, schools and private residences and values could be ation cost, which results in the benefit quantification for assigned to personal health, quiet enjoyment and duration this element. of exposure. When these values are integrated with the data Part III.- Faci1itie.y required by Air Traffic Services Section I, Chapter I.- General III-l-I-3 from the demographic comparisons, any favorable differ- should be considered as substantial support for a decision ences should then be added to the benefit column. Simi- to proceed with the necessary steps for procurement of the larly, loss or gain values could be assigned to the two areas equipment item in question. of real estate involved and a net favourable difference should also be added to the “benefit” side. 1.3 TYPES OF EQUIPMENT ASSOCIATED WITH 1.2.2.9 Replacement equipment may also be more ATC SERVICES reliable. Any benefits derived from this fact may take several forms. More reliable communications and/or radar will induce the controller to adhere more closely to 1.3.1 Major types of equipment associated with ATC minimum and thus more efficient separation standards, services include: while, with less dependable equipment, the controller will tend to apply larger separations for reasons of safety. This a) very high frequency omni-directional range (VOR); benefit is, however, too indefinite to be quantified but b) non-directional radio beacon (NDB); should be referred to in narrative terms on the “benefit” c) long-range radio navigation aids; side. In addition, increased reliability should reduce 4 communication equipment; maintenance efforts (see 1.2.2.3 above) and may permit e) primary and secondary radar; more dependable commercial air carrier operation which, f-l radar presentation equipment; in turn, may encourage an increasing number of passengers g) automated systems; to elect to travel by air. This intangible fact should also be h) instrument landing system (ILS); included in the narrative accompanying the benefit 0 very high frequency direction-finding (VDF). material. 1.3.1.1 The respective functional and operational 1.2.2.10 Further to the considerations in 1.2.2.4 and requirements for the equipment listed above are discussed 1.2.2.5, reliability may enhance air defence capability. If in the following chapters, with the exception of primary this is the case, it should also be mentioned in the benefit and secondary radar, radar display equipment and auto- material, even though economic values cannot be assigned mated systems (e) to g) above). It was believed advan- to such benefit. tageous to deal with the functional and operational requirements of this equipment together with the use made 1.2.3 Whenever the total benefit, as expressed in material of it because of the close interrelation which exists between terms alone or together with those benefits described in these two aspects of such equipment (Part II, Section 3, narrative form, is found to be higher than the costs, it Chapters 2 and 3 refer).  Chapter 2 VOR/DME and TACAN 2.1 FUNCTIONAL REQUIREMENTS the greater the effective range. In addition, VORs are subject to co-channel or adjacent channel frequency inter- ference problems with other VORs or ILS localizers if care 2.1.1 The VHF omnidirectional radio range (VOR) is an is not taken in the frequency assignment planning made for omnidirectional (360” of azimuth) range station which these aids. operates in the very high frequency (VHF) band of the radio spectrum between 108 to 118 MHz, sharing the band 2.1.4 When overflying the VOR, aircraft will enter a from 108 to 112 MHz with the localizer component of “cone” of signal “softness” but its horizontal dimension instrument landing systems (ILS). Since it is normally used at any level is relatively small and has, therefore, normally within approximately 130 NM of the station, the VOR is no noticeable effect on navigation. The ratio of altitude to considered a short-range navigation aid. VORs are used at horizontal “soft” signal distance is probably less than 1.7 times beyond 130 NM; however, the accuracy of navigation to 2; for example, at 1 700 ft above the station, irresolution guidance derived from it decreases with increased range. will exist, at most, for 2 000 ft longitudinally. The basic navigation guidance derived from a VOR is a radial line of position (magnetic) with respect to a known 2.1.5 A Doppler VOR (DVOR) is an improved, but more geographic point (the VOR site). The radial line is read in expensive version of the VOR. It has the advantage of degrees of azimuth from magnetic North and is technically being able to overcome many electronic interference accurate to within k 2.0”. The over-all system accuracy is problems of a particular site. DVORs are, as a rule, also + 5.0” (see Part I, Section 2, Chapter 5, Appendix B). more precise than the basic VOR. The precision VOR Bearing information may be used by aircraft to fly toward (PVOR), a modified DVOR, is significantly more precise or away from the station at any azimuth selected by the than a VOR or DVOR, but it is still more expensive. Its use pilot. The 180” ambiguity in this indication is resolved by of DVOR is clearly advantageous in all those cases where the provision of a “to/from” (the VOR) indicator in the very accurate track guidance is required by aircraft. A aircraft avionics. terminal VOR (TVOR) is a low power (50 W) VOR used for terminal navigation guidance. 2.1.2 The identification of specific VORs is provided by means of a Morse Code identifier or by voice recording. The VOR may also be provided with a voice channel for 2.1.6 Distance measuring equipment (DME) is a useful ground-to-air communications. VORs can be remotely adjunct to, and is normally collocated with a VOR. In such operated by the use of telephone lines from the control cases, the VOR is referred to as “VOR/DME”. DME is facility. Where standby or dual equipment is provided, an also subject to line-of-sight limitations, but is normally automatic transfer between the equipment is made usable up to 200 NM at appropriate levels. A DME whenever the operating VOR is subject to malfunction. In provides a continuous digital readout of the slant-range case of malfunction of a VOR and/or in case the VOR distance, in nautical miles, between the aircraft and the signal received by the aircraft is not adequate to give DME site. It is a rather precise aid, the slant distance reliable navigation guidance, a visual alert is triggered in accuracy being ‘/z NM or 3 per cent of the distance, the cockpit display, e.g. a warning flag appears on the whichever is greater. Slant range differs from horizontal airborne receiver indicator. distance when projected onto a plane, the former being always larger, and the difference will be greatest when 2.1.3 The VOR is subject to line-of-sight limitations; that aircraft are at their highest level directly over the station. is to say that its signals can only be received at increasingly When using a VOR/DME, the tuning of the airborne higher altitudes as the distance of the aircraft from the receiver to the VOR will automatically couple the DME station increases. The usable range of a VOR is also receiver to the associated DME ground station. DME proportional to its power, i.e. the greater the power output, operates in the ultra-high frequency (UHF) band between 111-1-2-I m-1-2-2 Air Tr&fic Services Planniw Manual 962 MHz and 1 213 MHz. This band is relatively free of separation criteria between routes, resulting in a more interference from atmospherics and precipitation static. efficient use of the airspace. 