Visual flight rules
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Visual flight rules (VFR) are a set of aviation regulations under which a pilot may operate an aircraft, if weather conditions are sufficient to allow the pilot to visually control the aircraft's attitude, navigate, and maintain separation with obstacles such as terrain and other aircraft.
Under VFR, the pilot generally controls the attitude of the aircraft by relying on what can be seen out the window (see visual flight), although this may be supplemented by referring to the instrument panel. A pilot flying under VFR is usually required to stay at least a specified distance away from clouds and must stay in areas where the visibility meets minimum requirements. There may be other requirements which vary by country, such as not flying over a solid layer of clouds, or not flying at night. The pilot is responsible for seeing and avoiding other aircraft, terrain, and obstructions such as buildings and towers. Being in contact with air traffic control is optional in most airspace, and the pilot is usually allowed to select the course and altitude to be flown even when in contact with ATC. The pilot may navigate either visually (using pilotage), or by reference to instruments and electronic aids to navigation.
The minimum meteorological requirements for VFR are called visual meteorological conditions (VMC). If they are not met then the flight must be flown under instrument flight rules (IFR), the pilot must have an instrument rating and meet recency of experience requirements pertaining to instrument flight, and the aircraft must be equipped and type-certified for instrument flight. In some types of airspace, generally at extremely high altitudes, a flight must be flown under IFR regardless of the meterological conditions.