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24 Airports

E V Finn CEng, FICE, FIStructE, FRSH,MIWEM, MConsE

R H R Douglas BSc(Eng), CEng, FICE,FIHT, MConsE and

D J Osborne BSc(Eng), CEng, FICE, FIHT,MIWEM, MBIMSir Frederick Snow and Partners

Contents

24.1 Introduction 24/3

24.2 Airport location 24/324.2.1 Basic considerations 24/324.2.2 Criteria for comparative analysis of sites 24/3

24.3 Standards 24/524.3.1 Airport reference codes 24/524.3.2 Runway length 24/524.3.3 Runway width 24/524.3.4 Runway vertical alignment 24/524.3.5 Runway transverse slopes 24/624.3.6 Taxiway widths 24/624.3.7 Taxiway vertical alignment 24/624.3.8 Taxiway minimum separation distances 24/624.3.9 Aprons – clearance distances 24/724.3.10 Aprons – slopes 24/724.3.11 Obstruction surfaces 24/7

24.4 Airport concept and layout 24/824.4.1 General 24/824.4.2 Runways 24/924.4.3 Runway length 24/924.4.4 Temperature and elevation effect on

runway length 24/924.4.5 Wind effect on alignment 24/924.4.6 Taxiways 24/924.4.7 Terminal area 24/1024.4.8 Centralized concepts 24/1024.4.9 Decentralized concept 24/1224.4.10 Apron layout 24/1224.4.11 Terminal building layout 24/1424.4.12 Car parking layout 24/1424.4.13 Airport access 24/14

24.4.14 Ancillary buildings 24/1524.4.15 Control tower 24/1524.4.16 Apron control 24/1524.4.17 Aircraft catering building 24/1524.4.18 Cargo terminal building 24/1524.4.19 Maintenance hangars 24/1524.4.20 Buildings for electrical and electronic

equipment 24/1524.4.21 Airfield lighting 24/1524.4.22 Telecommunications 24/1524.4.23 Airport security 24/15

24.5 Traffic forecasts 24/15

24.6 Aircraft pavements 24/1624.6.1 General 24/1624.6.2 Function of aircraft pavements 24/1624.6.3 General requirements of an aircraft

pavement 24/1624.6.4 Construction 24/1624.6.5 Choice of construction 24/1624.6.6 Rigid pavements 24/1624.6.7 Composite pavements 24/1824.6.8 Flexible pavements 24/1824.6.9 Overlays of existing pavements 24/1824.6.10 Pavement design, UK method 24/1924.6.11 Pavement design-FAA method 24/21

24.7 Surface water drainage design 24/2124.7.1 General 24/2124.7.2 Drainage for runways 24/2124.7.3 Taxiways 24/2224.7.4 Aprons 24/2224.7.5 Subsoil drainage 24/22

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24.7.6 Stilling ponds 24/2224.7.7 Main drainage channels 24/22

24.8 Ancillary services 24/2224.8.1 Aircraft sanitation 24/2224.8.2 Fuel installation 24/2224.8.4 Ground movement signs 24/2224.8.5 Crash and rescue services 24/2224.8.6 Boundary and security fences,

including crash access 24/22

24.9 Definitions 24/2324.9.1 Aerodrome (airfield or airport) 24/2324.9.2 Aerodrome beacon 24/2324.9.3 Aerodrome elevation 24/2324.9.4 Aerodrome reference point 24/2324.9.5 Aerodrome reference field length 24/2324.9.6 Apron 24/23

24.9.7 Barette 24/2324.9.8 Clearway 24/2324.9.9 Crosswind component 24/2324.9.10 Instrument approach runway 24/2324.9.11 Non-instrument runway 24/2324.9.12 Obstacle 24/2324.9.13 Runway effective slope 24/2324.9.14 Shoulder 24/2324.9.15 Stopway 24/2324.9.16 Strip 24/2324.9.17 Taxiway 24/2324.9.18 Threshold 24/23

References 24/23

Bibliography 24/24

24.1 Introduction

The planning and design of an airport is complex and involvesspecialists in airport planning, traffic forecasting, aeronauticalground lighting, telecommunications and navigational aids, airtraffic control, baggage handling, and many other activities. Thedevelopment of an airport will involve architects, structural,electrical, mechanical and telecommunications engineers, plan-ners, economists, interior designers, quantity surveyors andother specialists, as well as civil engineers.

Traditionally, civil engineers have played a major role in thedevelopment of airports and the co-ordination and managementof all the disciplines involved. This is, perhaps, because so manyaspects of civil engineering have always been involved, such asthe design of loadbearing pavements, access roads and carparks, surface water drainage, water supply, fire-fighting mains,foul drainage (including sewage treatment), as well as majorbuilding structures.

Airports have been required to cope with the increase inpassenger traffic, the number of aircraft movements, and the sizeand weight of aircraft. The character of the airport has alsochanged, with greater emphasis on security, safety, comfort andconvenience of passengers, efficiency and economical operation,and with the need for the involvement of more specialists intheir planning and design.

In order to consider the civil engineering aspects of an airportin perspective, reference is made in this chapter to the location,standards and general concepts of airports, as well as to theother facilities which together make an airport. Only thoseaspects of civil engineering which are particular to airports aredealt with in detail.

24.2 Airport location

24.2.1 Basic considerations

The site selected for a new airport development must be capableof providing the longest possible useful life in order to secure themaximum return on the large investments which are requiredfor its development. Many factors require examination in orderto determine the most suitable site, but before consideration isgiven to the criteria involved, it is necessary to define thepurpose for which the airport is required, and the size of thefacilities to suit this requirement.

The need for an airport might be because: (1) none exists andit is believed air services will meet a specific physical oreconomic demand; (2) an existing airport cannot be expanded tomeet growing traffic; or (3) an existing site has become environ-mentally unacceptable.

The facilities to be accommodated and considered will includethe length and direction of the runway, the number of runways,the terminal building and apron, and ancillary requirementssuch as cargo handling, airport maintenance, catering and carparking. The scale of these facilities and, hence, the overall areaof land needed for the airport site, will be assessed in relation tonational or regional planning of airspace use (if such exists),traffic forecasts, and an assessment of aircraft types appropriateto predicted use.

24.2.2 Criteria for comparative analysis of sites

The essential factors to be considered in selection of an airportsite include:

(1) Passenger catchment area.(2) Environment.(3) Economic appraisal.

(4) Financial appraisal.(5) Airspace.(6) Topography.(7) Obstructions to aircraft operations.(8) Meteorology.(9) Construction problems.

(10) Utility services.

There is no particular order in which these should always beconsidered, and there are few fundamental criteria to provide aclear basis for rejection of a site from further consideration,other than perhaps the intrusion of unacceptable obstructionsinto the approach surfaces. There are clearly wide variationsbetween what might be an acceptable site high in the Andes, inthe desert of Jordan, on the southern tip of Shetland, or on theshores of Loch Neagh. An initial selection of sites for subse-quent comparative analysis has to be made in the knowledge ofthese factors, but the final selection is made from an objectivecomparison of each.

24.2.2.1 Passenger catchment area

Where regional airports are concerned, a journey time of about45min from a centre of population is normally consideredacceptable. In developed countries it will be necessary to assessthe effect on journey time of any planned improvement or newhighways. In less developed countries, it may be necessary toconsider the effect the airport may have on the existing highwaysystem.

A major international airport will attract passengers from amuch wider catchment area, including those using feeder airroutes from regional airports, and the proximity to a centre ofpopulation may be less critical.

24.2.2.2 Environment

An airport affects the environment in three major ways,through: (1) land use; (2) noise and (3) ecology.

In the UK most existing airports have been developed fromwartime airfields. Where new sites have been sought, as for thethird London Airport, there have been objections and lengthyinquiries, essentially on these environmental issues. In develop-ing countries the emphasis is likely to be different.

The area required by an airport is large. A modest regionalairport may occupy 450 ha; a major international airport mightrequire 5000 ha. Unfortunately, one of the requirements for anairport site, namely relatively flat and well-drained land, is oftenalso the best agricultural land in an area, or alternatively is anarea suitably distant from a population centre to be designatedfor industrial use.

To avoid these conflicts, areas unsuitable for other use need tobe looked at. Such sites may involve major earthwork problemsas, for example, the site being considered for the new BangkokAirport, which is largely waterlogged, or incur the possibility ofdisturbing the natural ecological balance, as was a majorobjection to proposals for the proposed development of thethird London Airport at Maplin.

Noise became a major environmental issue in the 1960s and1970s and is an important aspect of airport planning. Certifica-tion procedures introduced by the International Civil AviationOrganization (ICAO) in 1972 have resulted in a new generationof quieter aircraft, such as the Boeing 757, introduced intoservice by British Airways on domestic routes in the UK early in1983. It is no longer permissible for earlier and noisier aircraft,such as the Trident and the BA 1-11, to be used in the UK. Suchimprovements and restrictions are unlikely to apply to develop-ing countries for many years.

24.2.2.3 Economic appraisal

An economic appraisal compares the total cost of each site tothe whole community.The comparison will take into account:(1) the capital cost of site acquisition and construction; (2)access to the airport by airport employees; (3) access forpassengers and cargo; (4) noise and other environmental fac-tors; and (5) operation of the airport. These costs will be offsetby the revenue earned directly by the airport operator, theairlines, and airport-associated and airport-attached businesses.Many of these will be the same regardless of the site, but othersmay be affected considerably.

24.2.2.4 Financial appraisal

A financial appraisal compares alternative sites on the basis ofthe capital costs of development only, although it can beconsidered as including direct costs and revenues related tooperating the airport, loan receipts, repayments and interestcharges.

24.2.2.5 Airspace

All countries who are members of ICAO have a governmentauthority responsible for Air Traffic Control. In the UK,National Air Traffic Services (NATS) is responsible and pro-vides a combined service to both the Civil Aviation Authority(CAA) and the Ministry of Defence. The siting of an airport

may be critical if there is the possibility of aircraft operationsconflicting with operations from an adjacent airport, particu-larly if this is sited across a national border in another country.Otherwise, air traffic control services, and particularly landingand take-off procedures, can usually be adapted to meet theparticular site requirements.

24.2.2.6 Topography

For the purpose of comparison of several sites it is not neces-sary, initially, to quantify the amount of work required toconstruct the airport on that site. It is necessary to compare theadvantages and disadvantages and to identify any difficulties.

Ideally, an airport should be located on relatively flat ground,having effective natural drainage. The site should not behemmed-in by hills, rivers, roads or development which mayhinder future expansion, or form potential obstructions toaircraft approaching or departing.

