Ash clouds may affect aircraft engines and systems even at great distances from the volcano. Ash clouds due to volcanic eruptions on Iceland are causing considerable delay at European airports. Large parts of the airspace across North-western Europe have been closed and more will be closed this evening. In this fact-file, the NLR Air Transport Safety Institute provides background information about volcanic ash clouds and the safety of air traffic.
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Incidents due to ash clouds
Some five encounters between airliners and volcanic ash clouds are reported. Most probably, the actual number of encounters is somewhat higher as not all encounters are reported. Seven very serious incidents have occurred over the last 30 years, in which multiple engines failed. Three of the most important ones are:
- On 24 June 1982, a British Airways Boeing 747 entered the ash cloud of the eruption of the Galunggung volcano in Indonesia. The flight was at an altitude of 11 kilometres at the time, some 130 miles Southeast of Jakarta. All four engines failed. Only after 13 minutes of powerless descent the crew succeeded in relighting three of the engines. Although the cockpit windscreens were severely damaged, the flight landed safely at the airport of Jakarta.
- Two weeks later, on 13 July 1982, a Singapore Airlines Boeing 747 entered the ash cloud of the same eruption. Serious damage to the aircraft occurred and three of the four engines failed. Eventually, the aircraft landed on two engines, also with heavily damaged windscreens.
- On 15 December 1989, a KLM Boeing 747 underway from Amsterdam to Anchorage flew into the ash cloud caused by the eruption of the Mount Redoubt volcano. All four engines failed, as well as many aircraft systems including part of the cockpit instruments, and the emergency electrical system. After many attempts all four engines could be re-started after loosing some 12,000 ft of altitude. The aircraft landed safely at Anchorage, but damages to the aircraft and engines amounted to some thirty million US$.
More recently (21 March 2010), an Icelandair Boeing 757-200, underway from Seattle (USA) to Keflavik (Iceland), had to divert to Boston about halfway into the flight due to an eruption of a volcano at the Eyjafjallajokull glacier in the South of Iceland. Due to the eruption all airports in Iceland had to be closed.
What is being done to manage the risk related to ash clouds
Since the occurrence of the serious incident in the Eighties, considerable international effort to better manage the risks of volcanic ash has led to considerable improvements. Some of the main safety measures taken are:
 A global network of nine Volcanic Ash Advisory Centres (VAAC) has been set up. These centres monitor volcanic activity and in case of important eruptions, they send out a special warning message (Volcanic Ash SIGMET). The messages are then entered into the so-called NOTAMS (Notice to Airmen) that are aircrews receive before flight. The operations centres and planners of airlines also receive this information and may decide to re-plan or cancel flights. The VAAC also monitor the movement of ash clouds through the atmosphere and provide forecast of the movement of the clouds. This is very important because ash clouds may travel great distances and may still pose a threat at considerable distance from the point of eruption. There are known cases of engine failure due to volcanic ash at some 600nm distance from the volcano, and encounters affecting engine performance at some 2400nm from the point of eruption.
ICAO, the International Civil Aviation Organisation, together with many international partners has set up a Volcanic Ash Manual which describes among others, how the information collection and distribution regarding volcanic eruptions and ash clouds must be organised, and how aviation authorities and airlines should prepare for and deal with volcanic ash hazards.
The US aviation authority FAA has developed a video to train air traffic controllers in dealing with volcanic ash events.
Aircraft manufacturers have prepared information, procedures and training videos to assist airlines and aircrew in preparing for volcanic eruption hazards.
Airlines, particularly those operating into areas of frequent volcanic activity, provide (simulator) training to their pilots on how to deal with ash clouds, both regarding avoidance of encounters as well as regarding the appropriate action to be taken in case of an inadvertent encounter of ash clouds.
Why do ash cloud incidents still occur?
The prediction of the transport of volcanic ash clouds through the atmosphere always involves some uncertainty. Also, lines of communication for ash cloud information may occasionally still be less than adequate. Moreover, visual detection of ash clouds by the cockpit crew is not always possible, for example when ash concentrations are low, when ash cloud are embedded in normal cloud, or when operating at night, when it is dark. Ash clouds are not shown on the onboard weather radar because the ash particles do not sufficiently reflect radar energy.
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