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Generally, VMC requires greater visibility and cloud clearance in controlled airspace than in uncontrolled airspace. In uncontrolled airspace there is less risk of a VFR aircraft colliding with an instrument flight rules (IFR) aircraft emerging from a cloud, so aircraft are permitted to fly closer to clouds.
Under visual meteorological conditions, the minimum visual range, distance from clouds, or cloud clearance requirements to be maintained above ground vary by jurisdiction, and may also vary according to the airspace in which the aircraft is operating. [4] In some countries, VFR flight is permitted at night, and is known as night VFR.
VFR visibility and cloud clearance requirements are the same as for class C and D airspaces when below 10,000 feet (3,000 m) MSL. Above 10,000 ft MSL, the visibility requirement is extended to 5 miles (8 km) and the cloud clearance requirement is extended to 1,000 feet (300 m) below clouds, 1,000 feet (300 m) above, and 1 mile (1.6 km) laterally.
A pilot's view of the runway just before landing in thick fog at night. In aviation, instrument meteorological conditions (IMC) are weather conditions that require pilots to fly primarily by reference to flight instruments, and therefore under instrument flight rules (IFR), as opposed to flying by outside visual references under visual flight rules (VFR).
Flight under SVFR is only allowed in controlled airspace, and always requires clearance from air traffic control (ATC). [4] It usually happens when the aircraft is inside controlled airspace, and the local weather is less than the minimums required for flight under visual flight rules (VFR) within the airspace in question.
The departure clearance may contain an assigned heading, one or more waypoints, and an initial altitude to fly. The clearance can also specify a departure procedure (DP) or standard instrument departure (SID) that should be followed unless "NO DP" is specified in the notes section of the filed flight plan. [citation needed]
The world's navigable airspace is divided into three-dimensional segments, each of which is assigned to a specific class. Most nations adhere to the classification specified by the International Civil Aviation Organization (ICAO) and described below, though they might use only some of the classes defined below, and significantly alter the exact rules and requirements.
Although the altitudes near the tropopause are usually cloudless, thin cirrus cloud can form where there are abrupt changes of air velocity, for example associated with jet streams. Lines of cirrus perpendicular to the jet stream indicate possible CAT, especially if the ends of the cirrus are dispersed, in which case the direction of dispersal ...