But if potential vacationers are naturally upset With their plans disrupted, it is worth remembering that it is 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 planes, anyway?

What does volcanic ash do on a plane?

Volcanic ash particles are very, very abrasive. They can cause permanent damage to aircraft windshields and can even cause windshields to become opaque, as if someone had covered them with sandpaper.

Imagine putting on goggles and scraping them over and over again with sandpaper: that’s what you would see if you were sitting in the cockpit.

Volcanic ash can also obstruct or damage external sensors, leading to erroneous readings, and can leak into an aircraft’s ventilation system. This can affect cabin air quality and lead to possible respiratory problems.

But the main problem, in fact, is the impact of volcanic ash 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 plane) forward.

The correct balance between fuel and air flow is crucial. When you disrupt the airflow, the engine may stall.

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

Volcanic ash contains a lot of silica, 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 get very high temperatures.

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

Fortunately, the pilot was able restart the engines and land safelyeven though the pilots were not able to see through the front windshields.

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 would review the situation in real time today and make the decision based on their risk assessment.

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

Different airlines may approach risk management slightly differently; some flights may be canceled earlier than others. But, generally speaking, the more sophisticated airlines would come to similar conclusions and they probably all communicate with each other.

Most of the time, their decision is based on the extent of the plume, that is, the size of the ash cloud and its direction, keeping in mind that winds vary with altitude. As winds become stronger with altitude, ash can drift quite far from the source.

There is also a United Nations agency called International Civil Aviation Organizationwhich publishes guidance on risks from volcanic ash. Various weather agencies around the world work together and liaise with aviation authorities to get the message out quickly in the event of an eruption.

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

Passenger safety is the priority

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

Naturally, people are upset about the delay in their vacation plans. But it is in the interests of passengers not to travel through volcanic ash.

(Patrick Murrayprofessor emeritus of aviation, University of Southern Queensland

This article is republished from The conversation under Creative Commons license. Read the original article.)