Volcanic ash forces plane to make a major detour over Canada

Imagine taking an 11-hour flight, only to end up back where you started.

That's what happened to passengers aboard a KLM flight at the end of November when it had to make a U-turn over Atlantic Canada. The flight, bound from Amsterdam to Mexico City, made it all the way to the Gaspe Peninsula before the captain chose to divert.

The culprit? Volcanic ash.

One of Mexico's most active volcanoes, Popocatépetl, not far from Mexico City, has regularly been erupting this year. A single night in October saw the volcano blow its top 14 times. While more recent eruptions haven't been as prolific, explosive activity at the end of November did spark ash plume advisories for flight level in central Mexico.

Speaking to the BBC, a KLM spokeswoman said there were "many reasons" behind the decision to divert, but did confirm the plane was carrying a large number of horses, which may have factored into the decision.

While planes can fly through clouds of volcanic ash, doing so can be dangerous, and have serious long-term consequences.

Volcanic ash is made up of tiny glass particles and bits of rock, which can erode or build up on components in the engine, even when the plane flies through low concentrations of ash. Those tiny glass particles, once heated in the plane's combustion chamber, can also re-solidify onto engine blades. In higher concentrations, ash can obscure a pilot's view and impact the plane's external sensors. Ash clouds are also associated with toxic gases, in liquid and vapour form, that can be damaging to an aircraft's systems as well as the health of those aboard.

According to a report, The International Civil Aviation Organization (ICAO) has records for 83 "encounters" between aircraft and volcanic ash between 1935 and 2008, eight of which led to temporary engine failures.

While immediate failures like those are relatively rare, given the risk involved and the cost of repairs from long-term exposure, the ICAO recommends aircraft avoid airspace contaminated by volcanic ash.

Sources: ICAO | BBC | Volcano Discovery |