Volcanic Ash Hazards to Airliners

Between 1980 and 2004, more than 100 jet aircraft sustained damage after flying through volcanic ash clouds. The repairs cost more than $250 million. At least 7 of these encounters resulted in temporary engine failure, with 3 aircraft losing power from all engines. These engine failures have occurred at distances ranging from 150 to 600 miles from the erupting volcano. Aircraft damage from these volcanic ash encounters has been reported from as far as 1,800 miles from the volcano.

Two passenger airline flights involving temporary failure of all four engines on Boeing 747s highlight the hazards of volcanic ash in flight.

On the night of June 24, 1982, a British Airways Boeing 747 suffered a temporary four-engine flameout after flying through the otherwise undetected ash plume from Indonesia's Mt. Galunggung. The airplane descended from 37,000 feet to about 14,000 feet over the ocean before the flight crew was able to restart two engines. They later started the other two, but re-entered the ash cloud and had to shut down one engine after it began backfiring and shaking violently.

On Dec. 15, 1989, a KLM Boeing 747 flew into the ash plume from Alaska's Mt. Redoubt and similarly lost power from all four engines within less than a minute. The pilots were able to restart the engines, but could not obtain full power. The pilots landed the airplane safely at Anchorage despite their windshield being sandblasted so badly that they could only see out of a small portion of it.

The principle danger to jet airplanes from volcanic ash-small, hard particles that may stay aloft for weeks-is that the hot gases inside the engines may melt the ash, which then resolidifies or "ceramitizes" in the engines, altering airflow and plugging cooling vents in critical engine parts.

Volcanic ash also damages windshields, windows, and external probes that tell pilots their airspeed and altitude, and can ruin antennae for communication and navigation radios. Ash can almost instantly contaminate onboard electronic equipment, air conditioning, equipment cooling systems, the fuel system, and hydraulic systems that move flight controls and extend landing gear. The KLM Boeing 747 suffered all this damage, and more, costing the airline $80 million.

The threat to air transportation posed by volcanic ash has increased in recent years because of two factors: (1) increased volcanic activity worldwide (the jet age began during a period of relative inactivity of volcanoes worldwide) and (2) increased traffic in geographic areas at higher risk for volcanic activity.

The North Pacific averages 5-6 eruptions per year, with ash at flight levels on 4-5 days per year. During an additional 10-12 days per year, ash clouds are estimated to be close enough to flight routes to be a concern to aviation. These empirical estimates are based on historical records compiled and analyzed by the USGS.

What needs to be done? Nine Volcanic Activity Advisory Centers (VAACs) have been established worldwide to detect volcanic activity and disseminate information about it to the aviation community in a timely manner. Despite this important step having been taken, airlines have suffered significant financial losses caused by volcanic ash encounters in VAAC areas since their inception. The VAAC structure must be strengthened. Government agencies must continue to adequately fund both satellite-based and ground-based systems for detecting volcanic eruptions that threaten the safety of the flying public.

Airlines need accurate, detailed information about a volcanic eruption within 5 minutes after it occurs. In that first 5 minutes, the ash cloud can rise to the altitudes at which airliners fly. The explosive eruption of Mount St. Helens on May 18, 1980 topped 80,000 feet, and the ash plume was climbing through 60,000 feet-higher than all airliners fly-10 minutes after the eruption.

A turboprop airplane, flying at 250 miles per hour, could approach a volcanic ash cloud at 4 miles per minute; a Boeing 747 at cruise altitude could close on the ash cloud at 10 miles per minute. The five-minute warning needed to allow flight crews to divert around the ash cloud is only possible with monitored volcanoes.

Cockpit weather radars do not detect or display ash clouds because of the small size of the ash particles and their low radar reflectivity. Visually identifying an ash cloud when it is dispersed can be difficult because the cloud takes on the characteristics of a normal weather cloud. Also, volcanic ash can be embedded in, or otherwise obscured by, normal weather clouds.

ALPA has worked closely with the U.S. Geological Service, the National Oceanic and Atmospheric Administration, the National Weather Service, airline managements, flight dispatchers, the academic community, and various international scientific and aviation organizations since the early 1980s to improve the airline industry's ability to deal with this risk to aviation safety. ALPA has been the exclusive voice of line pilots at both international symposia on volcanic ash hazards to aviation held during that time.

ALPA Contacts: John Mazor, Linda Shotwell, (703) 481-4440, media@alpa.org.