jimp
In your research, how many volcanoes did you find that had any effect
on aviation in the past 50 years?

Well....I've done no research, but I know of at least one.

A B-747 flying in the South Pacific area had all four engines
flame-out due to volcanic ash. Once out of the cloud, the crew
was able to restart the engines. ATC routed traffic around that
area for some time.

Bob Moore
ATP B-727, B-707
Pan Am (retired)