Britain Is an Island 不列顛是一個島

After six days of being grounded aeroplanes have been given the all-clear to fly in British airspace again.

The UK has effectively been a no-fly zone since last Thursday when a huge cloud of volcanic ash was thrown up into the atmosphere by a volcano in Iceland.

The eruption beneath an Icelandic glacier created an ash cloud that forced airspace closures across northern Europe, stranding many thousands of air travellers.

The ash cloud posed a risk to jet planes because it rose to around 30,000ft (9100 metres) which is the normal cruising altitude for passenger planes.

Volcanic ash can clog up and damage jet engines while the tiny particles of glass in the ash can also melt and block the ventilation holes which can cause the engines to overheat and stop working.

The obvious risk of this happening to crowded passenger planes in British airspace was enough for the UK's Civil Aviation Authority to enforce a total ban on flights – a move which was mirrored by other northern European countries.

The dangers of flying through volcanic ash were demonstrated in 1982 when a British Airways flight from Malaysia to Australia lost power in all four engines after flying into a cloud of dust spewed out by an eruption of Mount Galunggung in Indonesia.

After 15 minutes of gliding in a controlled descent from 37,000 feet (11,000 metres) to 12,000 feet (3700 metres), the pilot, Captain John Moody, managed to restart the engines once enough of the molten ash in the enginessolidified and broke off. The plane went on to land safely in Perth.

Speaking to the BBC last week, Captain Moody demonstrated the typically phlegmatic attitude of his profession.

"It was, yeah, a little bit frightening," he said.