The assessment can be made largely from examination ofexisting maps and aerial photographs, but an inspection of thesite should be considered essential.

24.2.2.7 Obstructions to aircraft operations

Objects which project above the imaginary obstruction surfaces(Figure 24.1) are classified as obstructions and will need to beremoved if possible, or marked, if a particular site is chosen and

Conical surface

Rise 5%

Outer limits of conical surfaceare such that the height of thesurface here is b above theinner horizontal surface

Figure 24.1 Plan view of obstruction surface (second andhorizontal sections of approach surface for non-precision andprecision approach are not shown for clarity)

Radius from aerodromereference point = a(see Table 24.9)

Inner horizontal surface45 m above aerodrome

Take-off surfaceRunway

Slooe

Transitional surfacesslope 0%

Approach surface

*Distance between the outside edges of the main gear wheels.

developed. At a stage of initial site appraisal, possibly beforeeven the alignment of a runway has been determined, it is thepotential of objects becoming obstructions which needs to beassessed, together with the degree of problems they could createin terms of removal or by inhibiting the location or alignment ofa runway.

24.2.2.8 Meteorology

For any site to be appraised properly, meteorological records ofwind direction, strength and frequency, together with visibilityrange and cloudbase height are necessary. This informationprovides the data for determining the runway alignment, andthe need for and type of approach aids needed to provide therequired level of usability.

There is usually sufficient data available in the general vicinityof an airport site in the UK for a valid interpolation to be made.This is frequently not the case in developing countries.

24.2.2.9 Construction problems

Any particularly difficult construction can usually be recognizedin the initial stages of appraising a site. Such a problem in theUK is usually limited to the particular site characteristics, whichmay be poor soil conditions or bad drainage. In other countriesthese difficulties may extend to difficulties of access and lack ofsuitable materials for construction.

24.3 Standards

Details of international requirements for the layout of airfieldsare covered in the ICAO Standards and recommended practicesfor aerodromes,' Annex 14, and this publication is revisedperiodically. Any aerodrome (airfield or airport) requires alicence to accept a commercial service. The technical and otherrequirements for the licensing of a site on an aerodrome in theUK are incorporated in Civil Aviation Publication CAP 168,Licensing of aerodromes, published by the CAA.2 In general, thisconforms with and amplifies the information given in ICAOAnnex 14, except for certain modifications which have beenfound appropriate to aerodromes in the UK.

The detailed standards and recommendations regarding air-port layout, including recommendations for length, clearanceand for the vertical alignment of runways and taxiways aregiven in Annex 14 with respect to the various airport referencecodes. The following excerpts from Annex 14 are given forguidance only and reference should be made to Annex 141 orCAP 1682 for full details.

24.3.1 Airport reference codes

From 24 November 1983, ICAO Annex 14' was subject toamendment. Two-element reference codes, incorporatingnumbers 1 to 4 together with letters A to E are now assigned toairports depending on the main runway length, aircraft wingspan and outer main gear wheel span in accordance with Table24.1.

24.3.2 Runway length

The actual runway length should be adequate to meet theoperations requirements of the aeroplanes for which the runwayis intended and should not be less than the longest lengthdetermined by applying the corrections for local conditions tothe operations and performance characteristics of the relevantaeroplanes.

It may be noted that the actual runway length can be reducedwithin certain limits if a stopway or clearway is provided.Further comment on the design of runway length is made insections 24.4.3 and 24.4.4.

24.3.3 Runway width

The width of a runway should not be less than the appropriatedimensions in Table 24.2.

Table 24.2 Runway widths (m)

Code letter

Codenumber A B C D E

1 18 18 23 - -2 23 23 30 - -3 30 30 30 45 -4 - - 45 45 45

Note: The width of precision approach runway code number 1 or 2 should be notless than 30 m.

24.3.4 Runway vertical alignment

Recommendations in relation to the various components ofvertical alignment are given in Table 24.3.

Codenumber

1

12

3

4

Code Element 1

Aeroplane reference field length

2

Less than 800 m800 m up to but not including120Om1 200 m up to but not including180Om180Om and over

Codeletter

3

AB

C

DE

Code Element 2

Wing span

4

Up to but not including 1 5 m1 5 m up to but not including 24 m

24 m up to but not including 36m

36 m up to but not including 52 m52 m up to but not including 60 m

Outer main gear* wheel span

5

Up to but not including 4.5 m4.5 m up to but not including 6 m

6 m up to but not including 9 m

9 m up to but not including 14 m9 m up to but not including 14 m

Table 24.1 Aerodrome reference codes

Table 24.3 Runway vertical alignment

Code letter

4 3 2 1

Maximum effective slope 1 % 1 % 2% 2%Maximum slope 1.25% 1.5% 2% 2%Maximum change between

consecutive slopes 1.5% 1.5% 2% 2%Maximum rate of change of

slope per 30m 0.1% 0.2% 0.4% 0.4%Minimum radius of curvature

(m) 30000 15000 7500 7500Minimum distance between

successive points ofintersection of verticalcurves is the sum of theabsolute numerical values ofthe corresponding slopechanges multiplied by thefactor given in metres 30000 15000 5000 5000

Notes: (1) The maximum slope for a runway code number 4 should not exceed0.8% for the first and last quarters.

(2) The maximum slope for a runway code number 3 precision approachcategory II or III should not exceed 0.8% for the first and last quarters.

24.3.5 Runway transverse slopes

Recommendations for the transverse slopes are given in Table24.4.

Table 24.4 Runway transverse slopes

Code letter

E D C B A

1.5% 1.5% 1.5% 2% 2%

Note: The transverse slopes should not exceed 1.5 or 2% as applicable nor be lessthan 1 % except at runway or taxiway intersections where flatter slopes may benecessary.

24.3.6 Taxiway widths

The width of a straight portion of a taxiway should be not lessthan that given in Table 24.5.

Table 24.7 Taxiway minimum separation distances

Table 24.5 Taxiway widths

Taxiwaywidth (m) Code letter

23 E or D and the taxiway is intended to be usedby aeroplanes with an outer main gear wheelspan equal to or greater than 9 m.

18 D and the taxiway is intended to be used byaeroplanes with an outer main gear wheel spanof less than 9 m; C and the taxiway is intendedto be used by aeroplanes with a wheel baseequal to or greater than 18m.

15 C and the taxiway is intended to be used byaeroplanes with a wheel base less than 18 m.

10.5 B7.5 A

Note: The second subdivision of the 18 and the 15m widths are defined by thewheel base, not the wheel span.

24.3.7 Taxiway vertical alignment

Recommendations in relation to the various components aregiven in Table 24.6.

Table 24.6 Taxiway vertical alignment

Code letter

E D C B A

Maximum slope 1.5% 1.5% 1.5% 3% 3%Maximum change of slope

per 30m 1% 1% 1% - -Minimum radius of

curvature (m) 3000 3000 3000 - -Minimum change of slope

per 25m - - - 1% 1%Minimum radius of

curvature (m) - - - 2500 2500Maximum transverse slope 1.5% 1.5% 1.5% 2% 2%

24.3.8 Taxiway minimum separation distances

Recommendations for taxiway minimum separation distancesare given in Table 24.7.

The separation distances shown represent ordinary combinations of runways and taxiways. The basis for development of these distances is given in the 'Aerodrome DesignManual, Part T.

Codeletter

ABCDE

Codenumber

Distance between taxiway centreline and runway centreline

Instrument runways* Other runways*

1 2 3 4 1 2 3 4

82.5 82.5 - - 37.5 47.5 - -87 87 - - 42 52 - -- - 168 - - - 93 -- - 176 176 - - 101 101- - - 180 - - - 105

Taxiwaycentreline totaxiwaycentreline

2131.546.568.576.5

Taxiway &aprontaxiwaycentreline toobject

13.519.528.542.546.5

Aircraftstandtaxilanecentreline toobject

1216.524.53640

24.3.9 Aprons - clearance distances

An aircraft stand should provide the clearances between anaircraft using the stand and any adjacent building, aircraft onanother stand and other objects as shown in Table 24.8.

Table 24.8 Apron clearance distances

Code letter Clearance (m)

A 3B 3C 4.5D 7.5E 7.5

Note: These clearances can be reduced in special circumstances where the codeletter is D or E - for details reference should be made to ICAO Annex 14.Consideration must also be given to the provision of service roads and tomanoeuvring and storage area for ground equipment.

24.3.10 Aprons - slopes

Slopes on an apron including those on an apron taxilane shouldbe sufficient to prevent accumulation of water on the surface ofthe apron but should be kept as level as drainage requirementspermit. On an aircraft stand the maximum slope should notexceed 1%.

24.3.11 Obstruction surfaces

Imaginary surfaces which extend over the area occupied by the

Table 24.9 Approach runways: dimensions for obstacle limitation surfaces

airport and beyond its limits are defined. It is necessary torestrict the creation of new objects and to remove or markexisting objects (whether man-made or naturally occurring)which project above these imaginary surfaces. A plan view ofthem is shown in Figure 24.1 and dimensions are given in Tables24.9 and 24.10. The main components are:

(1) An inner horizontal surface located 45 m above the airportelevation extending to a horizontal distance a measuredfrom the aerodrome reference point.

(2) A conical surface with a slope of 5% above the horizontal, alower edge coincident with the periphery of the innerhorizontal surface and an upper edge located at a height babove the inner horizontal surface.

(3) Transitional surfaces along the side of the strip and part ofthe side of the approach surface q that slopes upwards andoutwards at c% to the inner horizontal surface.

(4) Take-off surfaces established for each runway direction. Thelimits of the take-off surfaces are determined by an inneredge, two sides of which initially are diverging and thenparallel and an outer edge, the inner and outer edges beingperpendicular to the flight path. The inner edge has a length/ and is at the end of the clearway if provided (and if itexceeds the specified distance) or at a distance m from theend of the runway. Each side diverges at a rate of n%relative to the extended centreline of the runway until aspecified maximum width p is reached, continuing thereafterat that width to the outer edge. The distance between theinner and outer edges, or length of take-off surface, is q andthe surface slopes up at r% to the horizontal.

