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 flight conditions 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 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. A third type of approach, available only to IFR flights but not considered a true instrument approach, is discussed below. Precision approaches utilize both lateral (localizer) and vertical (glideslope) information. Non-precision approaches provide lateral course information only.
The publications depicting instrument approach procedures are called Terminal Procedures, but are commonly referred to by pilots as approach plates. These documents graphically depict the specific procedure to be followed by a pilot for a particular type of approach to a given runway. They depict prescribed altitudes and headings to be flown, as well as obstacles, terrain, and potentially conflicting airspace. In addition, they also list missed approach procedures and commonly used radio frequencies.
In the past, the requirement for large land-based navigation aid (NAVAID) facilities has generally limited the use of instrument approaches to land-based (i.e. asphalt, gravel, turf, ice) runways (including those aboard aircraft carriers). However, recent advances in GPS approach technology have permitted the creation of instrument approaches at water aerodromes such as Rangeley Lake Seaplane Base in Maine, USA.
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