7 Aerodromes and airports
In International Civil Aviation Organization (ICAO) Annex 14, the term aerodrome is described as
a defined area on land or water (including any buildings, installations and equipment) intended to be used either wholly or in part for the arrival, departure and surface movement of aircraft.
The reference to a defined area suggests that aerodromes are systems, designed and operated for the purpose of both facilitating the efficient handling of departing and arrving aircraft as well as providing all the processes required by aircraft between take-off and landing. As such, aerodromes do not only have to be land-based. Rather, water-based as well as floating structures, such as oil rigs or ships, can be considered as aerodromes. Consequently, aerodromes are not solely designed for fixed-wing aircraft, but also for rotary-wing vehicles.
Since aerodromes have such a diverse range of applications, a distinction is made between different types of aerodromes. This typification often varies from country to country or region to region and (unfortunately) is not internationally standardised. For instance, an aerodrome designed for use of rotary-wing aircraft, i.e., helicopters, is called a heliport. A facility specifically designed for seaplanes and/or amphibian vehicles, which are aircraft able to land both on land and on water, is referred to as a water aerodrome. An aerodrome designed for the usage of small, often propeller-driven, general aviation aircraft, is called an airstrip, an airfield, or small aerodrome. Quite frequently, these type of aerodromes are equipped with a grass runway. An aerodrome used exclusively for military air operations is called a military air base. Finally, civil airports refer to facilities which are mainly available to commercial air transport. This refers to flight movements in which passengers (or cargo) are transported by an airline for a fee. For the remainder of this section, the focus is primarily on land-based civil airports designed for use by fixed-wing aircraft.
According to European Regulation (EU) 2018/1139, all aerodromes in the European Union which
- are open to public use;
- serve commercial air transport; and
- have a paved instrument runway of 800 metres or more, or exclusively serve helicopters using instrument approach or departure procedures;
fall under the scope of the Basic Regulation (BR) of the European Union Aviation Safety Agency (EASA) and its Implementing Rule (IR). These aerodromes are therefore subject to legally binding requirements that define how they must be designed, maintained, and operated. Aerodromes which handle no more than 10’000 commercial air transport passengers per year and no more than 850 movements related to cargo operations per year can be excempted from an applicablility of Regulation (EU) 2018/1139. For this reason, EASA publishes on its website a list of aerodromes specifying for which Regulation (EU) 2018/1139 is applicable and which aerodromes are exempted.
Aerodromes falling under the scope of the basic regulation must be certified. In simple terms, in this certification procedure an aerodrome must show how and in what way the certification specifications of EASA are complied with or, if they cannot be complied with, what measures are/were taken to ensure an equivalent level of safety. The demonstration of an equivalent level of safety is particularly important for aerodromes that have grown over many decades and can only make certain changes to the facilities to ensure specifications under great financial constraints or not at all, e.g., due to topographical reasons.
Certification specifications are stipulated by the EASA in the CS-ADR document for aerodromes and the CS-HPT document for heliports. These certification specifications define to a great detail, how large parts of an aerodrome and a heliport have to be designed and built. For example, CS-ADR defines how runways, taxiways, or aprons of an aerdrome must be designed, sized, or marked.
7.1 Anatomy of an aerodrome
An aerodrome can be divided into two distinct parts: the airside and the landside. Although there are different definitions for these two terms both in the literature and in the industry, we use the following definitions in this document:
- The airside of an aerodrome covers all areas which can be used by aircraft. This includes both the maneouvring area as well as the apron(s) of an aerodrome.
- The landside of an aerodrome covers all areas which are not accessible for aircraft. This includes the terminals, docks, the baggage handling system (BHS), ground access infrastructure, etc.
In the following, aerodrome infrastructure and components associated to the airside and the landside are introducted and described in more detail.