(5) Approach surfaces established for each runway direction

Runway classification

Surface and dimensions

Inner horizontalHeightRadius a

ConicalSlopeHeight b

TransitionalSlope c

Approach*Length of inner edge dDistance fromthreshold eDivergence (each side) /

First sectionLength gSlope H

Second sectionLength /Slope j

Horizontal sectionLengthTotal length

Non-instrument code number

4 3 2 1

45 45 45 454000 4000 2500 2000

5% 5% 5% 5%100 75 55 35

14.3% 14.3% 20% 20%

150 150 80 60

60 60 60 3010% 10% 10% 10%

3000 3000 2500 16002.5% 3.33% 4% 5%

Non-precision approachcode number

4 3 2, 1

45 45 454000 4000 3500

5% 5% 5%100 75 60

14.3% 14.3% 20%

300 300 150

60 60 6015% 15% 15%

3000 3000 25002% 2% 3.33%

360Ot 360Of2.5% 2.5%

^40Ot 840Ot15000 15000 2500

Precision approach

Category I code Category II ornumber III code number4, 3 2, 1 4, 3

45 45 454000 3500 4000

5% 5% 5%100 60 100

14.3% 14.3% 14.3%

300 150 300

60 60 6015% 15% 15%

3000 3000 30002% 2.5% 2%

360Ot 1200Ot 300Ot2.5% 3% 2.5%

840Ot 840Ot15000 15000 15000

*A11 dimensions are measured horizontally.fVariable length. Under certain circumstances the length of the second section may be increased but the length of the horizontal section will be reduced by the same amount.

used for the landing of aeroplanes. The limits of theapproach surfaces are determined by an inner edge, twodiverging sides (when viewed from the runway end) and anouter edge, the inner and outer edges being perpendicular tothe flight path. The inner edge of length d is located at adistance e from the runway threshold. Each side diverges ata rate/% from the extended centreline of the runway to theouter edge and the length to the outer edge is g. The slope ofthe surface above the horizontal is /2%. Non-precisionapproach and precision approach runways have an ap-proach surface in which the outer section length j is at aflatter slope k% and with a horizontal section beyond.

24.4 Airport concept and layout

24.4.1 General

Growth of aviation over recent years has been accompanied bya continuous process of change, and airport planners haveincreasingly become aware of the need to provide flexibility forfuture extensions and modifications of the facilities, bearing inmind that 10 to 15 years may elapse between master planningand commissioning of a major airport.

Conceptual planning has been influenced by the trend to-wards larger aircraft for handling the increasing numbers ofpassengers. The number of air passengers carried throughoutthe world on scheduled services by airlines of ICAO memberstates has risen from 111 million in 1961 to 639 million in 1981.

The size of aircraft has increased greatly; the Boeing 747, forexample, is 70.5m long and has a wingspan of 59.7m and amaximum height of 19.4m, whereas the earlier Boeing 707 hadcorresponding dimensions of 44.2, 39.8 and 12.7m.

The ability of modern aircraft to land in crosswinds hasresulted in a much reduced need for subsidiary runways indifferent directions. Also, the potential capacity of two indepen-dent runways means that few airports now need to be plannedwith more than two runways which can be parallel. Thus, asimple pattern of widely separated parallel runways hasemerged which assists the planner to achieve a rational layoutwith the ground handling facilities located between the runwaysand served by a common access 'spine' as illustrated in Figure24.2.

Examples of such layouts can be seen at Amman, Changi(Singapore), Munich and Athens. It will be noted that this type

Figure 24.2 (1) Maintenance and cargo zones; (2) Terminalzones

of layout allows considerable scope for future extension of theairport facilities.

An airport is designed to meet many needs but compromise isinevitable since some of the most important requirementspresent varying degrees of incompatibility. The main factorsare:

(1) Rapid and efficient handling of passengers.(2) Minimum walking distances.(3) Simple directional guidance for passengers.(4) Maximum runway movement rates.(5) Minimum taxiing times.(6) Rapid aircraft turnround on the apron.

Whilst layouts of the airside facilities of runways, taxiways andaprons are governed by international standards described pre-viously, no such standards exist for the design of passengerterminal buildings and other ground facilities. It is therefore inthis part of the airport plan that the designer can exercise hisindividual skill.

No two terminal buildings are the same but modern airportsfor large- and medium-sized aircraft generally follow the patternof parallel runways with the terminal facilities based on one oftwo principles, either: (1) centralized handling; or (2) decentral-

*The take-off climb surface starts at the end of the clearway if the clearway length exceeds the specified distance.flSOOm when the intended track includes changes of heading greater than 15% for operations conducted in IMC, VMC by night.

Runway classification

Surface and dimensions

Take-off climbLength of inner edge /Distance from runwayend* mDivergence (each side) nFinal width p

Length q

Slope (%) r

Non-instrument code number

4 3 2 1

180 180 80 60

60 60 60 3012.5% 12.5% 10% 10%1200 1200 580 380180Ot 180Ot15000 15000 2500 1600

2 2 4 5

Non-precision approachcode number

4 3 2, 1

180 180 60

60 60 60/3012.5% 12.5% 10%1200 1200 580/380180Ot 180Ot15000 15000 2500

1600

2 2 4/5

Precision approach

Category I code Category II ornumber III code number4, 3 2, 1 4, 3

180 80/60 180

80 60/30 6012.5% 10% 12.5%1200 580/380 1200180Ot 180Ot15000 2500 15000

1600

2 4/5 25

Table 24.10 Take-off runway: dimensions for obstacle limitation surfaces

ized handling. In the former, all the facilities such as check-in,baggage-handling, customs and immigration, restaurants, bars,concessions, banks, etc. are concentrated in one location, withassociated car and aircraft parking facilities. There is, however,limited airside and landside frontage. Aircraft sometimes haveto be parked away from the building with access by piers orapron buses and landside car parks tend to involve long walkingdistances.

Decentralization involves the distribution of these facilitiesover several centres in the terminal complex. The conceptincludes the range of variations from independent, or unit,terminals, each with the full complement of facilities, to theprovision of facilities at the aircraft whereby passengersundergo a complete check-in (the gate check-in concept).

The small airport for light aircraft will almost certainly havecentralized handling facilities and it may well require one ormore cross-runways owing to inability of light aircraft tooperate in strong crosswinds.

Various aspects of planning the airport layout follow ingreater detail.

24.4.2 Runways

The number of runways at any airport, other than one for lightaircraft, will be determined from the number of aircraftexpected in a given period, usually an hour, but it is difficult togive general guidance since the capacity of any runway orrunway system depends on a variety of factors such as:

(1) Aircraft types.(2) Landing aids.(3) Air traffic control techniques.(4) Ground movement capability (e.g. taxiway and apron facili-

ties).

There will be significant differences between the capacities underinstrument flight rules (IFR) and visual flight rules (VFR) andthe IFR capacities will be lower. The major airports handlinghigh rates of commercial air transport movements operateunder IFR even in good weather conditions.

As an indication, the capacity of a single runway handling amixture of air transport and general aviation aircraft will be inthe order of 37 movements per hour, assuming roughly equalnumbers of landings and take-offs. The maximum figure mayrise to about 50 movements per hour under VFR but, of course,VFR operations are entirely dependent on favourable weatherconditions.

For parallel runways, maximum capacity is achieved whenseparation is sufficient to enable each runway to be operatedindependently with mixed landings and take-offs. The totalcapacity will then be in the order of 74 movements per hour. Aminimum runway centreline spacing of 180Om is required forthis mode of operation.

The staggering of the parallel runways depicted in Figure 24.2reduces taxiing distance at the expense of increased total landrequirements.

24.4.3 Runway length

Runway length is dependent on the following main variables:

(1) Aircraft performance.(2) Aircraft take-off or landing weight.(3) Aircraft reference temperature.(4) Airport elevation.(5) Runway gradient.

Performance curves are published by aircraft manufacturers

and enable runway length to be computed for given sets ofconditions.

At a specific airport runway take-off length will be determinedby range considerations. Landing length is controlled by themaximum landing weight of an aircraft with allowance beingmade for the condition of the runway pavement in terms ofbraking ability.

It should be noted that runway lengths quoted in documentssuch as the 'UK Air Pilot' do not necessarily equate to actualphysical lengths of pavement as account may be taken of theexistence of a stopway, a clearway or a displaced threshold.

24.4.4 Temperature and elevation effect on runwaylength

The average daily temperature (over 24 h) for the hottest monthof the year is of interest to the designer and it will be necessary toincrease the length of the runways where high temperatures arerecorded (see ICAO Annex 14).' The elevation of the airport hasa like effect, and the basic length of a runway should beincreased as also described in Annex 14.

24.4.5 Wind effect on alignment

The use of an airfield is controlled to a certain extent by thewind. Crosswind components may prevent safe usage of therunway and the direction of the runway should be aligned tokeep instances of unacceptably high crosswinds to a minimum.To do this, a full summary of wind duration, speed anddirection is required, taken over a period of years. From this aconvenient graphical method of determining runway orien-tation as devised by Marwick is as follows.

The recorded hours (as percentage total) for each range ofvelocities are plotted in the sectors intercepted between concen-tric circles representing these velocities (Figure 24.3). The run-way is then drawn in a trial direction through the centre of thecircles and two parallel lines representing 13 knots (or anypermissible crosswind component) to the same scale as thecircles.

All winds falling outside these lines are in excess of the criticalfor that particular runway direction. Further trial and errorestablishes the desired pattern.

Alternatively, a computer may be employed to follow asimilar process in order to establish the percentage usability ofan airfield having one or several runways in various orien-tations.

In a multi-runway layout, the main runway may be set in thedirection of the prevailing winds and the subsidiary runways arelaid in the direction which yields the minimum crosswindcomponent effect and the maximum percentage usability for thewhole system. The present tendency is to aim for a singlerunway system with high permissible crosswind components.

The prevalence and nature of gusts and air turbulence in thearea must be considered separately.

24.4.6 Taxiways

At busy airports there will certainly have to be a parallel taxiwayfor the full length of the runway and, at some of the moresophisticated airports, there may be double or even trebleparallel taxiways. Exit taxiways linking the runway and paralleltaxiway must be conveniently located so that landing aircraftcan vacate the runway as soon as possible. The exit taxiwaysmay either be perpendicular to the runway and parallel taxiwayor, where particularly rapid turn-off from the runway is desir-able, they may be angled up to 45° to the runway centreline forsmall aircraft although, for the larger aircraft, the maximumangle should be about 30° which will permit runway exit speeds

Figure 24.3 Graphical method to determine runway usability

up to 60 m.p.h. (96 km/h). At the other end of the scale, anairport with only low movement rates may not require a paralleltaxi way, and back-tracking on the runway would be acceptable.

Taxiways should lead directly on to the end of the runway toenable aircraft to move rapidly into the take-off alignment withmaximum occupancy of the runway, although again, at airportswith low movement rates, taxiing along the runway may beacceptable to achieve economy in taxiway construction costs.

