In aviation, visual meteorological conditions (or VMC) is an aviation flight category in which visual flight rules (VFR) flight is permitted—that is, conditions in which pilots have sufficient visibility to fly the aircraft maintaining visual separation from terrain and other aircraft. They are the opposite of Instrument Meteorological Conditions (IMC). The boundary criteria between IMC and VMC are known as the VMC minima. As part of private pilot training, pilots are required to demonstrate some instrument flying skills. This is usually done in the aircraft with simulated IMC conditions using products like blockalls.
Visual meteorological conditions are usually defined by certain visibility minima, cloud 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 statute miles (many countries define these in metric units as 1,500m to 8km). Typical cloud clearance requirements vary from merely remaining clear of clouds to remaining at least one mile away (1,500m in some countries) from clouds horizontally and one thousand feet away from clouds vertically. For instance, in Australia, VMC minima outside controlled airspace are clear of cloud with 5,000m visibility below 3,000ft AMSL or 1,000ft AGL (whichever is higher), and 1,000ft vertical/1,500m horizontal separation from cloud above these altitudes or in controlled airspace. Above 10,000ft, 8,000m visibility is required to maintain VMC. Air Traffic Control may also issue a Special VFR clearance to VFR aircraft, to allow departure from a control zone in less than VMC - this reduces the visibility minimum to 1,600m.
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 IFR aircraft emerging from a cloud, so aircraft are permitted to fly closer to clouds. An exception to this rule is class B airspace class, in which ATC separates VFR traffic from other VFR traffic and from IFR traffic, which is why in Class B Airspace lower cloud clearance is required.
Famous quotes containing the words visual and/or conditions:
“I may be able to spot arrowheads on the desert but a refrigerator is a jungle in which I am easily lost. My wife, however, will unerringly point out that the cheese or the leftover roast is hiding right in front of my eyes. Hundreds of such experiences convince me that men and women often inhabit quite different visual worlds. These are differences which cannot be attributed to variations in visual acuity. Man and women simply have learned to use their eyes in very different ways.”
—Edward T. Hall (b. 1914)
“Each victim of suicide gives his act a personal stamp which expresses his temperament, the special conditions in which he is involved, and which, consequently, cannot be explained by the social and general causes of the phenomenon.”
—Emile Durkheim (1858–1917)