Grounding jets over volcanic ash alert was right, say scientists

Safety fears led to the action as fine-grained ash from the Eyjafjallajökull volcano blew into the flight path of aircraft over the UK and continental Europe.

The decision disrupted travel for 10 million passengers in April and May 2010 and cost between £1.3 billion and £2.2 billion, leading to questions about whether a safety-first culture had trumped common sense.

Regulations and safety fears led to a halt on commercial aircraft from flying in areas subject to volcanic ash clouds leading to a furious row between airlines, facing millions in lost revenue, and aviation authorities.

But a new report in the American science journal Proceedings of the National Academy concludes the precaution of grounding services was sensible after researchers analysed samples of ash from the volcano and found they were capable of causing an air disaster.

The fragments remained “sharp and abrasive” even after attempts to blunt the particles by stirring them in water.

They would have sandblasted aircraft windows, making them impossible to see through, and had the potential to stall engines.

The explosive eruption on April 14 last year was caused by glacial meltwater coming into contact with hot volcanic magma.

Tiny pieces of extremely hard and abrasive material were ejected to heights of more than nine kilometres (30,000 feet) and carried as far as Russia.

In the absence of specified tolerance levels from engine manufacturers, authorities based their restrictions over volcanic ash in airspace on a previous incident in 1982, when a British Airways 747 few through debris from the eruption of Mount Galunggung in Indonesia.

The pilot reported sparks from the windows and wings and all four engines failed when melted ash coated their interiors.

Luckily it proved possible to restart three engines as they cooled during the descent. The pilot landed while peeking through a two-inch strip on a side window that had avoided sandblasting.

Laboratory tests carried out on the Icelandic ash suggested that a similar event could have happened again.

The researchers, led by Sigurdur Gislason of the University of Iceland, report: “The very sharp, hard particles put aircraft at risk from abrasion on windows and body and from melting in jet engines.

“In the lab, ash particles did not become less sharp during two weeks of stirring in water, so airborne particles would remain sharp even after days of interaction with each other and water in clouds. Thus, concerns for air transport were well grounded.”

The study could form the basis of a safety protocol for rapidly assessing the risk from future volcanic eruptions, said the scientists.

Size, shape and hardness of ash particles were the “key parameters” for estimating abrasiveness and the risk to aircraft.

“Together with estimates of the mass of ash produced, plume height, grain size distribution, and the dispersion rate, these data would provide input for modelling to predict the hazard level for aircraft.”

The big eruption from Eyjafjallajökull on April 14 2010 caused six days of widespread aviation shutdown – the highest level of air travel disruption since the Second World War. Some flight cancellations continued through most of May and the eruption was not declared over until October 2010. Even then, the University of Iceland warned, the area remained “geothermally active” and might erupt again.