same plane, different birds?

[tulsaweather]

sounds like a compressor stall in a way.

 

[Dilligas]

While overjoyed over the positive outcome, I reserve judgment on aviation incidents until the investigation is completed. Things are rarely as they seem and it's just prudent to let the facts play out.

It's refreshing to read an intelligent comment on here. Bobbie is right on target. Those that are talking, don't know, and those that know, aren't talking.

There is a chain of events in any accident/incident that are reviewed and investigated step by step. This one is not an exception, with a typical knee jerk media reaction, oversimplification, or sensationalization of events. Rational thought and discussion however is not as titallating as what passes for news today... a culture of info-tainment, superficial "reporting", inane questions, blather, and endless repetition. Much of the same is posted on these boards on a regular basis.

Stay tuned.

D

 

[Dilligas]

Those people crying to the media need to shut the :censored: up!

Why?

I wonder if you could argue a rational, intelligent reason as to why someone's experience on the same aircraft would not be germane to this discussion, rather than make a superficial put down.

Seems to me one would want to know all the facts.

 

[Dilligas]

Bobster,

Hey, I get it. We live in a world full of control-freaks and know-it-alls that live to digest every kernel of information on the planet. That has got to be exhausting.

I don't think you do get it.

Intellectual curiousity and being open minded are traits to be emulated, not denigrated.

But hey, enjoy your tv.

D

 

[tech2101]

It's refreshing to read an intelligent comment on here. Bobbie is right on target. Those that are talking, don't know, and those that know, aren't talking.

There is a chain of events in any accident/incident that are reviewed and investigated step by step. This one is not an exception, with a typical knee jerk media reaction, oversimplification, or sensationalization of events. Rational thought and discussion however is not as titallating as what passes for news today... a culture of info-tainment, superficial "reporting", inane questions, blather, and endless repetition. Much of the same is posted on these boards on a regular basis.

Stay tuned.

D

Exactly.

Am I the only one that thought the whole "key to the city" press conference was a little premature???

This is going to be a long and intensive investigation with much to be learned.

I look forward to reading the report.

 

[flybynite]

That CNN story was in the Disturber this morning. It goes into more detail and apparently it was a compressor stall.
The company is looking into it.

And the aviators on here can explain a compressor stall better than me.

 

[Crzipilot]

http://news.yahoo.com/s/ap/20090120/ap_on_...lane_splashdown

simply states there was a compressor stall 2 days prior. Also says US sent out 5k checks to each pax to replace luggage and such.

 

[Crzipilot]

The answer to that will come from the NTSB. Compressor stall could mean alot, it could mean nothing. Again, there is no way to tell, when the NTSB states what the significance of it is, then we will know.

For those that want to know what a compressor stall is....here ya go...

http://en.wikipedia.org/wiki/Compressor_stall
(1549 is already mentioned)

 

[nycbusdriver]

So my question is how does a compressor stall 2 days earlier impact on the events of the 15th and our feathered friends that were ingested apparently by both engines?

Or does it?

Bingo! It's purely coincidence. How could the flock of geese know that the airplane had a compressor stall 2 days previously? They could not have possibly read the logbook entry.

 

[BoeingBoy]

Or does it?

Just some background generalities, Piney...

Compressor stalls are pretty rare, and those not associated with some kind of foreign object damage are rarer still. However, as the engine ages - spends more time hung on the wing - it tends to become more susceptible to compressor stalls...they don't become common but just less rare. This is primarily due to erosion of the leading edges of the fan/compressor blades from sucking up sand and other fine debris from the ramps/taxiways/runways, although minor leading edge nicks can be smoothed out just like on a propeller. The fan/compressor section just isn't as efficient at pushing air through the engine as it was when the engine was new.

It turns out that the right engine had been on the wing nearly a year and a half longer than the left engine, accumulating over 7,000 additional hours. That would have made it slightly more susceptible to compressor stall. In other words, if you put the two engines on a test stand and introduced foreign objects starting with small and gradually increasing in size/amount the right engine would probably experience compressor stalls first.

In this specific case, it certainly appears that the size/amount of foreign objects (birds) was great enough to not just produce compressor stalls but cause both engines to fail.

Jim

 

[flybynite]

I seem to remember reading something about compressor stalls sometimes being caused by ice crystals. Is that correct or am I thinking about something else?

