In aviation

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, visual meteorological conditions (or VMC) is an aviation flight category in which visual flight rules

Visual flight rules

Visual flight rules are a set of regulations which allow a pilot to operate 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 minimums, as specified in the rules of the...

 (VFR) flight

Flight

Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....

 is permitted—that is, conditions in which pilots

Aviator

An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 have sufficient visibility to fly the aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

  maintaining visual separation from terrain and other aircraft. They are the opposite of Instrument Meteorological Conditions

Instrument meteorological conditions

Instrument meteorological conditions is an aviation flight category that describes weather conditions that require pilots to fly primarily by reference to instruments, and therefore under Instrument Flight Rules , rather than by outside visual references under Visual Flight Rules . Typically, this...

 (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

Visibility

In meteorology, visibility is a measure of the distance at which an object or light can be clearly discerned. It is reported within surface weather observations and METAR code either in meters or statute miles, depending upon the country. Visibility affects all forms of traffic: roads, sailing...

 minima, cloud ceilings (for takeoff

Takeoff

Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...

s and landings), and cloud clearances.

The exact requirements vary by type of airspace

Airspace

Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....

, 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 3,000m.

Generally, VMC requires greater visibility and cloud clearance in controlled airspace

Controlled airspace

Controlled airspace is an aviation term used to describe airspace in which ATChas the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:...

 than in uncontrolled airspace

Uncontrolled airspace

Uncontrolled airspace is airspace where an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled...

. In uncontrolled airspace there is less risk of a VFR aircraft colliding with an IFR

Instrument flight rules

Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

 aircraft emerging from a cloud, so aircraft are permitted to fly closer to clouds. An exception to this rule is class B airspace class

Airspace class

The world's navigable airspace is divided into three-dimensional segments, each of which is assigned to a specific class. Most nations adhere to the classification specified by the International Civil Aviation Organization and described below...

, 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.

UK Weather Minima for VFR Flight within Controlled Airspace (Classes C to E)

• At and above FL 100

8 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• Below FL 100

5 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• At or below 3000ft

For fixed wing aircraft operating at 140kt or less
5 km flight visibility
Clear of cloud and in sight of surface

For helicopter
Clear of cloud and in sight of surface
UK Weather minima for VFR flight outside Controlled Airspace (Classes F and G Airspace)

• At and above FL 100

8 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• Below FL 100

5 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• At or below 3000ft

for any aircraft:
5 km flight visibility, Clear of cloud and with the surface in sight

or

for an aircraft, other than a helicopter, operating at 140kt or less:
1500 m flight visibility, Clear of cloud and with the surface in sight.

for helicopters:
1500m horizontally from cloud
Clear of cloud, with the surface in sight and in a flight visibility of at least 1500m.

UK Weather Minima for VFR Flight within Controlled Airspace (Classes C to E)

• At and above FL 100

8 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• Below FL 100

5 km flight visibility, 1500m horizontally from cloud, 1000ft vertically from cloud

• At or below 3000ft

For fixed wing aircraft operating at 140kt or less
5 km flight visibility
Clear of cloud and in sight of surface

For helicopter
Clear of cloud and in sight of surface
US Weather minima for VFR flight outside Controlled Airspace (within Class E Airspace)

• At or above 10,000 ft. MSL

5 statute miles visibility, 1 statute mile horizontally from clouds, 1000ft above and below clouds

• Below 10,000 ft. MSL

3 statute miles visibility, 2000 ft. horizontally from clouds, 1000ft above and 500 ft below clouds

US Weather minima for VFR flight in Class C and D airspace

3 statute miles visibility, 2000 ft. horizontally from clouds, 1000ft above and 500 ft below clouds

External links

• U.S. Federal Aviation Regulations defining visual meteorological conditions.

• Guide to Visual Flight Rules in the UK