Why is Volcanic Ash so dangerous for aviation?

Air operations are exposed to different hazards during their operation. For this reason, procedures must be provided to ensure safety at all times. Sometimes some of these dangers are invisible or even undetectable. Such is the case with volcanic ash. This has generated several setbacks and some incidents, such as the Boeing 747s (British Airways in 1982 and KLM in 1989), where their four engines were turned off simultaneously during the flight. Since then, procedures have been enacted to mitigate the risk posed by flying over the airspace near an active volcano.

Volcano erupting. Photo: Wikimedia Commons.

During a volcanic eruption, large amounts of material can be expelled into the atmosphere reaching high altitudes and representing a danger to aviation. These particles are undetectable by meteorological radars due to their size and that most of these radars concentrate on detecting water particles.

What at first glance looks like a cloud, could hide a serious danger in its composition. Volcanic ash is made up of glass-like particles. Despite their tiny size, they are sharp and hard particles, giving them impressive abrasion power. Due to their chemical composition, they melt at a temperature lower than the internal temperature of the engines. This easily turns it into a liquid as it is inside the combustion chambers.

The presence of suspended particles in the atmosphere (haze), such as dust, sand and volcanic ash can be detected with the naked eye depending on their concentration. Therefore, before a flight, it should be observed if there is presence of clouds or haze that may contain ash inside.

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During a flight, it is possible to detect that an aircraft has entered a volcanic ash cloud when one of the following events exists:

  • The crew or passengers smell a smell of smoke or sulfur
  • Inner calm. Due to the size of the ash particles, it is possible for it to pass through the aircraft’s air filters, introducing particles that cloud the view into the cabin. Or, “dust” may accumulate on the surfaces.
  • Variable motor parameters. Explosions, changes in the internal temperature of the motor and / or extinction of the flame may occur.
  • Variable airspeed. Ash particles can block pressure measuring instruments (such as the Pitot tube or static ports). Therefore, the reading will be incorrect.
  • Static energy discharge. A phenomenon similar to the “San Telmo fire” may occur where some blue sparks appear to rise outside the windshield or a glow may appear on the front surfaces of the aircraft.
  • Possible failure of pressurization and air conditioning systems due to ash accumulation in filters and ducts. After an encounter with volcanic ash, a comprehensive review of these systems should be performed.

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Any of these indicators should be a reason to alert the crew of a possible encounter with volcanic ash where appropriate measures must be taken to preserve the safety of the flight. Currently there are constant monitoring of active volcanoes and modeling software that predict the dispersion of ash according to the prevailing wind. These models and forecasts are published for the purpose of safe flight planning. All this information must flow effectively between air navigation services, aeronautical information services, meteorological service providers, aeronautical authorities and aircraft operators.

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The behavior of a volcano is unpredictable. Therefore, the risk of a volcanic ash encounter should be reduced by planning and collecting existing information. For this, among other types of notifications, ASHTAM is used.

Quito International Airport on November 3, 2002, after the eruption of the Reventador Volcano. Photo: Hugo Yepes.

In addition to reporting in METAR, SIGMET and NOTAM’s, there is also a specific report for volcanic ash called ASHTAM. This report indicates the current situation of a volcano when it has unusual activity and that can affect air operations. It expresses the level of alert, presence of ash, extent of movement, air routes and flight levels affected. It is valid for 24 hours.

Volcanic ash represents a significant risk to air operations. It is best to avoid it completely. Properly planning a flight with all the available information is the best way to preserve our safety.

Photo: Augustine Volcano in Alaska by Crateau Edward. Wikimedia Commons

  • author's avatar

    For: Uri Luna

    Eng. In Aeronautics and Commercial Pilot, passionate about airplanes and outer space. In his spare time, he is a swimming, travel and food enthusiast.

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