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For aircraft operating under instrument flight rules (IFR), an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument meteorological conditions (IMC) from the beginning of the initial approach to a landing, or to a point from which a landing may be made visually. The concept was also commonly known as a blind landing or blind approach when first introduced, although these terms are no longer common. There are two main classifications for IAPs: ''precision'' and ''non-precision''. Precision approaches utilize both lateral (localizer) and vertical (glideslope) information. Non-precision approaches consist of localizer only, circle-to-land, VOR, and all GPS approaches. Publications depicting instrument approach procedures are called terminal procedures, but are commonly referred to by pilots as approach plates. These documents depict the specific procedure to be followed by a pilot for a particular type of approach to an airport. They depict prescribed altitudes and courses to be flown, as well as obstacles, terrain, and potentially conflicting airspace. They list missed approach procedures and commonly used radio frequencies. Before satellite navigation was available for civilian aviation, the requirement for large land-based navigation aid ("navaid") facilities generally limited the use of instrument approaches to land-based (i.e. asphalt, gravel, turf, ice) runways (and those on aircraft carriers). GNSS technology allows, at least theoretically, to create instrument approaches to any point on the Earth's surface (whether on land or water); consequently, there are nowadays examples of water aerodromes (such as Rangeley Lake Seaplane Base in Maine, USA) that have both land navaid-based as well as GNSS-based approaches. ==Basic principles== Instrument approaches are generally designed such that a pilot of an aircraft in IMC, by the means of radio, GPS, INS navigation, or ground based radar can navigate to the airport, hold in the vicinity of the airport if required, then fly to a position from which he or she can either obtain sufficient visual reference of the runway to make a safe landing, or execute a missed approach if the visibility is below the minimums required to execute a safe landing. An instrument approach procedure may contain up to five separate segments (some of which are mandatory). These segments are: * Arrival segment: The segment from where the aircraft leaves an en-route airway to the initial approach fix (IAF). * Initial approach: The segment from the initial approach fix (IAF) to either the intermediate fix (IF) or the point where the aircraft is established on the intermediate or final approach course. * Intermediate approach: The segment from the IF or point, to the final approach fix (FAF). * Final approach: The segment from the FAF or point, to the runway, airport, or missed approach point (MAP). * Missed approach: The segment from the MAP to the missed approach fix at the prescribed altitude. When an aircraft is under radar control, air traffic control (ATC) may replace some or all of these phases of the approach with radar vectors (the provision of headings on which the controller expects the pilot to navigate the aircraft) to allow traffic levels to be increased over that which is possible when following the full procedures. It is very common for ATC to vector aircraft to intercept the final approach navaid's course, e.g., the ILS, which is then used for the final approach. In case of the rarely used ground-controlled approach (GCA), the instrumentation (normally Precision Approach Radar) is on the ground and monitored by a controller, who then relays precise instructions for adjustment of heading and altitude to the pilot in the approaching aircraft. 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「instrument approach」の詳細全文を読む スポンサード リンク
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