As Bali’s Mount Agung continues to spew ash, the island’s only airport is closed for business. But authorities say a bigger eruption could take place, and that would affect air travel for a much wider region. So why is it so dangerous to fly into an ash cloud?
What does ash do to a plane?
The biggest danger of flying through an ash cloud is the impact on the engines.
An erupting volcano spews ash and particles into the sky, predominantly made up of silicates.
The very high temperature inside a jet engine will melt these particles but in cooler parts of the engine, they will solidify again forming a glassy coating.
This disrupts the airflow which can lead to the engine stalling or failing completely.
Aside from shutting down the engines, ash clouds can affect many of the sensors on the plane giving, for instance, faulty speed readings.
It also affects visibility for the pilots and can affect air quality in the cabin – making oxygen masks a necessity.
The sharp particles in the ash also cause abrasions and damage to the exterior of the plane though this is not an immediate danger to the flight.
- In pictures: Prayers and preparations
- Story behind the spectacular pictures
- Bali tourism hit by volcano threat
How dangerous is it?
The worst case scenario is a complete engine failure. It means a big jumbo jet may be forced to turn into a glider within minutes.
However, once an engine stops, it will cool down quickly and when restarted, there is a good chance the solidified material inside will at least partly come loose and the engine can function again.
If the engines were to fail during take-off or landing, there would not be enough time for that and a crash would be highly likely.