Volcanic Ash Clouds, Is It Safe To Fly Through Them ?
To answer this question, I asked a pilot (oh yes, these are the social circles I wallow in you know) and he told me this tale.
On a British Airways flight cruising at 37,000 feet over Indonesia, the plane flew through an ash cloud that the flight crew had not been notified of. At the moment the plane went into the cloud, the pilot was at the rear of the plane chatting to some travellers. One engine clogged up with ash and turned off, the co-pilot summoned the pilot back tot he cockpit but by the time he had walked the length of the aeroplane all 4 engines had shut down.
"In about ten seconds the craft had turned into the world's heaviest glider," he told me.
Over the next few minutes the plane went from 37,000 feet to 13,000 feet. I don't know exactly where the plane was flying, but Indonesia has mountains that reach 16,000 feet. At 13,000 feet the pilot managed to get a single engine lit and pulled the plane out of its stall, when a second engine fired up they managed a safe emergency landing.
As the super fine ash was sucked into the incredibly hot jet engines it melted and was sprayed onto the interior surfaces of the engines, effectively coating the blades and surfaces with a thickening layer of heavy glass. All four engines had to be replaced before the plane was brought back to the UK.
According to my source then, flying through volcanic ash is definitely not a wise course of action.