The direction that aircraft take off or land depends on the wind direction. For performance and safety reasons, aircraft will take off and land into wind. Due to prevailing south west winds, around 70% of aircraft movements arrive from the North and depart to the South. When the wind is calm, the direction of runway is determined by the wind direction at between 1000ft and 3000ft. On the unusual occasion that the wind is light and variable at 3000ft, several factors are taken into consideration when determining which runway direction to use, including the most accurate approach system for arrivals, the weather, and the current air traffic in airspace around the airport. Due to the geography around Southampton Airport and its effect on the local weather patterns, it is important to note that the runway in use can change many times in a day.
If the wind is calm at ground level, the wind direction at 1000ft plus may determine the runway in use. Aircraft aim to get as high as possible, as quickly as possible, therefore, winds at altitude are a key factor in flight planning.
If aircraft land from the north or depart to the south i.e. from the Eastleigh end, in aviation terms they are described as using runway 20 as they are following a compass heading of 200 degrees. If aircraft land from the south or depart to the north i.e. from the Southampton end, they are described as using runway 02 and will be following a heading of 020 degrees. These numbers are clearly marked on the respective ends of the runway.
Weather and noise
Aircraft will always produce a similar level of noise during day to day operations. Aircraft have to meet and maintain strict guidelines on noise levels as part of their certificate of airworthiness so noise levels directly emitted tend to remain consistent on a day to day operational basis.
One factor that does affect the way aircraft noise is perceived is the atmospheric conditions at the time of the flight. If we experience calm atmospheric conditions usually associated with warmer weather, sound waves will travel further and as such, it is perceived that the noise is greater. In more turbulent conditions associated with wind and rain, sound waves get dispersed and thus making aircraft appear quieter. It’s a similar scenario to dropping a pebble in a pond; the ripples travel further if the water is still. If you introduce waves, the ripples are dispersed more quickly so travel less distance.
Low clouds also have an insulating effect on aircraft noise. This is another reason why on a cloudless day, the noise seems greater.
During strong wind conditions, it has been shown that sound waves can be carried for large distances. This means that aircraft taxiing on the ground at Southampton can be heard some distance away from the airport in a similar manner to road noise.