At least three airlines
canceled flights between Australia and Bali this week after a volcanic eruption in eastern Indonesia spewed a vast plume of volcanic ash into the air.

But while potential vacationers are naturally
angry if their plans are disrupted, it’s worth remembering that 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 to aircraft, anyway?

What does volcanic ash do to an airplane?

Volcanic ash particles are very, very abrasive. These can cause permanent damage to aircraft windshields and can even make windshields appear opaque – as if someone had sandpapered them.

Imagine taking glasses and scraping them over and over with sandpaper – that’s what you’d see if you were sitting in the cockpit.

Volcanic ash can also clog or damage external sensors, leading to erroneous readings, and can seep into the aircraft’s ventilation system. This can affect cabin air quality and lead to potential respiratory problems.

But the main problem, in fact, is the impact of volcanic ash on the engines.

A jet engine works by taking in air, compressing it, mixing it with fuel and igniting it. This creates high-pressure exhaust gases that are expelled backwards, which pushes the engine (and the aircraft) forward.

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

Ash particles that get inside the engines will melt and build up, causing airflow to be interrupted. This could cause the engine to “cut out” or stall.

Volcanic ash contains a lot of silica, so when it melts it turns into something like glass. It won’t melt unless exposed to very high temperatures – but inside a jet engine, you get very high temperatures.

There was a famous incident in 1982 in which a
British Airways Boeing 747 plane was flying in the vicinity of Indonesia and lost all four engines after encountering volcanic ash flowing from Mount Galunggung in Java.

Fortunately, the pilot made it
restart the engines and land safelyalthough the pilots could not see through the windshield.

This week’s episode covers British Airways 9, a 747 that flew through volcanic ash. Here’s the eruption, the damaged engine parts from the Auckland Museum, the flight crew and the plane after the emergency landing in Indonesia. pic.twitter.com/LgWl9sRiuY

— BlackBoxDown (@BlackBoxDownPod) October 8, 2020

How do airlines decide it’s not safe to fly when a volcano erupts?

The decision is made by the operational staff of each airline. The operational team of each airline will analyze the situation in real time today and make the decision based on the risk assessment.

Every airline has a risk management process, which is required by the Australian Civil Aviation Safety Authority.

Different airlines may approach risk management in slightly different ways; you may have some flights cancel earlier than others. But in broad terms, more sophisticated airlines would come to similar conclusions, and they probably all communicate with each other.

They mostly make the call based on the extent of the plume — how big the ash cloud is and where it’s headed, keeping in mind that winds vary with altitude. As you get stronger winds with altitude, the ash can move quite far from the source.

There is also a United Nations agency called
International Civil Aviation Organizationwhich issues guidance on volcanic ash hazards. Various weather agencies around the world work together and collaborate with aviation authorities to quickly spread the word in the event of an eruption.

For airlines to resume flights, the ash must clear and there must be a low probability of further eruptions.

How passenger safety is the priority

The reason behind these flight cancellations is safety. If you lose engines and can’t see out the window, the risk to passenger safety is obvious.

Naturally, people are upset that their vacation plans are delayed. But it’s actually in the passengers’ best interest not to fly through volcanic ash.

Patrick Murrayprofessor emeritus of aviation,
University of Southern Queensland

This article is republished from
conversation under a Creative Commons license. Read on
original article.