a writes:

That would be any jet driven airplane flown anywhere in the world,
given that is how widely dispersed volcanic is. There are many who
also overestimate risks. The more rational approach is to weigh risk
and benefits without one's thumb or ego on the scale.

So how would you weigh the risks with significant amounts of ash in the air
from a nearby volcano? The airlines cared only about money, not safety, so
their "evaluation" of risk was straightforward, and again thanks to money,
they twisted the arms of aviation authorities.

Alaska Airlines does have a policy for volcanic ash, but nobody asked them
about it, apparently.