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Faro
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Uncontained Engine Failures: A Thing Of The Past?

Tue Jan 12, 2010 9:04 am

I understand that stand-alone uncontained engine failures (ie, internal engine failures not caused by bird strikes or other external causes) are becoming rarer and rarer. On present trends, may they substantially disappear one day?

Faro
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RE: Uncontained Engine Failures: A Thing Of The Past?

Tue Jan 12, 2010 6:27 pm

Yes. The day a failure-proof engine is designed.  Wink

Look, as long as engines are made out of protons, neutrons, and electrons, there will never be a day when a "failure-proof" engine is made. We can strive for perfection, but there ain't no such animal and there will never be.

Case in point: even today, several thousand years after the first rope was ever made, ropes still break from time to time, even new ropes that haven't been pushed to their limits yet.
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RE: Uncontained Engine Failures: A Thing Of The Past?

Tue Jan 12, 2010 7:22 pm



Quoting DocLightning (Reply 1):
Yes. The day a failure-proof engine is designed.  

I get your point but my question had a very practical point to it: if you can demonstrate that stand-alone uncontained engine failures are rarer and rarer -not totally eliminated mind you- you may conceivably be able to argue that your fan/compressor/turbine casing can be made lighter. From a neighbouring thread, fan casing size especially is one of, if not *the* principal criterium that will determine the necessary size and sturdiness of the engine. Therefore a smaller fan casing will have a cascade effect and allow you to downsize many other parts of the engine resulting in a significantly lighter engine.

The only remaining consideration are bird-strikes but I would be interested in knowing what % of bird-strikes result in uncontained engine failures. I suspect that it would be quite low.

Faro
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tdscanuck
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 13, 2010 12:13 am



Quoting Faro (Thread starter):
On present trends, may they substantially dsappear one day?

Depending on you define "substantially disappear", we might already be there. Stand-alone uncontained engine failures are already extremely rare.

Quoting Faro (Reply 2):
I get your point but my question had a very practical point to it: if you can demonstrate that stand-alone uncontained engine failures are rarer and rarer -not totally eliminated mind you- you may conceivably be able to argue that your fan/compressor/turbine casing can be made lighter.

Not without a change to the FAR's. 33.94 requires that the engine must contain a failure of the most critical fan/compressor blade and most critical turbine blade, without any allowance for probability of the failure (there are several FAR's of this type that require you withstand a certain failure, regardless of likelyhood).

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 13, 2010 9:02 am

Quoting Tdscanuck (Reply 3):
Not without a change to the FAR's. 33.94 requires that the engine must contain a failure of the most critical fan/compressor blade and most critical turbine blade, without any allowance for probability of the failure (there are several FAR's of this type that require you withstand a certain failure, regardless of likelyhood).

If an engine manufacturer were to go to the regulator with a detailed proposal demonstrating (statistically) a substantially equivalent level of safety for an engine with lighter casings, would they be taken seriously? Or are the relevant FAR's based on quasi-philosophical principals that are untouchable? After all, technical progress is being made all the time and should be reflected in suitably adapted regulations. I find it inconsistent that certain regulations should be based on probabilities and others on absolute criteria when you may statistically demonstrate that an equivalent level of safety is possible for the latter.

Faro

[Edited 2010-01-13 01:15:14]
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Jan 14, 2010 2:23 am



Quoting Faro (Reply 4):
Quoting Tdscanuck (Reply 3):
Not without a change to the FAR's. 33.94 requires that the engine must contain a failure of the most critical fan/compressor blade and most critical turbine blade, without any allowance for probability of the failure (there are several FAR's of this type that require you withstand a certain failure, regardless of likelyhood).

If an engine manufacturer were to go to the regulator with a detailed proposal demonstrating (statistically) a substantially equivalent level of safety for an engine with lighter casings, would they be taken seriously? Or are the relevant FAR's based on quasi-philosophical principals that are untouchable?

