The UK Met Office, which operates the London Volcanic Ash Advisory Centre, stands by the quality of its atmospheric ash tracking systems despite the absence of the only test aircraft normally available to it.
The atmospheric test aircraft, a BAE Systems BAe 146 operated by the Natural Environment Research Council, is at work in North Africa on a project it was booked to carry out a long time in advance, said the Met Office.
IATA director general Giovanni Bisignani on 24 May voiced his anger about the lack of a research aircraft in a letter to the UK Department for Transport: "It is astonishing and unacceptable that Her Majesty's government cashes £3.5 billion [$4.9 billion] a year in air passenger duty but is incapable of using a small portion of that revenue to purchase another Cessna to use as a backup aircraft. I ask please that you ensure that all possible efforts are made to get the existing aircraft operational in the shortest possible time."
The Met Office pointed out that airborne monitoring is only one of the many ways in which ash is tracked and its concentration measured. It suggested that "we shouldn't be too hung up" about the lack of available aircraft-mounted sensors because they are only one of an arsenal of ash analysis weapons, and not guaranteed to be any more useful than the alternatives.
Airborne reporting in real time can also be achieved by weather balloons, and many are being released specifically for ash tracking, added the Met Office. The ground-based sensor tools include lidar, laser cloudbase recorders and radar.
Satellite analysis is rapidly getting smarter, said the Met Office, because light and infra-red spectrum analysis is yielding more detail about ash density and dispersal than it was in 2010.
The German Aerospace Centre (DLR) on 26 May plans to fly a Fairchild Dornier 228 test aircraft in UK airspace in co-operation with the VAAC, said the Met Office.
A British Airways Airbus A320 flown in co-operation with the UK Civil Aviation Authority into the ash "red zone" on 24 May did not discover any problems. However, the carrier has yet to analyse various filters that were renewed specifically for this flight.
The Met Office described the BA flight results as "useful", and stated that there have also been several pilot reports of visible ash in UK airspace and over the North Sea. All data from all sources is useful, the Met Office said.