Weather

Pilots’ weather concerns normally include visibility, the ceiling (how close the bottoms of clouds are to the ground), strong winds, turbulence, the danger of ice forming on their airplanes, and storms that could concentrate all or several of these hazards along their routes of flight.

From time to time a volcano adds another dangerous element: debris blasted more than 40,000 feet into the sky. It’s called volcanic ash, but this “ash” isn’t the soft material left when paper burns. “Volcanic grit” would be a better name. An eruption shatters solid rocks and can blast molten rock from deep within the Earth to high in the air. Once in the air the tiny pieces of magma solidify into fragments of glass and rock mixed with pieces of shattered rocks. While the tiny pieces that rise high into the sky are smaller than grains of sand, they can be stronger than steel and extremely sharp.

When a jet aircraft runs into a cloud of this stuff it quickly starts eroding all forward-facing surfaces, including the windshield—which in some cases has become too opaque to see through.

That’s only the beginning. The ash melts in the hot sections of a jet engine, and then fuses as a kind of dirty glass onto internal engine parts, causing the engines to surge and often flame out. The ash also can clog pitot tubes, causing dangerously unreliable airspeed readings.

As with other kinds of extremely dangerous atmospheric conditions such as huge thunderstorms, wise pilots avoid volcanic ash. The size of the airplane and the importance of the passengers or mission make no difference. Air Force One flights taking President Barack Obama overseas are a good example. In April 2010 the huge eruption of Mount Eyjafjallajokull in Iceland kept Obama and leaders of several other nations from flying to Poland for the funerals of Polish President Lech Kaczynski, his wife, and other Polish officials who had died in an airplane crash.

In November 2010 Obama had to cut short a visit to Indonesia so Air Force One could take off before ash from Indonesia’s Mount Merapi could have grounded his flight. In May 2011 the eruption of another Icelandic volcano, Grimsvotn, forced the president to cut short a visit to Ireland because of fears that ash could keep Air Force One from flying to London for a high-profile state visit.

Fortunately, the May 2011 Icelandic eruption, which wasn’t as large or as lengthy as the 2010 eruption, caused only minor disruptions to European air travel. The April 2010 eruption closed large parts of European airspace for six days and stranded more than 10 million people at an estimated cost of $1.7 billion.

Reasons to pay attention. The pilots of Air Force One, which is a military version of a Boeing 747, had good reasons for concern about volcanoes. Since the 1970s volcanic ash has damaged more than 90 passenger jets. These included three Boeing 747s that became gliders after all four engines flamed out.

The first was a British Airways 747 that flew into ash from the Mount Galunggung volcano in Indonesia while 37,000 feet above the Indian Ocean on January 24, 1982. The pilots were unable to restart any of the engines until the airliner had glided down to 12,500 feet. The airplane landed safely. Three weeks later a Singapore Airlines 747 flew into ash from the same volcano with similar results, including a safe landing after the pilots restarted some engines.

A KLM airliner lost all four engines on December 15, 1989, while descending through 27,000 feet on approach to Anchorage, Alaska. The airplane had encountered volcanic ash from Alaska’s Redoubt volcano. It descended to 13,300 feet before the pilots managed to restart engines and land at Anchorage.

In these cases the pilots were eventually able to restart at least some of the engines because the glass that forms in jet engines is brittle and repeated attempts at restarts will break enough of it loose for the engine to begin producing thrust.

Less danger to piston engines. Volcanic ash isn’t as much of a danger to piston-engine airplanes as it is to jets because piston engines don’t produce the continuous high temperatures that fuse ash inside a jet engine. Also, the ash is not as likely to scratch the windshield and other surfaces as badly as on a faster-moving jet.

In fact, in 2010—when aviation authorities across Europe closed airspace because of the ash danger—AOPA-United Kingdom congratulated the nation’s Civil Aviation Authority “on its deft handling of the Eyjafjallajokull volcanic ash issue as it affected general aviation, which effectively allowed flight training and other operations to continue while commercial air transport was grounded.”

The U.K. CAA said that “closed” airspace meant there would be no air traffic control services in the closed areas. Pilots who didn’t need ATC services were free to fly if the pilots judged the flight would be safe. Aviation authorities in other European nations closed airspace to all flights.

Even though volcanic ash isn’t likely to stop a piston engine as it can a jet, this doesn’t mean you should fly into ash.

In 2010, in response to the Icelandic eruption and the closing of European airspace, Lycoming Engines issued a bulletin advising against “engine operation in areas where volcanic ash is present in the air or on the ground.

“Piston engines can be adversely affected by inlet air contaminated with volcanic ash. Solid deposits from any number of sources can accumulate on engine baffles or other engine surfaces, significantly impacting engine cooling. Accumulation of deposits on the induction air filter can restrict or block air flow to the engine and significantly reduce engine power. Contamination of engine oil can lead to engine malfunction and/or failure from abrasive wear,” the bulletin said.

Your lungs won’t like it. You also should be concerned about what breathing volcanic ash particles could do to your lungs. The particles can be smaller than 0.001 millimeters in diameter. When enough particles this small from any of several possible sources are in the air, the U.S. Environmental Protection Agency will forecast that the air quality index will fall into the “hazardous” range, which means that everyone could be affected.

Sulfuric acid from volcanoes and other sources could adhere to such particles, which are tiny enough to travel deep into your lungs, to the end of the line in the alveoli where the oxygen you breathe goes into your blood and the carbon dioxide your body produces goes into the air to be exhaled. This is annoying at best to anyone, and potentially fatal to someone with respiratory problems.

The 1980 eruptions of Mount St. Helens in Washington were the last major volcanic eruption in the 48 contiguous U.S. states, but volcanologists fear that eruptions could occur at any of several volcanoes from Lassen Peak (which erupted several times from 1914 to 1917) north across Oregon, Washington, and into British Columbia. Alaska is the volcanic hot spot in the United States, with an average of one or two eruptions a year since 1900.

Even though volcanic ash isn’t ordinary “weather,” you will learn of any volcanic ash threat during a Flight Service standard weather briefing. Volcanic ash is one of the hazards for which a sigmet (SIGnificant METeorological information) is issued. Sigmets warn of conditions that could endanger any aircraft. The notices to airmen that you should receive as part of a briefing will include any flight restrictions caused by volcanic hazards.