Airborne volcanic ash; a global threat to aviation

U.S. GEOLOGICAL SURVEY—REDUCING THE RISK FROM VOLCANO HAZARDS

The world’s busy air traffic corridors pass over or downwind of hundreds of volcanoes capable of hazardous explosive eruptions. The risk to aviation from volcanic activity is significant—in the United States alone, aircraft carry about 300,000 passengers and hundreds of millions of dollars of cargo near active volcanoes each day. Costly disruption of flight operations in Europe and North America in 2010 in the wake of a moderate-size eruption in Iceland clearly demonstrates how eruptions can have global impacts on the aviation industry. Airborne volcanic ash can be a serious hazard to aviation even hundreds of miles from an eruption. Encounters with high-concentration ash clouds can diminish visibility, damage flight control systems, and cause jet engines to fail. Encounters with lowconcentration clouds of volcanic ash and aerosols can accelerate wear on engine and aircraft components, resulting in premature replacement. The U.S. Geological Survey (USGS), in cooperation with national and international partners, is playing a leading role in the international effort to reduce the risk posed to aircraft by volcanic eruptions.

Volcanic eruptions pose a serious hazard to aviation when highly abrasive, pulverized rock debris (ash) and gas are ejected explosively into the atmosphere and dispersed over long distances. Worldwide, more than 100 reported encounters of aircraft with volcanic ash have resulted in hundreds of millions of dollars in damage and, in three dramatic cases, caused the near loss of wide-body passenger jets. For aircraft to avoid encounters with volcanic ash, air traffic controllers, pilots, and dispatchers must be rapidly notified when explosive eruptions occur and ash is in the atmosphere.

In cooperation with national and international partners, the U.S. Geological Survey (USGS) Volcano Hazards Program is playing a leading role in the global effort to reduce the risk of aircraft encounters with ash through timely eruption forecasts and warnings, education about the hazard, and scientific investigation of volcanic processes and ash-cloud properties. Hundreds of active volcanoes around the globe have the potential to severely affect aviation operations, and each year dozens of these volcanoes erupt explosively. On a global basis, volcanic ash is a daily concern to aviation. Volcanic ash clouds are carried by prevailing winds and can drift in different directions at many flight levels for thousands of miles from the erupting volcano. The hazard is complicated by the fact that ash and aerosol clouds from volcanoes can remain aloft at cruise altitudes for days to weeks. These clouds are difficult to distinguish visually from weather clouds and are invisible to air traffic control and aircraft radar. Volcanic activity can also have serious impacts on lowaltitude aircraft and on airport operations.

Hazards and Risks

Volcanic ash consists of small (less than 2 mm or 0.08 inch across) solid, sharp-edged fragments of quickly cooled volcanic glass and minerals blasted at high velocity into the atmosphere during explosive eruptions. This material is abrasive and melts at the high operating temperatures of modern jet engines. When ingested into a jet engine, volcanic ash erodes turbine blades, and the melted ash can adhere to critical parts, causing engine failure (“flameout”). Any forward-facing surface of an airplane engulfed in a volcanic ash cloud is likely to be eroded, including the cockpit and forward cabin windows and

ONE AIRCRAFT’S HARROWING ENCOUNTER WITH VOLCANIC ASH

landing-light covers. Cockpit windows may become so abraded that pilots have a serious loss of forward visibility. Ash entering sensitive aircraft electronics can interfere with navigation and other onboard systems. As a result of electrical disturbances within the ash cloud, a flight crew may also lose the ability to transmit a distress call.

Sulfur and other gases released in large eruptions also affect aircraft and their occupants. Acidic aerosols formed by the hydration of these volcanic gases produce a corrosive mist that may cause respiratory problems for passengers and flight crews and accelerate deterioration of vulnerable aircraft components. Over a period of many years, such exposure can significantly increase aircraft maintenance costs. Chronic “degassing” of nearby volcanoes upwind of airports can also affect ground operations or even close airfields for years.

Volcanic ash and aerosol clouds above airports and ash falling on and near airports can be hazardous to aircraft on approach and departure, as well as to operations on the ground. Ash on runways reduces braking effectiveness of aircraft, and wet ash is extremely slippery. The fine particles can be resuspended by surface winds and airport ground operations until removed from the tarmac, an expensive and difficult pro-

VOLCANIC ASH CAN IMPACT AIRPORT OPERATIONS

cess. When an airport is closed or operations curtailed because of the presence of ash, significant and costly disruptions result, including the loss of required alternate landing sites for aircraft aloft. This is particularly a concern for twin-engine aircraft operating under ETOPS (Extended-range Twin-engine Operational Performance Standards) flight rules on oceanic flights.