 

[Crzipilot]

Also understand, that just because an engine injests something, does it mean it's going to have a compressor stall and or engine failure.

Your almost talking the same, though in your example piney, your audi has trashed the turbo from injestion of a foreign object. I.E. the compressors have actually been damaged and shattered apart. With the jet engines, there doesn't always have to be damage to the engine to produce compressor stalls. On older engines we've had them stall due to angle of attack issues, bleed issues and such. It's simply a matter of the compressor (front part of engine) unable to efficiently move the air backwards into the actual turbine section of the engine. It gets starved for air.

Another example, friend of mine, different airline, had a take off, hit a flock of birds......

Heard the thump thump, and continued on. Flight was about an hour long, all engine indications were normal, nothing to indicate anything was wrong. When they landed and f/o did the post flight. As he looked at the left engine, the whole first stage of the engine was trashed, Almost 1/4 of the blades had been damaged, with blood and feathers everywhere. On the flight deck they had no indications that the engine had been damaged at all, much less that a bird had been sucked into the engine. So these engines are pretty durable, at the same time they can be finicky and fragile........

 

[Crzipilot]

This was some info on the condition of the engine from the NTSB briefing....

First stage fan blades intact on number 2 engine. Some damage/debris on nosecone.

 

[sharktooth]

I seem to remember reading something about compressor stalls sometimes being caused by ice crystals. Is that correct or am I thinking about something else?

Anything that interferes with the normal flow of air can cause a compressor stall. Ice, compressor blade degradation, fan blade deformation, improperly operating bleed valves and a host of other issues can cause such. Generally, a compressor stall is a symptom of other problems and, more often than not, causes (further) damage.

In any case, the stall indicates that the engine is operating close to the margins, closer than it should, and even subtle airflow disruptions can cause further damage.

The very rarity of such demands an inspection of an engine for the cause. Many times, as Jim says, the reduced operating margins can be mitigated, though, without engine rebuild, cannot be eliminated.

To answer those who ask, why would something two days prior affect the results of the 15th?

A compressor stall can be brought on by a disruption of airflow. A simple, yet sudden change, can be enough to bring on further compressor stalls, adding to damage and likely causing shutdown. Remember, this engine has already demonstrated that it is very close to compressor stall during certain regimes of flight.

One way to do that is a sudden yaw of the aircraft, changing the airflow in such a way that the fuel control cannot keep up with the flow changes. The subsequent, and likely, flameout will cause further damage. This yaw could come from a sudden shutdown of the other engine.

Also, these reduced operating margins means the engine has less chance of surviving further airflow disruptions, the bird-strike that normally would be survivable results in catastrophic shutdown.

It may not have anything to do with the events of the 15th. The investigation might reveal otherwise. That is why it is important to have a seat on as many committees as possible.

 

[BoeingBoy]

Sounds like what we're talking about here or am I comparing apples and grapes?

A little apples and grapes...

A jet engine (and it's a jet engine that turns the big fan up front - the whole assembly is called a turbofan) works on the same 4-stroke sequence that the engine in your Audi uses. It's what some call "suck, squeeze, burn, and blow":

1 - Suck the air in (the intake stroke in your Audi)

2 - Squeeze the air that's been taken in (the compression stroke in your Audi)

3 - Burn the air by mixing in the fuel and igniting the air/fuel misture (the power stroke in your Audi)

4 - Blow the resulting gases out (the exhaust stroke in your Audi)

What your turbocharger does is pump more air into the engine than would be achieved without the turbo - sorta equivalent to the ram effect that speed has - and use the exhaust flow to turn the compressor that pumps that extra air in (which is exactly what the turbine section of the jet engine does - turn the fan and compressor stages).

In your Audi there are barriers between the 4 cycles - the valves and spark plugs. The intake valve opens allowing air into the cylinder, all the valves are closed for the compression stroke and remain closed for the power stroke which is initiated when the spark plug fires, and the exhaust valves open for the exhaust stroke.

In a jet engine there are no barriers between the 4 cycles - it's only airflow that separates the cycles since those cycles occur in different sections of the engine. Air comes in the front, is compressed in the compressor section, goes into the burner cans where fuel and ignition takes place, and exits through the turbine section at the rear. If the intake or compressor airflow is disrupted enough there is nothing to prevent the hot expanding gases of combustion from going toward the front of the engine.

Jim