Aerodrome Physical Characteristics

An aerodrome is designed around the aeroplanes it serves. How wide the runway strip is, how far a taxiway must be from the runway, where aircraft hold before entering it and how much ground is kept clear beyond its end all follow from the size and performance of the largest types expected. ICAO Annex 14 turns this into standard dimensions and definitions, and the AIP publishes the result for each aerodrome, runway by runway.

For pilots the subject matters in two ways. It is the vocabulary of every AIP aerodrome entry and of every performance calculation, since declared distances and pavement strength decide whether a flight can operate at all. And it explains the protected areas around a runway, which are what make a veer-off or an overrun survivable (see runway excursion).

ICAO Annex 14 and the European rules

ICAO Annex 14, Aerodromes, has two volumes: Volume I, Aerodrome Design and Operations, and Volume II, Heliports. It contains the Standards and Recommended Practices for physical characteristics, visual aids, obstacle limitation and aerodrome services. Under Article 15 of the Chicago Convention it applies to aerodromes open to public use.

In the European Union, aerodromes are certified under Regulation (EU) 2018/1139 and its implementing rules for aerodromes, Regulation (EU) No 139/2014, which are based on Annex 14. The EU rules apply to aerodromes open to public use that serve commercial air transport and have a paved instrument runway of 800 m or more; a State may exempt one handling fewer than 10,000 commercial passengers and fewer than 850 cargo movements a year. Aerodromes outside that scope follow national rules, and each State lists its differences from Annex 14 in AIP GEN 1.7. In the United States, airport design standards are set by the FAA, and some of its figures differ from ICAO's, as the runway safety area below shows.

Aerodrome reference code

The aerodrome reference code ties the design of an aerodrome to the aeroplanes it is intended to serve. It has two elements:

The aeroplane reference field length is the minimum field length the aeroplane needs for take-off at maximum certificated take-off mass, at sea level, in standard atmospheric conditions, in still air and with no runway slope. It describes the aeroplane, not the runway: the code does not set the length of a runway or the strength of its pavement.

The code letter now depends on wingspan alone. Older texts also used the outer main gear wheel span, and French national rules still do. An A320 spans 34.1 m, or 35.8 m with sharklets, so both versions are code letter C.

Movement area, manoeuvring area and apron

Annex 14 divides the aerodrome surface into nested areas:

• the manoeuvring area is the part used for take-off, landing and taxiing, excluding the aprons and maintenance areas;
• the movement area is the manoeuvring area plus the aprons and any part of the aerodrome provided for the maintenance of aircraft;
• the apron is the area where aircraft park, load and unload and are refuelled, and may have its own apron management service, which regulates movement there and coordinates entry to and exit from the apron with the aerodrome control tower.

Airside, a term from Annex 17, is wider still: the movement area of an airport together with the adjacent terrain and buildings, access to which is controlled. The aerodrome reference point (ARP) is the designated geographical position of the aerodrome, normally near its geometric centre.

Runway types

Annex 14 classifies runways by the approaches they serve:

• a non-instrument runway, also called a visual runway, is intended for visual approach procedures only;
• an instrument runway serves instrument approach procedures. It is a non-precision approach runway when the approach uses aids such as a VOR, an NDB or a localiser alone, and a precision approach runway, Category I, II or III, when the approach is flown on a precision aid such as the ILS (see instrument landing system).

The type decides much of what surrounds the runway: the width of the strip, the holding distance, the markings and the lighting. National definitions vary; the French AIP notes that its national rules define an instrument runway as one with at least one instrument approach or departure procedure.

The number and orientation of runways should give a usability factor of at least 95 per cent: the runways should be usable, as far as the crosswind component is concerned, at least 95 per cent of the time for the aeroplanes the aerodrome serves.

Runway strips and safety areas

Each runway sits in a runway strip, an area that includes the runway and any stopway and is kept as free of obstacles as possible. It protects aircraft that run off the runway and aircraft flying over it during take-off and landing, and anything that must stand in it, such as a sign or a light, must be frangible. On code 2, 3 and 4 runways the strip extends at least 60 m beyond each end of the runway, or of the stopway where there is one.

Beyond the strip, the runway end safety area (RESA) is provided at each end of code 3 and 4 runways and of code 1 and 2 instrument runways, to reduce damage to an aeroplane that undershoots or overruns. It must be at least 90 m long and at least twice the width of the runway; Annex 14 recommends 240 m for code 3 and 4 runways and 120 m for code 1 and 2. At Lyon Saint-Exupéry, whose main runway is 4,000 m by 45 m, the AIP gives a strip of 4,120 m by 300 m and runway end safety areas of 240 m by 150 m and 185 m by 130 m.

The FAA's equivalent, the runway safety area (RSA), is often 500 ft wide and 1,000 ft beyond each runway end. Where there is no room for it, US airports install an engineered materials arresting system (EMAS), a bed of crushable material that stops an overrunning aircraft in a short distance.

