Visual flight rules make reference to the outside environment both for attitude reference and navigation purposes. If visual reference is lost, for example flying unexpectedly into cloud or reduced visibility, the results may be disastrous. To avoid this, minimum flight visibility and cloud distance should be established and maintained. You may know these as Visual Flight Rules.
Visual Meteorological Conditions (VMC) Minima For Airspace Classes
Each airspace class has VMC minima specified for VFR flights (except for class A where VFR is not permitted). These rules are specified under rules 27 and 28 in the rules of the air.
VMC In Controlled Airspace
Class A - VFR flights are not permitted.
Class B - Only found at and above FL245 in the UK. So no significance to most VFR flights VMC minima in Class B airspace are 8km visibility and clear of cloud.
Class C - currently allocated above FL245 so not significant to VFR flights.
Class D - Above FL100, minimum visibility of 8km. Below FL100, minimum visibility of 5 km. Minimum cloud clearance of 1,500 metres horizontally and 1000ft vertically.
Class E - Same as Class D
VMC Outside Controlled Airspace
Class F - Above FL100, minimum visibility of 8km. Below FL100, minimum visibility of 5km. Minimum cloud. Clearance of 1,500 metres horizontally and 1000 ft vertically. But when flying at or below 3000ft amsl, the pilot must fly clear of cloud, with a minimum flight visibility of 5km. This can be reduced to 1,500 meters when flying at speeds of less than 140knots (restricted to 3km if not IMC or INSTRUMENT rated).
Class G - Same as Class F
Services Provided Outside Controlled Airspace
There are a few services that can be helpful to all types of pilot flying Outside Of Controlled Airspace. In the UK ATSOCAS are provided by both civil and military Air Traffic Controllers providing a service to commercial airliners, military and private pilots.
The UK’s Air Traffic Services Outside Controlled Airspace offer four types of services.
A Basic Service is intended to offer the pilot maximum autonomy and the avoidance of other traffic is solely the pilot’s responsibility. The controller/ FISO will pass information pertinent to the safe and efficient conduct of flight. This can include weather, changes of serviceability of facilities, conditions at aerodromes and general activity information within a unit's area of responsibility.
A Traffic Service provides the pilot with surveillance derived traffic information on conflicting aircraft. No De-confliction advice is passed and the pilot is responsible for collision avoidance. A Traffic Service contains the information available in a Basic Service. In addition, controllers provide surveillance derived traffic information on relevant conflicting traffic. Headings and/or levels may also be issued for positioning and/or sequencing.
A De-confliction Service provides the pilot with traffic information and De-confliction advice on conflicting aircraft. However, the avoidance of other aircraft is ultimately the pilot’s responsibility. A De-confliction Service contains the information available in a Basic Service. In addition, controllers shall aim to assist the pilot with his responsibility for the safety of the aircraft by passing traffic information and De-confliction advice. Headings and/or levels will also be issued for positioning, sequencing and/or De-confliction advice.
A Procedural Service is a non-surveillance service in which De-confliction advice is provided against other aircraft in receipt of a Procedural Service from the same controller. The avoidance of other aircraft is the pilot’s responsibility.