Time-lapse video of ash spread from the Norwegian Meteorlogical office. Click here to watch. Pretty cool.

At the time KLM made the "no adverse" announcement on Sunday they had not yet taken the engines apart for inspection. So all they know is that the engines didn't fail during that flight, not whether they'd survive even another 100 hours without failure.

NATO has taken apart a couple of engines from fighters that did have damage from this ash cloud.

The ash cloud does not extend uniformly from ground-level upwards: vertical wind sheer means many altitudes are ash-free, yet a few thousand feet above or below have ash.

"Big Icelandic banks went bust and blew a lot of money from quite a number of British citizens. They are quite eager to get it back..."

Bloody huge letter bomb somebody sent... they really must have been peeved!

Very dramatic photo of the volcanic cloud, compliments of NASA: Fire and ash

Sue

Some stranded tourists are probably thinking more along the lines of Hotel California "... you can never leave"!

Imagine if this had taken place at a peak vacation travel period.

If the EU allows flight then the FAA in the USA has a problem: do they require tear-downs of those engines before allowing them into the US? And will the Chinese allow those airplanes? (China has a very strong aviation safety record in the last few years, better than the US)

Ash damage to turbine engines and other airplane systems can be very subtle. The hot sections of modern jet engines have very tight operating tolerances and operate very near the temperature limits of the materials involved. Minor loss in cooling efficiency or excess wear could lead to at least a loss of efficiency and increases the possibly of several different engine failure scenarios.

For Commercial Air Transport flights (Airlines) the general rule is to keep the likelihood of a catastrophic failure (one leading to the loss of the airplane) to less than one chance in 1,000,000,000 hours. This focus on safety leads to a very conservative approach to managing the airspace when things like volcanic ash are floating around. Loss of an engine, or even significantly reduced performance from one or more engines is a significant flight hazard.

- Eric

Hmm, strange happenings again, another ash cloud was reported to be on its way this morning, but now for some reason all airports within the UK will now be operating normally but with some limited restrictions on some airspace routes. Must have started to run out of Kiwi fruits, Asparagus and Mange Tout at Notting Hill Sainsbury's.

http://news.bbc.co.uk/1/hi/uk/8633601.stm

The airlines operating in the UK are complaining about Britain being overly cautious. Evidently other nations restarted flights much earlier. Report on NPR was that the airlines were losing $200 million a day they were shut down.

I suspect that this is one of those times when government is going to get thrashed either way. Damned if they do, damned if they don't. They have to make the call and expect the complaints.

It has to be pointer out that, as one person put it on the radio, 'It is better to be on the ground wishing you were flying than flying wishing you were on the ground'.

Modern jet aircraft have roughly the same glide characteristics as a brick if all the engines stop. Even one engine out is a flight emergency. Also that $200 million would just about make the down payments on the legal costs of 200 people dead in a plane crash. And that only if it comes down in a friendly, uninhabited, area. Take out a high-rise full of people or a nuclear power plant while struggling to make the airport and things could get downright expensive.

True, better safe than sorry.

On the other side, there are lots and lots of indications that the issue with flying through thin ash clouds is more about drastically shortened life span of engines. The risk of engines stopping dead in air seems to be slim to non-existent. Trouble is - it is hard to guarantee, and the expert just don't know enough about it. Yet.

This is not correct. Modern jets are very aerodynamically clean and glide quite well thank you. Lets not exaggerate the seriousness of the situation beyond reality.


See "Gimli Glider" ( aka Air Canada Flt 143)

See the story of Air Transat Flt 236 pumping all fuel overboard mid-ocean due to an undiagnosed fuel leak and landing as a glider in the Azores.

And don't forget the recent ditching into the Hudson. That was a most excellent glider flight ending in a fine landing in the safest place available.

All airplanes are gliders at heart. Bricks are just projectiles.

18:1 glide ratio is a number that comes to mind for jets. I've flown sailplanes with a much worse glide ratio.

It's not the glide characteristics that are the problem. It's the uncertainty about where the aircraft might revert to unplanned gliding as well as any additional damage due to engine spontaneous disassembly that can cause really big issues.

Gliding is GOOD! (says the former glider flight instructor)

To add to what unimogbert said, modern commercial aircraft are designed to maximize lift and minimize drag for fuel efficiency. This also maximizes their glide performance.

One engine going out is considered an emergency because if you don't know why that engine quit, you don't know if the others are about to quit, too. So you want to get that plane back on the ground as soon as you can.