19 Aerodromes - Physical Characteristics

Aerodrome Data

19.15 Aerodrome Reference Point (ARP). An aerodrome reference point must be established for an aerodrome. It is defined as the designated geographical (Lat and Long) location of the aerodrome and is to be reported to the aeronautical information services authority in degrees, minutes and seconds. The ARP should be located near the initial or planned geometric centre of the aerodrome and will normally remain where first established. In reality, it is usually the centre of the longest runway.

19.16 Pre-flight Altimeter Check Location. One or more pre-flight altimeter check locations are required for an aerodrome. These should be located on an apron to enable an altimeter check to be made prior to obtaining taxi clearance and thus eliminate the need for stopping for that purpose after leaving the apron. Normally an entire apron can serve as a satisfactory altimeter check location. The elevation of a pre-flight altimeter check location is given as the average elevation, rounded to the nearest metre or foot, of the area in which it is located. The elevation of any portion of a pre-flight altimeter check location must be within 3 m (10 ft) of the average elevation for that location.

19.17 Aerodrome and Runway Elevations. The aerodrome elevation and geoid undulation at the aerodrome elevation position (the highest point of the landing area) is measured to the nearest half metre or foot. For precision runways, it is to be measured to the nearest 0.25 m or foot. Note: The geoid is the gravitational level of mean sea level extending continuously through the continents. It is irregular due to local gravitational disturbances, hence geoid undulations.

19.18 Pavement Strengths. Where paved areas (runways, taxiways, aprons) are used by aircraft with maximum take-off mass greater than 5700 kg, the strength of the pavement is reported by the aircraft classification number - pavement classification number (ACN-PCN) system. An aircraft can safely use a paved area if the PCN is equal to or greater than the ACN.

19.19 PCN. The Pavement Classification Number (PCN) is used to indicate the strength of a runway, taxiway or apron. It is of primary importance for the apron as this is where the aircraft

	19	mass will be greatest. PCN is only used for paved areas.
	Aerodromes
		19.20 ACN. The Aircraft Classification Number (ACN) is a single unique number expressing
		the relative effect of an aircraft on a paved area relating to pavement type and thickness. It is a
	-	number on a continuous scale increasing from 0 with no upper limit. Each aircraft has an ACN.
	Physical	19.21 Aircraft of 5700 kg or less. The strength of the pavement for use by aircraft with
	Characteristics	maximum mass equal to and less than 5700 kg is calculated from the maximum allowable mass
		or the maximum tyre pressure.
		19.22 Declared Distances. The following distances must be calculated to the nearest metre
		or foot for a runway intended for the use by international commercial air transport:
		• Take-off run available (TORA);
		• Take-off distance available (TODA);
		• Accelerate-stop distance available (ASDA);
		• Landing distance available (LDA).
		19.23 TORA. Definition: The distance between the point at which an aeroplane can
		commence the take-off run to the nearest point in the direction of take-off at which the surface
		is incapable of bearing the mass of the aeroplane under normal operating conditions.

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Aerodromes - Physical Characteristics 19

19.24TODA. Definition: The distance from the start of TORA to the nearest obstacle in the direction of take-off projecting above the surface of the aerodrome and capable of affecting the safety of an aeroplane in flight (up to a maximum distance of 1.5 × TORA). Usually, TODA is TORA plus clearway if a clearway exists.

19.25ASDA. Definition: The distance from the start of the take-off run to the nearest point in the direction of take-off at which the aircraft cannot roll over the surface and be brought to rest in an emergency without risk of accident. ASDA used to be called EDA (Emergency Distance Available). Usually ASDA consists of TORA plus the stopway if available.

19.26LDA. Definition: The distance from the point where an aeroplane can commence its landing to the point where the surface is incapable of bearing the mass of the aircraft under normal operating conditions. Usually this is the full length of the runway, but may include a paved stopway (if available) where the threshold is displaced.

26	08
TORA/TODA/ASDA/LDA
26	08	CLEARWAY
TORA/ASDA/LDA
	TODA
26	08	STOPWAY
TORA/TODA/LDA
	ASDA
26	08
TORA/TODA/ASDA	LDA

Figure 19.3 Declared distances

19.27 Condition of the Movement Area and Related Facilities. Information on the condition of the movement area and the operational status of related facilities must be provided to the appropriate aeronautical information service units, and similar information of operational significance to the air traffic service units, to enable those units to provide the necessary information to arriving and departing aircraft. The information must be kept up to date and changes in conditions reported without delay. The condition of the movement area and the operational status of related facilities are to be monitored and reports on matters of operational significance or affecting aircraft performance given, particularly in respect of the following:

Aerodromes - Physical Characteristics 19

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19 Aerodromes - Physical Characteristics

•Construction or maintenance work;

•Rough or broken surfaces on a runway, a taxiway or an apron;

•Snow, slush or ice on a runway, a taxiway or an apron;

•Water on a runway, a taxiway or an apron;

•Snow banks or drifts adjacent to a runway, a taxiway or an apron;

•Anti-icing or de-icing liquid chemicals on a runway or a taxiway;

•Other temporary hazards, including parked aircraft;

•Failure or irregular operation of part or all of the aerodrome visual aids; and

•Failure of the normal or secondary power supply.