If I'm reading Tdscanuck's quote correctly, I think that FAR 33.94 requires that the casing must contain the failure, but does not stipulate what materials or designs are used in accomplishing this goal. So basically, if Ed's Jet Engines comes up with a design that verifiably does the job of meeting the appropriate FAR yet weighs only 3 pounds installed, then there's no reason why Ed's design wouldn't be approved.
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Jan 14, 2010 4:51 am



Quoting Faro (Reply 4):
If an engine manufacturer were to go to the regulator with a detailed proposal demonstrating (statistically) a substantially equivalent level of safety for an engine with lighter casings, would they be taken seriously?

Maybe...it would depend, a lot, on which ACO they were working with, and which engineers within that ACO. I think it's possible, if handled correctly.

Quoting Faro (Reply 4):
Or are the relevant FAR's based on quasi-philosophical principals that are untouchable?

Some of them are based that way, but their "untouchable-ness" is primarily a function of which person(s) at the FAA you're trying to convince.

Quoting Faro (Reply 4):
I find it inconsistent that certain regulations should be based on probabilities and others on absolute criteria when you may statistically demonstrate that an equivalent level of safety is possible for the latter.

It's not as bad as it sounds...it's mostly meant to head off overly optimistic engineering. For certain things, experience has shown that "Don't worry, it won't fail" is not an acceptable justification of safety. It also has some basis in the nature of aviation accidents; they're almost always a chain of failure that, by themselves, are individual harmless but when connected cause a disaster. By putting in "you *must* be able to withstand this failure* regulations, you put breaks in the chain of causation that will prevent some failure chains from getting all the way to a catastrohpic event. They also provide some allowance for unknown-unknowns..."We don't care how or why it failed, but you have to be able to handle it if it does."

Quoting TSS (Reply 5):
If I'm reading Tdscanuck's quote correctly, I think that FAR 33.94 requires that the casing must contain the failure, but does not stipulate what materials or designs are used in accomplishing this goal.

Correct.

Quoting TSS (Reply 5):
So basically, if Ed's Jet Engines comes up with a design that verifiably does the job of meeting the appropriate FAR yet weighs only 3 pounds installed, then there's no reason why Ed's design wouldn't be approved.

Correct. But, under the current wording, "we've designed an engine that won't throw turbine blades" would not be an acceptable means of compliance with the FAR. You could always request an AMOC (alternate means of compliance)...this is, for example, how the 747 and 787 get away without any openable cockpit windows. You could also go for a finding of equivalent level of safety, but when dealing with events that are really low probability anyway (like rotor bursts) you'd be hard pressed to prove that because the error bands are so wide.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Jan 14, 2010 9:11 am



Quoting Tdscanuck (Reply 6):
Maybe...it would depend, a lot, on which ACO they were working with, and which engineers within that ACO. I think it's possible, if handled correctly.

I wonder why no-one is trying it? Or maybe they have and were rebuffed. It seems a comprehensive way to reduce engine weight, which the American manufacturers especially would appreciate. Will drop a IM to Lightsaber on this one...

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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 15, 2010 12:54 am



Quoting Faro (Reply 7):
I wonder why no-one is trying it?

I suspect they might not know how...jet rotors already get about as comprehensive an NDT inspection as we know how to do with today's technology, and rotor bursts still happen. They'd need to come up with some manufacturing process that could "guarantee" (to some level of certainty acceptable to the FAA) that a failure wouldn't occur in some interval (likely 1e-9) and I don't think they know how to do that yet.

Quoting Faro (Reply 7):
Or maybe they have and were rebuffed.

Also possible...this is not the sort of thing that would likely ever see public light if it had been tried.

Quoting Faro (Reply 7):
It seems a comprehensive way to reduce engine weight, which the American manufacturers especially would appreciate.

Well, GE has gone to carbon fiber fan cases which, according to their PR, save several hundred pounds per shipset, so they're definitely chasing the goal.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Pa

Fri Jan 15, 2010 9:05 am



Quoting Tdscanuck (Reply 8):
I suspect they might not know how...jet rotors already get about as comprehensive an NDT inspection as we know how to do with today's technology, and rotor bursts still happen. They'd need to come up with some manufacturing process that could "guarantee" (to some level of certainty acceptable to the FAA) that a failure wouldn't occur in some interval (likely 1e-9) and I don't think they know how to do that yet.

