Could aircraft dodge the volcanic ash cloud? (BBC)

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Could aircraft dodge the volcanic ash cloud?

By Mulvey, BBC News

If the 1820s are any guide, the volcanic ash from Eyjafjallajokull could be with

us for a while - so can we find ways of flying around or under the cloud?

The last time it erupted, in December 1821, it continued puffing out ash for

about about a year, on and off. So, if the pattern is repeated, ash clouds can

be expected to waft across Europe every time there is a sustained north or west

wind.

That means a lot of disrupted travel plans, unless airlines can learn to

navigate a safe path through or around the obstacles.

However, while this may be technically possible, experts say it is not a

practical solution.

Lidar

The current combination of high pressure and a northerly wind has created what

atmospheric scientist Professor Geraint Vaughan likens to a " pile of poppadoms "

in the air above us.

Using a cousin of radar, known as lidar, he is able to pick out thin layers of

fine ash at different heights in the atmosphere above Aberystwyth, in Wales.

On Tuesday, a lidar instrument is being taken on a Met Office BAe 146 jet

aircraft to get a picture of the " highly-laminated structure " of the atmosphere

across the UK.

The pilot will be able to use it to find an ash-free altitude to fly at - though

the plane may need to fly through some ash to get there.

" We can measure where the ash is, at what heights, and the thickness of the

layer, " says Professor Vaughan. " We have learned it's at all kinds of heights,

from about 1km to the aircraft-cruising altitude of 10km-12km. "

So, would one solution to the problem be to add lidar to the controls on a

commercial aircraft and allow pilots to dodge the ash?

Absolutely not, says the Civil Aviation Authority (CAA).

Going under?

" You would massively increase the dangers of a collision, " says CAA spokesman

.

" The whole point of flying in controlled airspace is that pilots are under the

control of an air traffic controller. He tells them what altitude to fly at, to

ascend or descend a couple of thousand feet, to get out the way.

" You cannot take that responsibility away from air traffic control. The pilot

cannot see what's around him, air traffic control can. "

What about flying under the ash? Some European airlines have conducted

low-altitude test flights and claim to have experienced no problems.

Professor Vaughan's observations make clear that there is no altitude at which

aircraft are guaranteed to avoid ash.

Also, at very low altitudes, the air contains a range of fine particles that it

is best for jet aircraft to avoid.

Kjetil Toerseth, director of regional global pollution at the Norwegian

Institute for Air Research, told the AFP news agency: " There is no altitude that

is completely safe below 11,000m. "

But that is only part of it.

A British Airways spokesperson said flying at low-altitude would only be an

option for short-haul flights, because of the vastly increased fuel consumption.

" You could not do it across the Atlantic... Cruising at 35,000 feet the

fuel-burn is very low, because the air is thin. You could not load enough fuel

to fly at low altitude, " the spokesperson said.

She added: " If everyone flew at low altitude, there would not be enough room in

the sky. "

Hard slog

Flying round the ash cloud - another option - is complicated by the fact that it

cannot be seen.

Satellites only show dense ash, and you cannot judge its altitude.

Using computers to model the likely drift of the cloud, as experts have been

doing in Europe for the last few days, gives only an approximate location.

at the CAA said a more feasible solution to the problem, in the

long-term, would be to make changes to aircraft engines.

" We are talking to manufacturers at the moment. They are reviewing their policy

on how much ash they think it's safe for engines to ingest, and they are

preparing to build into the design process more robust measures for ingesting

ash, " he said.

Learmount, operations and safety editor of Flight International magazine,

also argued that the vital next step was to gather more information about the

effect of widely dispersed very fine ash particles on engines.

" Is there a silver bullet? Absolutely, definitely not, " he said.

" It's going to be a hard slog. We have to send as many aircraft up there as

possible - without passengers - to find out what we don't know. The airlines

that carried out test flights say they had no problems, but how do they know

they didn't get lucky?

" When the weather changes the ash will go away, but we must not forget it,

because it will come back. "

http://news.bbc.co.uk/2/hi/8632583.stm