7.1.1 Airside components of an aerodrome
The airside of an aerodrome consists of the maneouvring area and the apron(s). In CS ADR-DSN.A.002, the manevouvring area is defined as the “part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, excluding aprons”. Consequently, the maneouvring area consists of both runway(s) and taxiway(s). As such, CS ADR-DSN.A.002 defines a runway as a “rectangular area on a land aerodrome prepared for the landing and take-off of aircraft”, while a taxiway is a “defined path on a land aerodrome established for the taxiing of aircraft and intended to provide a link between one part of the aerodrome and another”. Finally, the apron(s) of an aerodrome are according to CS ADR-DSN.A.002 defined as an “area intended to accommodate aircraft for purposes of loading or unloading passengers, mail or cargo, fuelling, parking, or maintenance”.
Facilities on the airside of an aerodrome are designed and sized for a critical aircraft, which is either a real-world of fictitious aircraft. Consequently, aircraft that put higher requirements to the facilities than the critical aircraft, e.g., greater weight, longer wingspan, etc., cannot use the airport or parts of the airport. To prevent each aerodrome from having to describe individually which critical aircraft was used, an aerodrome reference code (ARC) which describes certain characteristics of the critical aircraft applied is used instead. As such, the ARC consists of two components: an aerodrome code number and a code letter. The aerodrome code number describes the reference field length of the critical aircraft in four categories:
| Aerodrome code number | Reference field length |
|---|---|
| 1 | \(<\) 800 m |
| 2 | \(\geq\) 800 m and \(<\) 1200 m |
| 3 | \(\geq\) 1200 m and \(<\) 1800 m |
| 4 | \(\geq\) 1800 m |
The aerodrome code letter describes in six categories the maximum wingspan of the critical aircraft:
| Aerodrome code letter | Maximum wingspan |
|---|---|
| A | \(<\) 15 m |
| B | \(>\) 15 m and \(\leq\) 24 m |
| C | \(>\) 24 m and \(\leq\) 36 m |
| D | \(>\) 36 m and \(\leq\) 52 m |
| E | \(>\) 52 m and \(\leq\) 65 m |
| F | \(>\) 65 m and \(\leq\) 80 m |
For example, an aerodrome with an ARC of “4F” can be used by aircraft with a reference field length of more than 1800m and a wingspan of up to 80m, whereas on an aerodrome with an ARC of “4E” the wingspan is limited to 65m.
7.1.1.1 Runways
Runways facilitate the landing and taking-off of aircraft. In terms of their geometric properties, a runway can be described in terms of its width, slope(s), length, and orientation.
The width of a runway is defined in CS ADR-DSN.B.045 and is usually measured from at outside edges of the runway. As such, the width of the runway depends both on the Aerodrome Code Letter (see Table Table tbl-arc-number) and the Outer Main Gear Wheel Span (OMGWS) of the critical aircraft as indicated in Table Table tbl-rwy-width. Thereby, the OMWGS describes the distance between the outside edges of the main gear wheels of the critical aircraft.
| Aerodrome Code number | 4.5m \(\leq\) OMGWS | 4.5m \(\leq\) OMGWS \(<\) 6m | 6m \(\leq\) OMGWS \(<\) 9m | 9m \(\leq\) OMGWS \(<\) 15m |
|---|---|---|---|---|
| 1 | 18m | 18m | 23m | - |
| 2 | 23m | 23m | 30m | - |
| 3 | 30m | 30m | 30m | 45m |
| 4 | - | - | 45m | 45m |
The slope of a runway is specified both longitudinally and transversely. The longitudinal slope refers to the slope of the runway along its longitudinal axis. The average longitudinal slope of a runway is determined “by dividing the difference between the maximum and minimum elevation along the runway centre line by the runway length” (CS ADR-DSN.B.060). Additionally, CS ADR-DSN.B.060 specifies the maximum longitudinal slope which must not been exceeded in any portion of the runway. Finally, airport designers must ensure that the change in slope between two consecutive portions of the runway is below a certain value. The applicable values for the average longitudinal slope, maximum longitudinal slope, and the maximum longitudinal slope change, which all depend on the aerodrome code number (see Table Table tbl-arc-number), are summarized in Table Table tbl-rwy-lgnt-slope
| Aerodrome Code number | Average longitudinal slope | Maximum longitudinal slope | Maximum longitudinal slope change |
|---|---|---|---|
| 1 | 2% | 2% | 2% |
| 2 | 2% | 2% | 2% |
| 3 | 1% | 1.5% | 1.5% |
| 4 | 1% | 1.25% | 1.5% |
The transverse slope describes how a runway is sloped along its width to allow efficient drainage of rainwater. In practice, two different profile types of transverse slopes are used. Chambered profiles have their highest point at the centre of the runway, allowing water to drain to both sides of the runway, while the single crossfall profiles have thei highest elevation at one edge of the runway, allowing water to drain in the direction of the other edge. On runways of airports with an aerodrome code letter of A and B, see Table Table tbl-arc-letter, the transverse slope must be between 1% and 2% according to CS ADR-DSN.B.080, on airports with an aerodrome code letter of C to F the transverse slope must be between 1% and 1.5%.
