That a cloud of volcanic ash can paralyse flights across Europe has raised serious questions about the aviation industry’s efforts to understand the risks of flying in such conditions.
International Civil Aviation Organisation rules prohibit flights through volcanic ash, but aircraft and engine manufacturers have not fully investigated the effects. What information they have has been gleaned from inspecting planes after they have accidentally flown into ash plumes.
Manufacturers could have run tests in wind tunnels to see how much volcanic ash an engine can run through without flaming out or being badly damaged, but the industry rejected the option.
Analysts said engine tests would have a limited value, as volcanic ash differs from almost all other environmental threats an aircraft faces.
The danger is that silica particles in the ash melt inside the engines and clog cooling systems. This is likely to shut down all aircraft engines at once, rather than just one or two, which airliners are designed to cope with.
“The manufacturers’ view is that you simply do not expose a plane to that level of risk,” said Riti Singh, an authority on aircraft engines at the Cranfield University.
Then there is the issue of responsibility. “Some level must be considered safe, but who takes responsibility if all the engines fail on a plane and everybody dies?” asked Singh.
Colin Brown, of the Institute of Mechanical Engineering in London, said volcanic ash clouds are so rare that manufacturers did not consider engine tests worthwhile.
The ash plume has reached Europe because of a perfect storm of conditions: the Icelandic volcano erupted beneath a glacier, causing hot magma to explode on contact with the ice and taking the plume to a high altitude. The ash was then carried by unseasonal northerly winds to Europe.
Even if manufacturers decided that aircraft could fly safely in low ash levels, it would not help much.
The wealth of cutting-edge equipment, from satellites, ground-based lasers and computer models, used by meteorological offices are not accurate enough to say which regions of airspace will be clear enough to cross for any useful length of time. The ash moves unpredictably, meaning an airliner could set off on a clear corridor and unwittingly fly into dense ash.
Several airlines have flown test flights since last weekend (April 17-18), but these are meaningless unless planes are fitted with equipment to analyse ash en route, or follow a research aircraft along the same path.
Last Sunday British Airways flew a test flight from Heathrow over the Atlantic and back to Cardiff, but only after a research plane flew the same path and declared it clear.
“You have to know what you flew through or it’s worthless. You can be in almost clear air one moment and suddenly find you’re in a much higher density of particles,” said Stephen Mobbs, director of the National Centre for Atmospheric Science at Leeds University.
“It’s almost impossible to define a flight corridor,” said Manchester University’s Grant Allen.
“The models can’t give you enough information on where the cloud will be thick or thin.”
Weather balloons have revealed a 600m thick layer of ash at a 4km altitude, containing highly abrasive particles at concentrations of 300 micrograms a cubic metre. A typical jet engine would ingest 60-billion particles every second.
Conventional radar equipment on airliners cannot pick up volcanic ash clouds, but airliners could conceivably be fitted with laser systems to spot dangerous ash clouds in time for pilots to change course.
The United Kingdom’s Meteorological Office has tracked the ash plume using a geostationary satellite called Meteosat-9 that orbits above the equator. It uses infrared light to take snapshots, but can discern the cloud’s position only to within five to eight kilometres. It also cannot tell how thick the plume is at different heights.
Across the UK laser equipment used to monitor cloud cover has been adjusted to scan for ash. These light-detection and ranging facilities produce 3D maps of clouds that are accurate to within a few metres.
They give a clearer picture of the cloud’s size and position, but are too few to cover all British airspace. —