United B777 engine failure

[GlobalNav]

Nevertheless, it seems like such (internal) cracks would be difficult to detect. Was this test/inspection methodology evaluated and proven on the basis of its effective detection of external and internal cracks?

[lomapaseo]

but if they remain internal then the blade never fails

I think that a fatigue life-limit has to be developed here assuming a critical condition, unless of course if this is driven by an abnormal operating condition

still waiting a more clear assessment of this

[etudiant]

Exactly, the issue is whether an internal crack can potentially produce a catastrophic failure without externally visible manifestations.
If it can, fatigue life limits must be set appropriately, not an easy task.

[JPcont]

True, but it seems that the fatigue crack has penetrated the surface and the fatigue region is quite long. It would be interesting to hear how long it took from the detectable "surface penetration" to the catastrophic failure.

[Droop Snoot]

JPcont:

From the UAL 1175 report:

"Beyond 0.032” deep from the origin was a region of predominantly fatigue striations, suggesting stable low cycle fatigue (LCF) propagation (Figures 17– 1 9). A striation count performed within a rectangular zone through this stable LCF region ~0.032” –0.153” from the origin estimated 5500 cycles of LCF crack propagation (Figure 20). The blade was last inspected via thermal acoustic imaging (TAI) ~1400 cycles ago in 2015. "

[bsieker]

Exactly, the issue is whether an internal crack can potentially produce a catastrophic failure without externally visible manifestations.
Not exactly. It is well-known that such internal cracks can cause catastrophic blade failures.

If it can, fatigue life limits must be set appropriately, not an easy task.
Internal cracks is exactly what the Thermal-Acousting Imaging process is designed to find, before they are visible from the outside, and crucially, long before they grow large enough to cause in-flight failures. The NTSB found problems with how those inspections were handled at P&W, and it will certainly be a point of close scrutiny if and how those processes have changed, or if assumptions about crack propagation were flawed.

The assumption is that cracks which are too small to be found during TIA will not propagate during the inspection interval to a size that could make a blade fail in flight.

And you are right, setting this interval correctly is hard.

[etudiant]

Thank you for this informative post
It suggests that the inspection process was ineffective at Pratt, which ties into the earlier reports that the signal was noted but dismissed as a flaw in the sensing material.

[iranu]

Dye pen can only be used on the outer surface. The method of flaw detection for internal surfaces is Thermal Acoustic Imaging (TAI). This is a P&W technique developed in 2005 for the specific purpose of finding internal fan blade cracking.

[BDAttitude]

Never heard of TAI - and what comes up on wikipedia does not seem to relate to metallurgy but to tissue materials.
So after some googling ... TAI seems to be a P&W internal/proprietary designation for ultrasound lockin thermography.
A body is excited by an ultrasound transducer which is then subjected to thermal imaging. Defects will create hotspots by friction in cracks.
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/902x596/image_16cb1b9c1c7db08a37e0d94af04b0514730bd739.png

[bsieker]

That's thermoacoustic imaging (https://en.wikipedia.org/wiki/Thermoacoustic_imaging). That wikipedia article links to the article about the P&W technique called thermal acoustic imaging (https://en.wikipedia.org/wiki/Thermal_acoustic_imaging).

[Ex FSO GRIFFO]

So NOW I read that the (some of the ) pax have started a 'class action' against the airline for the 'emotional stress' of seeing the engine 'on fire'......despite the successful handling of the EMERGENCY and NIL pax injuries.

I reckon that ALL of the pax should be 'passing the hat around' and buying the flight crew a beer ...or two....or three....or as many as they can hold......
"Say When".....
That's an 'Aussie' viewpoint.!

Cheeerrrsss....

[BDAttitude]

You know, being of european origin, when I was 10 years younger, I very much opposed the 'murican way of dealing with litigation.
However having matured somehow ... if the manufacturers and airlines can get away with calling this dismantled smoldering lump of scrap metal and the corresponding hole in the fuselage a "contained failure" ...
... buy the crew some bottles of the finest whisky on earth but sue the hell out of that airline, that after a merger gave away more modern planes with a more reliable engine option for these .....