24.4.7 Terminal area

The terminal area has three main constituents: the aircraftapron, the terminal building and car parking with the associatedroad system. Their relation to each other will be determined inprinciple by whether the centralized or decentralized concept isadopted and, at major airports, by the method of internalsurface transport. There are other factors which influence therelationship such as the pattern of airline operations, the ratio ofdomestic to international passengers, number of transfer pas-sengers, etc.

The various centralized and decentralized concepts are illus-trated in Figure 24.4.

24.4.8 Centralized concepts

The centralized concept may be considered to include thefollowing variations: (1) simple terminals; (2) linear terminals;(3) finger terminals; (4) satellite terminals; and (5) mobile loungeterminals, although, depending on the extent of facilities pro-vided in the satellite and mobile lounge terminals, these lattervariations may tend towards the decentralized concept.

The simple terminal consists of a common area for allpassenger handling facilities with several exits on to a smallaircraft parking apron. It is only suitable for airports with lowpassenger and aircraft movements or is adaptable to generalaviation operations whether located as a separate complex in alarge airport or as an airport used exclusively by small generalaviation aircraft.

The linear terminal concept is merely an extension of thesimple terminal concept in which the latter is repeated toprovide additional apron frontage and increased space forpassenger processing which may feature a two-level arrange-ment for separating arriving and departing passengers. Pas-senger walking distance from set-down kerb to aircraft isrelatively short. Linear terminals can easily be extendedalthough this may destroy the advantage of short walking

Figure 24.4 Terminal area concepts

distance if directional signing is inadequate, and passengerscannot leave their cars opposite the appropriate aircraft depar-ture gate with its adjacent passenger processing facilities.

The finger or pier terminal has evolved from the earlyprovision of a covered walkway between the simple terminaland the aircraft such that later arrangements now incorporateholding lounges at the gate and vertical separation of departingand arriving passengers. A disadvantage of the concept is thelong walking distance involved from the central processingfacilities to the aircraft gate. There are many examples of thisarrangement, that for Belfast Airport being illustrated in Figure24.5. The necessity for provision of adequate space betweenfingers for manoeuvring aircraft is to be noted.

The features of the satellite concept are similar to those of thefinger concept except that aircraft gates are located at the end ofa long concourse rather than being spaced at intervals along it.Walking distances are relatively long and later developmentshave incorporated a people-mover system between the centralterminal and satellites, as at London Gatwick. An advantage isthat satellite gates can be served from a common holdinglounge. The aircraft parking arrangement more readily allowsthe introduction of self-manoeuvring stands although the Figure 24.5 Belfast airport

Westpier

Terminalbuilding

Primaryreceptionbuilding

Eastpier

Unit terminalsMobile lounge terminals

Finger terminals Satellite terminals

Linear terminals

Simple terminals

Figure 24.6 Roissy, Paris. Note 'drive-through' parking (A) carpark

24.4.8.1 Heathrow Terminal Four

One of the largest terminal building projects in the world cameinto operation in 1986 at Heathrow Airport and is a goodexample of centralized passenger processing. The need for afourth passenger terminal was recognized back in 1975 whenpassenger forecasts suggested that the three terminals in thecentral area would reach saturation capacity by the early 1980s.As there is not sufficient space within the central areas toprovide for the extra capacity it was decided that the only sitethat could be made available for development to meet demandon time was to the south of the airport.

The Terminal Four complex occupies some 40 ha of land andhas direct access to London's orbital motorway (M25) and theA30. It is also linked directly to the underground system as wellas to the other three terminals by a frequent bus service throughthe cargo tunnel.

The designed annual throughput of Terminal Four is 8million international passengers with one-way flow of 2000

passengers. The terminal is served by twenty wide-bodied air-craft stands of which sixteen are linked to the building by a pier.The planning of the building is based on the principle ofcentralized processing which is provided in three levels.

Upper level: Departing passengers are processed onthis level where after check-in, immigra-tion and security passengers enter a com-mon departures lounge which in effect is apier 25 m wide and some 640 m long withsatellite areas at each end.

Mezzanine level: Immigration and health control arelocated on this level where arriving pas-sengers are processed and then proceed tobaggage reclaim at the lower level.

Ground level: The baggage hall, customs and arrivalsconcourse are located on this leveltogether with associated public facilitiesand access to road transport.

The major function criteria adopted in the design include:

(1) Centralized passenger processing.(2) Complete segregation of arriving and departing passengers

for security reasons.(3) Maximum unassisted walking distance from the check-in to

aircraft gate is 200 m.(4) 75% of aircraft stands are served via loading bridges.(5) Complete vertical separation of arriving and departing

passenger flows.(6) Maximization of non-aeronautical revenues.

24.4.9 Decentralized concept

In this concept, independent unit terminals, each incorporatingthe complete passenger processing and aircraft parking facilitiesare built around a system of interconnecting access and serviceroads. The separate terminals may take the form of any of thecentralized concepts previously described and be built to therequirements of specific airlines or groups of airlines (as atKennedy, New York) or may be split for operation by routetype (as at Heathrow, London) into arrival and departure;alternatively, they may be split into domestic and internationalfunctions.

This concept is usually justifiable at high-volume airportswhere walking distances become excessive with finger terminals.It can, however, cause problems for transfer passengers unless ahigh level of inter-terminal connecting services is provided, as atDallas, Forth Worth, US, illustrated in Figure 24.7. Futureextension of the decentralized concept can be difficult because ofthe land requirements for each terminal. Development costs arehigh because similar facilities must be provided at each unitterminal.

Sophisticated developments of the centralized satellite ter-minal can result in this concept merging towards a decentralizedsystem if each satellite contains complete passenger processingfacilities. Complete decentralization is not achieved, however, ifa central terminal is retained with common car-parking pro-vision.

24.4.10 Apron layout

The overall size and layout of the aircraft apron will depend onthe number and type of aircraft likely to be parked at any onetime. The number of stands is derived from the aircraft standardbusy rate (SBR, see section 24.5 for general definition) and is acomplicated process often necessitating computer simulationstudies. Small airports are treated empirically and a rough rule

wedge-shaped stands tend to impair the operation of aircraftservicing equipment. Expansion is difficult with the satelliteconcept other than by introduction of additional satellites. Theultimate satellite arrangement is depicted at Paris Roissy (seeFigure 24.6) where the main building containing the commonfacilities is completely surrounded by satellites containing wait-ing-lounges, access between terminal and satellite being bytunnel.

The mobile lounge or passenger transporter concept has beenused at Dulles International Airport, Washington, D.C. Themobile lounges transport passengers between the common pro-cessing facilities in the central terminal and the aircraft parkingapron or aprons, where they can be used as holding lounges.This arrangement reduces walking distances and allows con-siderable operational flexibility for aircraft parking-apron ar-rangements with excellent opportunities for future expansion.The cost of providing and operating independent service build-ings and mobile lounges together with time involved in movingpassengers by the mobile lounges will, however, often prove adisadvantage.

Figure 24.7 Dallas, Forth Worth (A) car park

is to increase the SBR by 10% and round up to the next wholenumber.

Minimum wing-tip clearances between adjacent aircraft andfrom aircraft to buildings must be maintained according to thestandards previously referred to. The area of the stand will alsobe governed by the mode of parking. Nose-in parking, in whichthe aircraft must be mechanically pushed backwards on leavingthe stand, requires special vehicles for this purpose but is moreeconomical in overall area requirements than stands where theaircraft is self-manoeuvring. Most large and busy airports tendto adopt nose-in parking. Typical stand areas for various groupsof aircraft are given in Table 24.11.

Access of aircraft to and from the parking stand is obtainedby defined taxilanes on the apron surface. The width and otherdesign parameters required for these taxilanes should be similarto those for independent taxiways as previously described suchthat the necessary wing-tip and obstacle clearance are main-tained.

Table 24.11 Aircraft stand areas

Nose-in parking Self-manoeuvring(m) (m dia.)

Airbus 85 x 85 100Long haul 65 x 65 90Medium haul 50 x 50 60Short haul 40 x 40 50General aviation — 30

Each stand position must be of sufficient area to accommo-date the wide variety of mobile ground service equipment whichis required for the modern aircraft. Generally, a minimum 3 mshould be added to the apron depth to permit service access and10m additional depth may be required for operation of thepush-out vehicle used in the case of nose-in parking.

A service road, typically 7 to 10m wide, should be providedadjacent to the terminal building. Vertical clearance of 5mshould be available over the road.

A graphical design method for determining the separation ofaircraft parking stands has been devised by the ICAO in theAerodrome design manual? Part 2 and, in Airport aprons* theFAA has published graphs and equations for the determinationof clearances for aircraft turning and taxiing out of a parkingposition. The Apron and terminal building planning report,5

prepared for the FAA, provides scaled outlines for six groups ofaircraft and gives general guidance for planning airport apron-terminal complexes.

24.4.11 Terminal building layout

The functions, flow pattern, accommodation, configuration andsize of the terminal building or buildings need individualassessment for the factors of influence are many and differ ineach case. Simulation and computer models have been de-veloped to aid design of this most complex of buildings and arelikely to be used for the larger terminals.

The usual approach to determining the required floor area isto estimate the requirement for each facility derived from thepeak hour or SBR passenger demand (see section' 24.5). Aftercategorizing the peak hour passengers into international anddomestic types and also into terminal and transit passengers, itis possible to estimate the number of passengers to be processedin each facility, such as check-in desks, lounges, customs andimmigration, etc. and, hence, to determine the space require-ment for each facility to ensure reasonable provision. Variousguides are obtainable for estimating the space requirements ofthe different facilities. The Federal Aviation Administration andIATA have published the guidelines summarized in Tables 24.12

Table 24.12 Federal Aviation Administration standards

and 24.13. Perrett6 gives the following approximate guide for thetotal capacity of the terminal:

(1) 1500 passengers per hour in each direction for every15 000 m2 of area available to the public.

(2) 1500 passengers per hour each way for every 25 000 m2 oftotal terminal (excluding office accommodation).

Reductions of 30 to 40% could be made in the areas forterminals handling predominantly domestic traffic. Conversely,the space could be increased drastically if, for example, therewere a high proportion of visitors.

Perrett gives additional useful data on terminal buildingdesign and the Airport terminals reference manual1 (IATA) isalso helpful.

