Experts call for further improvements in warning time and plume prediction
The ash must not hit the fan. The ash is hurled skyward by volcanoes. The effect on a modern fan-jet engine is akin to sandblasting. Encounters are expensive and potentially deadly.
Two factors raise the concern: more airplanes are flying, and their routes take them over or close to active volcanoes, many of which remain unmonitored, complicating early warning of eruptions.
A volcanic eruption can hurl tens of thousands of tons per minute of ash-like material and gases into the air. The 1992 eruption of the Spur volcano in Alaska ejected 300,000 cubic yards of material per minute into the atmosphere. The heated cloud can race skyward, reaching the cruising altitudes of jetliners in a matter of minutes. The safest mitigation strategy is to avoid flying into the plume, but avoidance requires knowledge of where the ash is airborne and where it’s drifting. The nature of the threat puts a premium on early detection and prompt advisories.
The “gold standard” is five minutes’ warning to operators from the moment of eruption. Today, the nominal time is on the order of an hour, but many volcanoes near air routes remain unmonitored, and even the five minute warning goal can be clouded by uncertainty. The challenge of achieving the five-minute warning was given a thorough airing at last week’s 2d International Conference on Volcanic Ash & Aviation Safety in Washington, D.C.
The facts are that while nature appears constant, in terms of man’s short-term time reference, potential encounters with volcanic ash are on the rise. A few statistics paint the picture:
- Globally, volcanic ash clouds rise to cruising altitude about 11 times per year. This number is considered a low estimate, given gaps in reporting of volcanic activity, and the fact that clouds and nighttime conditions can mask detection.
- About 300 flights per day carry roughly 10,000 passengers over the Ecuadorian volcanic corridor, according to Hugo Yepes of Ecuador’s Instituto Geofisico. The November 2002 eruption of El Reventador hurled ash up to 60,000 feet, which spread in two directions from wind shearing, threatening aviation routes for thousands of square miles.
- About 475 airports are located within 100 kilometers (62 miles) of volcanoes that have erupted since 1900. Over the last 60 years, volcanic activity disrupted operations 108 times at 75 of those airports.
- There are some 100 active volcanoes dotting the Northern Pacific region, where air traffic has grown greatly in recent years. There are more than 200 airline flights per day flying downwind of those volcanoes, putting tens of thousands of passengers and millions of dollars of air cargo at risk every day, according to Tom Miller of the U.S. Geological Survey (USGS).
- On average, about four to five eruptions will occur annually among these Northern Pacific volcanoes. Ash from these volcanoes will rise to contaminate air routes above 30,000 feet about four to five days per year.
- An average of five advisories of volcanic activity are issued daily to the world’s aviation community.
Vulnerable to volcanism
Encounters with volcanic plumes are rather like in-flight icing. The pilots may be unaware that they’ve penetrated an ash cloud, and the effects can range from immediate to delayed. The physical effects include erosion of paint and windscreens, eroded leading edges of engine fan blades, clogged cooling holes in engines, buildup of a glasslike material in the hot section (engine core temperatures being hot enough to melt the ash), and clogged pitot tubes (with conflicting/erroneous airspeed readings), failed flight management computers, electronic engine control failures, cockpits filled with volcanic dust, and multifarious other effects. For example, repeated exposure to volcanic gases, such as sulfur dioxide, can create acids when combined with water vapor that adhere to the aircraft’s skin and penetrate microcracks in the metal, causing structural deterioration. Ash particle in the air conditioning system can abrade ductwork and clog filters.
In the worst case, engines can fail outright. Capt. Eric Moody of British Airways [BAB] was the first to experience a total engine failure from volcanic activity on a night flight 22 years ago. On his four-engine B747, Moody had five engine shutdowns in 20 minutes (having to shut down one badly damaged engine after a successful in-flight restart). Moody said the sulfur dioxide and carbon dioxide in an ash cloud could starve the engines of oxygen, the ash can make the air less compressible, and the glasslike contamination can gum up the inner works. After an unpowered glide to an altitude below the bottom of the ash cloud, Moody was able to restart his engines and make a successful emergency landing at Jakarta.
