Volcanic ash, invisible to weather radar, presents serious danger to aircraft
Monday April 19, 2010
There have been 90 incidents over the last 30 years in which aircraft have encountered volcanic ash, invisible to weather radar and totally undetectable at night, and several of the encounters created very dangerous situations.
Made up of pulverized rock and glass, the ash gets into virtually every aircraft system and can paralyze engines in minutes. The ash turns molten in a jet engine's combustion chamber and melds with moving parts like spray paint. It blasts cockpit windows, compromising visibility in seconds, and also clogs vital speed sensors, rendering an aircraft's flight computers almost useless. The deposits additionally coat the fuel system's temperature sensors, creating a false and lower temperature reading that causes the automatic monitoring system to pour in more fuel. This makes the engine dangerously hot, damaging the turbine and potentially leading to a shutdown.
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. In both cases, all of the engines failed and eventually were restarted at much lower altitudes but later were scrapped because of the damage. The KLM 747's environmental control system was replaced, its fuel tanks were cleaned and the hydraulic systems needed repair.
When Mt. St. Helens erupted in 1980, a 727 and a DC-8 encountered separate ash clouds. Both experienced damage to their windshields and several systems but both landed safely despite the damage.
The increased availability of satellites and the technology to transform satellite data into useful information have reduced the number of volcanic ash encounters. But extensive ash clouds, such as the one now hovering over Europe, still present an enormous challenge.
In 1991, Mount Pinatubo on the island of Luzon in the Philippines erupted just 90 km. northwest of Manila. Over the course of several eruptions, the volcano ejected 10 cu. km. of material, making it the second-biggest eruption of the 20th century. There were 20 volcanic ash encounters with aircraft. Despite the more advanced ability to predict where ash could be found, the wide extent of the ash cloud made it difficult to avoid.
The eruption of Mt. Popocatepetl in Mexico in 1997 and subsequent intermittent eruptions forced the Mexico City airport to close multiple times for up to 24 hr.
Scientists working with the University of Iceland suggest it is a distinct possibility that the Eyjafjallajokull volcano will continue to erupt on and off for months to come, as occurred during the last eruptive period in 1821-1823.
by Geoffrey Thomas
http://www.atwonline.com/news/story.html?storyID=20058
Monday April 19, 2010
There have been 90 incidents over the last 30 years in which aircraft have encountered volcanic ash, invisible to weather radar and totally undetectable at night, and several of the encounters created very dangerous situations.
Made up of pulverized rock and glass, the ash gets into virtually every aircraft system and can paralyze engines in minutes. The ash turns molten in a jet engine's combustion chamber and melds with moving parts like spray paint. It blasts cockpit windows, compromising visibility in seconds, and also clogs vital speed sensors, rendering an aircraft's flight computers almost useless. The deposits additionally coat the fuel system's temperature sensors, creating a false and lower temperature reading that causes the automatic monitoring system to pour in more fuel. This makes the engine dangerously hot, damaging the turbine and potentially leading to a shutdown.
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. In both cases, all of the engines failed and eventually were restarted at much lower altitudes but later were scrapped because of the damage. The KLM 747's environmental control system was replaced, its fuel tanks were cleaned and the hydraulic systems needed repair.
When Mt. St. Helens erupted in 1980, a 727 and a DC-8 encountered separate ash clouds. Both experienced damage to their windshields and several systems but both landed safely despite the damage.
The increased availability of satellites and the technology to transform satellite data into useful information have reduced the number of volcanic ash encounters. But extensive ash clouds, such as the one now hovering over Europe, still present an enormous challenge.
In 1991, Mount Pinatubo on the island of Luzon in the Philippines erupted just 90 km. northwest of Manila. Over the course of several eruptions, the volcano ejected 10 cu. km. of material, making it the second-biggest eruption of the 20th century. There were 20 volcanic ash encounters with aircraft. Despite the more advanced ability to predict where ash could be found, the wide extent of the ash cloud made it difficult to avoid.
The eruption of Mt. Popocatepetl in Mexico in 1997 and subsequent intermittent eruptions forced the Mexico City airport to close multiple times for up to 24 hr.
Scientists working with the University of Iceland suggest it is a distinct possibility that the Eyjafjallajokull volcano will continue to erupt on and off for months to come, as occurred during the last eruptive period in 1821-1823.
by Geoffrey Thomas
http://www.atwonline.com/news/story.html?storyID=20058