Table 24.13 International Air Transport Association standards

Passenger requirements in any specific Space required perarea peak hour passenger

(m2)

Standing passengers 1.0Seated passengers 1.5Plus 10% additional circulation and

airline requirements space at lounges

24.4.12 Car parking layout

The problems arising out of making provision for car parkingare among the most difficult facing the airport designer. Ingeneral, the majority of passengers travel to and from airportsby car. Visitors and airport workers must also be catered for.There are five main categories of car parking:

(1) Kerbside - for setting down and picking up.(2) Short term - say up to 15 h.(3) Long term.(4) Staff - both airport and airline.(5) Visitors - accompanying departing passengers, meeting

arriving passengers and casual spectators.

The parking areas required to accommodate these variousdemands can be considerable and air travellers may comprise asmall proportion of the total car users. No standard guidelinesare available for determining the various parking requirementswhich are likely to differ from airport to airport. Estimates oftraffic flow must be made by conventional methods such ascensus sampling. A decision must be made on the comparativeproportion of short-term and long-term parking if, indeed, thealternatives are considered desirable. It is normal to price thesefacilities differentially to encourage rapid turnover in the short-term car park, which is usually located closest to the terminalbuilding. On large airports, long-term parking may be extensiveand the distance from the terminal building may necessitate ashuttle bus service.

24.4.13 Airport access

In addition to the terminal building, apron and car parkingarrangement, the airport planner must consider and makeprovision for the alternative modes of surface access by whichair passengers, airport workers and visitors may move to andfrom the airport.

Although road access for cars must invariably be provided,consideration must also be given to provision for taxis and

Domestic terminal space facility

Ticket lobbyAirline operationalBaggage claimWaiting roomsRestaurantsKitchen and storageOther concessionsToiletsCirculation, mechanical and

maintenance, wallsTotal:

International terminal space facility(additional to domestic requirements)

Public healthImmigrationCustomsAgricultureVisitors' waiting roomsCirculation, baggage assembly, utilities,

walls, partitionsTotal:

Space required perpeak hour passenger(m2)

1.04.81.01.81.61.60.50.3

11.624.2

Space required perpeak hour passenger(m2)

1.51.03.30.21.5

7.515.0

public buses. Other modes of access such as railways may alsobe favoured - London Gatwick and Heathrow have surface andunderground railway links respectively from the city centrewhich carry in excess of 42% of all persons passing through theairports.

The design of access road systems and other modes of airportaccess are outside the scope of this chapter.

24.4.14 Ancillary buildings

It has been customary to collect the remaining airport buildingsunder this heading but some, such as large hangars, cargoterminals, etc. may be major projects in their own right.

24.4.15 Control tower

This should give controllers a view of all the runways and isdesigned round the equipment required for air traffic control.Large areas of false floor to accommodate cabling may beneeded. The tower is generally a separate building and not a partof the terminal building.

24.4.16 Apron control

Some airports include an apron control cabin located so that anapron controller can direct aircraft to the apron stands from thetaxiways.

24.4.17 Aircraft catering building

This should preferably be located close to the terminal area andis a specialist catering building run by the airlines.

24.4.18 Cargo terminal building

This facility may be a simple framed building or a sophisticatedterminal such as that of British Airways at Heathrow Airportwhich comprises transit sheds housing computer-controlledmechanical handling equipment, office blocks, vehicle parking,loading bays and circulation. There are no particular civilengineering requirements.

24.4.19 Maintenance hangars

These may range from a simple framed building to a majorstructure such as the British Airways hangar for the Boeing 747at Heathrow Airport, London. The structure basically is acladding for the maintenance requirements but consideration oflarge clear spans and door openings will determine the struc-tural forms.

24.4.20 Buildings for electrical and electronicequipment

These, generally, are simple buildings designed to house particu-lar items of equipment, some of which may require a controlledenvironment. The manufacturers advise on this point. Thebuildings for certain navigational aids cannot have ferrousmetal above a specified level and the manufacturer's adviceshould be sought. Others may require special shielding. Gener-ally speaking, there are no particular construction problems.

24.4.21 Airfield lighting

The extent of the approach and runway lighting provided notonly depends on the airport classification but should be compat-ible with the radio and radar landing aids provided. It generallyconsists of high-intensity centreline and crossbar lighting for the

approach areas, together with runway centreline and edgelighting. Taxiway lighting usually consists of green centrelinelights supplemented with blue-edged lights at junctions andaround the apron area.

For visual guidance in the angle of descent, visual approachslope indicators (VASIs), or precision approach path indicators(PAPIs) are provided.

24.4.22 Telecommunications

Telecommunications is a general term covering radio naviga-tional aids and radar in addition to data and voice communi-cations.

All modern airports require telecommunication services tosome degree and in the case of a larger international airportthose can be quite extensive. These services will consist of someor all of the following:

(1) Air-ground radio communication.(2) Land mobile radio.(3) Navigational aids.(4) Final approach and landing aids.(5) Radar.(6) Direct speech communication.(7) Direct data communication.(8) Public communication services.

Recommendations and requirements concerning telecommuni-cation requirements are given in the ICAO Annex 108.8

The positioning of the various telecommunication facilities isextremely important and must conform to the accepted ICAOrecommendations in respect of siting and the grading of sur-rounding areas.

The following electronic services, not covered by the term'telecommunications', are also required in most cases:

(1) Meteorological systems.(2) Flight information display systems.(3) Public address systems.(4) Security systems.

24.4.23 Airport security

Attacks on civil aircraft for the furtherance of extreme politicalaims, both on the ground and in the air, have become a majorfeature of air travel since around 1970. Security on the groundat airports has therefore had to be developed to counter thistrend.

New technology is playing a significant role in upgrading thestandard of security at airports but there are some basicproblems that remain unsolved. Airport security has mademajor advances since the early 1970s but it is only new terminalsor airports that incorporate security as part of initial planning.In most cases, the attempt was to make secure an existingbuilding, which in most cases proved very expensive and not100% successful.

Computers play a prominent role in sophisticated securitysystems together with more advanced X-ray and electronic'sniffer' equipment but the process is in a continuous state ofevolution in order to cope with new types of explosives andplastic guns that are not easily detected on X-ray machines.

Apart from the severe high cost of security, the human factoris always at the centre of most security systems used at airportsfor screening passengers and their baggage.

24.5 Traffic forecasts

The capacity of the apron, terminal building and car parks is

determined from the traffic forecasts. Such forecasts are nor-mally made on an annual basis and are split into scheduled andcharter flights for both domestic and international services.

These annual forecasts are determined by one of two mainmethods: firstly, extrapolation of historical data and, secondly,by analysis of such factors as future income levels, regional andnational development plans, future population forecasts, touristpotential, etc. This analysis is usually carried out on a computer.

The annual figures are then converted to hourly flows, eachcalled standard busy rate (SBR).

The SBR is defined as that rate which is exceeded 29 times inthe year, and has been found to give a reasonable basis fordesign.

It is essential to obtain an estimate of the short-period flowrates for passengers and aircraft. This can be done by ananalysis of monthly, weekly, daily and hourly aircraft move-ment patterns but, unless the relevant data is available, anassessment using ratios of standard busy hour passenger rates toannual movements is more likely to be the only suitable method.In general the ratios decrease with increasing annual movementsand they tend to be higher at airports with high proportions ofinternational leisure traffic. They also tend to be high where oneroute dominates the schedules, as occurs at many small airports,and therefore such airports need to be independently con-sidered. Special consideration should clearly also be given atairports such as Aberdeen and Sumburgh where there is a highproportion of helicopter operations. Table 24.14 gives an indi-cation of the ranges of ratios.

The passenger SBR is then used to determine the SBR of theaircraft movements estimating the likely mix of aircraft, capa-city and load factors, taking future trends into account.

Table 24.14 Standard busy rate (SBR) values

Annual passenger movements SBRfannualmovement ratio

100000 0.002-0.003250000 0.001-^0.002500000 0.0007-^0.00121 million 0.0006-0.00102-5 million 0.0004-0.0009

24.6 Aircraft pavements

24.6.1 General

Pavements suitable for the aircraft that will use them arerequired for runways, taxiways, aprons, maintenance areas, etc.The determination of pavement type and thickness is complexwith many interacting variables involved which are often diffi-cult to quantify. The first mathematical approach to airfieldpavement design was introduced in 1945. Since then, there hasbeen progressive refinement of the approach to suit increasingloads and complex landing gear configurations.

This section is intended to provide guidance to the principalconsiderations and methods used in aircraft pavement design.

24.6.2 Function of aircraft pavements

The general functions of aircraft pavements are as follows:

(1) Adequate strength for all aircraft types likely to use theairport.

(2) Adequate strength to resist the effects of repetitive loading.(3) Absence of loose particles which could be sucked into

aircraft engines.(4) Imperviousness to water - resistance to jet blast.(5) Resistance to fuel spillage (particularly on aprons and

maintenance areas).(6) Good surface drainage.(7) Ability to accept temperature movements.(8) Good skid resistance.(9) Good riding surface for comfort in the aircraft.

(10) Economy in construction and maintenance.

24.6.3 General requirements of an aircraft pavement

From an operational point of view it is difficult at busy airportsto close down a runway, taxiway or apron for the purposes ofpavement maintenance or strengthening; indeed, routine main-tenance may have to be carried out at night. Pavements designedto fulfil the needs of only the immediate future may prove to beexpensive in the long term. A runway may be required to have alife of 20 years or more and the designer must anticipaterequirements as far into the future as possible.

24.6.4 Construction

The three types of pavement construction may be grouped asfollows: (1) rigid; (2) composite; and (3) flexible.

An example of each of the three types is shown in Figure 24.8.In the UK it is usual practice to provide for all pavement

types a 100mm thick layer of dry lean concrete directly on thecompacted subgrade. This gives immediate weather protectionand acts as a working platform for placing subsequent layers. Itis interesting to compare this with American practice where,under certain conditions, full-depth asphalt flexible pavementsmay be laid directly on the subgrade.

24.6.5 Choice of construction

The choice of type of construction and of materials depends onthe location and function of the pavement, or overlay, theground conditions or existing pavement and, very importantly,the cost. It is normal to carry out several designs, using allpossible materials combinations, and to cost each design forcomparison. A compromise between technical excellence andeconomy is often necessary.

24.6.6 Rigid pavements

Concrete surfacing is resistant to fuel spillage and to engineexhaust blast, has good friction characteristics and good resis-tance to scuffing. It is thus often preferred for aircraft parkingand fuelling areas and for turning areas at runway ends.However, because of the need for construction in bays, withjoints at regular intervals, it is often considered less suitable forrunways and taxiways, where the uniform surface afforded bybituminous surfacing is of advantage.