According to CS ADR-DSN.B.035, the length of a runway is to be sized in such a way that the operational requirements of the critical aeroplane for which the runway is designed can be met. In this context, the operational requirements are described by means of the following declared distances:
- Take-off run available (TORA):
- Take-off distance available (TODA):
- Accelerate-stop distance available (ASDA):
- Landing distance available (LDA):
The orientation of a runway describes its magnetic direction along its length. For example, a runway running in a north-south direction has an orientation of 360° or 180°, while a runway running in a west-east direction has an orientation of 090° or 270°. To enable pilots and air traffic controllers to identify runways unambiguously, each runway is given a designator. To this end, two-digit numbers are used as designators, e.g. 27, 07, 15, etc., which designate the nearest one-tenth of magnetic direction of a runway when viewed from the direction of approach. Example: If a pilot taxis onto runway 15 and aligns the aircraft so that its nose points in the direction of the other end of the runway, the aircraft’s magnetic compass will indicate a value of 150° +/-5°. At airports with two parallel runways, the designator is supplemented with the letter “L” for “left” and “R” for “right”. At airports with three parallel runways, the designator of the runway in the middle is supplemented with the letter “C” for “centre”.
The orientation of runways depends on a number of factors such as prevailing wind conditions, topographical conditions, etc. Flight crews are encouraged to take off and land into the wind whenever possible. For each aircraft type, there are clear guidelines that specify how strong the so-called crosswind component may be during a landing. For this reason, airport planners take into account long-term weather records on the strength and direction of the wind at an airport in order to orient the runway(s) in such a way that the crosswind componente (i.e. the amount of wind perpendicular to the runway) can be minimised. For this task, the so-called usability factor is used, which measures the percentage of time during which the operation of a runway is not restricted due to crosswind. According to GM1 ADR-DSN.B.015, a runway is considered optimally oriented if a usability factor of greater than or equal to 95% can be achieved. In addition to considering the wind direction, airport planners must also ensure that the runway can be operated safely. In this respect, topographical conditions (mountains, valleys, etc.) are of great importance. Furthermore, runways are often aligned in such a way that sensitive areas such as residential areas, hospitals, etc. are not strongly affected by the emissions of air traffic. In places where several airports are located in a relatively small area (e.g. London, New York, Los Angeles, etc.), care is also taken when choosing the runway orientation that these airports do not influence each other’s operations.
There is no requirement as to the number of runways an aerodrome must offer. Basically, the more runways an aerodrome is equipped, the greater its maximum capacity. At the same time, however, the provision of runways is associated with high investments and operating costs, which suggests that aerodrome should build as few runways as possible.
