why flights are cancelled

Why ash and aircraft don't mix

A volcanic ash cloud is an abrasive combination of fine rock, minerals and glass particles. Concentrated ash clouds near a volcano can cause catastrophic damage, but even planes that fly through diluted clouds hundreds of miles away must be checked for potential problems.

SOURCE: David Schneider, research geophysicist; U.S. Geological Survey; FAA | Bonnie Berkowitz and Alberto Cuadra/The Washington Post - April 17, 2010

LONDON STRANDED

YESTERDAY BECAUSE   OF VOLCANO ERUPTION IN ICELAND
A THICK PALL OF SMOKE ERUPTED AND OCCUPIED THE SKY OVER
BRITAIN AND EUROPE
BRITISH AIRPORT AUTHORITIES DIDNOT WANT TO TAKE A CHANCE ON AICRAFT
SAFETY HENCE ALL FLIGHTS  IN AND OUT AND THRO LONDON WAS CANCELLED

ON 15APR2010
Fearing that microscopic particles of highly abrasive ash could endanger passengers by causing aircraft engines to fail, authorities shut down air space over Britain, Ireland, France, Denmark, Norway, Sweden, Finland and Belgium. That halted flights at Europe's two busiest airports — Heathrow in London and Charles de Gaulle airport in Paris — as well as dozens of other airports, 25 in France alone.