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In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to wake turbulence. Air traffic controllers apply rules, known as ''separation minima'' to do this. Pairs of aircraft to which these rules have been successfully applied are said to be ''separated'': the risk of these aircraft colliding is therefore remote. If separation is lost between two aircraft, they are said to be in a ''conflict''. When an aircraft passes behind or follows another aircraft, wake turbulence minima are applied due to the effect of the wingtip vortices of the preceding aircraft on the following aircraft. These minima vary depending on the relative size of the two aircraft. This is particularly acute on final approach with a smaller aircraft following larger aircraft. ==Which aircraft need separating?== It is a common misconception that air traffic controllers keep all aircraft separated. Whether aircraft actually need separating depends upon the class of airspace in which the aircraft are flying, and the flight rules under which the pilot is operating the aircraft. As stated by the U.S. FAA, ''The pilot has the ultimate responsibility for ensuring appropriate separations and positioning of the aircraft in the terminal area to avoid the wake turbulence created by a preceding aircraft''.〔http://www.faa.gov/air_traffic/publications/ATpubs/AIM/Chap7/aim0703.html〕 There are three sets of flight rules under which an aircraft can be flown: *Visual Flight Rules (VFR) *Special Visual Flight Rules (SVFR) *Instrument Flight Rules (IFR) Public transport flights are almost exclusively operated under IFR, as this set of rules allows flight in regions of low visibility (e.g. cloud). On the other hand, a large amount of private flying in light aircraft is done under VFR since this requires a lower level of flying skill on the part of the pilot, and meteorological conditions in which a pilot can ''see and avoid'' other aircraft. As its name suggests, SVFR is a special infrequently-used set of rules. For the purposes of separation, controllers consider SVFR to be the same as IFR. Airspace exists in seven classes, A to G, in decreasing order of air traffic control regulation. Classes A to E are controlled airspace and class G is uncontrolled airspace. At one end of the scale in classes A and B airspace, all aircraft must be separated from each other. At the other end of the scale in class G airspace there is no requirement for any aircraft to be separated from each other. In the intermediate classes some aircraft are separated from each other depending on the flight rules under which the aircraft are operating. For example, in class D airspace, IFR aircraft are separated from other IFR aircraft, but not from VFR aircraft, nor are VFR aircraft separated from each other. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Separation (aeronautics)」の詳細全文を読む スポンサード リンク
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