The question is what are their priorities? To address weight issues via composites and other material innovations or to launch a wholesale campaign to improve reliability with the specific goal of updating/abrogating FAR 33.94? In the traditional sense engine manufacturers are closer to the physical world than they are to the law and that is a pity because the gains to be had from a revised FAR 33.94 are potentially much more significant.

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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 15, 2010 11:38 am

Well, the regulations are about uncontained blades. There is nothing that is going to contain a disk failure. Nothing designed for it. A botched disk repair, or a flaw on the original disk could lead to this. It will always be a possibility.

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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 15, 2010 3:02 pm



Quoting MarkC (Reply 10):
Well, the regulations are about uncontained blades. There is nothing that is going to contain a disk failure. Nothing designed for it. A botched disk repair, or a flaw on the original disk could lead to this. It will always be a possibility.

Other than UA-232 and the 767 on the ground at LA, how many times has there been a disk failure? As far as I know, UA-232 is the only crash on record due to a disk failure, pointing out how rare an event it is.
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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 15, 2010 7:31 pm



Quoting Faro (Thread starter):
uncontained engine failures (ie, internal engine failures not caused by bird strikes or other external causes)

?? This is not the meaning of the term "uncontained" engine failures. Uncontained failure means that fan blades or other material breach the nacelle and possibly cause damage to the airframe, as the engine disintegrates at high speed. For example, early Il-62 engines had "uncontained" failures where one engine sabotaged the engine next to it.

Maybe you meant Unprovoked engine failures. Then, yes they have already been reduced nearly to the limit of human capability. Considering redundancy, then yes, total engine failure has been eliminated. This is the logic of ETOPS. The probability both engines will fail on your flight to Hawaii is so low, that it is assumed to be zero.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 9:15 am

Delta had an MD80 throw a disk due to a manufacturing flaw about 10 years ago. I know someone who had to testify on that one. It was on the takeoff roll, and I believe it killed 2 or 3 people.

Air New Zealand, USair, and American had the identical B767 CF6 1st stage HPT disk uncontained failure over the course of about 2 years, with the last happening about 3 years ago. New Zealand and USair got lucky as the debris did not go through the plane. American was during a ground run up, and the disk did go through the plane, damaged the fuel tanks, and the plane was destroyed by fire. This was a design flaw.

There was a regional jet uncontained failure about 2 years ago. I think it was MESA.

I know of several others that never made the news. Even if you were on a plane that had it, would you know? If the holes were not visible from the cabin, all you know is that the captain said they lost an engine, and had to land. Of course, the FAA is very interested, but to the mainstream media, an engine failure is an engine failure. No need to elaborate.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 9:21 am



Quoting Flighty (Reply 12):
Maybe you meant Unprovoked engine failures.

Exactly, yes. The engine throwing a tantrum despite of the birdies.

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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 10:25 am

Quoting Faro (Thread starter):
I understand that stand-alone uncontained engine failures (ie, internal engine failures not caused by bird strikes or other external causes) are becoming rarer and rarer. On present trends, may they substantially disappear one day?

I have been around and worked on jet engines since 1980, and can count on one hand, and maybe borrow a finger or two from the other hand, how many uncontained engine ( non F.O.D. related) failures I have seen. They may have tapered off some in the last decade, but all in all, they are very rare. You just can not plan for everything.

[Edited 2010-01-16 02:28:40 by ex52tech]
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 11:41 am



Quoting MarkC (Reply 13):
I know of several others that never made the news. Even if you were on a plane that had it, would you know? If the holes were not visible from the cabin, all you know is that the captain said they lost an engine, and had to land. Of course, the FAA is very interested, but to the mainstream media, an engine failure is an engine failure. No need to elaborate.

I fully agree.
Uncontained engine failures mostly don't reach the media.

If you want to read some recent (uncontained) disk failures try the following :

http://rgl.faa.gov/Regulatory_and_Gu...95d2!OpenDocument&ExpandSection=-4

http://www.flightglobal.com/articles...re-ravages-american-767-200er.html

http://cryptome.org/ge-failures.htm

http://www8.landings.com/cgi-bin/get...ass=12345&ADS/2005/2005-25-09.html

http://www.gpo.gov/fdsys/pkg/FR-2009-12-10/html/E9-28858.htm

So, uncontained engine failures (GE,P&W and RR) are no thing of the past, but still reality.
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 4:24 pm



Quoting MarkC (Reply 13):
Delta had an MD80 throw a disk due to a manufacturing flaw about 10 years ago. I know someone who had to testify on that one. It was on the takeoff roll, and I believe it killed 2 or 3 people.

