Engine stall after bird ingestion

[BlackandBrown]

Damage to which part of the engine, following bird ingestion, is most likely to cause an engine stall? N1 fan blades? Compressor blades/ stators? Any other parts? I appreciate it is subject to variables but I'm just curious which part is most susceptible. Thanks.

[barit1]

The compressor (HP compressor in a twinspool engine) is the most vulnerable - smallest airfoils, fastest turning, easiest to damage. I'll try to find teardown photos from Sully's Hudson landing after his birdstrike.

Download the teardown report HERE (http://dms.ntsb.gov/pubdms/search/document.cfm?fileid=419254&ntsbnum=DCA09MA026)

[lomapaseo]

Two probabilities at play here

1) the probability of what part of the engine will be damaged by birds

2) the probability of a stall for a given bird damage result.

In the large fan engines common to most large transports today (not turboprops) The highest probability for damage location is the fan. This is 10-100 times more likely than any other engine part.

A damaged fan alone may lead to an engine compressor stall, and if so, usually due to the resulting mismatch between the turbine workload between the Low speed and high speed turbines.

The Sully event was a rare outlier in a bird induced damage cause-effect

[Willit Run]

My opinion, the core engine is the one that will cause the compressor stall. That's the section that drives the fan. From personal experience and many stories from other folks, you can have an unbelievable amount of damage to a N1 fan and never know it from the performance or engine indications. I'm not saying that a N1 fan won't cause a stall, but the core engine is more likely to be the culprit.

[lomapaseo]

My opinion, the core engine is the one that will cause the compressor stall. That's the section that drives the fan. From personal experience and many stories from other folks, you can have an unbelievable amount of damage to a N1 fan and never know it from the performance or engine indications. I'm not saying that a N1 fan won't cause a stall, but the core engine is more likely to be the culprit.


All true :ok:

mostly the talk about the core compressor is the highest speed compressor which does not drive the fan. However its the effect on the core compressor that causes the surge and the effect that goes with birds is the flow capacity loss out of the fan due to damage unbalancing the airflows into the core compressor.

Yes indeed there are lots of horrible looking fan damages that never bother the core compressor (good news). And most of the bird stuff gets centrifuged out the fan duct or doesn't cause mechanical damage in the core (good news).

... but for those few events that do result in a surge coupled with damage (not just the temporary blockage of the air by the bird itself) is how I thought the question was posed

as always in the tech section we tend to provide random bits of info and hope that the question gets answered and we all learn something :)

[3holelover]

Great responses so far!
I think the simple, direct answer to the specific original question, is B - "compressor blades".
..but for fun, I'll add a bit of detail too....

With high bypass turbine engines, in the few percent of cases where a bird is ingested through the core (in my own experience, I'd guess that to be around 10% of ingestion incidents), after the fan, the bird first meets the Low Pressure (LP) compressor. (Sometimes referred to as the "booster" section). The interruption to airflow, though potentially problematic and/or itself damaging, is probably not as worrisome as the potential for damage by breaking some of the LP compressor blades, whose bits would then carry on downstream, possibly causing much damage to later stages of compressor...

I'd offer a rough estimate/educated guess that about half of those engines unfortunate enough to ingest a bird into their core, will have suffered enough damage to warrant removal.
Much is dependent on bird size, and engine speed.
In any core ingestion event, a boroscope is necessary... often damage has been caused, in the form of bent tips and corners, or small tears and even missing pieces, of compressor blades... As I said, I'd guess half the time the damage is all found to be within limits, but necessitating a more frequent boroscope schedule to monitor for further deterioration.

Cases, such as Sully's, where bird ingestion immediately renders the engine U/S, are relatively few and often include either very large, or very many birds.

Lomapaseo, I love your last statement! Great attitude! .... Learning something only requires an open mind... In my attempts to add something, I hereby offer my apologies for any incorrect info I may provide, and I hope I can learn with humility. :)