71.53 Control areas
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(a) The Director may specify a control area designated under this Part
as--
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(1) a terminal control area if the Director determines that an
approach control service is required at the confluence of ATS
routes in the vicinity of one or more major aerodromes; or
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(2) an upper control area if the Director determines that an area
control service is required; or
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(3) an oceanic control area if the Director determines that an area
control service is required over the high seas.
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(b) The upper limit of a control area must not exceed flight level 660.
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(c) The lower limit of a control area must--
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(1) be at least 500 feet below the flight paths of IFR flights that the
Director determines to require an air traffic control service; and
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(2) be established at--
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(i) the highest practical altitude; and
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(ii) not less than 700 feet above the surface of the earth; and
- (3) when the lower limit of a control area is above 3000 feet AMSL,
coincide with a VFR cruising altitude or flight level prescribed
in Part 91.
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(d) If a portion of airspace below a control area is designated as another
control area, the upper limit of the lower control area must extend to the
lower limit of the control area directly above it.