Volcanic Disruption

Readers may have noted in last week's ASW, that a Seattle landing Continental [CAL] 737 had reported flying through volcanic ash clouds that erupted after Mt. St. Helens unexpectedly let loose again on that day (March 8) - after 25 years of near dormancy. "There was an eruption at 5:25 p.m. local time (8:25 p.m. ET) and the cloud of ash is estimated at 36,000 feet (10,800 meters)," Rob Harper of the Washington State Emergency Management service told Agence France-Presse. "We are monitoring the situation."

It would appear that a scant few months after the Indian Ocean Tsunami, Mother Nature has yet again bested our warning systems. It's not known how long after the eruption the CAL 737 flew through the ash cloud, but one would have thought that a general broadcast on relevant regional frequencies may have been made by air traffic control and/or a timely SIGMET (Significant Meteorological Event) warning issued to airborne aircraft.

The U.S. Geological Service (USGS) Web site informs us that "under current eruptive conditions, small, short-lived explosions may produce ash clouds that exceed 30,000ft altitude and produce ash that can fall in trace amounts 100 miles or more downwind."

More than 80 commercial aircraft have unexpectedly encountered volcanic ash in flight and at airports in the past 15 years. Seven of these encounters caused in-flight loss of power, which nearly resulted in the crash of the airplane (see ASW, June 28, 2004). Heavy ash-cloud penetration of a primary plume will lead to an immediate deterioration in engine performance and probable failure. The principal cause of engine failure is the deposition of ash in the hot sections of the engine. Glass from melting volcanic ash will coat fuel nozzles, the combustor and turbine, which reduces the efficiency of fuel mixing and restricts air passing through the engine. This causes surging, flame out and immediate loss of engine thrust. Lighter ash depositions picked up from outside the primary and secondary plumes will also seriously erode moving engine parts, including the compressor and turbine blades, which will reduce the efficiency and thrust of the engine. Aircraft surviving an encounter with heavy ash will be severely damaged and forward facing transparencies will be somewhere between opaque and translucent, making landing a further hair-raising experience.

Explosive eruptions of Redoubt and Mt. Spurr volcanoes in Alaska in 1989-90 and 1992, respectively, highlighted the impact of ash clouds on aircraft operating in areas of active volcanism. Expanded monitoring by the USGS of volcanoes in the Alaskan Peninsula and the Aleutians and cooperative agreements with the National Oceanic and Atmospheric Administration (NOAA), the Federal Aviation Administration (FAA), and other agencies resulted. Vastly improved ash cloud-notification procedures were developed for the Volcanic Ash Advisory Centers (VAACs). The VAACs were established in September 1995 in Darwin, Australia, at a meeting of the International Civil Aviation Organization (ICAO).

At this meeting it was decided that to ensure that volcanic cloud hazards were addressed, there must be an interface between volcano observatories, meteorological agencies and air traffic control centers. In order to meet their goal they decided the world should be divided into different regions by their volcanic activity and volcano observatories in the designated regions would be in charge of keeping track of the activity in their areas by analyzing satellite imagery.

ASW observes that if an unalerted encounter can happen near Mt. St. Helens, it can probably happen anywhere in the world - and queries whether the alerting system is sufficiently keyed to the required hair-trigger status.