This isn't purely an Earth science question, but I don't know where else to post it. Recently, the Kasatochi volcano erupted in Alaska. It brought to mind something that happened to me a long time ago that I have always wondered about. In 1989 I was flying from Alaska to Seattle. Days earlier, Mt Redoubt - a volcano in the Aleutian chain - had a big eruption. Most flights out of Anchorage were cancelled but I was surprised that my flight was scheduled to go. Just minutes into the flight, the cabin was filled with airborne ash. It was so thick that it bothered everyone's eyes and if you ground your teeth together, you could feel the grit. I recall a slight sulfur smell. It only lasted maybe 10 seconds. The flight went on without incident. I always wondered were ever really in danger? What's the protocol for flying through a volcano plume?