Two other B747s have experienced total engine loss and last-minute recovery from encounters with ash clouds, and seven cases of partial temporary engine failure have been recorded. Repairs have been costly, to include total engine change-outs costing millions of dollars per engine. So far, no aircraft have crashed from these ash cloud encounters. Better yet, since the early 1990s there have been no cases of in-flight engine failures from ash encounters. Faster alerting has helped. Today, a worldwide network of nine volcanic ash advisory centers (VAACs) provides warning of eruptions, and these are translated into reports of significant meteorological activity (SIGMETS). Nonetheless, Charles Groat, USGS director, warned, “We can’t be complacent.”
Aircraft continue inadvertently to penetrate volcanic ash clouds. One case shows that the effects may not be immediate, but can be costly. In February 2000 an instrumented DC-8 operated by the National Aeronautics & Space Administration (NASA) encountered a thin cloud of ash while flying some 200 miles north of Iceland’s Hekla volcano. Aware that the volcano was active, the flight route had been planned to fly well north but the ash was encountered anyway. “We saw nothing,” pilot Frank Burcham said. Because the research airplane was heavily instrumented, “we were well aware of what happened,” he recalled. Upon landing in Sweden after the long flight from Edwards AFB in California, the airplane appeared undamaged. Upon return to Edwards two weeks later, the engines were inspected in detail, and significant damage was found. Leading edge coatings on engine blades were eroded, cooling holes were plugged with ash, and ash was built up in convoluted portions of the engine airways. NASA’s Tom Grindle said that 7-minute encounter caused $3.2 million in damage. “Even diffuse or ash-poor clouds can cause costly damage that won’t show up right away,” he cautioned. In this case, he said, “Significant damage was buried in the engines. The ash can take a 4,000-hour hot section down to 50 hours [between overhaul] and it will manifest a week later.”
The Federal Aviation Administration (FAA) does not require carriers to perform maintenance checks on aircraft that have come in contact with an ash cloud.
Given the insidious nature of the threat, and the fact that a volcanic ash cloud will not appear on an airplane’s weather radar, avoidance is key. That gambit imposes costs, too. Leonard Salinas, manager of dispatch flight safety and operations at United Airlines [UALAQ], said his airline imposes a 200 NM separation from ash clouds, maybe a bit less if the planned flight is on the upwind side of the plume. The avoidance can create a need to carry up to 45 minutes of additional fuel or an enroute stop for additional fuel and avoidance.
Volcanic activity affects the airline’s planning for ETOPS (extended range operations). For example, if a potential alternate airport is threatened by an oncoming ash cloud, or it already has had a layer of ash dumped on it, the airport is considered unusable for ETOPS planning purposes.
As far as airport operations generally, Salinas said flatly, “If there’s any ash at all [on the airport], we’re not operating.”
When New Zealand’s Ruapehu volcano erupted, airspace closures in 1995-1996 cost airlines $10 million in direct costs, according to Peter Lechner of that country’s Civil Aviation Authority (CAA). In New Zealand, most of the international air flights arrive flying from northeast to southwest, while prevailing winds take ash clouds in a southwest to northeast direction – putting ash and airplanes on a collision course.
Given the potential for costly repairs and the potential for catastrophic damage leading to a crash, airlines today want better and more timely information of volcanic activity. “A few years ago, the airlines’ only concern was when, where and how high?” said Tom Miller, emeritus scientist of the USGS’s Alaska Volcano Observatory. “Now they want to know the ash content, where the cloud is going, and how long it will be present.”