[WillowRun 6-3]

A necessary part of having a court system and legal system open to all citizens (or that's the goal, obviously with inequalities still present) is the truism that people can and do file frivolous lawsuits (. . . .SLF/attorney).

This one, I'll venture to predict, will have a very short life. The airline did not breach any duties to anyone. Even if we set aside the rather important fact that the flight ended safely despite the challenges imposed by the emergency, and just looking at the alleged upsetting visual of an engine in serious failure and distress, as far as my legal knowledge goes there is no legal obligation on the part of an airline to guarantee that the inherently hazardous activity of travel by air will never present scary moments. (Yes, air travel is the safest mode of travel statistically, but it's still inherently hazardous -- it's just that people and machines have become very good at doing it safely.)

For some other community on some other forum, maybe this case is grist for the mill which grinds on and on about changing court rules so that "the loser pays" the other side's attorney's fees becomes the rule, not the exception, in courts in the U.S.

[GlobalNav]

I suppose the aviation version of ambulance chasers abounds. If I’m distressed by what I see on TV, I turn it off or change the channel. The window shades were still working, right? To be fair, just about anyone would be scared spitless. These pax should kiss their loved ones and be grateful they still can.

[DaveReidUK]

WillowRun 6-3

"Even if we set aside the rather important fact that the flight ended safely despite the challenges imposed by the emergency"

I'd have though that had already been allowed for, given that nobody is suing for serious injury, or death.

"the inherently hazardous activity of travel by air"

It's interesting to know how the lawyers view air transport.

[lomapaseo]

Big bucks $$$$ no matter who wins

[Alpine Flyer]

Not really in a quota litis system. US attorneys only get paid a percentage of what their clients get, so if there's no payout they should not get paid. Drawback is that the defendant has to pay for his own attorney (while in other countries the losing party pays for both attorneys), so there's always an incentive for the defendant to settle rather than draw things out in court and incur higher fees.

Plus with a jury of laypersons adjudicating you may not expect the "air travel is inherently dangerous, so don't sue us for being scared" logic to prevail.

[WillowRun 6-3]

Well, in the view of the law in the U.S. an inherently hazardous activity is something which carries very significant risks if not done correctly, significantly more severe than some concept of ordinary activities. Using dynamite in an excavation project is an example I seem to recall. It's very hazardous stuff, if it's not done the right way. The mode of transport has become very safe and reliable . . . but when the proverbial Swiss cheese holes fall or are pushed into alignment, "smoking hole in the ground". Thin aluminum tube, 30 thousand feet, perhaps Mach .8, not easy to walk away from something gone wrong.

Claiming injury from traumatic sightings of the engine in failure mode would not already discount for the safe return of the flight to Denver. I'm not a hundred percent convinced this is an actual claim being filed, but if it is, the suit would assert the injury being claimed didn't get canceled out by the fact of the safe return.

Of course there are the lawyers of ill-repute, chasing ambulances. There also are very highly experienced and effective attorneys who vindicate the rights of people harmed or killed by the kinds of negligence, malfeasance and other wrong-doing so knowledgeably decried on this and similar forums.

And I'd have to see it to believe it - how any advocate could present this case in a court of competent jurisdiction and give proper respect to the pilots, yet still claim the (supposedly) injured passengers are entitled to anything.

[DaveReidUK]

WillowRun

"And I'd have to see it to believe it - how any advocate could present this case in a court of competent jurisdiction and give proper respect to the pilots, yet still claim the (supposedly) injured passengers are entitled to anything."

So the legal argument is "With hindsight, you shouldn't have been scared because it all ended well, even though you had no way of knowing that at the time" ?

[WillowRun 6-3]

No. The legal argument is that the airline is not an absolute guarantor of a fun, care-free travel experience, or even an experience free of fear. There is no free-standing right to sue another party just on the basis of something happening that one does not like or enjoy. There must be a legal category of "duty", which the claim alleges that the party being sued has breached, or another similar category of legal right and corresponding legal remedy. (Sorry to get all pedantic, but you asked.)

There are people who become very upset and fearful when they travel by air, sometimes with knowledge of this tendency beforehand, sometimes without such knowledge. Do they have a right to claim legal injury because the plane took off, it went very fast down the runway, they felt the aircraft turn and bank, they were scared?