2.1.7 Tactical air navigation (TACAN) is a military 2.2.1.1 The VOR/DME route structure is normally development providing both the azimuth and distance established so as to make it possible for aircraft to fly from components by equipment operating in the UHF band. one VOR direct to the next, or along intersecting radials of Where a TACAN is collocated with a VOR, the distance two adjacent VORs. Reporting points and/or other measuring component of the TACAN substitutes for and significant points are normally established along radials, fulfils any civil requirement for DME. The VOR is then either together with a given DME distance from an associ- referred to as “VORTAC”. As with DME, tuning to the ated VOR, or by an intersection of radials from two VOR will automatically interlock with the associated different VORs and change-over from one VOR to another TACAN distance measuring element. When used by civil is normally made at the mid-point between the two VORs aircraft, the guidance derived from a VOR/DME and a concerned. VORTAC is identical. 2.2.1.2 The TVOR can serve as a landing aid at locations where no precision approach facility (ILS, precision approach radar (PAR)) is available. Where required by the local situation, it may also be provided with a collocated 2.2 OPERATIONAL APPLICATION DME in order to provide improved guidance along the approach path. 2.2.1 The VOR/DME is the basic short-range aid used to 2.2.1.3 Where standard instrument departure (SID) and provide navigation guidance along airways, air traffic standard arrival (STAR) routes have been established to services (ATS) routes and specified tracks. Its accuracy facilitate the flow of departing and/or arriving air traffic allows ATS routes to be kept at reasonable widths and these are frequently based on VOR/DMEs and TVORs (see permits the application of comparatively small lateral Part I, Section 2, Chapter 4, 4.4).  Chapter 3 Non-directional Radio Beacon 3.1 FUNCTIONAL REQUIREMENTS being displayed, the pilot must continuously monitor the NDB’s identification. 3.1.1 Non-directional radio beacons (NDB) transmit non- directional signals in the low and medium frequency 3.2 OPERATIONAL APPLICATION (L/MF) bands, normally between 190 to 1 750 kHz. With appropriate airborne equipment, the pilot can determine the bearing of the station, or can “home” on the station. 3.2.1 NDBs continue to be used as air navigation aids The specific identification of an NDB is normally despite the availability of improved aids, e.g. VHF omni- broadcast in Morse Code. directional radio range (VOR), and the deficiencies described in 3.1.2. This appears to be mainly due to the fact that, in many cases, NDBs were installed before the VORs 3.1.2 Although NDBs are comparatively inexpensive became available and because NDBs are, even now, so navigation aids and relatively simple to install and much less costly to install and maintain. Where operating, maintain, they have significant drawbacks. Bearing NDBs are mainly used: information derived from NDBs is not very precise and lightning, precipitation static, etc., cause intermittent or a) as a non-precision instrument approach aid (by itself); unreliable signals resulting in erroneous bearing infor- or mation and/or large oscillations of the radio compass b) in conjunction with an instrument landing system (ILS) needle. At night, since L/MF radio wave propagation (then designated as a “locator”); or increases, the radiation patterns of NDBs are subject to c) to define L/MF routes/airways, etc. considerable but unpredictable variations which might result in interference from distant L/MF stations which can 3.2.2 When NDBs are used to define L/MF render navigation with this aid difficult. Nearly all disturb- routes/airways, etc., they are normally operated as short- ances which affect the bearing radiation output also affect range aid. However, the power output is raised the facility identification. Usually noisy identification significantly when the NDB is serving as a landfall point occurs when the automatic direction-finder (ADF) needle used to define an “off-shore” or similar route. of the radio compass in the aircraft behaves erractically; voice, music, or erroneous identifications will usually be 3.2.3 The effective range of an NDB is proportional to its heard and a false bearing will be displayed on the radio power output. NDBs with a power output of less than compass. Since ADF receivers do not have a “flag alarm” 25 W are classified as “compass locators” and their to warn the pilot when erroneous bearing information is effective range does not exceed 15 NM during day time. 111-1-3-l  Chapter 4 Long-range Radio Navigation Aids 4.1 FUNCTIONAL REQUIREMENTS gational accuracy (at a cost of significantly less signal range) recent developments with OMEGA have shown that the accuracy requirements are now being met to a satisfac- 4.1.1 General tory degree. For universal application, a navigation system should provide accuracy, low cost, high availability and broad 4.1.2 OMEGA coverage. Since no single type of navigation aid meets all of these requirements, diversification has become a necess- 4.1.2.1 OMEGA is a VLF (10 to 14 kHz) circular or ity. The very low frequency (VLF) navigation aids, (e.g. hyperbolic navigation system whose propagation charac- OMEGA, LORAN-C), with their more extensive coverage teristics are such that eight strategically located trans- are better suited than very high frequency (VHF)/ultra mitting stations will provide world-wide coverage. The high frequency (UHF) aids (e.g. VHF omnidirectional eight stations now in operation are located in Norway, radio range (VOR)/distance measuring equipment (DME)) Liberia, Hawaii (United States), North Dakota (United to meet current long-range navigation requirements. States), Argentina, Japan, La Reunion (France) and Although VHF/UHF facilities contribute greater navi- Australia (see Figure 1). Figure l.- OMEGA transmitter locations 111-1-4-1 III-1-4-2 Air Traffic Services Planning Manual Liberia Haw aii I CI Nort h Da k o t a 0) L a Fm m l o n (E) Argw dna (F) Aurt ralla (0 1 1 1 l /3 1 0.2 Transm ldon - 0.9 +.2 + 1.O +.2 (- 1.1 ~.2 ~1.2 ~.2 ~1.1 ~.2 ~0.9 ~.2 ~1.2 ~.2 ~1.0 ~.2 Int erval Figure 2.- OMEGA transmission pattern 4.1.2.2 The existing OMEGA navigation system provides 4.1.2.4 The airborne receiving equipment computes a line coverage over more than 90 per cent of the earth’s surface, of position (LOP) based on the phase difference between including virtually the entire Northern Hemisphere. signals received from two transmitter stations. Using a OMEGA stations transmit omnidirectional, continuous minimum of three stations, the receiver computes at least wave (CW), coded and precisely timed signals. Each station two LOPS and the intersection of these two defines the transmits on four specified, basic, navigation frequencies aircraft position. The current position accuracy obtained in sequenced format. This time-sequenced format prevents with OMEGA is 2 to 4 NM. It is expected that this accuracy inter-station signal interference. The pattern is arranged so can be further improved when the system is completed. that during each transmission interval only three stations Position accuracy derived from OMEGA may be better at are radiating; each at one of four different basic fre- the end of a flight than at the beginning due to more quencies (see Figure 2). With eight stations and a silent favourable propagation conditions, i.e. errors may be time- interval of 0.2 s between each transmission, the entire cycle dependent since signal reception by aircraft is often a is repeated once every 10 s. An OMEGA station is function of the time of day. Heights of specific layers in the operating in full format when the station is transmitting on earth’s ionosphere and their degree of ionization vary (see the basic frequencies plus the unique frequency. Figure 3), a condition which affects the sky-wave correc- tions and consequently results in decreasing accuracy of the 4.1.2.3 Each OMEGA transmitter has a range of about system. Accuracy will be improved, however, with better 5 000 NM. The range will vary since it is dependent upon sky-wave correction prediction. Another limitation of noise (from lightning discharge), the frequency and inten- OMEGA is that signals from a particular station should sity of which change with latitude, season and time of day. normally not be used within a 600 NM (about 1 000 km) Propagation over the ocean suffers the least attenuation radius of that station, and this radius limitation is greater while propagation over areas covered with ice is most at night. Such a limitation is, however, not very significant affected. It is for this reason that the best coverage is since each transmitter has a useful range of about obtained over oceanic areas. In addition, at night the range 5 000 NM, and aircraft can generally receive signals from of individual stations is generally increased, thus improving at least 3 stations; the consequence of possibly using long the use of the system. baselines considerably increases the accuracy. Part III.