Iceland volcano pours out more ash Monday as airlines pressure regulators to open Europe's skies

According to CNN, "The eruption of an Icelandic volcano, which had slowed in recent days, strengthened Monday, spewing a new cloud of ash that officials said was heading toward the United Kingdom, possibly posing a renewed threat to air travel."

The photo at right was taken early Monday afternoon by ESA’s Envisat satellite.  It shows a heavy plume of ash from the Eyjafjallajoekull Volcano.  The new plume is 400km long.

Meanwhile European airlines are touting the results of "test flights" that apparently show no damage to engines.  On Lufthansa's recent test flight the pilot scrupulously avoided any area known to have heavy concentrations of ash.  Such tests prove nothing.

The truth is that it's hard -- if not impossible -- to know where the hazardous ash will be encountered in high concentration, as one aviation expert explains:

"While it remains possible to find clear air high above us, this doesn't necessarily mean there are no pockets of high concentrations of ash at the various flight levels," Mr Yates said. "I would therefore suggest it's better to err on the side of caution."

An incident involving the flight of a NASA DC-8 in 2002 revealed that 1) ash clouds themselves can be impossible to detect and 2) that severe damage to aircraft engines may not be readily apparent:

A study of the incident by researchers at NASA's Jet Propulsion Laboratory published in 2002 notes that satellites failed to pick up evidence of ash at the point where the DC-8 encountered it; instead it indicated cirrus clouds...

Once the crew landed, a cursory inspection of the engines and the plane's exterior showed no evidence of an encounter with volcanic ash. Technicians at the site didn't have sophisticated inspection gear at their disposal, so the plane was pronounced fit....  [readings from in-flight instruments] did not reveal a problem, yet hot section parts may have begun to fail [through blade erosion] if flown another 100 hours,"...

The fact that airlines may have successfully pressured regulators to partially open Europe's skies Tuesday, is no guarantee that it's safe to fly.