• Volcanoes erupt frequently, but normally only affect areas where air traffic is light and airspace is uncongested. The resulting ash clouds are tracked by nine global Volcanic Ash Advisory Centres which provide information to allow flights to (where possible) reroute their flight paths around any area of contamination.

    When the Eyjafjallajökull volcano in Iceland erupted the guidance used worldwide from the International Civil Aviation Organisation, was to avoid any amount of ash. The guidance actually stated: “in the case of volcanic ash, regardless of ash concentration — avoid, avoid, avoid.”

    The eruption of Eyjafjallajökull in Spring 2010 was very different to previous incidents in that it affected some of the most congested airspace in the world and, as the ash covered much of Europe, flying round it was not an option. There was no precedent for this type of situation and because of the ICAO guidance UK air traffic control body NATS announced that it would not provide clearance for flights in contaminated airspace.

    The UK was not alone in the action it took. Other European countries followed suit as ash clouds drifted into their airspace.

    UK work with International and European regulators

    The disruption to European airspace meant it was imperative that action was taken at a national, European and international level.

    International and European regulators, manufacturers and aviation experts, had to co-ordinate their expertise and agree a new zoning system for airspace affected by volcanic ash.

    The CAA took the lead in getting this work underway and after five days of intensive conference calls with hundreds of experts, the necessary data was amassed for the basis of the new guidelines.

    The CAA’s work on volcanic ash did not stop once the skies re-opened. The CAA has continued to put considerable effort and resources into improving the way aviation deals with volcanic ash. After Eyjafjallajökull the CAA led Europe in developing and implementing the regulatory regime that is now in place and was used during the 2011 Grimsvotn eruption.

    Timelines of ash events that have affected UK airspace

  • The Grimsvotn volcano in Iceland erupted in May 2011, sending ash into the atmosphere. This time, the aviation industry was better prepared.

    All the main players were involved in daily teleconferences and the new three zone system was brought into play as Scottish flights started to be affected. All airline companies had to establish a safety case if they wanted to operate in areas of medium or high density ash. The new zoning system meant that airlines had more freedom to operate in higher areas of ash than they had during the eruption of 2010.

    The Met Office's ash forecasting model was used to predict where areas of high density ash were likely to be. The Grimsvotn ash disruption lasted only a few days and its effects on UK airspace were much less widely felt than the eruption of Eyjafjallajokull the year before. Never the less further work is needed to be undertaken by the aviation community to look at how it deals with ash.

    A look at the role of the CAA following the Eyjafjallajokull volcanic eruption in Spring 2010.

    Wednesday 14 April

    More forceful eruptions start emitting plumes of ash.

    The CAA is informed and advice is provided to airlines.

    As the extent of the ash cloud becomes clear, the CAA-led National Airspace Crisis Management Executive meets for the first time. The group continues to meet three times a day throughout the crisis.

    Thursday 15 April - UK airspace affected

    Early morning - the ash cloud reaches Scottish airspace making it impossible to operate using existing ICAO guidance.

    In accordance with the ICAO guidance NATS announces that from midday to 6pm, it will not provide a service to commercial operators into the contaminated airspace. CAA follows this with a NOTAM (Notice to Airmen) reinforcing the decision.

    Six Met Office ground-based Light Detection and Ranging Radars (LIDAR) detect ash in the atmosphere and a test aircraft is launched for airborne evaluation.

    Friday 16 April

    Evidence of ash presence is detected at various locations throughout UK. A small window allows Manchester Airport to open briefly.

    The CAA, NATS and Met Office in contact with Eurocontrol. CAA meets Secretary of State for Transport and agrees further updates and briefings throughout the day, including afternoon meeting with airlines and airport representatives. Regular contact continues throughout the crisis.

    The CAA establishes international teleconference calls, drawing together almost 100 organisations to assess whether slightly denser contamination than the current ICAO level would be safe.

    Saturday 17 April

    There is no positive prognosis for allowing flights to recommence due to further eruptions and settled weather patterns which keep the ash over the UK.

    An aircraft operator in Penzance detects ash on airframe on landing. Similar reports from MoD in West Wales and North England.

    Tests throughout the weekend tests show the continued presence of contamination.

    Sunday 18 April

    Further International teleconference calls take place. More data is requested by engine manufacturers on likely levels of contamination before they will agree to a new level of safe ash.

    An instrumented test aircraft validates a British Airways flight to measure contamination levels and practical impact.

    Monday 19 April

    The CAA continues to seek agreement from aircraft engine manufacturers - overnight work in the US suggests a solution may be possible.

    European Transport Ministers meet and agree a three band model for classifying ash. Eurocontrol announces that a new zoning system will take effect from 0600 on 20 April.

    At the next international teleconference , data is examined from further instrumented flights which show low level contamination. But there is still no uniform agreement from engine manufacturers about changing the tolerance level.

    Tuesday 20 April

    A further international teleconference with the same participants takes place.

    A CAA emergency Board meeting held at 17:30 agrees a way forward with 2 milligrams per cubic metre of air set as an acceptable safety limit.

    Requirements are established for airlines, Air Traffic Control and aerodromes that include a range of inspections to engines and airframes between flights.

    Test flights continue to monitor ash density.

    The CAA briefs the Secretary of State for Transport and airlines and announces that airspace will be re-opened at 22:00.

    Nine engine manufacturers go public with support for the new safety thresholds.

    Airspace then remains open as normal until 3 May.

    3-5 May

    The ash plume returns to parts of UK airspace and contamination levels exceed the new safety threshold for several days. This results in airports being closed in Scotland and Northern Ireland.

    From then onwards UK airspace remains open as usual.

    8-10 May

    A high concentration of ash in airspace over parts of the south west, southern and central Europe, leads to airport closures in those areas.