Runway - A runway is a defined rectangular area on a land aerodrome prepared for the landing and take-off run of
aircraft along its length.
Runway in Use - Runway in Use is the term to indicate the particular runway or landing direction selected by aerodrome control as the most suitable for the landing and taking off of aircraft at any particular time.
Factors affecting selection of runway in use
There are many factors that may dictate the runway that should be in use. These include:
Of course, these should always be taken into consideration, but the main 2 important factors that will dictate the runway in use are:
Normally, the runway in use will be that most closely aligned with the surface wind direction. Where the surface wind is light and variable, the 2000ft wind should be taken into account.
Alternatively, these days, most aircraft have a wind readout in the cockpit so you could ask the pilot of an arriving or departing aircraft to pass you the direction and speed at 2000ft as indicated in the cockpit.
The reason the surface wind is the prime consideration is that it can greatly affect the take-off distance of aircraft. Aircraft prefer to take off and land into the wind. In a headwind, aircraft need less runway to take off in because there is already some airflow over the wings in the direction of take off. In a tailwind, aircraft need more runway to take off in because it needs to counter balance the wind already flowing over the wing in the wrong direction, by moving forwards. In a tailwind, aircraft are faster on approach so need a longer landing distance to slow down.
Where aerodromes are in close proximity, (e.g. Manchester and Woodford), conflicting operations can occur so the aerodromes have to try and ensure they are using similar runways i.e. Westerlies
Pilots are always looking for the most expeditious approach (straight in approach, for example). A pilot may request the use of a different runway if the route is quicker and he thinks the conditions are good enough for him to use the different runway. This can be approved by ATC, but the controller should take into account the current traffic levels and complexity of the airspace when making the decision.
Preferential Runway Procedures
Some airfields operate a Preferential Runway Procedure, whereby during certain conditions, a certain runway will be in use.