AEST & Windytoo
Correct I'm not a pilot and there is no need for European ANSPs to 'justify' closing the airspace. The ICAO guidance was out for 3 years and IATA/Engine Manufacturers were content with the 'zero ash tolerance'. It wasn't until the volcano exploded and the ANSPs closed airspace, exactly in accordance with the guidance, that industry suddenly sat up, took notice and stopped ignoring the situation. Now a 'safe' ash tolerance level has been arrived at with the engine manufacturers and airspace closures made in accordance with it.
BD