Q+A-Why is volcanic ash a threat to planes?

07 Nov 2010 06:50:14 GMT
Source: Reuters
JAKARTA, Nov 7 (Reuters) - Cloud of volcanic ash belched out by Indonesia's Mount Merapi caused widespread flight disruption on Sunday and could threaten a visit by U.S. President Barack Obama next week. [ID:nSGE6A600S]

Following are some questions and answers on the risk to aviation:

WHAT IS VOLCANIC ASH?

Plumes of dust spewed out by volcanoes usually contain tiny particles of glass, pulverised rock and silicates. The result is a cloud of material resembling sandpaper.

WHY IS IT A HAZARD TO AVIATION?

The problem is not visibility but the abrasive affect of the ash, which can both strip vital surfaces and bung up an engine.

Pulverised rock colliding at high speed with a speeding jetliner can blast away surfaces inside the engine.

Due to intense heat in the motor, the particles can fuse together when they penetrate the engine and stop it working.

Aircraft avionics and electronics can also be damaged.

Aviation authorities say clouds of ash are often accompanied by clouds of gas such as sulphuric acid and hydrochloric acid.

WHAT HAPPENS IF AN AIRCRAFT DOES FLY INTO VOLCANIC ASH? On June 24, 1982, the captain of a British Airways jumbo jet en route from Kuala Lumpur to Perth, Australia, came on the speaker system at around 37,000 feet and calmly told the 247 passengers on board that all four of its engines had failed. [ID:nLDE63E1NJ]

In an incident that went down in aviation history, Captain Eric Moody glided the jet down more than 20,000 feet and managed to restart one engine at 13,000 feet followed by others, according to the Flight Safety Foundation (aviation-safety.net).

It was only later that investigators found the combination of engine failure, an eerie luminous glow around the plane and acrid smoke inside the cabin had been caused by flying into a cloud of volcanic ash from the eruption of Mount Galunggung.

On Dec. 15, 1989, all four engines failed again when a KLM jumbo jet flew into a cloud that turned out to be volcanic ash while en route from Amsterdam to Anchorage, Alaska. The engines resumed working and the damaged plane landed safely. (Reporting by Tim Hepher; Editing by Alex Richardson)