Visual meteorological conditions
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In aviation visual meteorological conditions are those in which visual flight rules (VFR) flight is permitted - that is, those in which pilots can see so far that they don't have to rely on their instruments to fly safely.
Generally it includes minimum for distance visibility, ceilings (for takeoffs and landings), and cloud clearances.
The exact requirements vary by type of airspace, whether it is day or night (for countries that permit night VFR), and from country to country. Typical visibility requirements vary from one statute mile to five statue miles. Typical cloud clearance requirements vary from merely remaining clear of clouds to remaining at least one mile away from clouds horizontally and one thousand feet away from clouds vertically.
Generally, VMC requires greater visibility and cloud clearance in controlled airspace than uncontrolled airspace. In uncontrolled airspace there is no risk of a VFR aircraft colliding with an IFR aircraft emerging from a cloud, so airplanes are permitted to fly closer to clouds.