Ash up your pipes

I'm glad that it looks like we're going to be able to re-open the airways tomorrow, even if it's not for all that long.
I'm more glad that no aircraft have fallen out of the sky.
I'm rather pissed off with the people saying that nothing happened so the precautions were excessive.
If someone plays Russian roulette and doesn't die, would you say there was no danger at the start or that they were lucky? Would you say "they were fine so I'll give it a go"?

There is ash in the atmosphere, it's nasty shit.
If you think I'm overstating that, consider that this is made of rock (generally between 0.1 and 1 mm but sometimes much bigger than that) that can rather damage windscreens and paintwork, not to mention potentially breaking the skin of the airframe; there's volcanic glass mixed in (more so in this case as the silicon dioxide makes up 58% of the tested ash at Lerwick) which can melt in the combustion stage of a jet engine and form a layer of glass over the insides of the engine (check Flight Global for images of what volcanic ash can do to the engine on a F-18) as well as the fact that the ash itself can build up on surfaces and stick, ruining airflow and making the aircraft somewhat heavier. Oh, and did I mention the sulphur? Yeah, it's sulphurous, too much of it and it becomes a danger to respiration, add water and it can become sulphuric acid, oh and it stinks!
Can be pretty though, the effects of the particles cause a static buildup that results in lightning at the volcano and St Elmos fire on the surface of aircraft flying through it. Cop yer whack at this:
from NASA for an indication.
More pictures (some amazing ones as well) from the Big Picture from the Boston Globe.

We've had recorded ash across the entire UK, you can't see it but it's there. Or at least you can't see it in the air but it becomes visible when it builds up on cars and other surfaces. We've seen this from Lerwick, Aberdeen, Boscombe, all across Devon and most of the south. They took samples from West Freugh in southwest Scotland and they found 2000 ft of ash at two different levels in the atmosphere today. Some parachute dudes found a couple of layers (they reported some weird visual effects and "a stinging sensation on the lips" as well as dark areas in the air) and before you say "but the BA and Lufthansa flights were OK", we knew that we don't know the exact areas of the ash, it's distribution or exact makeup so we knew there would be clear areas and not clear areas, the research flights that went up found both.
We had some satellites but they were obscured by higher cloud, our radar isn't good (expensive) enough to find the ash, we don't have enough actual weather balloons spread across country (or upwind - it's ocean, which isn't really conducive to weather balloons) to get detail of the atmosphere and our wind profiler/lidar network needs so much investment any political party that suggested funding it properly would be laughed off the stage. We do have some of the best observers and forecasters in the world, one of (if not the) best set of models in the world, although they could do with being a bit more flexible, which we could do with more funding and a bit more flexible approach. But we haven't had a situation like this crop up, we've no experience of this type of thing on this scale and it takes us time to get the required information. It might even take us a week.

I was asked "how much ash is too much, because I've heard there is no safe amount?" and I can't answer this because I'm not an engineer or a Rolls Royce specialist. They (Rolls-Royce) are saying you need to cover the aircraft, put them inside and don't turn on the engines. Preferably cover them with fine silks and satins. OK, I'm exaggerating slightly, but only a bit.

In the 1980s a couple of 747s hit ash clouds and had all their engines cut off. These clouds are one of the few things that can kill all the engines on a multi-engine aircraft within minutes. To clear the engines of the glass build-up you need to put LOTS of clean air through the engines which generally requires about 12000 ft of free-fall. Our ash layers were around 4000-8000 ft.

Yes, it's been an embuggerance for many, many people, our mail up here is stalled (the post is sent by aircraft then driven on), my girlfriend is stuck at Brize Norton until at least Thursday and we'd both rather she could have waited up here until she was needed, not to mention the financial implications and all the people stranded.
But let me put it this way, I would rather she spent ten years waiting at Brize rather than be in an aircraft that took the risk of flying through an ash cloud at 8000 ft and having the aircraft turn into a glider.

Have a look at this for more explanation.

Could different levels of reaction be used in the future? Yes.
Yes if we know the exact distribution of the ash.
Yes if we know the composition of the ash.
Yes if we know how fast it's being produced.
Yes if we know the winds at every 500 ft interval and the vertical motion of the air over the entire area of the ash cloud.

Until that point ask yourself if fire engines need to drive so fast to every call out, or if you want your doctor to take you seriously any time you have a sharp pain in your chest. Or would you rather the fire brigade assumed you were burning toast rather than stuck in a building, your doctor assumed you were over-reacting rather than see if it was an heart attack.
Are you happy with the airline assuming that they know best and that because "they didn't hit any ash areas" means "we won't hit any ash areas."
Or wait until we know more about the circumstances and can say "OK, we've had a check and we think this area is safe while this area isn't."
Even if it takes a week.

Or the volcano stops.