secondary area(redirected from Endemism in birds)
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secondary area[′sek·ən‚der·ē ′er·ē·ə]
In air operations, that area within a segment in which ROC (required obstacle clearance) is reduced as distance from the prescribed course is increased.
A defined area on each side of the primary area located along the nominal flight track in which decreasing obstacle clearance is provided. Primary area is a defined area symmetrically disposed about the nominal flight track in which full obstacle clearance is provided (ICAO). When track guidance is provided in the design of an instrument approach procedure, each of the five segments of the approach composes a specified volume of airspace whose vertical cross section is an area disposed symmetrically about the centerline of each segment. The vertical cross section is broken down into primary and secondary areas. At any point, the width of the primary area is equal to one-half of the total width. The width of each secondary area is equal to one-quarter of the total width. Where no track guidance is provided during a turn specified by the procedure, the total width of the area is considered the primary area. See primary area. See also segments of an instrument approach procedure.