# The Rules of the Air Regulations 1991, Paragraph 25: Flight within controlled airspace


(a) Within Class B airspace:
(i) an aircraft flying within Class B airspace at or above flight level 100 shall remain clear of cloud and in a flight visibility of at least 8 kilometres;
(ii) an aircraft flying within Class B airspace below flight level 100 shall remain clear of cloud and in a flight visibility of at least 5 kilometres.
(b) Within Class C, Class D or Class E airspace:
(i) an aircraft flying within Class C, Class D or Class E airspace at or above flight level 100 shall remain at least 1500 metres horizontally and 1000 feet vertically away from cloud and in a flight visibility of at least 8 kilometres;
(ii) an aircraft flying within Class C, Class D or Class E airspace below flight level 100 shall remain at least 1500 metres horizontally and 1000 feet vertically away from cloud and in a flight visibility of at least 5 kilometres.

---
Source: https://www.legislation.gov.uk/uksi/1991/2437/schedule/crossheading/visual-flight-rulesn2/paragraph/25 (the official version)
Page: https://openlegislation.uk/rules-of-the-air-regulations-1991/schedule/crossheading-visual-flight-rulesn2/paragraph-25
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.