Yes, I recall that one now. The simple fact is that you have a lot of very highly stressed components rotating at very high speed in a jet engine, and weight is critical. So it is nearly impossible to totally eliminate failures. It is remarkable, though, how reliable they are.
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 16, 2010 7:42 pm



Quoting SEPilot (Reply 17):
Yes, I recall that one now. The simple fact is that you have a lot of very highly stressed components rotating at very high speed in a jet engine, and weight is critical. So it is nearly impossible to totally eliminate failures. It is remarkable, though, how reliable they are.

They are reliable, and you just can't catch every little flaw that can take years to manifest itself into a failure. As in the fan disk on that CF6 on the UA DC10 (Sioux City), or that DL MD80, those flaws had been there for years.

Every time I see an MD80 takeoff, I think of that incident, several fan blades penetrated the cabin, and killed that mother and her son.

The JT8-217/-219 had a weak design feature in the turbine vane sectors, they had pins that would hold the assembly in place, and if the pins all sheared the vane sector would start rotating with the turbine wheels, and eventually cut through the case like a saw. It happened on an AA MD80 inbound into MSP mid 80's. Actually saw that engine in the shop, and the case was cut clean like you meant to do it. This engine threw those turbine vanes all over, some striking the fuselage. We spent many nights Xraying those turbine pins for many years.
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RE: Uncontained Engine Failures: A Thing Of The Pa

Tue Jan 19, 2010 10:12 am

Quoting SEPilot (Reply 17):
The simple fact is that you have a lot of very highly stressed components rotating at very high speed in a jet engine, and weight is critical. So it is nearly impossible to totally eliminate failures. It is remarkable, though, how reliable they are.



Quoting Ex52tech (Reply 18):
They are reliable, and you just can't catch every little flaw that can take years to manifest itself into a failure.



Quoting Tdscanuck (Reply 8):
They'd need to come up with some manufacturing process that could "guarantee" (to some level of certainty acceptable to the FAA) that a failure wouldn't occur in some interval (likely 1e-9) and I don't think they know how to do that yet.

No-one can rule out future incidents/accidents due to unknown manufacturing/design flaws or faulty maintenance in the absolute. What to my mind is important is how likely they are per flight hour. From Tom's post, manufacturers cannot today demonstrate an insignificant probability of failure via the manufacturing process so that it is difficult to challenge FAR 33.94 on a manufacturing-process front.

On the other hand out of curiousity, it would be interesting to know what the *effective* failure rate per flight hour is these days for uncontained disk/blade failures on some of the more reliable engines...would it perhaps tend to the 1e-9 interval? A purely historical statistical approach won't give you comfort re the unkown failure modes but it would nonetheless be interesting...

Faro

[Edited 2010-01-19 02:45:16]
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RE: Uncontained Engine Failures: A Thing Of The Past?

Tue Jan 19, 2010 5:36 pm



Quoting Tdscanuck (Reply 8):
that a failure wouldn't occur in some interval (likely 1e-9) and I don't think they know how to do that yet.

The "fail safe" or "no single failure" concept is not going to be discarded either. Dual load path rotors with no latent failure modes? I don't see that happening any time soon  Wink
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 20, 2010 2:36 am



Quoting Faro (Reply 19):
On the other hand out of curiousity, it would be interesting to know what the *effective* failure rate per flight hour is these days for uncontained disk/blade failures on some of the more reliable engines...would it perhaps tend to the 1e-9 interval?

It's not down that low yet. The total fleet life of the CFM56 series engines, which is probably the most prolific modern engine out there, probably hasn't passed a billion hours yet (figure ~5000 aircraft running 10 hours per day for 10 years = ~180 million hours) and it's had more than one uncontained disk/blade failure (I think). But it is getting there.

