Visual flight rules
Visual flight rules (VFR) are a set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minima, i.e. in visual meteorological conditions (VMC), as specified in the rules of the relevant aviation authority. The pilot must be able to operate the aircraft with visual reference to the ground, and by visually avoiding obstructions and other aircraft.
If the weather is below VMC, pilots are required to use instrument flight rules, and operation of the aircraft will primarily be through referencing the instruments rather than visual reference. In a control zone, a VFR flight may obtain a clearance from air traffic control to operate as Special VFR.
VFR require a pilot to be able to see outside the cockpit, to control the aircraft's altitude, navigate, and avoid obstacles and other aircraft. Governing agencies establish specific requirements for VFR flight, including minimum visibility, and distance from clouds, to ensure that aircraft operating under VFR are visible from enough distance to ensure safety.
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.
The VFR pilot is required to "see and avoid" obstacles and other aircraft. 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 (ATC). Depending on the category of airspace in which the flight is being conducted, VFR aircraft may be required to have a transponder to help Air Traffic Control identify the aircraft on radar in order that ATC can provide separation to IFR aircraft.
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 (IMC), and a flight may only operate under IFR. IFR operations have specific training requirements and certification required of the pilot, and increased equipment requirements for the aircraft. Additionally, 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, California's Oakland (KOAK), Monterey (KMRY) and Santa Ana (KSNA) airports routinely grant temporary IFR clearance when a low coastal overcast forces instrument approaches, while the rest of the state is still under visual flight rules.
In most if not all countries of the world, VFR pilots also have an option for requesting Special VFR when meteorological conditions at an airport are below normal VMC minima, 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 in some States 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 except after failure of two way radio communications. In the United States, class A airspace begins at 18,000 feet msl, and extends to an altitude of 60,000 feet msl. An exception to IFR-only flying in this airspace is the occasional allowance of sailplanes within designated wave windows which may be opened by Air traffic control when high altitude flights are to be conducted into mountain Lee waves.
In the United States, Canada and Australia, a pilot operating VFR outside Class B, C, D airspace can request "Flight Following" from 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. In the United Kingdom, this is known as a "Traffic Service". In other countries it is known as "Flight Information Service".
In the United States and Canada, any certified pilot who meets specific recency of experience criteria may operate an airworthy aircraft under VFR.
VFR cruising altitude rules in the US
In the US, there are specific VFR cruising altitudes, based on the aircraft's heading, to assist pilots in separating their aircraft while operating under visual flight above 3,000 ft above the surface (AGL) but below 18,000 ft Mean Sea Level (MSL). Unofficially, most pilots use these rules at all levels of cruise flight. FAR 91.159 states that any aircraft:
- On a magnetic course of 0-179 degrees shall fly at an odd thousand ft MSL altitude +500 feet (e.g. 3,500, 5,500, or 7,500 ft); or
- On a magnetic course of 180-359 degrees shall fly at an even thousand ft MSL altitude +500 feet (e.g. 4,500, 6,500, or 8,500 ft).
Low flying rules in the US
- 500 ft rule
- An aircraft must maintain an altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
- 1000 ft rule
- An aircraft must maintain an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft over any congested area of a city, town, or settlement, or over any open air assembly of persons.
Other aircraft, such as helicopters, powered parachutes, and weight-shift-control aircraft, are not required to meet the FAR 91 minimums, so long as their operation is conducted without hazard to persons or property on the surface.
Low flying rules in the UK
In the UK, the Rules of the Air define clearly in the principles of Low Flying Rules in Rule 5. The main principle is that an aircraft must always be able to perform an emergency landing in a case of engine failure. Hence these three criteria:
- 500 ft rule
- An aircraft must not fly closer than 500 ft to any person, vessel, vehicle, building or structure.
- 1000 ft rule
- If an aircraft is flying over a congested area (town, settlement, etc.) it must fly high enough so that in the case of an engine failure, it is able to land clear without being a danger to people AND it must not fly less than 1000 ft above the highest fixed object within 600m of the aircraft.
Defined exemptions include normal take-off and landing at aerodromes, helicopters, police, air displays and hill-soaring in gliders.
Controlled visual flight rules
CVFR flight is used in locations where aviation authorities have determined that VFR flight should be allowed, but that ATC separation and minimal guidance are necessary. In this respect, CVFR is similar to Instrument flight rules (IFR) in that ATC will give pilots headings and altitudes at which to fly, and will provide separation and conflict resolution. However, pilots and aircraft do not need to be IFR rated to fly in CVFR areas, which is highly advantageous. An example of airspace where CVFR is common would be Canadian Class B airspace.
In Israel and the Palestinian territory, for example, VFR does not exist. All visual flights must be performed under CVFR rules.
- Barany chair
- Night visual flight rules
- Simultaneous opposite direction parallel runway operations
- Special visual flight rules