Note. The 3 defined states of frozen water on a runway are: snow, slush and ice.

Runways

		19.28	General. Runways are the parts of the manoeuvring area used for take-off and
		landing of aircraft. Except in remote areas, runways will always be prepared and usually paved
		(concrete and tarmac). A runway should be straight and not have excessive slopes. It is usual
		to be able to use the ‘concrete strip’ in either direction hence one concrete strip will provide
		two runways. In all cases, runways require markings (painted on the surface) which will give
		the pilot indications about the use of the runway and also assist the pilot to land the aircraft.
		It is true to say that no two runways are identical, and part of the learning curve for a pilot
		new to an airline is to become familiar with the aerodromes and the runways used during the
		operation. At a controlled aerodrome, the runway ‘belongs’ to the aerodrome controller. The
		pilot will be given permission to enter, backtrack, cross, take off from and land on a specified
		runway. The ATCO will always specify the runway and the pilot always reads back the runway
		designator in RTF communications. For instance: ATCO “G-AG clear take-off runway 01”; pilot
		“Clear take-off runway 01 G-AB”. In issuing this instruction, the ATCO is ‘lending’ the pilot the
		runway and after use it is returned to the ATCO.
		19.29 Usability. Many factors affect the orientation, position and number of runways at
		an aerodrome. One important consideration is the usability factor with regard to the wind,
		which could be affected by the alignment of the runway. The number and orientation of
	19
		runways should be such that the usability factor of the aerodrome is not less than 95% for the
	-Aerodromes	aeroplanes that the aerodrome is intended to serve. It is normal practice to take off and land
		19.30	Types of Runway. Runways are defined by the use to which the runway is put, rather
		into wind.
	Physical	than by physical characteristics. An ‘airfield’ (a defined area of grass on which runways may be
		marked out or the direction of landing is indicated) may have several or no defined runways,
	Characteristics	whereas an ‘airport’ (a point of entry or exit from a country by air) may have several defined

paved runways. The types of operations carried out on or to a runway determine the runway type. The service provided, markings, signs, and physical characteristics of a runway are type dependent.

19.31 Visual Runway. A non-instrument (visual) runway is used where take-off and landing criteria are determined visually. The criteria are usually defined by reference to ground visibility or RVR, cloud ceiling and day/night considerations. The markings of the runway will clearly indicate this fact.

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Aerodromes - Physical Characteristics 19

19.32 Instrument Runway. An instrument runway is one to which instrument departure and approach procedures are applied. For departing traffic, the instrument departure procedure will be defined in the form of a SID. For arriving traffic, instrument runways are sub-divided into:

•Precision runways (using ILS, MLS or PAR approaches)

•Non-precision (using VOR, NDB, SRA or ILS in azimuth only approaches)

19.33 Take-off Runway. A take-off runway is a runway that can be used only for take offs. This

is usually due to terrain preventing an instrument approach or precluding a missed approach. A

take-off runway is usually only in one direction (the reciprocal not being used).

19.34 Location of Runway Threshold. The threshold of a runway should normally be located

at the extremity of a runway unless operational considerations justify the choice of another

location. If the threshold is displaced from the beginning of the paved strip, the location of the

threshold is shown by a transverse white stripe across the runway surface and arrows leading

to the position of the threshold. Reasons for displacing a threshold may include unserviceable

runway conditions, RESA, radio altimeter operating area, glide path angle, obstacle clearance

etc...

19.35 Length of Runways. The actual length of a runway should be adequate to meet the

operational requirements of the aeroplanes for which the runway is intended and should be not

less than the longest length calculated to correct for local conditions (elevation, temperature,

runway slope, humidity and surface characteristics). There is no requirement to cater for the

worst case aeroplane at critical mass. Where a secondary runway is constructed, the length

criteria are applied in order to obtain a usability factor of 95%. Runway length is reported in

metres, however, fixed distance markers (distance to go signs) along the edge of runways

are in 1000s of ft but are defined in terms of 300 m starting 300 m from the threshold. For a

‘concrete strip’ to accommodate instrument approaches from either end it must be at least

1800 m between thresholds.

