Iceland coastline near Stykkisholmur

Ash clouds and aeroplanes

Stykkisholmur is a small fishing village in western Iceland. Ngurah Rai International Airport is in Indonesia, on the island of Bali. What’s the connection? Volcanic ash.

Right now, Ngurah Rai International Airport is a little quieter than usual; an ash cloud from Mount Raung, a volcano in East Java, has airlines so worried that they have cancelled flights out of the Denpasar airport. Stykkisholmur is home to the Eldfjallasafn Volcano Museum, where, along with amazing volcano-inspired art and a geological display, you can view an informative (read terrifying) video about the power of volcanoes. Watching this video last month was the first time I heard of ‘The Jakarta Incident’ – a narrowly averted air disaster in 1982 that showed the aviation industry just how dangerous an ash cloud is to aeroplanes.

Woodcut of Mt Hekla eruption by Sebastian Munster

Woodcut of Mt Hekla in Cosmografia, 1551 by Sebastian Munster. Volcano Museum Stykkisholmur.

On 24 June 1982 British Airways Flight 9 from London to Auckland was flying at night over West Java with 248 passengers and 15 crew on board. The radar indicated a clear sky but the plane became enveloped in cloud and the cabin filled with smoke. Then, one by one, each of the four engines failed.

“Good evening ladies and gentlemen. This is your captain speaking. We have a small problem. All four engines have stopped. We are all doing our damnedest to get them going again. I trust you are not in too much distress.” Captain Eric Moody

The pilots tried to restart the engines but to no avail. As the plane lost altitude, gliding towards Java’s mountainous south coast, the crew made rapid calculations to determine where it would land. They were just about to change course to try an emergency landing at sea when miraculously the engines came back to life.

The crew was able to land safely in Jakarta, but not without incident; one of the engines failed again as the plane regained altitude and the pilots had to land ‘blind’ as the windscreen was mysteriously opaque and the plane’s landing lights weren’t working.

The cause of the Jakarta Incident was an ash cloud from Mount Galunggung in West Java. Radar detects cloud by measuring moisture, but ash clouds are dry so they don’t show up. While the instruments reported a clear sky, the windscreen, engines and landing lights were being ‘sandblasted’ by tiny particles of ash similar to shards of glass. The ash also melted onto the engines. Luckily, as the engines cooled the molten ash solidified and enough of it broke off to allow the engines to restart.

The Jakarta Incident was the subject of an episode of the Mayday television series, which features interviews with passengers and crew – it is well worth a look unless you are a nervous flyer.

So that is why planes don’t fly into ash clouds if they can possibly avoid doing so. Keep it in mind if you’re ever stuck in Bali because your airline’s risk management team have decided to be cautious. And if you are affected by the current delays – you have my sympathy, but spare a thought for the 5000 people of Papua New Guinea’s Manam Island who are still waiting for urgent assistance a week after a volcanic eruption destroyed their food gardens.