Volcanic ash imposing new layer of ops, mx concerns

 - May 26, 2010, 5:45 AM

A bold move by British Airways in April–the launching of 26 airplanes toward the UK while British airspace was closed–finally broke the European airspace logjam caused by volcanic ash clouds from Iceland’s Eyjafjallajökull volcano. The UK Civil Aviation Authority claims that its decision to open the airspace was the result of new guidance about volcanic ash concentrations, coincidentally decided upon in time to allow the British Airways airplanes to land at their London bases.

While that effort underscored the confusion and the pressures among the various authorities responsible for each Balkanized bit of European airspace, the fact remains that flying through volcanic ash is not a good idea. Aircraft and engine manufacturers have spent countless hours disseminating advice to operators regarding ash effects and, while Eyjafjallajökull continues rumbling and burping ash into the atmosphere, operators have had to modify flight routes, consider how to deal with an engine-out emergency that causes driftdown into ash clouds and watch for potential ash encounters while en route. The situation remains as fluid as
the magma deep beneath Eyjafjallajökull’s jagged openings to the outside world.

“We were grounded the better part of five or six days,” said Dave Edwards, managing director of Gama Group. About 20 of the 35 aircraft in the Gama Aviation charter/management division were grounded during the mid-April airspace closures. “We can’t argue with what they were trying to achieve,” he said of the authorities’ decision to close European airspace. “Safety is paramount.” But if the authorities had had better information, they might have been able to make better decisions, he added. “It’s not something they could really plan for,” he said. “It had an impact that they had never foreseen.”

For aircraft operators, the ash clouds pose threats on multiple fronts. In just one example, the CAA’s Safety Regulation Group issued a policy statement on May 6. For pilots considering flight over an ash cloud, easily possible for business jets but not so attainable for airliners, words of caution in the statement add to the flight-planning dilemma:
“It has been postulated that the volcanic ash cloud may be treated as a ‘solid object’ for the purposes of flight planning, the most comparable situation being planning for flight over a mountain range.”

What that means is that if there is a problem, say, loss of an engine, then pilots need to consider the possibility of drifting down into an ash cloud. If pressurization fails, that means having to descend to 10,000 feet before oxygen runs out.
According to the CAA, “A detailed study of each route over the NFZ [no-fly zone] must show that one-engine-out net flight path and passenger oxygen system performance allow the aircraft to clear the NFZ by 1,000 feet in climb and by 2,000 feet in cruise or descent. If the aircraft in these circumstances cannot clear the NFZ on the route, a [critical point] should be determined and diversion procedures should be established.”

The statement makes an obvious point and one that will be true for as long as Eyjafjallajökull continues erupting: “Volcanic ash is continually moving depending on weather patterns. Therefore, the position and vertical extent of ash is not known with great accuracy. The density of ash will also vary.”

Eyjafjallajökull’s first eruption occurred on March 20, coincidentally just before the March 22 start of the 5th International Workshop on Volcanic Ash held in Santiago, Chile. Apparently that initial eruption, ranked as a “1” on the Volcanic Explosivity Index, didn’t generate much concern at the conference. It wasn’t until after April 14, when the volcano spewed a massive cloud into the atmosphere, that European officials decided to close a huge swath of European airspace, a shutdown that seemed to have no end in sight.

An issue during the initial closure from noon April 15 to 10 p.m. April 20 (UK local time) and during subsequent airspace shutdowns was whether there was a measurable amount of volcanic ash content in an ash cloud that could reasonably be determined to cause damage.

Ash Particle Size

The CAA and airlines have been publicly arguing over the modeling used to determine which airspace should be closed. Initially, the CAA placed a 60-mile buffer zone around the areas of densest ash concentration, but that buffer was removed on May 11. The ash concentration that engine and aircraft manufacturers and the CAA seem to have agreed on as being a safe threshold is 0.002 grams per cubic meter. The latest information from the CAA indicated that in addition to no-fly zones, a new type of airspace was created to allow limited operations, the time-limited zone. In this zone, according to the CAA, “ash concentrations are predicted to exist within which flight for a time-limited duration may be permitted before engine manufacturer tolerance levels are exceeded.” These zones are published in Notams issued by the CAA.

The ash concentration levels the CAA has determined to be safe are based on teardowns of engines after ash exposure, according to the agency. That ash can damage engines is not in dispute, and there are plenty of examples of past volcanic ash encounters that have caused engine failures. One of the principal contaminants in volcanic ash is glass formed when rocks are pulverized by the eruption, and this glass ranks at five on the Moh’s scale of hardness, equivalent to steel’s ranking.

If ash is encountered in flight, engine and aircraft manufacturers suggest specific techniques that pilots should use, as well as post-flight maintenance procedures.
According to Pratt & Whitney Canada, “P&WC does not recommend operation in conditions where volcanic ash is present. Volcanic ash may clog air filters of turbine engines, block cooling air passages, erode the gas path components and erode the protective paint on casings. Volcanic ash entering the engine can also melt in the combustor and then re-solidify on the static turbine vanes, potentially choking the turbine airflow and leading to surging and an inflight shutdown. It is also noted that there is a high level of acidity associated with volcanic ash, and this may also lead to deterioration of engine components.”

