The astrology of this event is clearly seen in the Virgo rising chart for the United Kingdom. In fact, the transits at that time were indicative of problems especially for those individuals and countries with Virgo as a rising sign (sidereal zodiac). In recent months, predictions based on the Systems' Approach have warned of a difficult time for this ascending sign during the month of April.
Astrology of the event
In general terms, all the functional benefic planets of Virgo as a rising sign were transitting in the sixth and eighth houses on April 15. Thereof, transit 1st lord Mercury and 2nd lord Venus in Aries and 8th house were under the close afflicting aspect of Rahu in Sagittarius and 4th house. Of several indications ruled by Rahu, one is smoke! Moreover, as Venus is a general indicator of air travel, this disruption was felt far and wide.
Astrology of the UK chart
 Volcanic ash spreads more travel misery across Europe, BBC, April 18, 2010