19.36 Width of Runways. Clearly, the width of a runway should not be less than that required

for the aeroplanes using the aerodrome. During the construction of an aerodrome this can

19

be easily achieved but with the introduction of big aeroplanes (e.g. the A380) previously

acceptable runways may be rendered inadequate. The primary factors in deciding the width of

Characteristics

a runway are wing span and outer main gear wheel span. The table below specifies the width

of runways in terms of the aerodrome reference code:

Physical-

Code number

Code letter

Width of Runways

Aerodromes

A

B

C

D

E

F

1(a)

18 m

18 m

23 m

-

-

-

2(a)

23 m

23 m

30 m

-

-

-

3

30 m

30 m

30 m

45 m

-

-

4

-

-

45 m

45 m

45 m

60 m

Note:(a): For a precision runway, w = 30 m where code is 1 and 2

Figure 19.4 Width of runways

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19 Aerodromes - Physical Characteristics

19.37Runway Strips. A runway strip is defined as an area including the runway, and stopway if provided, in which obstacles are kept to a minimum. Any that are there must be constructed so as to present the minimum danger to aircraft, in other words, they must be frangible (collapse upon impact). The purpose of the runway strip is to reduce the risk of damage to aircraft running off a runway, and to protect aircraft flying over it during take-off or landing operations.

19.38Length of Runway Strips. A runway strip should extend before the threshold and beyond the end of the runway or stopway for a distance of at least:

•60 m where the code number is 2, 3 or 4;

•60 m for a code 1 instrument runway; and

•30 m for a code 1 non-instrument runway.

19.39 Width of Runway Strips. A runway strip, wherever practicable, is to extend laterally on each side of the centre line of the runway and its extended centre line, throughout the length of the runway strip, to a distance defined in the table below.

					Width of Runway Strip
			Type of Runway			Runway code number
					1	2	3	4
			Precision		75 m	75 m	150 m	150 m
			Non-precision		75 m	75 m	150 m	150 m
			Non-instrument		30 m	40 m	75 m	75 m
				Figure 19.5 Width of runway strips
		19.40 Grading of Runway Strips. That portion of a strip of an instrument runway within a
	19
		distance of at least 75 m where the code number is 3 or 4, and 40 m where the code number is
	-Aerodromes	1 or 2, from the centre line of the runway and its extended centre line, should provide a graded
		must be flush with the surface of the runway, shoulder or stopway.
		area for aeroplanes which the runway is intended to serve in the event of an aeroplane running
		off the runway. The surface of that portion of a strip that abuts a runway, shoulder or stopway
	Physical	19.41 Objects on a Runway Strip. No fixed objects other than visual aids (PAPIs) are permitted
	Characteristics	on a runway strip within 77.5 m of the centre line for code 4F precision CAT I/II/III runways (60

m code 3 or 4 precision CAT I/II/III runways; or 45 m code 1 or 2 CAT I). No mobile objects are permitted on this part of a runway strip during landing or take-off. An object which is situated within the stated dimensions is to be regarded as an obstacle and, as far as is practicable, removed.

19.42 Runway End Safety Area (RESA). This is an area of land usually at each end of a runway strip either side of the extended centre line which does not form part of the runway for operational (performance or planning) purposes, which is free from obstructions and set aside in case an aeroplane either overshoots or overruns the end of the runway. It is primarily intended to reduce the risk of damage to the aeroplane. RESAs should be provided for all code 3 and 4 runways and for code 1 and 2 instrument runways. The RESA should be at least twice the width of the runway and extend from the end of the runway strip for a distance not less

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Aerodromes - Physical Characteristics 19

than 90 m. However, for a code 3 or 4 runway it is recommended to extend for 240 m, and for 120 m for code 1 and 2.

Figure 19.6 Runway strip - Code 4

	19.43 Clearways. This is a defined rectangular area on the ground under the control of the
	appropriate authority, selected or prepared as a suitable area over which an aeroplane may	19
	make a portion of its initial climb to a specified height. The origin of a clearway should be at
		Characteristics
	the end of the take-off run available (TORA). The length should not exceed half the length of
	TORA, and the width should extend laterally to a distance of at least 75 m on each side of the
	extended centre line of the runway.
	19.44 Stopways. A stopway is a defined rectangular area on the ground at the end of the	Physical-
	take-off run available (TORA), prepared as a suitable area in which an aircraft can be stopped
	in the case of an abandoned/rejected take-off. It is to have the same width as the runway with	Aerodromes
	which it is associated.

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