If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user
From SKYbrary Wiki
Instrument Meteorological Conditions (IMC)
Instrument meteorological conditions (IMC) are meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, less than the minima specified for visual meteorological conditions (VMC). (ICAO Annex 2)
IMC conditions exist when the outside view from an aircraft is restricted in such a way that aircraft control and navigation can only be carried out using special flight instruments. (EUROCONTROL EATM Glossary of Terms)
VMC are detailed in ICAO Annex 2: Rules of the Air, Chapter 4: Visual Flight Rules. Essentially, they are:
- When above 3,000ft or 1,000ft above terrain, whichever is higher:
- 1500m horizontally and 1,000 ft vertically from cloud;
- Flight visibility 5km below 10,000ft and 8km above 10,000ft.
- When below 3,000ft or 1,000ft above terrain, whichever is higher:
- Clear of cloud and in sight of the surface;
- Flight visibility 5km.
ICAO Annex 2: Rules of the Air, Chapter 4.