New Standard Permits Airlines to Fly Into Volcanic Ash

Fri, Apr 23, 2010 — David Evans

Articles, Featured

It’s safe to fly into Europe as of 20 April, according to the International Civil Aviation Organization (ICAO). Thus ended a week when volcanic ash from Iceland disrupted the continent’s air transportation. But the ICAO’s action allows aircraft to be exposed to some amount of airborne ash, as opposed to its “no tolerance” limit before. Just how safe is it?

A day later, 21 April, there were reports of two airplanes encountering ash. A Thomas Cook B757 made a U-turn back to Manchester, UK, after it was out over the North Sea and reported an engine bleed problem after an intense smell of volcanic ash in the cabin during the climb between 16,000 and 21,000 feet (ash clouds are supposedly higher). A contaminated valve was suspected. And a World Airways cargo B747 diverted into Ostend, Belgium, with two of its four engines shut down for operation outside limits.

There doesn’t appear to be any reconsideration of the okay to fly into volcanic ash clouds. Let the Great Experiment begin.

Volcanic haze seen from the top of the Eiffel Tower on 17 April.

Volcanic haze seen from the top of the Eiffel Tower on 17 April.

The Great Experiment was cleared by a 19 April press release from EUROCONTROL (European Organization for the Safety of Air Navigation). Based on a telephonic conference with “several” European States, EUROCONTROL decreed:

“Accordingly, a limited ‘no-fly zone’ will be established by the States concerned, based on forecasts from the VAAC [Volcanic Ash Advisory Center] … Aircraft Operators will be permitted to operate outside this zone. In their decision as to whether to fly, they will be supported by shared data including advice from the scientific community (meteo, volcanic ash proliferation etc.) – including safety assessments supported by tests under the oversight of the competent Safety Authorities …

“The [telephone] conference also concluded that, in time, it should be possible to move towards an approach in which full discretion [emphasis added] is given to Aircraft Operators.”

In other words, punt to the individual states. They are under intense pressure from the airlines to resume flying because of the losses estimated at $200 million per day from the grounding of thousands of flights.


In the UK, the Transport Ministry promptly cancelled adherence to ICAO Document 19, known as the “Volcanic Ash Contingency Plan EUR Region,” which had promulgated a strict policy of atmospheric ash avoidance:

“Valid: Immediately. ICAO doc 019 is cancelled together with all other rules connected to it.”

EUROCONTROL has said it is now working on a new Doc 019. Reportedly, this new document will say something like: You are not responsible for anything, just tell them ash might be there.

The original Doc 019 dates back to 1951. Longevity is not proof of validity, but it does indicate the long standing policy of ash avoidance, now cancelled. The simple fact is that a 20+ year-old, worldwide safety regime was overthrown at a two hour meeting of airline executives and British government officials.

These actions suggest the religious observance of volcanic ash precautions was causing too great an economic loss for airlines, so the authorities have cancelled the previous policy and recommenced flight operations, placing the onus on flight crews to duck and weave as necessary.

One factor in the decision to cancel Doc 019 seems to be the kind of ash hurled into the atmosphere. It appears that the Eyjafjallajökull ash consists of basalt, which melts at 1,200º C, a temperature normally reached in jet engines during take-off. The ash of many other volcanoes (including Mt. Pinatubo in the Philippines, Mount St. Helens in the U.S., and volcanoes in the Andes) consists of andesite, which melts at well below 1,000 º C, a temperature reached in the engines much more frequently (i.e., in the cruise).

However, the abrasive properties of basalt appear to be the same as andesite. In addition, there is a failure mode that is potentially terminal for the engine. If very fine material that the compressor and combustion stages can happily swallow enters the engine, there is a risk to the manner in which the turbine is cooled. The airflow past the turbine is sometimes several hundred degrees above the melting point of the turbine metal. Cooling air is vented through myriad small holes in the surface of the blades ensuring that they are encased in a cocoon of cool air.

Quite small particles of volcanic ash can clog this cooling. Worse, the volcanic particles can form a glass like build up on the blades. In the worst case, this glassy material could destroy the turbine in about a minute.

The UK Civil Aviation Authority (CAA) has announced that a threshold concentration of ash of 0.002 grams per cubic meter of air poses no danger. Therefore, airspace will be opened. Current data suggest that the concentrations of ash in UK airspace are on the order of 0.0001 grams per cubic meter.

Airlines must now conduct a safety assessment prior to flying into volcanic ash. According to a CAA notice of 21 April:

“The purpose of this FODCOM [foreign object damage communication] is to inform operators of the requirement to carry out a safety risk assessment before flying in airspace affected by volcanic ash.”