- Facilities required by Air Traffic Services Section I, Chapter 4.- Long-range radio navigation aids m-1-4-3 4.1.2.5 In the USSR a long-range navigation system LORAN-C does not provide world-wide coverage, similar to OMEGA is used. The Russian system has although its (sky-wave) signals are used in northern transmitters located within its territory (contrary to latitudes by some trans-oceanic flights. The ground-wave OMEGA); one full transmission cycle takes, however, only range of the LORAN-C transmitter is generally less than 3.6 s. This rapid data transmission rate is likely to be even 1 200 NM; the one-hop sky wave, less than 2 300 NM; more valuable for aviation. the two-hop sky wave, up to 3 400 NM. Between 1 200 and 1 800 NM from the stations used, the ground wave is sometimes received, but this reception is unpredictable. 4.1.3 LORAN-C 4.1.3.1 Long-range navigation (LORAN-C) is the 4.1.3.3 Sky waves normally provide a stronger signal to improved version of the LORAN navigation system. It is the LORAN-C receiver, but these signals should only be a pulsed, hyperbolic system operating in the frequency used when no ground wave signal is received because each band from 90 kHz to 110 kHz. Three or more transmitting LORAN line on the chart represents a difference in arrival stations are set up in chains in which the master station and time of two ground waves. The sky-wave correction is only its associated slave stations can be separated by up to an approximation, since the height of the reflecting layer 800 NM. varies (see Figure 3). Thus the system accuracy is 0.25 NM in published areas of ground wave coverage, whereas with 4.1.3.2 The LORAN-C receiver computes LOPS based on the use of sky-wave signals the position error is of the order time-of-arrival differences between signals from selected of 2 NM. combinations of two transmitters of the same chain, one of which must be the master station. The aircraft position is at the point where these LOPS intersect. LORAN-C 4.1.3.4 LORAN-C signals are available continuously chains provide geographic coverage ranging from 900 to regardless of the time of day or weather conditions, and the 2 400 NM by means of their ground-wave signals. system has a record of very high reliability. Over the years TWILIGHT DAY NIGHT Figure 3.- Earth-ionosphere relationship m-1-4-4 Air Traffic Services Planning Manual of operation of this system very few outages have occurred major, ground-based systems providing navigation cover- and these have been of very short duration. age over wide areas. OMEGA will continue in operation, due to its international civil character, coverage and economy of user equipment. LORAN-C will continue in operation because of its predictable and repeatable accuracy within its area of coverage and due to the economy of user equipment. However, its operation will be 4.2 OPERATIONAL APPLICATION restricted to specific areas because its extension so as to provide world-wide coverage would pose prohibitive ground equipment costs. When using both OMEGA and LORAN-C offers medium to high accuracy in position LORAN-C, the user has a purely passive function. He does determination over an extended range. OMEGA offers not transmit any signal for position fixing and, because of even greater range, i.e. world-wide coverage, but with a this, the systems are never saturated and the number of lesser degree of accuracy. LORAN-C and OMEGA are the users is unlimited.  Chapter 5 Landing Systems 5.1 FUNCTIONAL REQUIREMENTS distance of the localizer site from the approach threshold, so as to provide a linear signal width of approximately 210 m (700 ft) at the runway approach threshold. The 5.1.1 Instrument landing system course line along the extended centre line of a runway, in the opposite direction to the approach direction served by 5.1.1.1 The instrument landing system (ILS) is the ICAO the ILS is called the back course. Back course signals standard, non-visual aid to final approach and landing. should not be used for conducting an approach unless a Ground equipment consists of two highly directional trans- back course approach procedure has been published for the mitting systems and two marker beacons aligned along the particular runway and is authorized by ATC. The identifi- approach. A third marker beacon may be added along the cation of an ILS is transmitted in International Morse approach path if operationally desirable. The directional Code and consists of a two or three-letter identifier starting transmitters are known as the localizer and glide slope with the letter I (* *). It is transmitted on the localizer transmitters. The total landing system of which ILS is an frequency. Category I and II (see Part II, Section 5, integral part generally provides the pilot with: Chapter 2) localizers may provide a ground-to-air communication channel. a) guidance information regarding the approach path derived from the localizer and the glide slope; 5.1.1.4 The localizer provides course guidance b) range information at significant points along the throughout the descent path to the runway threshold from approach path by marker beacon or continuous range a distance of 18 NM from the antenna between a height of information from distance measuring equipment 300 m (1 000 ft) above the highest terrain along the (DME); and approach path and 1 350 m (4 500 ft) above the elevation c) visual information in the last phase of flight from of the antenna site. Distinct off-course indications are approach lights, touchdown and centre line lights, provided throughout the areas of the operational service runway lights. volume as shown in Figure 1. These areas extend: 5.1.1.2 At selected locations where the provision of a) 10” either side of the course within a radius of 18 NM marker beacons at the defined locations creates difficulties, from the antenna; they may be replaced by a DME which is associated with b) 35” either side of the course within a radius of 10 NM the ILS. This provision is particularly advantageous when from the antenna. approaches have to be made over water. At some locations a complete ILS system is provided for each landing 5.1.1.5 The ultra high frequency (UHF) glide slope trans- direction of a runway, or for a number of runways. When mitter, operating on one of the 40 ILS channels within the such is the case, only one of the ILS systems is, however, frequency band from 329.15 MHz to 335 MHz, radiates its put in operation at any time. signals only in the direction of the localizer front course. However, in some cases where a back course approach 5.1.1.3 The localizer transmitter, operating on one of the procedure has been established an additional glide slope 40 ILS channels within the frequency band from 108 MHz transmitter has been installed to radiate signals in the to 112 MHz, emits signals which provide the pilot with direction of the localizer back course to provide vertical course guidance onto the runway centre line. The approach guidance for this approach procedure. Where this is done, course of the localizer, which is used with other com- the two glide slope transmitters will operate on the same ponents, e.g. glide slope, marker beacons, etc., is called the channel but are interlocked so as to avoid simultaneous front course. The localizer signal emitted from the trans- operation and ensure that either the front course or the mitter site at the far end of the runway is confined within back course is provided with vertical guidance but not both an angular