The last major eruption lasted for a year. Some flights may be able to operate day VFR with favourable winds and carefully planned routes but the effect on tourism will be devastating. It’s now peak season and the holiday plans for thousands of people have been disrupted, not forgetting the local population who are in evacuation centres.
Few people would book a holiday knowing their outbound flight may be cancelled at short notice or that they could be unable to return home without an extended delay. Destinations such as Fiji and NZ will become more attractive for Australians.
Plans are in place to get visitors out with buses and ferries to Surabaya, currently there are around 60 000 in Bali.
Hopefully the scale won’t be on the level of Mt Pinatubo which deposited ash 30cm deep in parts of the Philippines. A massive ash cloud drifting around the airways between Australia and Asia will require extensive and costly rerouting for airlines.
Hopefully the knowledge gained from the eruption of the volcano in Iceland in 2010 can be applied, Europe was basically grounded for five days. Whilst no commercial aircraft suffered any damage, ash was found in the engines of some military jets. That eruption sent ash into the jet stream which spread it over a wide area.