Other defined areas at the runway ends are:

• a clearway, an area under the control of the aerodrome authority over which an aeroplane may make part of its initial climb; it starts at the end of the take-off run available, extends at least 75 m either side of the extended centre line and should not be longer than half the take-off run available;
• a stopway, a prepared area beyond the take-off run available, as wide as the runway, on which an aeroplane can be stopped in an abandoned take-off;
• a blast pad, the FAA term for a paved surface at a runway end provided to protect the ground from jet blast; it is marked with yellow chevrons and may not be used for taxiing, take-off or landing;
• a radio altimeter operating area, prepared ground before the threshold of a precision approach runway, extending at least 300 m before the threshold and 60 m either side of the extended centre line, so that the radio altimeter gives a steady reading on the approach (see radio altimeter).

Declared distances

Each runway direction has four declared distances, published in the AIP:

• TORA (take-off run available): the length declared available for the ground run of an aeroplane taking off;
• TODA (take-off distance available): TORA plus any clearway, and never more than 1.5 times TORA;
• ASDA (accelerate-stop distance available): TORA plus any stopway;
• LDA (landing distance available): the length available for the ground run of an aeroplane landing, measured from the landing threshold; a stopway is never part of it.

View full schematic

The differences reveal the runway's layout. At Nice, runway 04R has a TORA of 2,963 m, a TODA of 3,503 m and an ASDA of 2,963 m: a 540 m clearway and no stopway. Runway 04L has a TORA of 2,628 m but an LDA of 2,538 m, because its landing threshold is displaced 90 m into the runway. A displaced threshold shortens the LDA in that direction but not the TORA, and an intersection departure shortens the take-off distances but not the LDA. Declared distances can also be shortened temporarily by NOTAM, for example during works, and performance must be calculated with the figures in force (see takeoff distances and field length).

Pavement strength: from ACN/PCN to ACR/PCR

For many years pavement strength for aircraft above 5,700 kg was reported by the ACN-PCN method. The aircraft classification number (ACN) expressed the effect of an aircraft on a pavement and the pavement classification number (PCN) the pavement's strength; an aircraft whose ACN did not exceed the PCN could use the pavement without restriction.

On 28 November 2024 ICAO replaced it with the ACR-PCR method, the aircraft classification rating and pavement classification rating. The principle is unchanged: an aircraft may use a pavement when its ACR does not exceed the PCR. Pavements used only by aircraft of 5,700 kg or less are described instead by a maximum allowable mass and a maximum tyre pressure. The changeover is gradual: in 2026 the French AIP still published the Lyon runways as PCN 101 and 119, each followed by four code letters describing the pavement and how its strength was assessed.

Runway strength is one of the limits on the maximum take-off mass of a performance class A aeroplane, alongside field length, climb, obstacle clearance, brake energy, tyre speed and structural limits.

Taxiways and stands

A rapid exit taxiway lets landing aeroplanes turn off at higher speed and so frees the runway sooner. It is designed for turn-off speeds, on a wet runway, of 93 km/h (about 50 kt) for code 3 and 4 runways and 65 km/h (about 35 kt) for code 1 and 2. It meets the runway at an angle of not more than 45° and not less than 25°, preferably 30°, and includes a straight section after the turn-off curve so that an aeroplane can stop clear of any intersecting taxiway.

On the apron, an aircraft stand must give minimum clearances between a parked aeroplane and other aircraft, buildings and objects:

An isolated aircraft parking position, for an aircraft known or believed to be the subject of unlawful interference, must be at least 100 m from other parking positions, buildings and public areas.

A pre-flight altimeter check location is provided so that crews can check the altimeter before departure. It is normally on an apron, its published elevation is the average elevation of the area, rounded to the nearest metre or foot, and no part of it may differ from that average by more than 3 m (10 ft). Normally an entire apron can serve.

Rescue and fire fighting

Aerodromes provide a rescue and fire fighting service (RFFS), also called RFF. Its principal objective is to save lives, above all in survivable accidents on or near the aerodrome; building fires and other ground duties are not part of the aviation standard. What matters most is training, the effectiveness of the equipment and the speed with which crews and vehicles reach the scene.

Annex 14 sets the operational objective of a response time of not more than three minutes to any point of each operational runway, in optimum visibility and surface conditions, and recommends two minutes. The response time runs from the initial call to the first vehicle being in position to apply foam at no less than half the required discharge rate.

The level of protection, the aerodrome's RFFS category, is set by the size of the largest aeroplanes that normally use the aerodrome, and each AIP gives it in AD 2.6 together with the vehicles and agents available. Under the European and French rules the level of protection may be reduced when the aeroplanes of the highest category normally using the aerodrome make fewer than 700 movements in the busiest three consecutive months. Operators take the category into account when choosing destinations and alternates; for ETOPS alternates, for example, the FAA sets specific RFFS requirements (see alternate aerodromes).

Rescue vehicles responding to an emergency have priority over all other surface traffic, and they show flashing blue lights in addition to the flashing yellow lights required of vehicles on the movement area.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.