width between 3” and 6”, depending on the at the same time. III-I-5-l 111-l-5-2 Air Traffic Services Planning Manual NORMAL LI MI TS OF LOCALI ZER COVERAGE: THE SAME AREA APPLI ES TO A BACK COURSE WHEN PROVI DED. Figure 1 5.1.1.6 The glide slope transmitter is located between 5.1.2 Microwave landing system 230 m (750 ft) and 380 m (1 250 ft) from the approach end of the runway (down the runway) and offset between 75 m 5.1.2.1 The microwave landing system (MLS) is an (250 ft) and 198 m (650 ft) from the runway centre line. It improved version of the ILS and has been conceived so as transmits a glide path with a beam width of 1.4’ (“glide to meet the present and future ICAO functional require- path” means that portion of the glide slope that intersects ments for landing guidance systems. It is envisaged that the localizer). The glide path projection angle is normally MLS will be progressively implemented as of 1990. The adjusted to 3” above the horizontal plane so that it passes transition period where both ILS and MLS will be in oper- through the middle marker at about 60 m (200 ft) and the ation will extend to the year 2000, when it is expected that outer marker at about 426 m (1 400 ft) above the runway ILS will be completely replaced by MLS. elevation. The glide slope is normally usable to the distance of 10 NM. However, at some locations, use of the glide 5.1.2.2 The operation of the MLS is based on time refer- slope has been authorized beyond this range. The glide ence scanning beam (TRSB) principles. Electronic beams path provided by the glide slope transmitter is arranged so scan the volume of the service area to be covered in a clock- that it flares from 5 to 8 m (18 to 27 ft) above the runway. wise, then counter-clockwise (to-fro) manner. The Therefore, it should not be expected that the glide path will scanning generates the angular functions for azimuth, provide guidance to the touchdown point on the runway. elevation, missed approach azimuth and flare guidance and information. Usable navigation information is provided 5.1.1.7 Conventional ILS is subject to siting problems within an area + 40” from runway centre line, between 2” which, at certain aerodromes, can be acute. In addition, at to 10” in elevation and between 20 and 40 NM in range. high-density aerodromes further problems with ILS oper- ation may be caused by overflights or by other disturb- 5.1.2.3 The degree of sophistication of the MLS at ances. Glide slope and localizer signals are adversely specific locations can range from simple and inexpensive affected by reflecting objects such as hangars, etc. At some installations to complex systems. The more complex locations, snow and tidal reflections also affect the glide systems enable landing under zero visibility conditions. path angle to a noticeable degree. In addition, the limited Unlike the present ILS systems, which basically provide number of channels available for use by ILS may cause only a single approach path, MLS, while being less subject interference problems in areas where, due to the proximity to siting and interference problems, will cover a wider area, of aerodromes, a large number of ILS are required. thus providing a number of possible approach paths. In Part III.- Facilities required by Air Traffic Services Section I, Chapter 5.- Landing systems 111-I-5-3 addition, an integrated DME provides continuous distance permit the use of reduced minimum separation of 2 NM information, thus eliminating the need for marker beacons, between aircraft established on adjacent localizer courses, as with the present ILS. if the centre lines of the parallel runways are at least 914 m (3 000 ft) apart. 5.2 OPERATIONAL APPLICATION 5.2.1.4 ILS localizer courses can be used to define portions of standard instrument departures (SIDs) and 5.2.1 Instrument landing system standard instrument arrivals (STARS), thus contributing to the expedition of the traffic flow and a reduction in air- 5.2.1.1 The lowest authorized ILS minima, with all ground communications. required ground and airborne system components operat- ive, are normally as follows: 5.2.1.5 When considering the establishment of an ILS, care should be taken to ensure, not only that it serves the a) Category I - decision height (DH) 200 ft and runway preferential traffic flow at that aerodrome, but also to visual range (RVR) 2 600 ft. ensure minimum interference with the traffic patterns at b) Category II - DH 100 ft and RVR 1 200 ft; neighbouring aerodromes. In addition, environmental c) Category IIIA - DH (optional with State) and RVR (especially noise abatement) considerations are assuming 700 ft. an increasingly significant role in the orientation of an ILS. Note.- Special authorization and equipment are required for category II and MA. 5.2.2 Microwave landing system 5.2.1.2 ILS localizer and glide slope course disturbances may occur when surface vehicles or aircraft are operated 5.2.2.1 MLS reduces siting problems since it is less critical near the localizer and glide slope antennas. Antenna in respect to ILS and to the adequacy of its site. MLS locations are such that most installations could be subject permits the establishment of flexible, curved, multiple and to signal interference by surface vehicles, aircraft or both, segmented approach paths in azimuth and elevation and and it is for this reason that ILS critical areas are estab- provides improved flare guidance. Such capability lished on the surface about each localizer and glide slope increases the traffic handling capacity of ATC and/or antenna. Air traffic control (ATC) procedures provide for helps avoid overflying noise sensitive areas at low altitudes. the control of vehicles or aircraft on the taxiways and Such multiple paths also help reduce wake vortex runways. One of the aims of these procedures, in relation problems, and provide more guidance for missed to ILS critical areas, is to prevent arriving or departing approaches and departures. Finally, MLS permits the inter- aircraft from causing interference to the ILS when the ILS ference-free installation of more facilities in a given area is being used under weather or visibility conditions because there are up to 200 channels available in the requiring such use by other arriving aircraft. Appendix A frequency band in which it operates in comparison with a provides an example of procedures used in the United maximum of 40 channels for ILS. States for control of aircraft in the ILS critical area. 5.2.2.2 Additional information or application and ben- 5.2.1.3 Where ILS systems are installed to serve parallel efits for MLS and possible approaches to the introduction runways, some States authorize simultaneous ILS of the system are contained in ICAO Circular 165 - approaches if the served parallel runways are at least Microwave Landing System (MLS) Advisory Circular Issue 1 310 m (4 300 ft) apart. In addition, some States also No. 1. m-1-5-4 Air Traffic Services Planning Manual Appendix A General Procedures used in the United States for the Control of Aircraft in ILS Critical Areas 1. When the aerodrome control tower is in operation at 4. While no specific critical area is established outward controlled aerodromes, and with weather conditions less from the aerodrome to the final approach fix, an aircraft, than ceiling 243 m (800 ft) and/or visibility 2 miles, ATC holding below 5 000 ft above ground level and inbound issues control instructions to aircraft so that they do not toward an aerodrome between the ILS final approach fix interfere with ILS critical areas. and the aerodrome, can cause reception of unwanted local- izer signal reflections by aircraft conducting an ILS 2. Vehicles and aircraft are not authorized in the glide approach. Accordingly, such holding is not authorized slope critical area when an arriving aircraft is between the when weather or visibility conditions are less than a ceiling ILS final approach fix and the airport unless the aircraft of 800 ft and/or a visibility of 2 miles. has reported the airport in sight and is circling or “side stepping” to land on a runway other than the ILS runway. 