• Since the 2010 volcanic ash crisis, measures have been put in place to ensure that the UK and the aviation industry worldwide is prepared for a similar event. If UK airspace is affected by volcanic ash, the following arrangements now apply in UK airspace and across much of Europe.

    Areas of ash will be identified using information provided by the Met Office’s Volcanic Ash Advisory Centre. This is derived from the world-leading computer model the Met Office uses and is based on, and validated by, information from the source of the volcano, satellite images, test flights and weather balloons, as well as ground based instrumentation such as radar.

    The model shows different density levels of ash split into low, medium and high levels:

    Low density Airspace where volcanic ash may be encountered at concentrations equal to or less than 2 milligrams per cubic metre of air.
    Medium density Airspace where volcanic ash may be encountered at concentrations greater than 2 but less than 4 milligrams per cubic metre of air.
    High density Airspace where volcanic ash may be encountered at concentrations equal to or greater than 4 milligrams per cubic metre of air.

    This information is then used by the aviation industry to help make decisions on where it is safe to fly.

    • Based on information from engine manufacturers, areas of low density ash are safe to fly in for all aircraft
    • Information on the high and medium density zones is communicated to the aviation industry through a Notice to Airmen (NOTAM).
      This is a standard worldwide method to advise pilots of flight safety information.
    • Any UK airline wishing to operate in areas of medium or high density ash will need to have a safety case to do so accepted by the CAA. Many airlines already have such safety cases in place and agreed for medium density ash. 
    • Many also have safety cases allowing them to fly in predicted areas of high density ash if they are satisfied that no high density ash is present at the time of a flight.
    • Non-UK airlines can apply to their national regulator for similar safety cases.

    The new regime maintains high levels of safety while reducing disruption. According to the European air traffic control body Eurocontrol, only 900 of the 90,000 flights due to take place in Europe during the Grimsvotn eruption (23-25 May 2011) were cancelled. Work continues to implement one common regime worldwide and the CAA is directly involved in driving this work in Europe and through the International Civil Aviation Organisation.

    What is a safety case?

    Safety cases have been used by airlines for many years to set out how they will safely deal with unusual or challenging issues. They set out the measures that airlines will put in place to mitigate the risk of flying through ash. They also include input from aircraft and engine manufacturers. This is important as engine manufacturers can advise on the levels of ash that their engines can safely cope with.

    The case needs to show that the airline understands the hazard, its own limitations and has in place robust procedures and plans to safely fly in the unusual situation. These procedures may include extra training for crews, additional maintenance inspections and guidance for pilots as to how they should react to certain circumstances. The cases are put together by the airlines and presented to their regulator (for UK operators the CAA) for acceptance.

    How does the forecasting of ash work?

    The Met Office use a computer modelling system known as the NAME model to predict where ash will be present and in what density.

    The model has been widely endorsed by the international meteorological community and has been tested and proven during previous eruptions and events such as Chernobyl and Buncefield.

    The Met Office model forecasts the presence of ash, and is informed by a range of information including data from the source of the volcano, and validated by satellite, specialist aircraft, weather balloons and ground based instrumentation.

    Are small light aircraft also affected?

    Piston engine aircraft (typically used for recreational flying) are less affected by ash and in some cases may still operate when commercial jet airliners are not flying.