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The ash crisis

Deirdre Hutton recounts evidence-based policy under pressure

Although Eyjafjallajökull first began to erupt on 20 March 2010, it was not until 14 April that the Icelandic volcano hit the headlines. Being a glacial volcano, the interaction of magma with ice and water created an intense plume of ash and gas over 33,000 feet high which was then carried by north-westerly winds towards Scotland and Scandinavia. The extraordinary biochemical reaction caused by the volcano created very fine particles of ash with high concentrations of silica, the raw material of glass, which made it even more hazardous to aircraft than normal ash. By early morning on 15 April the ash cloud had moved down the length of the UK where it subsequently lingered in some of the world’s most congested airspace.

This had never occurred in the modern era so there was no template for aviation to draw on. The UK found itself in the frontline of this extraordinary situation. With volcanic ash being a known safety hazard to aircraft, the existing guidance from the International Civil Aviation Organisation was for aviation to simply AVOID, AVOID, AVOID. The air traffic control provider, NATS, had no alternative but to exclude all aircraft from ‘controlled’ airspace. This, however, was not a permanent solution. The challenge was to find something that was.

The task

We quickly co-ordinated activity with the Met Office, NATS and the Department for Transport, principally through activating the National Airspace Crisis Management Executive. However, it was abundantly clear that the airlines and aircraft manufacturers would have to work with us in finding a solution. 

We had to discover two things: how to robustly map the movement of ash clouds and assess their density; and also to evaluate just what the safe ash tolerance levels were for each engine on each aircraft type (something that no one had bothered to do before). We had to do it in hours, not months and all under the anxious gaze of an aviation industry already suffering from a prolonged recession. 

New limits

Data gathering was clearly the key, and we relied on the Met Office dispersion model and test flights into the ash clouds to provide vital information on the ash concentration levels.  We crunched the numbers fed back to us before setting up international conference calls involving dozens of aircraft and engine manufacturers, airlines, scientific agencies and regulators. We put our data on the table and asked the aero engine manufacturers to come up with safe limits on the atmospheric ash density their engines could cope with.

By the afternoon of Tuesday, 20 April, only six days after the volcanic ash arrived in UK airspace, key manufacturers had provided the Civil Aviation Authority (CAA) with revised guidelines, which would not compromise safety. The new limit, set at 0.002g/ash per cubic metre of air, meant that while no-fly zones would still exist in concentrations above this level, flights could take place in less dense clouds. A strict ground inspection regime was put in place to ensure any serious damage to engines was discovered quickly.

Public duty

As a regulator we have to stick scrupulously to the principle of evidence-based decision-making. The leadership of the CAA has been widely recognised across Europe and our actions have led to a greatly enhanced knowledge of the risks from volcanic ash. This will stand us in good stead when – probably not if – volcanic activity resumes.

We knew there was a risk, we identified the nature of that risk and we came up with a solution to that risk. To do anything else would have been a dereliction of our fundamental duty to take judgements in the public interest.

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Dame Deirdre Hutton
Dame Deirdre Hutton is the Chair of the Civil Aviation Authority
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