Ash Cloud, How Dangerous is it?

[jim]

They stretched everything to its absolute limits, with the approval of the FAA, yes - but that doesn't in itself explain the accident. I don't believe for a second that they were even living up to those limits, hence the crash. IIRC that jackscrew was meant to be replaced long before the failure but the change was ignored, and around half of the planes were lacking sufficient grease? They clearly didn't give a crap.

And if we're going to blame the FAA, then who else do you propose we trust? If the FAA wasn't there Alaska would've probably introduced even less frequent checks - it's better than the airlines on their own.

[Whiternoise]

Last time, large parts of the UK, Belgium, the Netherlands and elsewhere banned ALL aviation; including gliders and hot air balloons. Why? Because of the risk of "engine failure". Thankfully someone who did not have **** for brains was finally located in government, and they relaxed the restrictions a little.

No, they didn't. I was flying gliders during the last ash problem, we had a lot of GA folk down who normally fly jumbos or teach at powered fields who basically had a holiday. From the BGA:

"Volcanic Ash Risk 22nd April 2010 UPDATED 25th April

The CAA has issued a Flight Operations Communication (FODCOM 11/10) to provide guidance to general aviation pilots on deciding whether and where to fly when volcanic ash may be present. The FODCOM is of particular relevance to operators of motor gliders and tugs. (25/4 - FODCOM 11/10 superceded by FODCOM 13/10 with revised information on the use of carburettor hot air and maintenance actions.)"

Could well be that they banned it in Scotland, but it seemed to be mainly down to the duty instructor. If there was ash floating around, it's not so much the engines, it's that with gliding in particular stuff on the wings can be extremely problematic - probably not to the point of failure, but enough that you need to watch your ASI a bit more carefully.

[peterb]

First lets admire the staggering power of nature, if ever you need a reminder quite how insignificant we are look at this:
http://www.bbc.co.uk/news/uk-scotland-13519331

It is only a little volcano you know. But it is quite beautiful.

So what hazards do these things pose to planes?

Props, basically not much at all. A piston engine in a plane is almost the same as a car, the carburetter filter could get clogged, which would mean you'd have a bad time, but an experienced pilot would see this coming with strangely lean amounts of mixture (air + fuel) been required. Flying in desert at low altitude is more likely to create an issue.

So no one has ever suggested suspending GA flights in the ash clouds, in fact even in Iceland people are flying them to see the volcano.

So ignoring turbo props because no one gives a damn, on to the Jet engine.

Jets require quite a lot more air to fuel thanks to been a jet engine, but planes have gone through the ash clouds before and survived:
http://en.wikipedia.org/wiki/British_Airways_Flight_9
Now in this case its worth noting commercial jets shouldn't be flying through ash clouds. They shouldn't be flying through thunderstorms either (see Air France and unlike the ash cloud, those poor people have quite possible died at the hands of dangerous pilotage).

The thing is not all ash is the same, and no one really knows how dangerous it is so its all air on the side of caution. But after a little while googling I've been un-able to find something that even begins to state tolerance levels for an engine.

So lets try and keep this thread FUD free, and see what decent sources people have been able to find for why we should shut down scotlands airspace!

Leaving aside the point that a turbo-prop is a jet engine, but instead of propulsion by either a bypass fan or just the efflux of exhaust, the exhaust gases drive a power turbine...

It isn't just about an engine failing through lack of air in the combustion process. Flying through and exposing the aircraft and engines to abrasive materials may accelerate wear, leading to premature failure in the future (servicing and service life of components are based on the expected wear in normal use) and to damage to the aircraft fuselage. Sand (for example) blowing against a piece of metal at 5mph will have a considerably less abrasive effect than when it impacts a piece of metal at 500mph. Given the speed of rotation of the compressor blades on a gas turbine, there is the risk of increased erosion of the blades.

The problem really was that there was not enough data to make an informed decision. There is more data available as a result of the first eruption, and more is being gathered as a result of this one, so the rules may change as a result.

[TheAnimus]

Leaving aside the point that a turbo-prop is a jet engine, but instead of propulsion by either a bypass fan or just the efflux of exhaust, the exhaust gases drive a power turbine...

A turbo prop is a jet engine in the same way an iPhone is a cray.....

Its a turbine engine but has very different characteristics from a commercial airliner 'jet' engine.

I also wanted to remove it from the conversation because for commercial air travel that can't easily be done by hopping on the train or driving it, they represent a tiny percentage.

[peterb]

A turbo prop is a jet engine in the same way an iPhone is a cray.....

Its a turbine engine but has very different characteristics from a commercial airliner 'jet' engine.

I also wanted to remove it from the conversation because for commercial air travel that can't easily be done by hopping on the train or driving it, they represent a tiny percentage.

That is not true, the basic principles are the same, and many turbo-prop engines are used by commercial airlines. The same turbo-prop type engines are also used for helicopter propulsion, except that the power turbine drives the rotor gearbox, rather than a variable pitch propeller.

The basics of any jet engine is the gas generator, comprising the compressor, combustion chambers and compressor turbine, which are mounted on the same shaft. That can also drive a bypass fan (in a by-pass engine) or drive a power turbine with a separate output shaft that can drive a propeller or rotor gearbox.

But leaving that aside, the problem with the 'ash' cloud is as I stated in the last part of my post - there is (or was) insufficient data to make an informed decision about flight safety for commercial aircraft.

[Kata]

No, they didn't. I was flying gliders during the last ash problem, we had a lot of GA folk down who normally fly jumbos or teach at powered fields who basically had a holiday. From the BGA:

I'm talking Holland