5. Critical areas are not protected at aerodromes when weather or visibility conditions are above those requiring 3. Except for aircraft that may operate in or over the protective measures as specified above. critical area when landing or leaving a runway, or for departures or missed approaches, vehicles and aircraft are not authorized in or over the localizer criticai area when an 6. Vehicular traffic not subject to control by ATC may arriving aircraft is between the ILS final approach fix and cause momentary deviations of the ILS course or glide the aerodrome. When the ceiling is less than 200 ft and/or slope signals. the RVR is 2 000 ft or less, no vehicle and/or aircraft operations are authorized in or over the localizer critical 7. Critical areas are not protected at aerodromes without area when an arriving aircraft is inside the ILS. an operational aerodrome control tower.  Chapter 6 VHF Direction Finder 6.1 FUNCTIONAL REQUIREMENTS 6.1.4 Equipment specifications normally require a bearing accuracy of +4” on the azimuth indicator. This deviation may however be greater depending on site, 6.1.1 The VHF direction finder (VDF) is a ground based terrain or other factors. A small additional error is intro- radio aid used by the operator of a ground station and duced when the strobe line indication is superimposed on consists of a directional antenna system and a VHF radio the surveillance radar display. VDF equipment furnishes receiver. Each time the aircraft transmits on the frequency bearing information from any aircraft within communi- to which the VDF is tuned, its display indicates the cations range transmitting on the selected frequency. Any magnetic direction of the aircraft from the station. Recent signal within range affects it. Therefore, when two or more equipment presents this information as a digital readout. aircraft are transmitting simultaneously on the same At a radar equipped ATS unit, the VDF indications may be frequency, bearing indication is determined by the relative superimposed on the radar display. Where DF equipment strength of the two signals received. is co-located with radar, a strobe of light flashes from the centre of the radar display in the direction of the radar 6.1.5 ICAO provisions classify estimated bearing target representing the transmitting aircraft. accuracy as follows: a) Class A - within + 2” 6.1.2 VDF stations may operate independently or in b) Class B - within + 5” groups of two or more stations under the direction of a c) Class C - within + 10” main VDF station. A VDF network can supply azimuth as d) Class D - > Class C well as position information. In this case, the main VDF station integrates, computes and plots the bearings from Similarly, the classification of estimated position accuracy the individual VDF stations and from this derives the is made in accordance with the following: position of the aircraft so plotted. A single VDF station can determine only the relative bearing of the aircraft, unless a) Class A - within 9 km (5 NM) this bearing is correlated with a reported, intersecting VOR b) Class B - within 37 km (20 NM) radial. As VDF relies exclusively on air-ground communi- c) Class C - within 92 km (50 NM) cations, standby or back-up equipment is normally d) Class D - > Class C provided for VDF. 6.1.3 VDF stations are usually located on or near aero- dromes, a situation that frequently poses significant 6.2 OPERATIONAL APPLICATION problems with siting due to obstructions which reflect signals and due to electronic radiation which interferes with the signals. These disturbances will cause perceived signal VDF is of particular value in locating lost aircraft, in errors and consequently incorrect bearing and/or position helping to identify aircraft on radar and to guide aircraft results. If no suitable site is available at the aerodrome, the to areas of good weather or to aerodromes. At aerodromes VDF antenna may be located elsewhere; however, in this equipped with VDF, instrument approaches based on the case, the bearing information is then given in relation to the use of VDF may be offered to aircraft in a distress or antenna site rather than the aerodrome. urgency condition. 111-l-6-1  AIR TRAFFIC SERVICES PLANNING MANUAL PART III SECTION 2. FACILITIES REQUIRED BY ATS  SECTION 2 FACILITIES REQUIRED BY ATS Contents Page Page Chapter 1. General..................... 111-2-1-l Chapter 3. Requirements for an Area Control Centre........................ 111-2-3-l 1.1 Introduction......................... 111-2-1-l 1.2 Operational requirements............. 111-2-1-1 3.1 Operational requirements............. 111-2-3-l 1.3 Structural requirements............... 111-2-I-1 3.2 Structural requirements............... 111-2-3-2 1.4 Accommodations.................... 111-2-l-2 3.3 Accommodations and equipment...... 111-2-3-3 1.5 Security measures.................... 111-2-l-2 Appendix A. Check-list - Area control Chapter 2. Specific Requirements for an centre operations equipment............. 111-2-3-5 Aerodrome Control Tower.............. 111-2-2-l 2.1 Operational requirements............. 111-2-2-l 2.2 Structural requirements............... 111-2-2-2 Chapter 4. Requirements for a Flight 2.3 Accommodations and equipment...... 111-2-2-4 Information Centre.................... 111-2-4-l 2.4 Other considerations................. 111-2-2-7 4.1 Operational requirements............. 111-2-4-l Appendix A. Illustrations of aerodrome 4.2 Structural requirements............... 111-2-4-l control tower designs and layouts........ 111-2-2-8 4.3 Accommodations and equipment...... 111-2-4-l Appendix B. Check-list - Aerodrome control tower and approach control Appendix A. Check-list - Flight operations equipment................... 111-2-2-16 information centre equipment........... 111-2-4-3 III-2-(i)  Chapter 1 General 1.1 INTRODUCTION Appropriate equipment includes those items which enhance the controller’s ability to see and to communicate with aircraft, his colleagues, other ATS units, maintenance 1.l.l In view.of the fact that air traffic services (ATS) personnel, other aviation agencies or bodies, e.g. airlines or facilities form part of the public service institutions military authorities and supporting services such as provided by governments, their level of functional suit- meteorological (MET), aeronautical information service ability, convenience and comfort must correspond to that (AIS), etc. Typical items in this respect are lighting faci- which governs public service institutions in general. It is, lities, radio and telephone. however, also a fact that this level varies considerably from State to State or even within States, depending not only on the specific economic situation, but also on climatological conditions, acquired habits and tradition. 1.3 STRUCTURAL REQUIREMENTS 1.1.2 It is therefore nearly impossible to develop standard provisions regarding the layout, installation and furnishing 1.3.1 Special buildings or those parts of other buildings of ATS facilities, especially when covering the non- used by ATS should be designed specifically for the par- technical aspects which are more concerned with well-being ticular needs of the ATS unit concerned. The buildings and/or comfort than with purely operational factors. should be sufficiently durable to last for the expected life Nevertheless, under these circumstances and in order to of the facility they are to house and should be capable of provide some guidance in this respect, discussion of both accommodating all personnel, materials and visitors the essential and the desirable features of ATS facilities expected to occupy the structure. Additionally, each level follows. It is hoped that States, in consultation with rep- should be strong enough to support all equipment and resentatives of their ATS personnel will then be able to people expected to use that level. The structure should be decide which of the desirable features listed are reasonable fireproof. and can be provided in addition to those required to meet essential operational requirements. 