Quoting Mrocktor (Reply 20):
The "fail safe" or "no single failure" concept is not going to be discarded either. Dual load path rotors with no latent failure modes? I don't see that happening any time soon

Really good point. Although, if such a thing could be designed, that would be awesome. Keep in mind, though, that you've got two engines...completely shredding one is still OK by the fail safe and/or no single failure criteria.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 20, 2010 12:54 pm



Quoting Tdscanuck (Reply 21):
Quoting Faro (Reply 19):
On the other hand out of curiousity, it would be interesting to know what the *effective* failure rate per flight hour is these days for uncontained disk/blade failures on some of the more reliable engines...would it perhaps tend to the 1e-9 interval?

It's not down that low yet. The total fleet life of the CFM56 series engines, which is probably the most prolific modern engine out there, probably hasn't passed a billion hours yet (figure ~5000 aircraft running 10 hours per day for 10 years = ~180 million hours) and it's had more than one uncontained disk/blade failure (I think). But it is getting there.

FWIW, Aviation Safety Net has no CFM56-powered aircraft involved in uncontained engine failure occurences:

http://aviation-safety.net/database/dblist.php?Event=ACEU

I doubt though that this listing is complete but if it is, this would be a remarkable achievement.

Also, from CFM's site, total engine hours is advertised as "over 400 million flight hours" across all engine/aircraft combinations:

http://www.cfm56.com/products

Faro
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Jan 21, 2010 5:58 am



Quoting Faro (Reply 22):
FWIW, Aviation Safety Net has no CFM56-powered aircraft involved in uncontained engine failure occurences:

There's at least that Southwest 737 that barfed pieces of the fan through the nacelle in the last few years.

Quoting Faro (Reply 22):
Also, from CFM's site, total engine hours is advertised as "over 400 million flight hours" across all engine/aircraft combinations:

That sounds right...I forgot to double my back-of-the-envelope guess for the fact that each airplane hour is two engine hours.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Jan 21, 2010 11:17 am



Quoting Tdscanuck (Reply 21):
Keep in mind, though, that you've got two engines...completely shredding one is still OK by the fail safe and/or no single failure criteria.

Only because planes are designed to survive the damage from the first engine's debris (FAR25.903(c), AC 20-128A).

If we are speculating about regulations eventually accepting that "engines don't burst", we have to assume that this requirement would no longer be in place - and thus that the engine itself would have to guarantee an equivalent level of safety without relying on the airframe to survive fragment impacts.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 22, 2010 9:24 am



Quoting Faro (Thread starter):
On present trends, may they substantially disappear one day?

Well they have substantially dissappeared now, but still occur.

Quoting Ex52tech (Reply 18):
The JT8-217/-219 had a weak design feature in the turbine vane sectors, they had pins that would hold the assembly in place, and if the pins all sheared the vane sector would start rotating with the turbine wheels, and eventually cut through the case like a saw.

This is a very interesting comment and has raised several questions in my mind that maybe you can shed some light on.

Since you wrote this in the past tense, I am curious: has the design been revised and improved? If so, what was changed; if not, what MX protocols were instituted to reduce the likelihood of this failure mode? Is this a design feature found on other types of engines? Do you know what the perceived advantage of that design was? Thanks!
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 22, 2010 10:25 am



Quoting Tdscanuck (Reply 23):
Quoting Faro (Reply 22):
Also, from CFM's site, total engine hours is advertised as "over 400 million flight hours" across all engine/aircraft combinations:

That sounds right...I forgot to double my back-of-the-envelope guess for the fact that each airplane hour is two engine hours.

Just an after-thought: will blisks improve matters or would they reset the flight hours counter to zero given that they're (relatively) new and untried?

Faro
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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 22, 2010 11:43 pm



Quoting Faro (Reply 26):
Just an after-thought: will blisks improve matters or would they reset the flight hours counter to zero given that they're (relatively) new and untried?

I suspect they'd start you over, because they completely change the blade mounting (the major offender in blade liberations) and they alter the load path inside the rotor, which probably alters all your calculations about rotor life limits.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Pa

Sat Jan 23, 2010 12:00 am



Quoting Ex52tech (Reply 18):
Every time I see an MD80 takeoff, I think of that incident, several fan blades penetrated the cabin, and killed that mother and her son.

