These charts supplement the London Volcanic Ash Advisory graphics (VAG) and advisories (VAA). They are to be used with caution. The outer edge of the low concentration zones (indicated as cyan) on these charts represent the standard threshold (200 micrograms of ash per cubic meter) as used in the VAG and VAA. Due to the automated nature of production these charts will not be identical to the Volcanic Ash Graphic. In accordance with the definitions in the ICAO EUR/NAT Volcanic Ash Contingency Plan (ICAO EUR Doc 19 and NAT Doc 06 Part II, December 2010 edition), the following concentrations are indicated:
Low Concentration: (< 2000 micrograms per cubic meter), is indicated as cyan on the map graphics.
Medium Concentration: (≥ 2000 micrograms per cubic meter), is indicated as grey on the map graphics.
High Concentration: (≥ 4000 micrograms per cubic meter), is indicated as red on the map graphics.
Operators should refer to national NOTAMs for official guidance on any restrictions / actions regarding flight in affected airspace, and the official boundaries applicable to such restrictions/actions.
Airlines operating in UK airspace should review the document "Guidance Regarding flight Operations in the Vicinity of Volcanic Ash", issued by the CAA, found on the CAA website