A concrete pavement is usually considered as being rigidbecause the load is spread over a wide area of subgrade by virtueof its inherent flexural strength. The concrete can be reinforcedor unreinforced and is divided into rectangular bays to restrictthe tensile stresses which are induced by a combination of threefactors:

(1) Contraction of the slab due to falling temperature andconcrete shrinkage. This movement is restricted by thefriction between the slab and the subgrade and as a resulttensile stresses are induced in the slab.

(2) Warping of the slab due to a temperature gradient through

Figure 24.8 Alternative recommended types of aircraft pavements

the thickness of the slab. High surface temperatures causethe slab to dome until it is supported mainly at the edges,whilst low surface temperatures cause the corners to curlupwards.

(3) Loading. Slabs are usually most susceptible to loading neartheir corners which may cause cracks to form across thecorner. Acute angles in slabs should therefore be avoided.

The bays are separated by contraction joints and the bay sizedepends on the slab thickness. The maximum bay sizes shouldbe as indicated in Table 24.15.

Table 24.15 Maximum bay sizes of concrete runways

Slab thickness Bay size(mm) (m)

150 or less 3151-224 3.75225-274 5.25275 and over 6

The contraction joints may be formed by using crack inducersas shown in Figure 24.9. Load is usually transferred betweenadjacent slabs by aggregate interlock in which case no dowelbars are needed. If the aggregate particles in the concrete are nottoo hard, however, a more satisfactory solution is achieved bycontinuous casting of the slab, perhaps employing slipformingtechniques, followed by sawing the joints after the concrete hasset. Slots in the surface of concrete pavements, whether pre-formed or sawn, should be as narrow as possible; they should befilled with a semi-compressible material such as hardboard orfibreboard, depending upon the subgrade, and need not besealed.

Figure 24.9 Contraction joint

Expansion joints may be provided in thin slabs but may beentirely omitted in slabs more than 250 mm in thickness.

Single butt construction joints as shown in Figure 24.10 arerecommended since those incorporating a joggle are susceptibleto cracking. Dowels may be omitted for slabs 275 mm thick andover.

The pavement quality concrete (PQC) used in rigid pave-ments should be designed on the basis of its flexural strengthmeasured by loading 152 x 152mm test beams, rather than oncube strength. It is the strength of the concrete when it is firstloaded which is of importance so that age factors may be takeninto account. The aggregate/cement ratio should not exceed6.3:1 and the water/cement ratio should be less than 0.50.

Preformed crackinducer.Wood or concrete

Alternative shape

Slot Crack formsduring curing

Slot (in fresh concrete)

Hardenedconcrete

Dowel Freshconcrete

Figure 24.10 Construction joint

FlexibleCompositeRigid

Formation(Natural foundationin areas of cut)Level at which/lvalue is determinedfor all pavement types

Naturalfoundation

Cement, bitumen ortar bound basematerial

Bituminous surfacingConcrete surfacing

Originalground-level

Level afterremoval of •surface soil

Pavement qualityconcrete (PQC)surfacing

Surface dressing or 'friction course'Wearing course of rolled asphaltor dense tar surfacingRolled asphalt or densemacadam base course

PQC continuouslyreinforced

Lean concrete

Formation(Top of filling in areas of fill)Level at which K value isdetermined for all pavement types

Lean concrete

Lean concrete

Cut

Pave

men

t

Pave

men

t

The PQC. slabs should be placed over a layer of dry leanconcrete having an aggregate/cement ratio of 15:1 and aminimum cube strength of 5.2 MN/m2.

In order to improve the skid resistance of the concretesurface, the concrete may be wire combed or small transversegrooves may be cast into the wet concrete surface. It is essentialthat experiments are carried out to ensure that such treatment isapplied at the correct time. Alternatively, the hardened concretemay be scored with diamond cutting drums.

Well-constructed concrete pavements show little cracking andare resistant to both jet blast and fuel spillage. They are ideal atrunway ends, taxiway junctions, aprons and on maintenanceareas where aircraft stand or are slow-moving.

Joints can be largely eliminated if prestressed concrete con-struction is adopted but this form of construction is unlikely tobe economic under most conditions.

24.6.7 Composite pavements

Composite construction can often provide an economical solu-tion, with the advantages of a bituminous surfacing without thedisadvantages of a concrete pavement.

In a continuous reinforced concrete pavement, cracking(accentuated by exposure to heavy traffic) is likely to developwhatever quantity of reinforcement is incorporated. However, ifthe continuous reinforced concrete pavement is overlaid bybituminous surfacing, the cracking is reduced since the variationin the temperature in the concrete is lowered and those crackswhich do form in the concrete are not subject to wear and areunlikely to be severe. While there is some tendency for cracks toform in the bituminous surfacing above those in the concretethey are usually minor and can be resealed easily.

The flexural strength of the concrete slab gives this form ofconstruction good load-spreading properties, and a good ridingquality surface can be obtained. It is not as resistant to jet blast,heat and fuel spillage compared with the rigid pavement so it isoften used on runways and taxiways where aircraft are likely tobe moving fairly rapidly.

Pavement-quality concrete should be used for the reinforcedslab overlying 100mm of dry lean concrete. The minimumcross-sectional areas specified for reinforcement for the appro-priate concrete slab thickness, as recommended by Martin andMacrae,9 are given in Table 24.16.

The surfacing, normally 100mm in thickness, should berolled Marshall asphalt or dense tar surfacing laid in twocourses. This two-course work reduces the tendency to sym-pathetic cracking in the wearing course over cracks in theunderlying slab.

24.6.8 Flexible pavements

The top structural layers of flexible aircraft pavements areusually of a hot rolled asphalt, with the mix designed andcontrolled by the Marshall method (bituminous concrete inAmerican terminology). This achieves high density and stabilityand affords an excellent riding surface which has good frictioncharacteristics in dry conditions. In wet weather, however, flatgradients and surface tension lead to retention of surface water.It is common to provide an open-textured, non-structural,friction course on top of bituminous surfacings to prevent thebuild up of surface water where aquaplaning could otherwiseoccur.

Water drains through the interstices of the friction course andpasses to the runway edge along the impervious top structurallayer of the pavement. Bituminous surfacing is not resistant toaviation fuel and proprietary materials are available as surfacetreatments to provide fuel resistance where required. Examplesare 'Salviacim', an epoxy-based surfacing, and 'JetseaF, a tar-

Source: Martin, F. R. and Macrae, A. R. (1971) 'Current British pavement design',Paper 6, Proceedings, Conference on Airfield Pavement Design, Institution of CivilEngineers.

based surface sealant. Dense tar surfacing (DTS) by the Mar-shall method, where tar replaces bitumen as the binder, has alsobeen successfully used in areas subject to fuel spillage.

A flexible pavement is one which depends on its thickness andelasticity to disperse the load to such an extent that the subgradeis not overstressed. It is made up of a number of layers ofgranular materials increasing in rigidity and decreasing inflexibility towards the surface. The lower materials may beunbound, or bound with bitumen or cement. The middle layersshould be asphalt, bitumen or tarmacadam. The surface layersshould be impervious and Marshall asphalt or dense-tar surfac-ing specifications are usual. The following factors have to beconsidered in relation to the design:

(1) The overall depth of pavement must be such that thestrength of the subgrade is not exceeded.

(2) The strength of each individual layer of the pavement mustbe such as to resist the pressure at that level.

(3) The shearing strength of the surfacing and layers beneathmust exceed the shear stresses produced by the tyre load.

For very light-duty pavements several layers may be omitted.When dry lean concrete is used on the subgrade to provide agood working surface it must be weak, otherwise cracks whichform in this layer are likely to spread upwards towards thesurface. An aggregate/cement ratio of 18:1 for gravel or 22:1for crushed rock is usually suitable.

Well-designed flexible pavements have good riding qualitiesbut some surfaces are susceptible to jet heat and fuel spillagemay cause softening of the surface.

Relatively high landing and take-off speeds of modern air-craft, combined with the flat transverse slopes on runways, haveled to the problem of aquaplaning.

24.6.9 Overlays of existing pavements

It is often necessary to overlay existing pavements to provide

Slabthickness(mm)

100

125150175

200225

250

275300325350

Main steel

Minimumarea(mm2/mwidth)

425

530

635

740

825

Spacinglimits(mm)

125-175

Transverse steel

Minimumarea(mm2/mwidth)

295

170

Spacinglimits(mm)

125-175

150-225

Table 24.16 Steel reinforcement in rigid pavements

Schedule of reinforcement

greater strength or to repair a damaged surface, to improve rideor friction characteristics, or to provide resistance to fuelspillage. Overlays are usually of bituminous materials, for easeof construction and potential for minimizing disruption ofexisting operations. However, some work has been carried outusing concrete overlays bonded to original concrete slabs.Economic and practical considerations would generally mitigateagainst such treatment, except in cases where concrete surfacingmight be considered essential.

24.6.10 Pavement design, UK method

24.6.10.1 Development

The construction of aircraft pavements did not commence untilshortly before the outbreak of war in 1939 and design principlesat this time were based on experience of highway construction.

The use by heavy bomber aircraft rapidly overstressed someof these early pavements, and led to investigations into thebehaviour of paved surfaces and subgrades and the develop-ment of pavement design methods.

The first mathematical approach to airfield pavement designwas made in 1945 when a design manual for concrete pavementswas issued by the Air Ministry which contained design chartsfor single-wheel loads based on Westergaard's equations.

Investigations into the behaviour of pavements under increas-ing loads continued as heavier jet-powered military aircraft withlarger and more complex landing gears came into service.

24.6.10.2 The load classification number (LCN) system

The principle of relating aircraft loads and pavement strengthby means of a numerical scale, the load classification number(LCN), first established in 1945, remained the UK design andevaluation system until 1971.

The LCN was recognized by ICAO and incorporated into its'Aerodrome Manual, Part 2' as a recommended method ofaircraft and pavement classification in 1956.

In the late 1960s the LCN system was becoming increasinglydifficult to apply to the heavy gear loads and a reappraisal ofpavement design methods was undertaken utilizing both thelatest analytical methods available at that time and the ex-perience gained with the many heavy aircraft pavements con-structed between 1950 and 1965. A revised system which intro-duced the concept of load classification groups (LCGs) forpavement evaluation replaced the LCN system in 1971 and iscurrently in use in the UK. This is set out in Design andevaluation of aircraft pavements™ published in 1971 by theDepartment of the Environment, London.

24.6.10.3 The load classification group (LCG) system

The load classification group (LCG) system was published in1971, and was recognized as a rigid pavement system by ICAOin 1974.

