A KLM Boeing 747-406M PH-BFC is damaged after encountering ash cloud from Mt Redoubt in Alaska in December 1989. (Bauhaus345/Wikimedia Commons)

The travel chaos and dislocation for millions of passengers caused by the ash cloud from the eruption of Iceland’s Eyjafjallajökull volcano in April 2010 sent shockwaves around the world and shudders through airline boardrooms and no doubt in the corridors of political power.

Just one small eruption closed down Europe’s airspace for four days as scientists and meteorologists grappled with the danger of the cloud to aircraft against a background of limited industry consensus on the issue.

According to the International Air Transport Association (IATA), its member airlines lost over US$1.7bn (A$1.8bn), with 70,000 flights cancelled and 313 airports closed.

ICAO suggested “input of the aviation industry to this problem may have to be sought” through its sub-group on volcanoes, which has industry representatives. During the crisis, airlines were proposing daylight flights, restrictions to specific flight corridors, special climb and descent procedures and more frequent detailed boroscopic engine inspections to detect damage, but to no avail.

At the same time, doubts were fuelled by volcanic ash encounters for a Finnish Air Force F/A-18 and NATO F-16s.

There was also suspected volcanic ash damage to a World Airways MD-11 flying from Maastricht to Ostend-Bruges, and a Thomas Cook 757 was forced to return to Manchester due to the loss of compressor bleed air from one engine after crew sensed a smell of volcanic ash during the climb.

Australian Aviation has listened to ATC tapes of the Thomas Cook 757, G-JMCF, on a positioning flight as TCX952P, with pilots describing the intense smell of volcanic ash.

Volcanic ash, which is invisible to aircraft weather radar and undetectable at night, has proved deadly to aircraft. An aircraft’s jet engines are like giant vacuum cleaners and suck in the ash at near-supersonic speeds, magnifying the damage.

The deposits coat the fuel system’s temperature sensors, creating a false and lower temperature reading. The two most famous encounters with volcanic ash involved 747s, one a British Airways flight over Indonesia in 1982 en route to Perth from Kuala Lumpur, and another involving a 1989 KLM flight en route from Amsterdam to Anchorage.

When Mt St Helens erupted in 1980, a 727 and a DC-8 encountered separate ash clouds. Over the course of several eruptions the volcano ejected 10kmof material, making it the second biggest eruption of the 20th century. There were 20 volcanic ash encounters with aircraft. The second zone included areas where some ash may be present but generally not enough to affect aircraft systems, or around which aircraft can fly and where partial flight restrictions were allowed.

The eruption of Iceland’s Eyjafallajökull volcano brought into sharp focus how much we depend on aircraft and how important a benign natural environment is to the industry.

“The ash cloud has provided an unplanned social and economic experiment, with airlines again at the epicentre”, says Harbison.

Over the past 1,000 years all three known eruptions of Eyjafjallajökull have triggered eruptions at the far more dangerous Katla which has a crater diameter of 10km, with eruptions of Eyjafjallajökull in 1612 and 1823 quickly followed by much larger eruptions of its neighbour.

Collected and summarized from the source below by Minh Pham