Don’t dally
Above all, there’s a high interest in quick notification of volcanic activity. The goal is to provide notice of an eruption within five minutes. The genesis of this five-minute goal is embedded in the May 1980 explosion of Mt. St. Helens in Washington state. The eruption hurled an enormous cloud of ash and gas into the air. Rushing upward at 5,000 feet per minute, the plume was at aircraft flight levels in five minutes, at 30,000 feet within six minutes, and it had risen to 40,000 feet within eight minutes.
“This is why the five-minute warning is so important to us,” said United’s Salinas. If the explosion were to occur today, more than two dozen aircraft could be caught in the circle defining the extent of the shock wave and ash. “The clock keeps on ticking, the animal will be growing and spreading,” Salinas added, by way of pointing out the need for quick alerting.
But the five-minute goal raises a number of challenging questions. What seems a simple mandate may not be so straightforward.
The prediction problem
For the five-minute warning, at what point does the clock start ticking? From the seismic measure of an eruption, or from the time of visual confirmation?
Various officials expressed the concern that false alarms and resulting airspace closures could set the early-warning program back five years or more.
Is it possible to forecast eruptions before gas and ash get into the air? Gas trapped in the magma propels it skyward, but the biggest uncertainly is determining the extent of trapped gas in the magma, said Chris Newhall of the USGS’s Seattle, Wash., office.
Winds blowing in different directions can distort the plume, causing it to drift with the wind on one path at lower altitude, and in the completely opposite direction at a higher altitude.
One of the biggest unknowns is the threshold concentrations of airborne ash and gas that pose a threat to aviation. The DC-8 that flew through the Hekla plume was damaged by “very small ash concentrations,” said Ren� Servranckx of Environment Canada.
He presented a display of ash cloud migration, in which the extent of the cloud depended critically on the particle concentrations selected for display.
Thus, even if the changing and oftentimes chaotic nature of ash dispersal in the atmosphere eventually can be predicted with confidence, the boundary of the ash cloud depends critically on the concentration of ash deemed a threat. – which presently is a huge unknown.
However, volcano scientists are sticking to their goal. “Total avoidance of ash clouds is desired – ‘zero tolerance’ for cloud penetration,” declared David Schneider of the USGS’s Anchorage, Alaska, volcanic observatory.
An Air Traffic Controller’s Perspective on Volcanic Ash
According to Richard Hernandez, of the FAA’s San Juan, Puerto Rico, International Flight Service Station, “Most air traffic controllers have little or no knowledge or experience controlling aircraft in the presence of volcanic ash.” From his personal experience, these considerations emerged:
- Availability of altitudes: not all aircraft will be able to climb above an ash cloud.
- The sequence of arriving aircraft may have to be prioritized based on their fuel state, particularly if they have had to deviate around ash clouds.
- Arrival and departure delays likely will increase.
- Pilot weather briefings become more important.
- Ash limits an airplane’s braking action, a factor that must be considered not only for landing but for takeoff, where braking action is a key consideration in rejected takeoffs.
- Ash reduces the visibility of runway lighting.
Source: 2d International Conference on Volcanic Ash & Aviation Safety
The Socioeconomic Consequences on Aviation of Volcanic Eruptions
Ash vs. airplanes:
- Engine failures
- Surface abrasion
- Glazed windscreens
- Communications failures
- Fuel contamination
- Flight delays
- Flight deviations
- Passenger trauma
- A crash could cause a carrier to go out of existence
Ash on airports:
- Schedule disruptions
- Unusable runways
- Utility disruptions
- Vehicle damage
- Health impacts
- Costly cleanups
Source: 2d International Conference on Volcanic Ash & Aviation Safety
Volcanic Ash Detector
An infrared volcanic ash detector developed by an Australian-based company, Commonwealth Scientific & Industrial Research Organization (CSIRO). Described as a prototype, the company asserts that the sensor uses two types of infrared radiation to distinguish between normal water clouds and ash clouds, giving the pilot 5-10 minutes to take evasive action should an ash cloud appear in the flight path. Source: http://www.csiro.au/index.asp?type=mediaRelease&id=Prvolcanoash