A coarse scale of seven groups was superimposed upon theold LCN scale, reflecting broadly the seven ICAO aircraftclassification groups, as can be seen on the design and evalu-ation chart in Figure 24.11.

The seven groups are referenced by roman numerals indescending order as gear loads and pavement strengths increase,thus group VII is the group of lowest strength and group I is thehighest.

Since it is UK practice to construct rigid pavements withoutload transfer devices at joints, provision is made at the designstage for the increased stresses due to edge and corner load casesby increasing the theoretical slab thickness and by providing a

100 mm subbase of rolled dry lean concrete. As the system wasdesigned around the parameters of rigid pavements, the inclu-sion of flexible pavements into a common reporting systemcould only be accomplished by inserting in the group scaleflexible pavement thicknesses derived empirically and fromexperience.

24.6.10.4 The LCG method for rigid pavements

The LCG method requires the following data: (1) aircraft LCG;(2) subgrade modulus; and (3) concrete flexural strength.

The highest LCG corresponding to the aircraft expected touse the airport, excepting the occasional visitor, is selected forthe design. The soil subgrade is classified by its subgrademodulus or k value. The minimum flexural strength of theconcrete is estimated for the time the pavement is to be loaded;this may be 6 months after construction. If no informationis available it is reasonable to use the common value of3.5 MN/m2.

The design chart is entered at the upper value of the LCGband and the pavement quality concrete thickness is then readoff the corresponding band of the 'Rigid' column. An example isgiven on the published chart.

Some points should be noted:

(1) The LCG grouping for the aircraft or the LCN value mustbe taken from the corresponding column as the LCN valuesdiffer from that calculated by the original LCN method orwhich are given in the ICAO Aerodrome design manual"Part 3.

(2) The LCG system and design method is basically related toUK practice and to the soils commonly found in the UK.Not only are these often clay soils with low strength but withall-the-year-round rainfall it is normally advantageous toprepare a working surface on which to lay the pavement-quality concrete. For these reasons the LCG method alwaysincorporates a 100 mm layer of dry lean concrete. This couldbe omitted with certain suitable soils.

(3) The LCG system recognizes that over 95% of aircraftoperate on the central 30 m of runway and almost all taxialong the centreline of taxiways. Thus, the central strips ofrunways and taxiways, to which must be added all theaprons or holding areas, can be considered as channelizedareas. For 'non-channelized areas' one group lower can beselected to reduce the required design thickness.

24.6.10.5 The LCG method for composite pavements

The LCG method is also appropriate to design a pavementwhich is a composite of a reinforced concrete slab to spread theaircraft load with a bituminous surface. The design process isexactly similar to that of unreinforced rigid pavements exceptthat the composite column of the chart is used.

24.6.10.6 The LCG method for flexible pavements

The simplest way of designing a flexible pavement is to use asimilar process as for unreinforced rigid pavements except thatthe flexible column of the chart is used.

A flexible pavement constructed to such a design would besatisfactory, for the whole construction is in bound material.There is only one system of construction accepted which com-prises a 100 mm layer of bitumen bound surfacing, a thick layerof cement, bitumen or tar-bound base material on the standard100 mm of dry lean concrete.

Some confusion has existed between the LCN values and theLCG system since both use the common term LCN. The actual

REVERSE DESIGN EXAMPLE—The reverse design example shows the evaluation of 400 mm PQC on100 mm lean concrete. Cores show that the appropriate correctedminimum flexural strength is 3.0 MN/m2. The subgrade is bad (15 MN/m2/m).The finish point lies within the LGC Il band.Pavement may be used by LGC Il aircraft.Permissible future usage frequency may be assessed using relative positionof finish point to band boundaries, the anticipated loading pattern andother engineering factors.

DESIGN EXAMPLEThe example shown is for the design of the centre longitudinal strips of therunways, taxiways and aprons of a LCG II Aerodome founded on a goodsubgrade to carry aircraft of LCN < 100.Construction should be:(1) 350 mm PQC surfacing undowelled on 100 mm lean concrete, or(2) 100 mm bituminous surfacing on 180 mm continuously reinforced PQC on100 mm lean concrete, or(3) 100mm bituminous surfacing on 500 mm cemented base material on 100mmlean concretedepending on the surface required and the economics of the construction

The outer strips of the runways, taxiways and aprons for the same aerodromemay be based on the LCG Hl requirements.

Figure 24.11 Design and evaluation chart for rigid, compositeand flexible aircraft pavements

Pavement quality concrete (PQC)undowelledContinuously reinforcedpavement quality concrete (PQC)Dry lean concreteBituminous surfacingCement, bitumen or tar boundbase materialUnboundbase material

SYMBOLS

NOTE: For all pavements other thanthe RIGID construction, theheavy line coincident with3.5 MN/m2 must be used.

LCN values derived under the two systems are, however,different and unrelated and must not be confused or inter-changed.

24.6.10.7 Evaluation of existing pavements

The majority of aircraft pavement works have consisted ofstrengthening and extending existing pavements. The evaluationof these pavements is rarely an easy matter as there is nomathematical basis on which a calculated evaluation can bemade.

Pavement evaluations are normally made either by assess-ment or by physical testing. Assessments are made either by a'reverse design' procedure or by the professional judgement ofan experienced pavement engineer. Where a reasonably accur-ate assessment cannot be made, physical testing by means ofplate bearing rigs or, more recently, by means of deflectionmeasurements made with a heavy falling weight deflectometer,can be carried out.

24.6.10.8 The pavement classification number (PCN), anddesign system

The ICAO now requires airports to classify airfield pavementsby means of the pavement classification number (PCN) andpublishes in Design manual, Part 3, aircraft classificationnumbers (ACN) relating to types and thicknesses of pavement.The relationship between the ACN and PCN measures theability of the aircraft to use the relevant pavement. It is aclassification system but it is not a pavement design system.

The Airfield Pavements Branch of the Property ServicesAgency (PSA) has recently been developing a new design systemfor use in the UK and to be published in late 1987. It is expectedto provide the design relationship to pavement classificationnumbers which is currently absent from the ACN/PCN system.

24.6.11 Pavement design - FAA method

24.6.11.1 General

The FAA design method is based on the gross weight of thecritical aircraft operating at the maximum take-off weight. Theareas of traffic concentration are considered as 'critical areas',which comprise the central portion of the runway, aprons,taxiways and runway ends, where departing traffic will load thepavement. The design charts produce a pavement thicknesswhich is appropriate to critical areas; non-critical areas can havea reduced thickness.

24.6.11.2 Equivalent design aircraft departure

The design method requires the following initial steps:

(1) An estimate of the annual departures (half the total move-ments) of all aircraft forecast to use the pavement.

(2) Determination of the design aircraft.(3) Calculation of the equivalent number of departures of the

design aircraft.

It should be noted that arrivals are neglected since the landingweight of an aircraft is less than the take-off weight. The designmethod provides a pavement life of 20 years with the forecastannual departures.

24.6.11.3 Rigid pavement thickness design

The FAA advisory circular Airport pavement design and evalu-ationn gives design charts for groups and individual aircraft anduse of the charts requires the following:

(1) Concrete flexural strength.(2) Subgrade modulus.(3) Gross weight.(4) Number of the equivalent annual departures of the design

aircraft.

The charts give the total concrete slab thickness for criticalareas, which can then be reduced by the appropriate factors fornon-critical areas.

24.6.11.4 Flexible pavement thickness design

The FAA advisory circular 'Airport Pavement and Design' alsogives flexible pavement design charts for the same aircraftgroups and aircraft as for the rigid pavements. Use of the figuresrequires the following:

(1) The CBR value of the subgrade.(2) The gross weight.(3) The annual departures of the design aircraft.

The figures give the total pavement thickness of a three-layerconstruction and the thickness for the critical and non-criticalareas of the bituminous surface or wearing course, the thicknessof the granular base course and, by deduction, the thickness ofthe granular subbase.

In addition to the design charts, the FAA present a furtherchart which shows the minimum base course thickness, and thishas to be calculated as a check against the thickness determinedfrom the main charts.

24.6.11.5 Pavement evaluation

The advisory circular contains separate charts for evaluating thestrength of an existing pavement.

24.7 Surface water drainage design

24.7.1 General

As for all traffic-bearing pavements, a carefully designed waterdrainage system is a necessary requirement of an airport.Inadequate drainage may reduce the loadbearing capacity of thesubgrade, decrease skid resistance on the surface and causebreakdown of surface vegetation.

In general, the same basic design methods for calculatingrunoff are used for airports as for highways or urban areas. Onthe 'landside' of an airport, the methods of dealing with thecollection and disposal of surface water by way of gullies andpiped systems are conventional. On the 'airside' there areproblems which are particular to airports, largely related to theareas involved and the relatively flat grades, which are dealt within this section.

24.7.2 Drainage for runways

A runway has longitudinal gradients limited to being not steeperthan 1.25% on major runways and not steeper than 2% onminor runways. It is wide (up to 45 m), with transverse slopes,limited to between 1 and 1.5% on major, and between 1 and 2%on minor, runways. Gullies and gratings are not acceptable onthe runway itself, nor are open ditches within the strip.

It is normal to have a shoulder about 3 m wide adjacent to therunway edge, sloping at 5% away from the runway, often with asubsoil drain under. Ideally, the strip will then slope away fromthe runway at a slope of about 1.5% to carry surface waterrunoff either to a storm drain system with grated inlets andmanholes or, if the ground slopes away from the runway to theedge of the strip, to an open channel. Where the strip slopestowards the runway, as is permitted within the design standards,then a piped system with grated inlets has to be provided,preferably at the edge of the shoulder.

Because of the flat gradients and the potential for a film ofwater developing, friction courses have been used on manyrunways in the UK. These are a thin open texture of bituminousoverlay, whereby the water flows through the interstices on theimpervious surface of the runway, to the edge, where thecollection and disposal is normal.

24.7.3 Taxiways

Permitted gradients on taxiways are such that these, also, haveflat longitudinal and transverse gradients. They are dealt with ina similar way to runways.

24.7.4 Aprons

The maximum recommended gradient on an apron is 1%,sloping away from any buildings to minimize any risk arisingfrom fuel spillage. Drainage is usually by continuous grated slotdrains dividing the apron into drained areas such that drainagepaths are not excessively long. It is undesirable to have frequentchanges of gradient on an apron.