Development of U.S. and International Warning Systems

In response to in-flight engine failure incidents in 1982, the International Civil Aviation Organization (ICAO) created the International Airways Volcano Study Group, which later became the International Airways Volcano Watch program (IAVW). A major goal of the IAVW is to improve global ash detection and warning systems for air traffic controllers, dispatchers, and pilots. Major accomplishments of the IAVW include development of standards for in-flight ash warning messages from the worldwide system of Meteorological Watch Offices and the creation of nine Volcanic Ash Advisory Centers in the mid-1990s. The eruptions of Redoubt (1989–90) and Mount Spurr (1992) volcanoes in Alaska, both of which had a profound impact on regional aviation operations, prompted significant growth of the Alaska Volcano Observatory (AVO), increased monitoring along the Aleutian chain, and development of the first Interagency Operating Plan for Volcanic Ash Episodes. The United States has recently strengthened the ash-cloud warning program for aviation within its airspace by preparing a National Volcanic Ash Operations Plan for Aviation. This plan documents responsibilities, communication protocols, and hazard message formats for the Federal Aviation Administration (FAA), National Oceanic and Atmospheric Administration (NOAA), USGS, and the U.S. Air Force Weather Agency. The plan is available online at http://www.ofcm.gov/p35-nvaopa/pdf/FCM-P35-2007-NVAOPA.pdf.

Role of the Aviation Community

Pilot education is a key factor in mitigating the hazard from aircraft encounters with volcanic ash. (continued on page 5)

Aviation Color Code Used by U.S. Geological Survey Volcano Observatories

EDUCATION AND COORDINATION

(continued from page 3) To address this, a consortium of pilot organizations, the FAA, aircraft manufacturers, and other aviation interests have developed and promoted operating procedures for flight crews whose planes inadvertently enter a volcanic ash cloud. This guidance is now part of flight crew training and emergency checklists for many airlines.

During a volcanic eruption, flight crews are important partners in disseminating warning information to keep aircraft safe. Often pilot reports are the first direct observations of a volcanic event. Details of such observations are of great help to volcanologists trying to interpret data from distant eruptions and to meteorologists and aviation managers who issue warn-

VOLCANIC ASH ADVISORY CENTERS (VAAC)

ings and may have to restrict air space. Flight crews can greatly assist in these efforts by relaying key descriptive information contained in the Volcanic Activity Report Form (VAR) to air traffic control (ATC) centers.

Communicating the Hazard—The Aviation Color Code and the VONA

Volcano observatories provide important volcano hazard information for meteorological and aviation authorities who are responsible for issuing SIGMETs (advisories of Significant Meteorological information), NOTAMs (Notices To Airmen), and other warning products. Airlines can use warnings of impending or ongoing volcanic activity to select safe and efficient routes that avoid ash-contaminated airspace. In 1990, USGS scientists at AVO developed a four-color alert system for volcanic activity. This system was used to quickly inform the aviation community about the severity of hazard and level of activity at a volcano. ICAO has adopted a modified version of this color code system as the recommended guideline for volcano observatories worldwide. A change in the color code (either up or down) or a significant change within a color code prompts USGS volcano observatories to issue a specialized message for aviation users called a VONA—Volcano Observatory Notice for Aviation—that summarizes hazard information for pilots, aviation managers, controllers, and dispatchers in concise text.

The Future

The worldwide growth of air traffic, especially in volcanically active regions such as the Pacific Rim, means that volcanic ash will remain a serious hazard to aviation. Furthermore, the expected introduction of “free-flight” air traffic operations by the FAA and increased use of twin-engine aircraft across remote areas of the planet (areas having few alternate landing sites) make timely detection and reporting of eruptions, ash-cloud movement, and anticipated ash fall essential to

REMOTE SENSING OF VOLCANIC ASH CLOUDS

flight safety. The 2010 Icelandic eruption highlighted this and many other remaining challenges facing safe and efficient aviation operations during an explosive volcanic event.

Keys to reducing the risk to aviation are (1) increased ground-based volcano monitoring (only a very small percentage of volcanoes that threaten aviation are currently considered well-monitored with modern instrumentation) and improved eruption forecasts; (2) development of new and improved tools and techniques to detect, track, and characterize volcanic clouds that are a hazard to aviation; (3) improved forecasting of ash-cloud movement and expected ash fall; (4) research and education to better quantify and build awareness of the hazard; and (5) refinement of protocols to ensure rapid communication of ashhazard warnings to flight crews. Scientists in the USGS Volcano Hazards Program are continuing to work with national and international partners to accomplish these goals and improve flight safety and efficiency around the world.

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