What's different here is that the engine failed and presented a pretty scary sight on the wing. But while that obviously occurred, the airline did not, in my view, breach any known, existing duty (in the legal sense of that term) owed to passengers. It had complied with all mandated inspection timelines and procedures, for example (I'm assuming this would be factually correct). It operated the flight in accord with all required rules and procedures. And the pilots .... well, that's been said already more than enough times.

It's just not feasible to say much of anything worth anyone's time to read, dissecting the notion that many parties who are sued over nonsense claims nevertheless settle just to get rid of the nuisance. Just this: paying to get rid of nonsense claims does occur. So do hard-headed courtroom tactics that work out to much the same as "loser pays" attorneys fees of the vindicated defendant.

[DaveReidUK]

WillowRun

"But while that obviously occurred, the airline did not, in my view, breach any known, existing duty (in the legal sense of that term) owed to passengers. It had complied with all mandated inspection timelines and procedures, for example (I'm assuming this would be factually correct)."

Fair enough. That may or may not turn out to be a valid assumption.

[568]

WillowRun 6-3

"It had complied with all mandated inspection timelines and procedures, for example (I'm assuming this would be factually correct)".

As David pointed out that may or may not be the case.
Look back at the FAA fine Southwest received when required maintenance procedures weren't carried out.

Press Release – FAA Seeks $12 million Civil Penalty Against Southwest Airlines (https://www.faa.gov/news/press_releases/news_story.cfm?newsId=16754)

[WillowRun 6-3]

Sometimes lawyers get down to even lower repute because the profession has to say, "it depends." Oh well....

I think, after the prior United flight with a blade failure in the same type of engine, if the airline then failed to comply fully with all mandated inspection timelines and procedures...that could quite likely amount to something that the "it depends" expression is meant to cover.

Lurking in the background here is the fact that, at the time of a second anniversary of the ET 302 accident with far more significant losses and wrongful acts and the Lion Air 610 losses as well, a claim for fright, by itself and without any other harmful effects (reported so far), seems.... well, it seems trivial in comparison.

(As long as the prior United flight has become possibly relevant, just to note the interview of the Captain of that flight recently posted on another site was just a fascinating glimpse into a world an SLF ought to realize one knows virtually nothing, really, about.)

[tdracer]

If they are suing United (and assuming press reports are correct - which is a big assumption), I don't see that they have a case. The published inspection interval for the fan blades was 5,000 cycles, and (reportedly) the failed blade had ~1,600 cycles since inspected. So United had done due diligence.
OTOH, if they are suing Pratt, they might have a case. Given this was the third fan blade failure is less than 3 years - and all three had presumably passed inspection - P&W certainly had plenty of evidence that either their inspection process was inadequate, or the inspection interval was too long (or both).
All that being said, I really don't think just being scared is grounds for significant damages. If it was, there are plenty of drivers out there that have scared the :mad: out of me that I could be suing...

[WHBM]

There also are very highly experienced and effective attorneys who vindicate the rights of people harmed or killed by the kinds of negligence, malfeasance and other wrong-doing so knowledgeably decried on this and similar forums.
As none of these outcomes remotely apply in this case, this just seems to be taking a self-appointed opportunity to brag about one's profession.

[lomapaseo]

That's one jury vote (yours), let's see what the other jury members decide based on the arguments put forth by the lawyers on both sides.

The arguments may be a tad subjective, but the outcome is objective in deciding a level of fault

[WillowRun 6-3]

WHBM
Uh, no. The quote you criticize wasn't made gratuitously. See 265, GlobalNav asserted that aviation ambulance chasers "abound", usually meaning that they're abundant.

[568]

Non sunt nobis tere

Is this a technical aviation forum or what?

[WillowRun 6-3]

From Seattle Times story today on United's big aircraft order:

"Separately, [United Chief Commercial Officer] Nocella gave an update about the airline’s two dozen older 777-200s that have been grounded since February after a Pratt & Whitney engine on one blew up shortly after take-off from Denver.That incident, the third instance of a hollow metal fan blade breaking off and destroying the engine, grounded all of those 777 models with the same engine worldwide.

With international passenger travel at very low levels, United hasn’t needed those planes, but hopes they will be ready for the expected upturn.

