Should planes fly in Iceland volcano ash? Be careful, study says.
Some European airlines have begun test flights to see if it is safe to fly through the volcano ash from Iceland's Eyjafjallajökull. But a NASA study says a little ash can cause serious problems.
(Page 2 of 2)
The NASA flight
But on the night of Feb. 28, 2000, the crew of a DC-8 NASA used for atmospheric research discovered first-hand that ash plume forecasts are not perfect. The agency ended up paying a $3.2 million repair bill.Skip to next paragraph
In Pictures Iceland volcano
Subscribe Today to the Monitor
The DC-8 was en route to Kiruna, Sweden, for the start of a research project to study atmospheric ozone over the Arctic, according to a NASA technical report written by Thomas Grindell of NASA's Dryden Flight Research Center in Edwards, Calif., and Frank Burcham Jr. of Analytical Services and Materials, Inc., also in Edwards.
Some 35 hours earlier Iceland's Mt. Hekla volcano had sent clouds of ash and steam soaring to altitudes of 45,000 feet.
The DC-8 was cruising at just more than 500 miles an hour at 37,000 feet and some 200 miles north of where the plume was predicted to extend. The sky was generally cloudless with no moonlight. But the highly sensitive research sensors aboard the craft detected a sudden rise in ash particles and sulfur dioxide. For seven minutes, the craft flew through a tenuous ash cloud some 800 miles from the volcano.
The only visual clue they had: They couldn't see stars in the night sky, a common phenomenon when flying through high-altitude cirrus clouds. Cockpit instruments reported no unusual engine behavior. The crew smelled nothing unusual. And they saw no other visual clues that would tip them off to the presence of volcanic ash.
The crew reported the encounter to air-traffic controllers and continued to Kruna.
Damage wasn't immediately evident
Once the crew landed, a cursory inspection of the engines and the plane's exterior showed no evidence of an encounter with volcanic ash. Technicians at the site didn't have sophisticated inspection gear at their disposal, so the plane was pronounced fit and the research project began.
But Mr. Grindle and his colleague write that once the aircraft returned to Dryden, deeper inspections showed that internal cooling passages had been clogged, with some of the engines' areas of highest temperature showing signs of unusual heat stress. One of the aircraft's engines sustained the heaviest damage. It was enough to prompt technicians to dismantle the other three as well.
In essence, all the engine's internal parts were coated with fine white powder. The leading edges of turbine blade were pitted. The build-up of heat from clogged cooling passages blistered coatings on several internal components.
Moreover, some research suggests that if the plane had encountered the ash in daylight, the crew still might have had no visual clue because the ash could well have been encased in ice – looking like high-altitude cirrus clouds. A study of the incident by researchers at NASA's Jet Propulsion Laboratory published in 2002 notes that satellites failed to pick up evidence of ash at the point where the DC-8 encountered it; instead it indicated cirrus clouds.
The researchers posited that the ash in effect took a Trojan Horse approach. It served as seeds around which ice crystals could form. Ice striking the jet would leave no visible signs of collision. But once the crystals entered the engines, they would melt, freeing the ash. To weather satellites, the plume would look like icy clouds, not ash.
"The insidious nature of this encounter and the resulting damage was such that engine trending [readings from in-flight instruments] did not reveal a problem, yet hot section parts may have begun to fail [through blade erosion] if flown another 100 hours," the duo wrote.