Volcanic Ash Build-up
source: NASA/TM-2003-212030, Engine Damage to a NASA DC-8-72 Airplane From a High-Altitude Encounter With a Diffuse Volcanic Ash Cloud. Thomas J. Grindle, NASA Dryden Flight Research Center, Edwards, California and Frank W. Burcham, Jr. Analytical Services and Materials, Inc. Edwards, California, August 2003.
Erosion due to Volcanic Ash
source: NASA/TM-2003-212030, Engine Damage to a NASA DC-8-72 Airplane From a High-Altitude Encounter With a Diffuse Volcanic Ash Cloud. Thomas J. Grindle, NASA Dryden Flight Research Center, Edwards, California and Frank W. Burcham, Jr. Analytical Services and Materials, Inc. Edwards, California, August 2003.
Both pictures are from
SKYbrary - Volcanic Ash
Seems to be reason enough to not fly, or?