24.7.5 Subsoil drainage

Subsoil drainage may be necessary to drain low-lying water-logged areas, or to keep a fluctuating water table well belowsubgrade level. Open-jointed porous pipes laid in a 'herring-bone', 'parallel' or 'gridiron' system should be used. Depthsshould be as generous as possible, and should not be less than0.6 m or greater than 1.2 m below the surface.

24.7.6 Stilling ponds

Airports are most frequently sited on low-lying relatively flatland, and therefore it is common for problems to arise in thedischarge of surface water from the airport into the naturalmain drainage system, particularly when the flow is high in thelatter. The use of stilling ponds is common. These providestorage until the level in the main drainage system has fallen, orrelieve the peak flow in the main channel.

24.7.7 Main drainage channels

Another feature of airport sites is that there is often a naturalmajor watercourse flowing across them. Where possible thisshould be diverted, but if this is not possible and a culvert has tobe constructed, this should be sized generously, designed foraircraft loading, and be of sufficient length to pass underrunway and strip.

24.8 Ancillary services

There are several ancillary services associated with the airportand the main ones are described in the following sections.

24.8.1 Aircraft sanitation

The aircraft toilets are emptied into vehicles and the contentsare disposed of at airport sanitation buildings. These housemacerators or comminutors which discharge into the fouldrainage system. The buildings require an electrical powersupply.

24.8.2 Fuel installation

The supply of fuel to aircraft is normally carried out by the fuelcompanies who contract for a specified period. There are twomeans of distributing fuel to the aircraft aprons: (1) by aircraftrefuellers; and (2) by a hydrant system.

Aircraft refuellers are usually employed and they range from2250 to 820001. The larger is an articulated vehicle with anoverall length of 21.5m, a height of 3.65m (including radioaerial), a width of 3.2m, a turning circle of 21.4m absoluteminimum and a laden weight of 911.

Hydrant systems consisting essentially of a distributionnetwork terminating in pits in the apron which contain hosecouplings, have been installed at some airports but have, up tonow, not been very popular for two main reasons. The first is theinherent inflexibility. The mixes of aircraft at any airport changerapidly and the parking stands on aprons have rarely remainedconstant for more than 2 or 3 years with the result that thehydrant point has frequently been in the wrong position almostas soon as it has been installed. The second is that the fuelcompanies' tenure is normally shorter than the hydrant systemlife and individual companies have not been prepared to financethe high capital cost. However, with the advent of very largeaircraft of enormous fuel consumption, even larger fuel dis-pensers become less attractive and the hydrant system is likely tobecome of increasing interest in the future. Nose-in aircraftparking is becoming the standard with jet aircraft; this is tendingto prolong the life of fixed apron stand positions and is a factorencouraging the greater use of hydrants.

Both the aircraft refuellers and hydrant systems incorporatesafety features which prevent the pumping of fuel if the hosepipeshould become disconnected.

24.8.4 Ground movement signs

These are placed adjacent to taxiways and aprons to direct thepilots. Details are given in ICAO Annex 14 and CAP 168. Inaddition, aircraft stand number signs are provided either free-standing or fixed to the terminal buildings or pier.

All these signs will require an electrical power supply.

24.8.5 Crash and rescue services

Fire engines and crash tenders are housed in buildings withquick and easy access to the aprons, taxiways and runway. Thescale of provision for the UK is given in CAP 168 and therequirements are related to the heaviest aircraft in regularoperation at the airport.

At some airports where a crash in water is possible, rescueboats should be provided.

24.8.6 Boundary and security fences, including crashaccess

Airports should be fenced properly and the choice of fencedepends on availability and cost. Whilst a 1.2m fence isadequate over most of the perimeter, security and customs mayrequire a higher fence topped with barbed wire strands in theterminal area separating the landside from the airside. Theairside/landside fence will require manned gates at all accesses,which should be kept to a minimum.

The perimeter fence should be provided with a number offrangible gates so that crash and rescue services can get quicklyto the scene of any crashes which may occur outside theboundary.

24.9 Definitions

The following definitions are taken from these ICAO 'Standardand Recommended Practices for Aerodromes', Annex 14 andCAP 168, 'Licensing of Aerodromes'.

24.9.1 Aerodrome (airfield or airport)

Any area of land or water designed, equipped, set apart orcommonly used for affording facilities for the landing anddeparture of aircraft and including any area or space, whetheron the ground, on the roof of a building or elsewhere, which isdesigned, equipped or set apart for affording facilities for thelanding and departure of aircraft capable of descending orclimbing vertically, but shall not include any area the use ofwhich for affording facilities for the landing and departure ofaircraft has been abandoned and has not been resumed.

24.9.2 Aerodrome beacon

Aeronautical beacon used to indicate the location of an aero-drome.

24.9.3 Aerodrome elevation

The elevation of the highest point of the landing area.

24.9.4 Aerodrome reference point

The designated geographical location of an aerodrome.

24.9.5 Aerodrome reference field length

The minimum length required for take-off at maximum certifi-cated take-off weight, sea-level, standard atmospheric condi-tions, still air and zero runway slope as described by thecertificating authority or equivalent data from the aeroplanemanufacturer.

24.9.6 Apron

A defined area on a land aerodrome, intended to accommodateaircraft for the purpose of loading or unloading of passengers orcargo, refuelling, parking or maintenance.

24.9.7 Barette

Three or more aeronautical ground lights closely spaced in atransverse line so that from a distance they appear as a short barof light.

24.9.8 Clearway

A rectangular area at the end of the take-off run available andunder the control of the aerodrome licensee, selected or pre-pared as a suitable area over which an aircraft may take aportion of its initial climb to a specified height.

24.9.9 Crosswind component

The velocity component of the wind measured at or corrected toa height of 10m above ground-level at right angles to thedirection of take-off or landing.

24.9.10 Instrument approach runway

A runway intended for the operation of aircraft using non-visual aids providing at least directional guidance in azimuthadequate for a straight-in approach. Those runways served byinstrument landing systems (ILS) are designated precision ap-proach runways and are further identified as either category I, IIor III dependent on the sophistication of the ILS system and theability to permit operations in various levels of reduced horizon-tal and vertical visibility.

24.9.11 Non-instrument runway

A runway intended for the operation of aircraft using visualapproach procedures.

24.9.12 Obstacle

All fixed (whether temporary or permanent) and mobile objects,or parts thereof, that are located on an area intended for thesurface movement of aircraft or that extend above a definedsurface intended to protect aircraft in flight.

24.9.13 Runway effective slope

The slope computed by dividing the difference between themaximum and minimum elevations along the runway centrelineby the runway length.

24.9.14 Shoulder

An area adjacent to the edge of a paved surface so prepared asto provide a transition between the pavement and the adjacentsurface for aircraft running off the pavement.

24.9.15 Stopway

A defined rectangular area at the end of the take-off runavailable, prepared and designated as a suitable area in which anaircraft can be stopped in the case of an abandoned take-off.

24.9.16 Strip

An area of specified dimensions enclosing a runway to providefor the safety of aircraft operations.

24.9.17 Taxiway

A defined path, on a land aerodrome, selected or prepared foruse of taxiing aircraft.

24.9.18 Threshold

The beginning of that portion of the runway usable for landing.

References

1 International Civil Aviation Organisation (1983) Internationalstandards and recommended practices for aerodromes, Annex 14(8th edn). ICAO.

2 Civil Aviation Authority (1984) Licensing of aerodromes, CAP168. CAA.

3 International Civil Aviation Organization (1977) Aerodrome designmanual: taxiways, aprons and holding bays. (1st edn, Part 2)ICAO, Document 9157-AN/901, Montreal.

4 Federal Aviation Administration (1965) Airport aprons, AdvisoryCircular AC 150/5355-2, FAA.

5 Ralph M. Parsons Co. (1975) The apron and terminal buildingplanning report, Report FAA-RD-75-191, FAA. (Rev. March1976)

6 Ferret, J. D. (1971) The capacity of airports - planningconsiderations', Proc. Instn Civ. Engrs, paper no. 7372, 50,435-450.

7 International Air Transport Association (1976) Airport TerminalsReference Manual (6th edn), IATA.

8 International Civil Aviation Organization (1972) Internationalstandards and recommended practices: aeronauticaltelecommunications, Annex 108, VoIs I & II (3rd edn). ICAO.

9 Martin, F. R. and Macrae, A. R. (1971) 'Current British pavementdesign', paper 6, Proceedings, Conference on Aircraft PavementDesign, Institution Civil Engineers.

10 Department of the Environment (1971) Design and evaluation ofaircraft pavements, DoE.

11 International Civil Aviation Organization (1977) Aerodrome designmanual (1st edn) Part 4: Document 9157-AN/901, ICAO.

12 Federal Aviation Administration (1978) Airport pavement designand evaluation, FAA advisory circular AC150/5320-6C.

Bibliography

International Civil Aviation Organization (ICAO)publications

(a) 'International standards and recommended practicesenvironmental protection', Annex 16 (1st edn) VoI I.

(b) 'Aerodrome design manual' (1st edn) Part 4: 'Visual aids',Document 9157.

(c) 'Airport planning manual' (1st edn) Part 1: 'Master planning'.Document 9134.

(d) 'Airport services manual' (1st edn) Part 1: 'Rescue & fire fighting',Document 9137.

(e) 'Airport services manual' (1st edn) Part 2: 'Pavement surfaceconditions', Document 9137.

(f) 'Manual on air traffic forecasting' (1st edn) Document 8991.(g) 'Heliport manual' (1st edn) Document 9261.(h) 'Stolport manual' (1st edn) Document 9150.

US Federal Aviation Administration advisory circulars

(a) 150/5300-6A 'Airport design standards, general aviation airports,basic & general transport' (2.24.81).

(b) 150/5200-8 'Planning and design criteria for metropolitan STOLports' (11.5.70).

(c) 150/5325-2c 'Airport design standards - airport served by aircarriers - surface gradient and line of sight (2.6.75).

(d) 150/5325-4 'Runway length requirements for airport design'(4.5.65).

(e) 150/5325-5B 'Aircraft data' (7.30.75).(f) 150/5335-IA 'Airport design standards - airports served by air

carriers - taxiways (5.15.70).(g) 150/5335-4 'Airport design standards - airports served by air

carriers - runway geometries (7.21.75).(h) 150/5340-4C 'Installation details for runway centreline &

touchdown zone lighting systems (5.6.75).(j) 150/5340-19 'Taxiway centreline lighting system' (11.4.68).(k) 150/5340-24 'Runway & taxiway edge lighting system' (9.3.75).(1) 150/5370-10 'Standards for specifying construction of airports

(10.24.74).(m) 150/5390-1B 'Heliport design guide'.