Visual flight rules (VFR) are a set of aviation regulations under which a pilot may operate an aircraft, in a specific airspace, with meteorological conditions better than Basic VFR Weather Minimums. For example, weather conditions sufficient to allow the pilot, by visual reference to the environment outside the cockpit, to control the aircraft's attitude, navigate, and maintain safe separation from obstacles such as terrain, buildings, and other aircraft.
A VFR flight is a "flight conducted in accordance with the visual flight rules".
The essential collision safety principle guiding the VFR pilot is "see and avoid." Pilots flying under VFR assume responsibility for their separation from all other aircraft and are generally not assigned routes or altitudes by air traffic control. Near busier airports, and while operating within certain types of airspace classifications, VFR aircraft in Class B & Class C airspace are required to have a transponder. Governing agencies establish specific requirements for VFR flight, consisting of minimum visibility, distance from clouds, and altitude to ensure that aircraft operating under VFR can be seen from a far enough distance to ensure safety.
From a regulatory perspective, airspace is categorized as controlled and uncontrolled. In controlled airspace known as class B, air traffic control (ATC) will separate VFR aircraft from all other aircraft. In most other types of controlled airspace, ATC is only required to maintain separation to aircraft operating under instrument flight rules (IFR), but workload permitting will assist all aircraft. In the United States, a pilot operating VFR outside of class B airspace can request "VFR traffic following" from air traffic control (ATC). This service is provided by ATC if workload permits it, but is an advisory service only. The responsibility for maintaining separation with other aircraft and proper navigation still remains with the pilot.
Meteorological conditions that meet the minimum requirements for VFR flight are termed visual meteorological conditions (VMC). If they are not met, the conditions are considered instrument meteorological conditions, and a flight may only operate under IFR.
IFR operations have specific training, recency of experience, equipment, and inspection requirements for both the pilot and aircraft, and an IFR flight plan, must usually be filed in advance. For efficiency of operations, some ATC operations will routinely provide "pop-up" IFR clearances for aircraft operating VFR, but that are arriving at an airport that does not meet VMC requirements. For example, in the United States, at least California's Oakland (KOAK), Monterey (KMRY) and Santa Ana (KSNA) airports do so routinely when a low coastal overcast forces instrument approaches while essentially the entire state of California is basking in sunshine.
In the United States, VFR pilots also have an option for requesting Special VFR when meteorological conditions at an airport are below normal VMC minimums, but above Special VFR requirements. Special VFR is only intended to enable takeoffs and landings from airports that are near to VMC conditions, and may only be performed during daytime hours if a pilot does not possess an instrument rating.
VFR flight is not allowed in airspace known as class A, regardless of the meteorological conditions. In the United States, class A airspace begins at 18,000 feet msl, and extends to an altitude of 60,000 feet msl.
In Israel, for example, VFR does not exist. All visual flights must be performed under CVFR rules.