The FODCOM itself says:

“The process [of safety risk assessment] involves identifying the hazards associated with the activity (in this case airspace proximate to volcanic ash or flying to and from aerodromes affected by volcanic ash), considering the seriousness of the consequences of the hazard occurring (the severity), evaluating the likelihood or probability of it happening, deciding whether the consequent risk is acceptable and within the organization’s safety performance criteria (acceptability), and finally taking action to reduce the safety risk to an acceptable level (mitigation).”

The process of assessing the risk of flying into volcanic ash is shifted from the regulator to the operator, who has a financial stake in minimizing the estimated hazard. Not to mention that by shifting the problem to the operators, the “risk” appreciation formula may be highly variable among airlines. Some may take a conservative approach in their safety risk assessments and others may be willing to assume (and downplay) risks.

The passengers won’t know if they’re flying on an airline with a conservative or a risky safety assessment. There is no indication that the CAA will monitor these assessments among operators for uniformity. The worst aspects of SMS (Safety Management Systems) will be given free rein under this cavalier approach to go/no go. According to one definition of SMS, it is undertaken “to achieve acceptable or tolerable safety.” The words “acceptable” and “tolerable” are judgment prone and do not accord with risk as so many events per billion flight hours (e.g., improbable and remote by strict mathematical estimates of probability).

The 0.002 gram threshold for engine damage was established through ground tests. Dr. Colin Brown of the UK’s Institution of Mechanical Engineers, was skeptical. “You have to test the stuff that is actually there,” he told BBC News. “You can’t assess safety properly if you’re carrying out tests on the ground with the wrong ash.”

There are enormous unknowns. How were measures of engine durability taken? What time scaling was applied? Fifteen minutes? Hourly? Eight or 24 hours? In brief, where are the specifications?

“Previous to this, the regulations were, if you see ash, you fly 100 miles away from it,” Brown said.

The industry has pointed to the numerous airlines which have launched tests flights and found that the ash in the atmosphere had neither caused damage to the aircraft nor threatened the safe conduct of travel. However, long-term damage to aircraft engines may not be revealed by just a handful of test flights.

According to Joris Melkert, an assistant professor of aerospace engineering at the Delft University of Technology, the problem of airborne ash may be getting worse because of global warming:

“This is because the reduction in the ice load reduced the pressure in the mantle, leading to decompression melting there [at Iceland’s Eyjafjallajökull volcano]. Since the late 19th century the ice caps in Iceland have been shrinking further, due to changing climate. This will lead to additional magma generation, so we should not be surprised if more frequent and/or more voluminous eruptions start happening in the future.”

And let us mention improved detection technology and its implication. According to the September 2008 meeting of ICAO’s Volcano Watch Operations Group:

“As remote sensing techniques improve, it is likely that the aggregate areas where ash is sensed or inferred will increase, possibly leading to over-warning for ash and cost-blowouts for the airlines.”

Global melting could mean more ash, and improved detection means more airline disruption.

Flying in the face of such increased activity may not be the time to abrogate the risk assessment to the airlines, which have an enormous stake in flying, not sitting on the ground waiting for the ash to clear.

There seems to be a forgotten precursor in the recent decision-making. In 2002 a NASA (National Aeronautics and Space Administration) DC-8 research aircraft inadvertently flew through a volcanic plume spewed forth by Iceland’s Mt. Hekla volcano. The airplane was on a flight from California to Sweden. Sophisticated cabin-mounted instrumentation alerted scientists aboard that something had happened; the ash cloud was not visible to the crew and they were unaware of any hazard en route. According to the NASA report of this incident:

“All four engines were sent to the General Electric Strouther overhaul facility near Arkansas City, Kansas. Photographs were taken as the engines were disassembled. All engines exhibited a fine white powder coating throughout. There was leading edge erosion of HPT [high pressure turbine] vanes and blades, blocking cooling air holes, blistered coatings, and a buildup of fine ash inside passages. Serial number 692632 (the number four engine on the DC-8) had the most severe damage; this may be partially due to the older hardware still resident in this engine. [Photographs] of the damaged HPT blades, with clogged cooling air holes, leading edge erosion, buildup of ash in passages, and blistered blade coatings [were] clearly visible. Total cost of refurbishment (to standard flight condition) for all four engines was $3.2 million.”

Blistered thermal coating and plugged cooling holes.

Blistered thermal coating and plugged cooling holes.



That was the damage bill for a short-term “one off” encounter with ash. Extrapolate that cost to the number of airlines plying the same route numerous times daily. The mind boggles – but the engine overhaul mavens will doubtless become enthusiastic converts to Vulcanism. Vulcan was the blacksmith god of fire and volcanoes in Roman mythology.

The picture of the tiny vents used to cool the turbine blades, and comments about the possibility of pitot tubes clogging, should give pause for thought. Reducing risk to an “acceptable level” now means a judgment call by the airlines instead of a uniform policy of strict avoidance.

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