At midnight on 11 May the UK and Irish aviation authorities removed the arbitrary 60nm (111km) safety buffer zone around airspace where the ash cloud is predicted to be. The decision was taken on the basis of recent experience with aircraft operating in the vicinity of atmospheric volcanic ash over Europe.

The UK CAA says it expects other European national aviation authorities to follow suit.

This decision is one of a series of actions that the national aviation authorities have taken or planned since the ash cloud from the Icelandic Eyjafjallajökull volcano began to contaminate European airspace on 14 April. The first step - on 20 April - was to declare that aircraft would be allowed to fly in ash that was below a given intensity. The latest measure effectively increases the amount of usable airspace for airlines.

The UK CAA says that it has exhausted its short-term options for improving airline ability to operate safely in the vicinity of ash. It adds, however, that since volcanic ash could become a permanent risk around Europe's skies for many years, the industry in the medium term will have to address other options scientifically.

Among the options are reassessment of the ash intensity limits now deemed acceptable by engine manufacturers, to see if they can safely be raised; and reappraisal by the airlines, on a cost-benefit basis, of they are prepared to accept the costs associated with a quantifiable amount of cumulative degradation to their engine and airframe efficiency. The latter would be calculated against the benefit of fewer flight cancellations, and on condition that the damage does not affect safety.

Many European airlines are protesting that the US Federal Aviation Administration operates a more flexible ash risk regime that, if it were to be adopted in Europe, would allegedly result in fewer cancelled flights. The CAA, however, reveals that the FAA has advised Europe against adopting its specialist practices in an "off-the-shelf" manner.

An example of FAA flexibility is that it allows Alaska Airlines, which operates in airspace with a higher than average ash risk because there are several local volcanoes, more autonomy in it decisions about operating when ash is known to be in the atmosphere.

But this autonomy has been conferred because Alaska trains its flightcrews regularly in ash encounter drills. The airline says that it "does not even taxi" when volcanic ash is known to be present in the atmosphere, preferring total avoidance.

The Alaskan region, which has its own Volcanic Ash Advisory Centre, uses the same terms of reference for ash detection and advice as the London and Toulouse advisory centres, which cover the North Atlantic including Iceland, the British Isles and the whole of continental Europe.

Source: Flight International