1.3.2 The initial design should make allowance for flexi- bility in accommodating occasional relocations of control positions and/or radio or telephone lines. There should also be similar expansion capability in order to accommo- 1.2 OPERATIONAL REQUIREMENTS date additional or new, operational or administrative equipment. At all ATS units, the controller must be provided with 1.3.3 Sufficient dedicated power (and outlets) should be a suitable environment and appropriate equipment. The provided for all existent and anticipated equipment (radar, environment should be safe and comfortable and should data automation, etc.), lighting, heating, ventilation, etc. afford protection from the elements as well as adequate Critical items of equipment, including radio and telephone heating, ventilation and, where required by climatological equipment, should be connected to an uninterruptible conditions, air-conditioning. Operating space should be power supply, a back-up power generator, and/or two ample without being spacious. Controllers should be able independent power sources. to work at their positions without physical discomfort, e.g. chairs should be strong and comfortable while providing 1.3.4 Where necessary for the exercise of control proper back support, be adjustable in height, and easily function, windows must be provided. In all cases, windows movable. The environment should be sufficiently free from should be provided whenever feasible in order to create a noise so as to be conducive to mental concentration. normal working environment. 111-2-1-1 111-2-l -2 Air Traffic Services Planning Manual 1.3.5 In tall structures, a dual-purpose elevator should be 1.5.2 Security measures and procedures should take into included to be used by personnel and for freight lifting account the following factors: purposes. Space allocated for each function or item of equipment should be ample with reasonable allowance for a) self-contained ATS operational buildings are usually expansion. surrounded by a security barrier with controlled access points; 1.3.6 There should be provisions for emergency exits b) where guards are used to control an access point, a from all personnel areas. In addition, buildings should be communications capability to summon assistance in the provided with lightning protection, emergency lighting, fire event of an emergency will be required in addition to a alarm and extinguishing systems and security systems. structure to provide protection for the guard on duty during inclement weather conditions; c) at some ATS facilities an additional access control point may be considered necessary. It may be combined with 1.4.ACCOMMODATIONS an information or reception desk; d) in addition, the appropriate authority may require that specified areas be further protected by restricting access Further to the space required for the operations area, to designated personnel only. Such areas could be: buildings serving.4TS units should provide for a briefing 1) the ATC operations rooms, computer rooms, and room, administrative offices, equipment repair space, associated facilities; locker rooms, administrative supplies storage, technical 2) telecommunications areas and associated facilities; equipment storage, lounge facilities with cooking facilities, and toilet facilities, running water (where possible cold and 3) service areas housing standby diesel generators, hot), cold drinking water (if the normal running water is central heating and air-conditioning plants and like not suitable for drinking), outside lighting and a vehicle facilities; parking area. At smaller facilities certain space can serve a e) emergency exits from restricted ATS buildings, areas number of these requirements simultaneously, but at larger and rooms will need to be supervised by guards or alarm facilities this may not be possible. It should, however, be devices to safeguard against unauthorized use. noted that the arrangements for space needed for efficient operation and for the personnel should receive priority 1.5.3 Security measures can vary from posting security consideration in the design of an ATS structure. The guards at access points, to the installation of closed-circuit requirements in space for certain special equipment are television monitors and/or the security locks operated by critical, whereas other space requirements, while desirable, special keys or coded cards. are required for convenience only. Specific ATS accom- modations are treated in more detail in Chapter 2 to 1.5.3.1 While the use of guards is frequently recognized Chapter 4, which follow. as the most reliable method of access control, the cost of manpower involved in such a system should be weighed against the use of mechanical or electro-mechanical access control devices which may provide an acceptable level of 1.5 SECURITY MEASURES protection. 1.5.3.2 Systems based on the use of special keys, coded Note.- See also Part ZV, Section 2, Chapter 1. cards or a combination of both, are now in widespread use and provide an acceptable level of security. These systems 1.5.1 Security measures and procedures will be required can be encoded in such a manner that the individual is to ensure effective control of entry into all areas where air permitted access to all areas or is permitted access only to traffic control (ATC) operations are conducted. They must those areas which the individual is authorized to enter. cause a minimum of delay and inconvenience to persons Some coded card systems also provide for joint use, i.e. an who regularly need access to the secured areas. These identification card. A weakness in this system, which may requirements apply equally to self-contained ATS buildings be considered a major defect in specific circumstances, and as well as to an ATS operations area within a multi-tenant which may therefore have to be taken into account before building. In such a building control of access only to the implementation, is that any person in possession of an portion occupied by ATS may be required. appropriately coded card may enter the area to which Part III.- Facilities required by Air Traffic Services Section 2, Chapter I.- General III-2-l-3 access is controlled if that person knows the sequence of prior to access being granted an individual. Such systems use and related procedures in effect. tend to be complex and the installation and maintenance costs may prove to be excessive. In addition, ATS staff on 1S.3.3 Closed-circuit television monitors and intercom duty may be required to monitor and operate the system to systems provide a sophisticated means of identification the detriment of their regular duties.  Chapter 2 Specific Requirements for an Aerodrome Control Tower 2.1 OPERATIONAL REQUIREMENTS reflections. In this respect it should be noted that the less vertical supports, the fewer window panes are required. However, with fewer panes there will also be more reflec- 2.1.1 An aerodrome control tower has two major oper- tions. The height of the window sills, which support the ational requirements for an air traffic controller to be able windows in the cab, should be as low as practicable since to properly control aircraft operating on and in the vicinity they affect the controller’s ability to scan the surface area of the aerodrome. Those requirements are: extending from the base of the tower. For the same reason, tower consoles should be designed so as not to exceed the a) the tower must permit the controller to survey those height of the window sill. The depth of consoles has similar portions of the aerodrome and its vicinity over which he effects on sight limitations. Generally, the higher the exercises control; window sill and/or the deeper the consoles the larger the b) the tower must be equipped so as to permit the surface area extending from the base of the tower which controller rapid and reliable communications with cannot be seen by the controller. Suitable minimum glare aircraft with which he is concerned. or non-glare lighting must be provided to allow the