The BA 747 that went into a cloud at night over Jakarta is enough of a warning for anyone. Flying the aircraft with shot-blasted windscreen panels was "like trying to navigate one's way up a badger's @rse without a torch". Captain Moody and crew were terrific. Google the story and you will be amazed.
In the recent eruption, the Finns (mad as a box of frogs) intentionally flew a jet into the cloud, the results were not pretty.