The layout of an aerodrome runway system depends on how many runways are available at a site as well as how they are arranged and oriented in relation to each other. While in practice the runway systems of most aerodromes are unique, in theory a distinction is made between the following generic aerodrome layout types:
- Single runway: As the name suggests, aerodromes with a single runway layout have a single runway, as is the case, for example, for the airports of London Gatwick (EGKK), Geneva (LSGG), Luxembourg (ELLX), or San Diego International (KSAN). Thanks to the existence of a single runway, the single runway layout is the moste simple one, as no dependencies between runways exist. Consequently, the one runway can be optimally utilised by air traffic control, which in practice leads to single runway aerodromes having a remarkably high capacity. Indeed, depending on the aircraft mix at the aerodrome (i.e., the percentage of large aircraft vs. smaller aircraft utilising the aerodrome), single runway aerodromes can handle up to 98 aircraft movements per hour under visual flight conditions according to FAA Advisory Circular 150/5060-5. Under instrument flight conditions, up to 59 aircraft movements per hour are realistic. However, single runway layouts also comes with certain disadvantages. For instance, taxi distances can be long at single runway aerodromes, as the terminal(s), dock(s) and thus also the stands for the aircraft are often located at one of the two runway ends (e.g. at London Gatwick). Moreover, aircraft operations at single runway aerodromes can also be affected by weather conditions resulting in crosswind situations. In such cases, no other, differently oriented runways are available on which lower crosswind components would result. Finally, an incident or even an emergency on the runway of a single runway airport leads to the entire flight operation having to be suspended. The same can also happen if certain maintenance work has to be carried out on the single runway.
- Open-V or open-L runways: Airports that have an open-V or open-L runway layout have more than one runway, which have different alignments and do not cross at any point. In open-L layouts, the runways are perpendicular to each other, while in open-V layouts the angle between the runways is less or more than 90°. An example of an open-L layout can be found in Rome Fiumicino (LIRF), while Dublin Airport (EIDW) has an open-V layout. One of the advantages of open-V and open-L layouts is the circumstance that the capacity of the aerodrome can be substantially higher than with a single runway layout. According to FAA Advisory Circular 150/5060-5, aerodromes with an open-L or open-V layout can carry out up to 150 aircraft movements per hour under visual flight conditions and 59 movements under instrument flight conditions. Besides that, the aerodrome is less restricted with regard to crosswinds and, thanks to the availability of a second runway, incidents, accidents or maintenance on one runway do not lead to the complete closure of the airport. However, since the runways do not have the same orientation, aerodromes with an open-V or open-L layout have a greater land consumption. Furthermore, the expansion of the apron, terminals and docks may be limited by the runways. Moreover, incidents in the apex between the runways of airports with an open-V and open-L layout can lead to a strong impact on flight operations.
- Intersecting or crossing runways: At aerodromes with an intersecting or crossing runway layout, the runways physically intersect. A good example of an airport where the intersecting runways are arranged at 90° to each other is New York LaGuardia (KLGA), while the intersecting runways at Hamburg (EDDH) or Basel-Mulhouse (LFSB) airports, for example, have an angle not equal to 90°. At airports with intersecting runways, they can never be operated independently, which increases the complexity for air traffic control. Likewise, the capacity of the aerodromes depends on which pister to land on, which runway to take off on and where the intersection between the runways is located. To illustrate this, consider two runway configurations for New York LaGuardia Airport as shown in Figure Figure fig-capacity-crossing-runway. In configuration (a), the aircraft land on runway 13 and take off on runway 22. Consequently, both a taking-off and a landing aircraft have “quickly” passed the intersection point between the two runways, which means that after a take-off or landing clearance has been granted on one runway, the other runway can be used again by other aircraft relatively quickly. In configuration (b), on the other hand, in which aircraft land on runway 04 and take off on runway 31, the intersection point is relatively far away. In this configuration, once a take-off or landing clearance is given on one runway, air traffic control has to wait a “long time” until the other runway can be used again. Consequently, the capacity of the airport is higher under configuration (a) than under configuration (b). In addition to these effects of crossing runways on airport capacity, there is the further complication that incidents and accidents at the crossing point can lead to the suspension of all flight operations at the airport.
- Parallel runways and multiple parallel runways are characterised by runways which are parallel to each other. If an airport has two parallel runways, it is called a parallel runway system. However, if more than two runways are parallel, it is called a multiple parallel runway system. For the operation of parallel runways, two geometric properties illustrated in figure Figure fig-distances-parallel-runway are important, namely (i) the separation distance between two parallel runways and (ii) the stagger between parallel runways. The separation distance describes how far apart the centrelines are between two parallel runways, while the stagger distance describes how far apart the thresholds of the parallel runways are in the direction of the longitudinal runway axis.
