Encounters of aircraft with volcanic ash clouds; A compilation of known incidents, 1953-2009

http://pubs.usgs.gov/ds/545/

Of 129 reported incidents, 94 are confirmed ash encounters, 79 of which entailed airframe or engine damage; 20 are low-severity events involving suspected ash or gas clouds; for 15 the data are insufficient to assess severity.

by Guffanti, Marianne C.; Casadevall, Thomas J.; and Budding, Karin

U.S. Geological Survey Data Series 545