It wasn't fan blades, it was a large portion of the turbine hub that went through the fuselage.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 4:13 pm

I won't go into the detail of all the regulatory discussion, suffice to say the FAA-ECO has had an initiative together with industry participation for at least 15 years, under Safer Skies, to reduce uncontained failures. This is multi-pronged and several AC's have been released on the subject. I participated on this committee representing GE. One of the outputs was this AC

http://rgl.faa.gov/REGULATORY_AND_GU...256a84005b21ba/$FILE/ac33.14-1.pdf

which will give you a direct view of how the industry and FAA have approached this subject via elements in all aspects: design methods, manufacturing controls and in-service management.
My views are not necessarily the views of the GE Company
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 5:00 pm



Quoting Jetlife2 (Reply 29):

Thank you for sharing! I'm not in aviation, but a simple question: Does this methodology imply that inspections during the lifetime of a rotor are redundant? That is, if you design a component with a failure rate of 1 in 10**9, inspections will not affect outcome? Or is the goal of 10**9 based on an inspection methodology?
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 5:19 pm



Quoting Comorin (Reply 30):
Does this methodology imply that inspections during the lifetime of a rotor are redundant?

No. It actually requires them. Post manufacture inspections under the old methodology (safe life) are redundant from a purely technical perspective, although mid-life inspections can help protect you from a failed initial inspection.

Damage tolerance usually requires periodic inspection to place an upper limit on the probable flaw size at intervals during the service life.

Quoting Comorin (Reply 30):
That is, if you design a component with a failure rate of 1 in 10**9, inspections will not affect outcome? Or is the goal of 10**9 based on an inspection methodology?

Inspections under safe life won't affect the outcome; inspections under damage tolerance will.

Tom.
 
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 5:38 pm



Quoting Faro (Reply 22):
FWIW, Aviation Safety Net has no CFM56-powered aircraft involved in uncontained engine failure occurences:

Almost lost this one. The Vertical spar was cut, if the tail had come off,......

http://www.fss.aero/accident-reports/look.php?report_key=950
"Title: Uncontained engine failure, Boeing B737-300, September 12, 1999
Micro summary: This Boeing B737-300 experienced an uncontained engine failure on climb."
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 8:22 pm



Quoting Tdscanuck (Reply 31):
Damage tolerance usually requires periodic inspection to place an upper limit on the probable flaw size at intervals during the service life

I guess that is the other concept that needs to work hand-in-hand with safe life. Thank you for clarifying that.

I have on ongoing interest in Software Reliability as part of my work, and am always fascinated by the adoption of concepts from the Manufacturing domain.

Is the Safety Engineering behind IFSDs completely unrelated to Rotor issues? That is, do you look at other system components unrelated to rotor metallurgy?

Again, thanks for taking the time to answer these amateur questions!
 
tdscanuck
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RE: Uncontained Engine Failures: A Thing Of The Past?

Sat Jan 23, 2010 8:52 pm



Quoting Comorin (Reply 33):
Is the Safety Engineering behind IFSDs completely unrelated to Rotor issues? That is, do you look at other system components unrelated to rotor metallurgy?

Absolutely. An IFSD due to rotor burst is probably the least common of all IFSD's. The overall reliability of the entire propulsion system plays a far larger roll in flight operations and real world IFSD's than rotor issues.

Tom.
 
mrocktor
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RE: Uncontained Engine Failures: A Thing Of The Past?

Mon Jan 25, 2010 11:49 am



Quoting Tdscanuck (Reply 34):
Absolutely. An IFSD due to rotor burst is probably the least common of all IFSD's. The overall reliability of the entire propulsion system plays a far larger roll in flight operations and real world IFSD's than rotor issues.

 checkmark 

When concerned with multiple IFSD especially the engines themselves (i.e. gas turbine) are, by far, the most reliable parts.
 
ex52tech
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 27, 2010 6:52 am



Quoting Movingtin (Reply 28):

It wasn't fan blades, it was a large portion of the turbine hub that went through the fuselage.