First, let us look at how the separation distance affects the operation of parallel instrument runways, which are runways that allow for operations under instrument flight conditions. According to CS ADR-DSN.B.055, the minimum separation distances between parallel runways defined in table Table tbl-parallel-rwy-distance must be maintained so that the modes of operation illustrated in Figure fig-mode-operation-parallel-runway can be performed.
| Mode of operation | Minimum required separation distance |
|---|---|
| Indepedent parallel approaches | 1035m |
| Dependent parallel approaches | 915m |
| Independent parallel departures | 760m |
| Segregated parallel operations | 760m |
Mode of operation independent parallel approaches refers to an operational concept in which air traffic control can operate parallel runways independently of each other for approaching traffic. This means that landings on one runway do not lead to operational restrictions for arriving aircraft on the other runway, and vice versa. For independent parallel approaches to be possible, the centrelines of the parallel runways must be at least 1035m apart, which is the case at Munich Airport (EDDM) or London Heathrow (EGLL), for example. Because the runways can be operated independently of each other, such airports have capacities of up to 120 aircraft movements per hour under instrument flight conditions according to FAA Advisory Circular 150/5060-5. At airports where parallel instrument runways are at least 915m apart, dependent parallel approaches can be flown. This refers to simultaneous approaches on two parallel runways where air traffic control must ensure certain radar separation minima between the approaching aircraft. Since in this case the operation on one runway affects the operation on the other runway (and vice versa), the theoretically possible capacity of such runway systems is approximately 75 movements per hour. Consequently, the maximum capacity of aerodromes were only dependent parallel approaches can be flown is significantly lower than at airports with independent parallel runway systems. Parallel runway systems separated by at 760m allow for independent parallel departures and segregated parallel operations. While the former allows air traffic controllers to consider the runways independent from each other for departing traffic, the latter allows for the operation of one runway solely for arrivals and the other one exclusively for departures.
At some aerodromes with independent parallel runways, the thresholds are displaced, as can be seen in Figure fig-staggered-parallel-runway. In technical jargon, this is referred to as staggered runways. Staggered runways can have a positive impact on airport operations by allowing shorter taxiing distances for aircraft and additional vertical separation of approaching aircraft. The influence of staggered parallel runways on taxi distances can be illustrated using the example of Athens Airport, as shown in Figure fig-staggered-parallel-runway (a). If aircraft land on runway 03R (red dashed line) or take off on runway 03L (blue dashed line), the average taxiing distance is shorter than if runway 03R were used for take-offs and 03L for landings. The effect of the stagger on the vertical separation of approaching aircraft is illustrated in Figure fig-staggered-parallel-runway (b) and (c): If the glide path angles of the approaches to the parallel runways are identical, two simultaneously approaching aircraft are not at the same altitude since the thresholds of the runways are displaced.
7.1.1.2 Adjacent areas
To increase the level of safety of flight operations, airports have to install a number of so-called adjacent areas around runways. In particular, a distinction is made between the following adjacent areas for runways: (i) runway shoulder, (ii) runway strip, and (iii) runway end safety area (RESA):
- runway shoulder,
- runway strip,
- runway end safety area (RESA)
Some adjacent areas can be provided
- clearway
- stopway
7.1.1.3 Runway markings
7.1.1.4 Runway lights
7.1.1.5 Obstacle limitation surfaces (OLS) and obstacle free zones (OFZ)
7.1.1.6 Taxiways
- Taxiway dimensioning
- Taxiway marking, lighting, signage
Types of taxiways: * “Normal” taxiways * Apron stand taxilane * Apron taxiway * Rapid exit taxiway
7.1.1.7 Aprons
- Aprons
- Stands
7.1.2 Landside components of an aerodrome
List of Acronyms
- BR
- Basic Regulation
- EASA
- European Union Aviation Safety Agency
- ICAO
- International Civil Aviation Organization
- IR
- Implementing Rule