New measures to be introduced in the UK tomorrow will enable carriers greater freedom to operate in the vicinity of volcanic ash by allowing them to fly through areas of higher ash concentration for limited periods.

UK regional carrier Flybe is the first airline to have secured approval for the operations, which require airlines to present a safety case to the Civil Aviation Authority which includes agreement from the relevant airframers and engine manufacturers.

The new measures, effective from 12:00 on 18 May, introduce a 'time-limited zone' immediately adjacent to the 'no-fly' zone of hazardous ash concentrations. This time-limited zone allows carriers to operate aircraft through ash-contaminated airspace at concentrations of 4mg per cubic metre of air, twice the figure previously considered an upper safe limit.

"This means that areas of our airspace that would have previously been closed can safely open, further minimising flight disruption," says the CAA, which says that the new zone is the result of co-operation between the manufacturers who have been assessing - with data from test flights - the tolerance levels of their aircraft and powerplants.

Meteorological data will still be used to determine the extent of the new time-limited zone. The CAA adds that operations within this zone may require stricter maintenance checks and, as its designation suggests, limited exposure times.

Flybe says the new approvals would have led to just 21 flight cancellations in the past two days rather than 380.

"This level of cancellation would be more akin to a weather event and therefore much more bearable for customers and the industry," says Flybe chief Jim French.

The carrier says it has worked with Pratt & Whitney Canada - which manufactures the engines of its Bombardier Q400 fleet - as well as the Canadian airframer to support development of the new regulation.

French says the work has enabled the airline to present a "comprehensive" safety case to the CAA which was approved today.

While several airlines have criticised the modelling and forecasting that have resulted in airspace closures since mid-April, CAA chief executive Andrew Haines says: "It's the CAA's job to ensure the public is kept safe by ensuring safety decision are based on scientific and engineering evidence. "We will not listen to those who effectively say 'Let's suck it and see'."

Source: Air Transport Intelligence news