controller to read and write. It must also be arranged so 2.1.2 Surveillance by the aerodrome controller is that at night it does not diminish his ability to survey the normally done by visual means (eyesight) alone, mechan- aerodrome and its vicinity. ically through the use of binoculars to improve eyesight or electronically, through the use of radar or closed-circuit 2.1.5 The tower controller must be provided with the television. The controller must be able to discriminate capability to communicate rapidly, clearly and reliably between aircraft and between aircraft and vehicles while with aircraft in his area of responsibility. Normally, this is they are on the same or different runways and/or taxiways. accomplished through air-ground communications. It may The most significant factors contributing to adequate occasionally be done by means of a light-gun from the visual surveillance are the siting of the tower and the height tower using specified signals and prescribed acknowledge- of the control tower cab. The optimum tower site will ments from the aircraft. Since operations in and around a normally be as close as possible to the centre of the control tower generate a fair amount of noise (e.g. radios, manoeuvring part of the aerodrome, provided that at the aircraft engines, talking), the provision of sound- intended height, the tower structure itself does not become deadening features in control towers is very important. an obstruction or hazard to flight. Therefore, the acoustic qualities should be taken into account in the selection of structural materials used for 2.1.3 The height of the tower should be such that, at control tower construction. Sound-deadening materials normal eye level (about 1.5 m above the floor of the tower should also be used internally, e.g. carpets or similar cab) the controller is provided with the visual surveillance sound-absorbent material (dust-free and anti-static, if previously described. The higher the tower, the more easily possible) should cover the cab floor and the walls up to the this optimum surveillance is attained, but at greater window sills. financial cost and with a greater likelihood of penetrating the obstacle limitation surfaces. Reflections in the cab glass 2.1.6 The layout of working positions within the tower and sun or lamp glare through the windows should be kept cab and the consequential arrangement of operating to a minimum. consoles will obviously be determined by the location of the tower in relation to the manoeuvring area, and more 2.1.4 Vertical supports for the cab roof should be kept to especially, the approach direction which is most frequently the smallest feasible diameter so as to minimize their used at the aerodrome in question. It is also determined by obstruction of the controller’s view. The supports should the number of operating positions which are occupied also be as few as possible commensurate with minimizing simultaneously in the tower and the respective responsi- III-2-2-l 111-2-2-2 Air Traffic Services Planning Manual bilities of these positions (control of arriving and departing 2.2.1.1 The space reserved for the tower cab should be traffic versus that of ground movements, clearance delivery ample but not excessive. As its size is increased, the position, operation of the lighting panel, etc.). As a controller’s viewing angle out the opposite side of the tower consequence of this, the layout is most likely to vary from cab becomes more limited by the height of the window sill aerodrome to aerodrome and also at an aerodrome as (downward) and the roof line (upward). Similarly, physical traffic changes. Flexibility and far-sightedness are there- co-ordination problems between controllers increase with fore primary considerations in the initial installation in larger space. One State (United States) suggests polygonic order to avoid major structural or installation modifi- cabs of the following dimensions: cations that may result in the future due to changing oper- ational requirements. Approximate number 2.1.7 It should also be noted that, because of the respon- Level of personnel sibilities, and the frequent stress involved in the provision of simultaneously Cab area activity present in cab (square metres) of ATC, the provision of other than purely operational facilities contribute to no small degree to the efficiency of Low Not more than 6 21 the service provided and, as such, deserve careful consider- Intermediate Between 6 and 12 32 ation. They are more fully described in 2.2 and 2.3 below. Major More than 12 50 2.1.8 In view of the above and what has been said in 2.2.1.2 The size of the control cab should be primarily Part III, Section 2, Chapter 1, 1.l, it should be noted that dependent on the number, location and size of control the illustrations, shown in Appendix A, can only serve as positions and consoles (see Appendix A, Figures 3 and 4). examples of possible arrangements and that final decisions In relation to the primary runways, the cab should be regarding specific control towers must be based on detailed physically oriented so as to obtain the best unobstructed local studies conducted with the active participation of view of the aerodrome manoeuvring area. The orientation their eventual users. should also be such so as to minimize sun glare while controllers monitor the primary areas, especially at sunrise and sunset when the sun is low on the horizon. The window panes should tilt outward to eliminate reflections from the consoles and to provide shading at high sun angles. They 2.2 STRUCTURAL REQUIREMENTS should be double-pane, free of distortion, untreated, with the frame banded to the glass for an airtight, waterproof and vapour-proof seal. Interior wall surfaces should be 2.2.1 Ideally a control tower should be of the required painted in a dark, flat colour to avoid reflections and height and should have ample space to ensure an optimum vertical supports should also be non-reflective and also working environment for personnel and equipment (includ- painted in a dark colour. Minimum clear height from cab ing expansion capabilities), be energy efficient, durable and floor to ceiling should be 3 m. The ceiling may slope up at aesthetically pleasing - all at moderate cost. In the case of its perimeter to enhance upward visibility, especially from control towers located atop the aerodrome terminal the opposite side of the cab. It should be sound-absorbent building, it has often been found that such a location limits and painted charcoal gray or flat black to avoid reflections. the expansion capability of the facility when air traffic and consequently tower staffing and equipment increase (e.g. 2.2.1.3 For washing windows, there should be an auto- radar, automation, etc.). Therefore, at the more important matic window washer or a walkway around the exterior of aerodromes or at those where significant future traffic the tower cab. This walkway should be as narrow as developments are expected, it is better to have a separate possible and as low as possible (including railing) so as not control tower structure which is optimally sited, specifi- to impair the controller’s close-down view. The walkway cally designed to fulfil its operational purpose and whose may also serve as part of an emergency escape route. height is sufficient to best meet ATC needs (see 2.1.3 above). Free-standing control towers have three main 2.2.1.4 If the vertical supports between the window panes components: cab, shaft and base building (see Appendix A, are not sufficient to support the roof alone, an additional Figure 1). A tower need not have a base building provided minimum number of cab columns, with minimum diameter its offices, etc., can be integrated into the tower shaft (see may be used. However, their number should be kept to a Appendix A, Figure 2). minimum commensurate with engineering standards. Part III.- Facilities required by Air Traffic Services Section 2, Chapter 2.