THREE airlines cancelled flights between Australia and Bali after a volcano eruption in eastern Indonesia spewed a vast plume of volcanic ash into the air, reports Canada's Tech Xplore.

But while would-be holiday makers are naturally upset at having their plans disrupted, it's worth remembering it's not safe to fly planes through volcanic ash.

So, how do airlines decide it's not safe to fly when a volcano erupts? And why is volcanic ash so dangerous for aircraft, anyway?

Volcanic ash can also clog or damage external sensors, leading to erroneous readings, and can infiltrate an aircraft's ventilation system. This can affect cabin air quality and lead to potential respiratory issues.

But the main risk is the impact volcanic ash has on engines.A jet engine works by drawing in air, compressing it, mixing it with fuel and igniting it. This creates high-pressure exhaust gases that are expelled backward, which pushes the engine (and the aircraft) forward.

The correct balance of fuel and airflow is crucial. When you disrupt airflow, it can cause the engine to stall.

Ash particles that get inside the engines will melt and build up, causing disruption of the airflow. This could cause the engine to "flame out" or stall.

Volcanic ash has a lot of silica in it, so when it melts it turns into something similar to glass. It won't melt unless exposed to very high temperatures-but inside a jet engine, you do get very high temperatures.

There was a famous incident in 1982 where a British Airways Boeing 747 plane was flying in the vicinity of Indonesia and lost all four engines after it encountered volcanic ash spewing from Java's Mount Galunggung.