Atmospheric volcanic ash in quantities that matter is new to Europe, and the learning curve on how to deal with it is steep. But it needs to get steeper, because it seems the number of differences in the way national aviation authorities are reacting to it almost equals the number of authorities in the Eurocontrol countries.

An example is last week's UK Civil Aviation Authority decision to dispense with the 60nm (111km) safety buffer zone around the estimated position of the ash cloud. At the same time the European Aviation Safety Agency was continuing to refer to the need for a 120nm buffer. Also lacking is Europe-wide agreement on the acceptable ash contamination density. Europe may have unified agencies like EASA, Eurocontrol and the European Civil Aviation Conference, but Eyjafjallajökull has scattered national authorities like its ash, revealing how fragmented an aviation entity Europe still is.

Weather image
 © European Space Agency

The transatlantic picture is similarly confusing. North America has more experience of volcanic ash than Europe does, especially on the more northerly parts of its Pacific rim, but its worst-affected regions are relatively low-traffic areas. Europe's ash cloud is uniquely inconvenient because it can - and does - affect the busiest air traffic region in the world. The Alaska volcanic activity advisory centre (VAAC) works on the same International Civil Aviation Organisation terms of reference as the London VAAC, just as the US Weather Service International uses the same science as the UK Met Office to track weather and thus ash cloud drift. But that, apparently, is where the similarity ends.

Once the atmospheric data has been measured or calculated, how does the local system interpret it? As already observed, it depends where you are in Europe. Transatlantically, the mathematical models used by the WSI or the Met Office to calculate ash drift are based on the same algorithms, but it seems there is a difference in the assumed starting point. The Met Office assumes residual ash remains in the atmosphere until it is cleared by factors like gravity or rain, and that residual ash is topped up by continuing eruptions. The US Federal Aviation Administration's model works mainly on the ash newly emitted by the volcano and takes less account of the residual. They can't both be right. But since aircraft have not been falling out of the FAA's skies, maybe Europe had better look at whether they have the right model or have just been lucky. Eyjafjallajökull could mess up aviation for years to come, so the agencies had better sort out what best practice is.

Source: Flight International