Science Features

Ash cloud is scientific grey area

By Lennart Simonnson Apr 21, 2010, 16:16 GMT

A handout photograph released on 20 April 2010 by DLR Institue for Physics and Atmosphere, showing a false color composite taken on board the DLR Falcon on 19 April 2010. EPA/DLR Institue for Physics and Atmosphere / HANDOUT

Stockholm - A week ago, most regular airline passengers were unlikely to have made a connection between an erupting volcano in Iceland and massive disruptions of air traffic in Europe, which marooned hundreds of thousands of people.

But the eruption - and the volcanic ash it spewed out into the atmosphere - has served as a reminder of the forces of nature as well as how vulnerable, and globalized, the world is.

A key guideline for aviation is safety first. That principle came into play a week ago when ash in the atmosphere was first reported, resulting in the closure of airspace over Norway and subsequently other parts of Europe as the ash cloud spread.

Previous incidents had caused fears that the ash could clog jet engines.

In 1982, two Boeing 747 jets experienced engine failure after flying into ash from an Indonesian volcano.

A British Airways 747 with 240 passengers on board lost all four engines 150 kilometres downwind of the ash-belching Mount Galunggung on the western end of Java island.

The plane lost 7,500 metres of its 11,500-metre altitude before its captain managed to restart the engines.

A few days later, three of the four engines failed on a Singapore Airlines Boeing 747 which then plunged 2,400 metres before getting one engine going again and limping into Jakarta.

But aviation is a highly regulated business with rules and guidelines issued by manufacturers as well as national authorities.

A global tracking system for volcanic ash was set up in 1987 by the UN International Civil Aviation Organization (ICAO), and the World Meteorological Organization (WMO).

After the recent blanket flight bans, ICAO said there was a need to 'establish a global safety risk framework' for flights operating in airspace affected by volcanic ash.

During the recent Icelandic eruption, military jets operated by NATO members as well as the Finnish airforce reported that ash had formed a glass-like substance in some engines.

Swedish aircraft engine maker Volvo Aero said ash from a volcanic eruption had 'a much denser content than a normal dust or ash cloud.'

It comprised very small, hard rock-like particles which could also damage cockpit windowpanes. But the main threat was 'severe wear on all engine components,' the company said.

After five days of chaos, European transport ministers early this week agreed to introduce new rules for where flights could operate.

Three risk zones were introduced according to the concentration of ash. Flying remains banned in the high-risk zone, but individual countries were allowed to decide whether to allow flights in the medium-risk zone. The low-risk zone is open.

Andrew Haines, chief executive of the British Civil Aviation Authority, said manufacturers had established a threshold of ash concentration above which it was not safe to fly.

'It's been absolutely right to do that work properly,' Haines told the Today programme after the revisions were made and British airspace reopened late Tuesday.

But the European Cockpit Assocation (ECA) which represents nearly 39,000 flight crew from 38 European countries, said that more data was needed on where the volcanic matter posed a threat.

It added that 'commercial aircraft should not be used as test aircraft.'

The Swedish Transport Agency said it would continue to operate with two zones, without introducing a medium-risk zone.