- Specific requirements for an aerodrome control tower III-2-2-3 These cab columns may be multi-purpose and also serve as Normally, its primary function is to house an approach roof drain, sanitary vent, conduits for power and antenna control unit and/or to provide accommodations for cables and the grounding system. services associated withthe provision of air traffic services (ATS). Such an arrangement is preferable to housing these 2.2.1.5 Tower cab lighting of variable intensity should services in the control tower shaft. generally be recessed in the ceiling and directionally adjus- table. Operational lighting required to illuminate a specific 2.2.3.1 A free-standing functional shaft (without an working position should be placed and painted so as to associated base building) requires a very small area. It can minimize glare and reflections. Floor lighting and stair be readily constructed in prefabricated sections and lighting should be recessed and shielded. assembled on location in less time than a conventional building. The disadvantages of free-standing shafts are that 2.2.1.6 Carpeting of the tower cab floor should be wear- they provide for practically no expansion in accommo- resistant, sound absorbant, anti-static and flame resistant. dations and various services are distributed at different levels which generally results in poor communication. 2.2.1.7 Where airport movement radar/airport surface detection equipment (AMR/ASDE) or daylight radar 2.2.3.2 A base building combined with a functional shaft repeater equipment is available, the displays should be provides maximum utilization of space by using the vertical swivel mounted, or suspended from a trolley and track in space in the shaft thus reducing space requirements in the the cab, so that their orientation can be adjusted to remain base building. However, three separate air-conditioning in the field of vision of the controller concerned under and heating/cooling systems may be needed for the cab, varying conditions. shaft and base building. Another disadvantage is that the future expansion of those services accommodated in the 2.2.1.8 Due to its location, a control tower cab is shaft of the tower are limited. normally very exposed to changes in atmospheric conditions and a wide variance in temperatures. Therefore, in many cases, a good air circulation is required to retain 2.2.3.3 The combination of a base building with a non- reasonable working conditions. Where provided, it should functional tower shaft limits the use of the shaft to the be equally distributed around the cab perimeter and point where it houses only a minimal amount of mechan- operated so as to provide a stable environment. Experience ical and electronic equipment but no support personnel. has shown that air distribution from the window sill is This configuration provides great flexibility in the use of better than roof-mounted equipment since the latter space, offers maximum expansion potential and permits arrangement is frequently too noisy for personnel working separate construction of the two basic units. Additionally, in the cab as well as more difficult to maintain. A separate a single or two-story base building lends itself to a more air-conditioning and heating/cooling system for the cab convenient and efficient circulation of people. The will prevent interior fogging or frosting of windows disadvantages are that a larger site is required and the without overheating the cab. It will also prevent or remove associated design and construction costs are higher. the accumulation of ice on the outside of windows. In addition, the system will also serve to heat the cab alone, 2.2.4 The material used for the structure of a control when it is not yet necessary to heat the rest of the structure, tower should be fireproof and all internal material should which in certain areas amounts to considerable cost- be fire resistant. In addition, the structure should provide savings. The thermostat controlling such a system should for emergency exit especially from the tower cab and the be located away from exposure to direct sunlight or any upper shaft levels. Emergency exit points could be achieved other heat source. by permanently affixed steel ladders to the outside of the structure or a safety cage on the inside. The structure 2.2.2 The tower shaft has two primary functions; it should also be provided with a smoke detection and alarm supports the cab and provides access to the cab by a system and an ample supply of pre-positioned fire extin- stairway and/or elevator and as such, it encloses and guishers which are periodically checked. All stairways supports wires, pipes, etc. A secondary function of the should include a hand rail. An elevator should be provided tower shaft can be to provide accommodations for where the cab floor is 15 m or more above the ground. It personnel and equipment on its different levels. has also been found that the provision of a central vacuum cleaning system with outlets in each room and blower units 2.2.3 Where required, a building at the base of the tower remote from normally occupied areas help appreciably in shaft may be added as a single or multiple story structure. reducing noise. ZZZ-2-2-4 Air Traffic Services Planning Manual 2.3 ACCOMMODATIONS AND EQUIPMENT landing. If the highest elevator level is not on the floor level immediately below the tower cab, a hatch should also be provided on any intermediate floor. 2.3.1 The tower cab should be fitted with consoles to house equipment and provide desk space of the same height 2.3.4 For a tower performing a combined as the consoles for writing as well as space to mount aerodrome/approach control function, where APP is monitoring equipment such as aerodrome lighting panels, equipped with radar and operated from the cab, there may instrument landing system (ILS) monitor panels, telephone be an additional requirement for special screening of the and radio selector panels and brackets to hold microphones radar displays to minimize reflections and glare. This and telephone handsets. The console desks should also special screening may be required despite the use of provide support for flight progress strip holders and should daylight radar displays (see Appendix A, Figure 5). have radio/telephone connexions, including those used for monitoring. There should also be drawers for pens, pencils, 2.3.5 In a tower with low activity, the junction level in the paper, etc. Drink holders as well as ashtrays should be tower shaft is primarily reserved to house the equipment located safely away from radio and telephone selector work room, control tower mechanical equipment, elevator panels and other equipment sensitive to liquid or ash equipment, toilet and washing facilities. The level below spillings. A supervisor’s desk(s) should be provided with that usually houses the uppermost elevator landing lobby, necessary telephone and radio terminals and a bookcase electronic equipment room and other spaces as required. If should be available to keep appropriate reference material. the toilet and washroom facilities cannot be located on the level immediately below the tower cab, they must be 2.3.2 Where equipment is enclosed in fixed consoles located on the next lower level in order to keep absences which are backed to the outer walls of the tower cab, the from duty by controllers as short as possible. In radar- consoles should open at the front for ease of maintenance. equipped towers, equipment rack space for ASDE radar Modular consoles which are easily plugged in and out will and microwave links may be located on either level. In similarly help in the maintenance work. If plexiglass tops towers with non-functional shafts, the levels between the are provided on consoles and other writing surfaces, regu- base level and the next to last level normally serve only to larly used essential charts and other materials may be add height to the tower shaft and to provide access to util- inserted under the plexiglass. If the consoles and desks are ity and elevator shafts at the various elevations (see not overlayed with some transparent material, the top Appendix A, Figure 6). Space in these l