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The public often wonders why airport runways are not always oriented to avoid overflying populated areas; why the aircraft do not always use the same runway or the same flight paths; why some aircraft fly nominal tracks more accurately than others than others; why some airports with two runways handle almost twice as many operations as others with the same or more runways, etc. Each airport is unique and must be studied, with its particular physical characteristics and weather conditions. Using simulation tools to minimise the number of noise-exposed people requires the knowledge of basic aspects of the airport and its operations, which cannot be modified for safety reasons.

 Key determinants of airport operations (and the noise they generate) include:

• Aviation and air operations are highly regulated sector. At the international level, it is regulated by ICAO, at the European level – by EASA, and at the national level – by the civil aviation authorities;
   
• Any flight procedure must be designed following strict safety regulations, approved and published in the Aeronautical Information Publication (AIP) with enough time to allow aircraft and airlines to familiarise themselves with the requirements. In addition, new technologies require new certification of aircraft and flight crews. It is a lengthy procedure that involves many different stakeholders;
   
• The runways are not oriented randomly, and they cannot change the orientation without safety or capacity penalties. Aircraft take-off against the wind, and they cannot land when the tailwind is excessive or when the crosswind is very strong. For this reason, the runways are always oriented in the direction of the prevailing wind in the area;
   
• The length of the runway is determined by the weather conditions, the altitude of the runway, and the heaviest aircraft which can use the aerodrome. Heavy aircraft operating in hot weather conditions and at high altitude airports require longer runway length. In comparison, the take-off of the same unloaded aircraft at a sea-level airport and in mild temperatures can be accommodated by a smaller runway;
   
• In general, all aircraft require much less runway length to land than to take-off;
   
• The capacity of an airport is determined by its physical configuration: terminal design, take-off and landing routings and disposition of platforms and taxiways. Not all two-runway airports can handle the same number of aircraft – it depends on multiple factors;
   
• Several operational factors affect airport capacity, such as the mix – heavy, medium and light – of the fleet operating at the airport. For example, after one heavy take-off, the next light aircraft will wait twice as long as another heavy aircraft;
   
• Weather conditions limit the ability to move aircraft – storms, fogs, winds, etc. will reduce the airport's capacity to keep the same safety conditions;
   
• The slots per season regulate the capacity of all airports, and these are published in the General part of Aeronautical Information Publication. Airports maximum capacity is determined in their master plan;
   
• Adverse weather conditions force changes in airport operations. Some changes are normalised, like the pre-established airport configurations, and others are extraordinary;
   
• Depending on the navigation system, the flight adjustment to the nominal flight paths will be more or less accurate, both for the vertical and horizontal adjustment.

Relevant information

ECAC/CEAC Doc 29 "Report on Standard Method of Computing Noise Contours Around Civil Airports" (4th edition) Volume 1: Applications and Guide