Has anybody bothered to study similarities between this eruption and Mt. St-Helens in 1980 in N. America? I remember my car, in Eastern Canada, having a fine ash coating at the time. I don't recall any massive airspace closures nor aircraft falling out of the sky at the time (which was when I was doing my PPL); however Google isn't turning much up on the subject. I do recall that eruption produced massive quantities of ash.
Airspace was closed for up to two weeks in places, with up to 1/4 inch ashfalls across Idaho, Wyoming, Dakotas and beyond.
1,000 + flights were cancelled at the time, when fewer travelled by air and in a sparsely populated area.