'We’re working with the FAA, Boeing and the Pratt & Whitney company to return those aircraft to service late this summer or early fall,' Nocella said. 'We think that timing lines up with the international rebound we expect later this year or next year.'”

[LandIT]

The bird seems to be bound for storage in the Mojave desert for a while.

https://simpleflying.com/united-boeing-777-engine-failure-storage/

[DaveReidUK]

... joining several more of its less newsworthy stablemates there.

AFAIK, there are no longer any non-ER B772s flying anywhere in the world.

[WillowRun 6-3]

Sixty (60) days after the last publicly stated projection of when these aircraft could be expected to return to scheduled service (see a few posts above), today's Wall Street Journal publishes an article describing the projected return as occurring early next year, rather than the timing this summer previously hoped-for by United.

Article relates that Pratt & Whitney is continuing work on blade inspection methods (reportedly, ultrasound) and that Boeing is working on modification of the engine cover. Not new information itself, IIRC.

United executive quoted as noting certain constraints on system flight ops imposed by continuing unavailability of these aircraft.

[WillowRun 6-3]

Several major news outlets reporting FAA has issued a statement directing changes to PW4000 powerplants on United's 777s, aimed at strengthening the covers [correction: cowlings]. Also directing inspections. As described in this reporting, these directions are aligned with previously announced FAA guidance or updates.

Boeing, Pratt & Whitney, and United each issued statements (reportedly) generally signaling concurrence with FAA's directives. (Not located any of the actual statements yet.)

[FLCH]

Yeah UAL should make those 777’s into beer cans .

[DaveReidUK]

Several major news outlets reporting FAA has issued a statement directing changes to PW4000 powerplants on United's 777s, aimed at strengthening the covers.

Fair enough, I struggle with legal terminology. :O

"The proposed directives would require: strengthening engine cowlings, enhanced engine fan-blade inspections and inspections of other systems and components, [and] specific corrective actions depending on the inspection results"

FAA proposes modifications and inspections of Boeing 777 engines (https://www.flightglobal.com/safety/faa-proposes-modifications-and-inspections-of-boeing-777-engines/146951.article)

[tdracer]

Nothing surprising here. It's a big no-no that the engine nacelle fell apart after a fan blade out event - that's not supposed to happen (and it's long been recognized as a safety of flight concern). I'm sure Boeing has been working on a design change for the PW4000/112" nacelle (especially after it happened a second time - indicating the first one wasn't some sort of fluke). But Boeing can't mandate that operators incorporate the retrofit - only the regulators can do that.
Similarly, two FBO events on the PW4000/112" (in a fairly short period of time) was pretty damning evidence that the existing inspection requirements were inadequate and needed to be changed. Again, Pratt can recommend the change, but you need the feds to mandate it.

[BFSGrad]

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.

NTSB Final Report for UAL 328 / N772UA (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/102652/pdf)

[kiwi grey]

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.

NTSB Final Report for UAL 328 / N772UA (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/102652/pdf)

I found this rather significant
Simulation studies indicated that the carbon fiber reinforced plastic (CFRP) honeycomb structure of the event engine inlet and inlet aft bulkhead was unable to dissipate and redistribute the energy of the loads imposed by the (Fan Blade Off) event in the same manner as the aluminum structure inlet that was used during certification tests.
This reads to me that the fundamental design of an element that is subject to certification testing was changed, but the new design was not subjected to certification testing.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?

[tdracer]

I found this rather significant

This reads to me that the fundamental design of an element that is subject to certification testing was changed, but the new design was not subjected to certification testing.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?
Disclaimer - I had no knowledge or involvement in the nacelle change in question.
That being said, there definitely would have been testing done on the new CFRP nacelle components in order to certify the change. However, they are NOT going to do a full-blown repeat of the fan blade out test - such a test is terrifically expensive (at least $50 million) to demonstrate a nacelle material change. Rather, testing and analysis would have been performed to show that the new CFRP could handle the same loads as were measured in the original FBO tests. However FBO test are highly dynamic and the loads that are measured may or may not be fully representative of what the structure will actually see, and the associated analyses are something of an art rather than an exact science. Apparently in this case they got it wrong.