DL MD88 N927DA July 6 1996 PNS FL. Failure of the fan hub on the LH #1 engine caused fan blades to penetrate the fuselage killing two passengers, and injuring two more. That is the incident I was talking about.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
ex52tech
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 27, 2010 7:14 am



Quoting PGNCS (Reply 25):

Since you wrote this in the past tense, I am curious: has the design been revised and improved? If so, what was changed; if not, what MX protocols were instituted to reduce the likelihood of this failure mode?

My writing it in the past tense was a slip on my part, it was simply because I have not worked on a JT8-217/-219 in over ten years, and have not overhauled one in over twenty. There were some mods to make that assembly more robust, but we were X raying those engines up until we got rid of the type. As long as you keep a close eye on that area, the engine can be removed and the problems can be addressed before there is a failure.

Quoting PGNCS (Reply 25):
Is this a design feature found on other types of engines? Do you know what the perceived advantage of that design was?

I am not sure if any other design used that method of securing the vane sectors, none of the other engines I overhauled used that design.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
ex52tech
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 27, 2010 7:32 am



Quoting Ex52tech (Reply 36):
DL MD88 N927DA July 6 1996 PNS FL. Failure of the fan hub on the LH #1 engine caused fan blades to penetrate the fuselage killing two passengers, and injuring two more. That is the incident I was talking about.

3 had minor injuries. NTSB identification: DCA96MA068. NTSB report AAR-98/01
"Saddest thing I ever witnessed....an airplane being scrapped"
 
MarkC
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RE: Uncontained Engine Failures: A Thing Of The Past?

Wed Jan 27, 2010 12:01 pm



Quoting Faro (Reply 26):
Just an after-thought: will blisks improve matters or would they reset the flight hours counter to zero given that they're (relatively) new and untried?

Now thats interesting. The PW1000G is going to have blisks. I want to say this is the first commercial engine to have them, but I am not sure of other MFGs. I wonder if PW is able to get away with less casing material for a blisk than a bladed disk.

I'm going to have to find out.
 
jetlife2
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RE: Uncontained Engine Failures: A Thing Of The Past?

Fri Jan 29, 2010 2:18 am



Quoting MarkC (Reply 39):
I want to say this is the first commercial engine to have them, but I am not sure of other MFGs.

Blisks have been in commercial service for a long time. The largest in service is the GE90-115B HPC Stage 1 Blisk. Others are the CF34-3B, -8C/D/E, -10...plus GEnx upcoming. Casing design is not much affected by use of a blisk vs a bladed disk. However the blisk itself brings weight benefits to the assembly.
My views are not necessarily the views of the GE Company
 
mrocktor
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RE: Uncontained Engine Failures: A Thing Of The Past?

Tue Feb 02, 2010 5:03 pm



Quoting MarkC (Reply 39):
I wonder if PW is able to get away with less casing material for a blisk than a bladed disk.

No. The blade out test specifies 80% of the blade must be released and that is that.
 
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jambrain
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Feb 04, 2010 1:23 am



Quoting MarkC (Reply 39):
I want to say this is the first commercial engine to have them, but I am not sure of other MFGs.

RR have already flown a BR725 on flight test with blisks (EIS in 2012 as the sole powerplant for the Gulfstream G650)

http://www.rolls-royce.com/civil/products/smallaircraft/br725/

Quote:

Ten-stage high-pressure compressor incorporates the latest aerodynamic improvements and stages of blisks for improved performance and optimized weight

GE say 3 out of 10 stages of the GEnx-2B compressor are blisks for 748i
http://www.kuwaitairtransport.com/ge2.pdf
Jambrain
 
Viscount724
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RE: Uncontained Engine Failures: A Thing Of The Past?

Thu Feb 04, 2010 2:24 am



Quoting Ex52tech (Reply 38):
Quoting Ex52tech (Reply 36):
DL MD88 N927DA July 6 1996 PNS FL. Failure of the fan hub on the LH #1 engine caused fan blades to penetrate the fuselage killing two passengers, and injuring two more. That is the incident I was talking about.

3 had minor injuries. NTSB identification: DCA96MA068. NTSB report AAR-98/01

Photo of the aftermath of that event.

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