Post-ash Encounter Procedures

Honeywell issued a recommendation to operators on April 20, warning, “Volcanic ash consists of particulate matter that ranges from powder-like dust to grit [and is] highly abrasive.” Damage can occur because of “erosion of flow path components, blockage of pneumatic system components with mechanical linkages, blockage of cooling passages [and ash material can] collect on turbine components [and] cause long-term detrimental effects such as corrosion.”

For pilots who encounter ash clouds, Honeywell suggests turning on engine bleeds to improve surge margin; reducing power immediately to idle, if possible, which will lower turbine inlet temperatures and “reduce chances of melting ash forming deposits on turbine hardware”; and attempting to get out of the ash cloud as soon as possible, notifying ATC and landing. On May 18, Honeywell technicians began teardowns of two TPE331 engines from a Dornier Do-228 that was used for ash cloud research, and Honeywell planned to release details of what was found in those engines (see box below).

Williams International issued a service letter on April 21 covering ash effects on the FJ44 engine, including inspection and maintenance procedures for engines exposed to volcanic ash. According to the letter, “This material is highly abrasive and may also contain varying amounts of sulfur and other elements known to contribute to hot corrosion of turbine section components. These elements, when in sufficient concentration, can also chemically corrode exposed surfaces, particularly when combined with moisture.

“The erosive and corrosive effects of volcanic ash may cause a reduction in engine life and will generally result in the need for increased maintenance and inspection activity.” In addition to oil and filter changes and borescope inspections, the letter strongly advises operators not to try to wash engines after an ash encounter. “Do not use water or detergent wash for engines exposed in any form to volcanic ash.
Water can cause the foreign material to accumulate, resulting in reduced cooling flow, and can cause rotor imbalance from accumulation of material settling and drying in the rotor spools.”

Cessna issued advice about how to protect parked airplanes during volcanic ash fallout, especially those parked outside. The advice includes sealing openings with vinyl tape and installing engine, pitot and windshield covers.

Gulfstream has made available extensive advice for operators on the mygulfstream. com Web site.

According to Michael McQuay, president of Bombardier’s service center network, “Our position is, don’t operate into areas susceptible to ash.” Near the end of April, technicians at Bombardier’s new factory-owned service center in Amsterdam examined a Challenger 604 that had an ash encounter and found no ill effects.
Bombardier has issued three bulletins to operators, outlining precautions and post-flight maintenance procedures in case of ash encounters.

Maintenance cost-per-hour provider Jet Support Services (JSSI) pointed out that its engine care program does not cover damage caused by volcanic ash. “Although JSSI carefully reviews each maintenance event and the relevant JSSI contract to make a determination of coverage, damage attributed to foreign material (including volcanic ash) is not covered by JSSI.

Regardless of coverage, JSSI is always willing to assist our clients in a consultative role as they deal with the maintenance and repair of their aircraft.” Customers should contact the engine and airframe OEM for any questions regarding ash encounters as well as JSSI. “Exposure to volcanic ash can cause damage to both airframe and engine components,” the company said.

Rolls-Royce is analyzing the impact of volcanic ash, and “is working closely with a multinational, cross-industry group to ensure that the level of the impact of volcanic ash on our engines is properly understood.”

Aircraft insurance may provide some relief for serious ash damage, but only under specific one- time circumstances. “The damage because of volcanoes would be covered as far as foreign-object damage [FOD],” said William Lovett, managing director of insurance underwriter Allianz Global Corporate & Specialty’s Aviation Market Management. If an operator can link a specific ash encounter event to damage to an engine, that would be covered. “There has to be a single recorded event for there to be a relationship between that event and the damage,” he said.

This doesn’t mean that engine wear caused by flights through ash-laden skies will be covered if the damage occurs over a series of flights. The FOD coverage applies only to single events. “Engines wear and tear any time you use them,” Lovett explained. “It’s well known that ash does have an erosion effect on engines, but you can’t go to the insurance company six months down the road and say, ‘By the way, we flew into volcanic ash six months ago.’”

To make a claim, an operator would not only have to experience the single-event damage but also document that it did occur by borescoping the engine directly after the flight. It would be wise for operators to maintain documentation of where the aircraft has flown, but most operators should already have these records from electronic flight plans. “If you believe this could be a cause, you need to borescope the engines and find out what the issues are.”

Prolonged Disruption

The problem with Eyjafjallajökull is that it could continue erupting for a year or even longer. Recent ash plumes have shot up to 30,000 feet, which may signal worse problems for airliners that can’t climb very high and easier options for higher-flying business jets.

The volcano discussion and issues are scaring some operators away from flying across the Atlantic, but Ron Freswick, director of aviation for a large company, recently flew a trip to Asia in the company Global Express that included a stop at Keflavik in Iceland. “We could see the volcano 70 to 80 miles away,” he said.

Rather than being overcautious and not flying for fear of violating warranty or maintenance cost-per-hour program limits, Freswick urged his fellow pilots to evaluate the situation and, if sufficient alternatives are available, go flying. Of course, the Global Express can carry enough fuel to give any suspicious cloud a wide berth, and when Freswick arrived at Iceland, he still had enough fuel to fly safely to London or Paris. “Research it, see where it is; if you think it’s a problem, don’t go,” he said. “Get yourself options.”

www.caa.co.uk (see Technical Notices)
U.S. Geological Survey: