According to Business Insider, "Hawaii's Mount Kilauea erupted Thursday morning at 4:00am local time. The eruption sent ash clouds as high as 30,000 feet. Ash clouds wreak havoc on modern airliners and their jet engines." For instance, on June 24th, 1982 British Airways Flight 009 flew through ash caused by an erupted Mount Galunglung. Almost immediately, the cabin immediately filled with sulfuric smoke and the jet engines began to fail. That's why planes shouldn't fly near erupted volcanoes.