United B777 engine failure

[nicolai]

Reports on Twitter that a UAL 777-200 has had an uncontained engine failure on the way from DEN (Denver, Colorado, USA) to HNL (Honolulu, Hawai'i, USA) and returned safely to DEN. Local news report: https://thepostmillennial.com/colorado-residents-shocked-falling-debris-united-airlines

There's a twitter post by user @stillgray with video of the failed engine from in the aircraft that pprune doesn't seem to want to include here...

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/800x400/1613859028_bfa90ab22ac53d454b9d408b228b58c1bbed57fd.jpeg
UAL 777
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/eusp_qruuaiubbl_jpeg_3753a703c961585ca56d2e7fcd59348e31d1b38 5.jpg
Ground debris

[atakacs]

Whoops fairly dramatic, both the footage and the debris.
Pretty lucky that no-one was hurt.

[flynerd]

Looks mostly contained, but perhaps a couple of compressor blades seem missing. There is a gap there when you slow down the video.

[armagnac2010]

The high vibration would support a fan blade issue. See the recent JAL event.

Busy days at PW flight safety department.

[tdracer]

Yep, fan blade release, extreme vibration fails the inlet attachment and it detaches, resultant aero loads and vibration fail most of the rest of the nacelle.

It was during the 777 program that Boeing discovered that the fan blade out vibration levels where considerably higher than what had been previously assumed (presumably aided by the much higher bypass ratio that the 777 engines had compared to previous big fan engines).
Given this even and the fore mentioned JAL event - it would seem that even the higher loads that were used during the 777 design/cert program were not high enough :uhoh:

[dumbled0re]

Local radio station KDVR has the tower audio. About what you would expect.

Evidently I'm not allowed to post URLs. Try this instead:
kdvr dot com slash news/local/listen-mayday-call-from-crew-of-united-flight-328/

[armagnac2010]

Given this even and the fore mentioned JAL event - it would seem that even the higher loads that were used during the 777 design/cert program were not high enough :uhoh:

Underestimation of the fan blade out loads has been a general trend, apparently. See the 737NG and the Southwest event. Perhaps nobody really wants to carry around that heavy structure to cover a rare event.

[Mr Joshua]

It looked like the engine was still receiving fuel and burning away happily after the pilot would no doubt have hit the fuel cutoff switch. Why would that be?

[nicolai]

There is also the engine oil, and some hydraulic fluid, out there.

[krismiler]

Who was the engine manufacturer ?

[jewitts]

It might just be some of the epoxy composite containment got hot enough to burn. Plenty air to feed the combustion.

[MLHeliwrench]

Would of been interesting midway between the west coast and the destination Hawaii.

[Back at NH]

Pratt & Whitney

[EDML]

Engine oil or maybe hydraulic fluid.

[lomapaseo]

Some similarity with the South West secondary events. The engine itself does a good job of capturing the high energy blade pieces. Unfortunately some of the blade pieces find their way forward of the containment belts and chew into the soft inlet. with a big slashing effect. If the slash gets very long circumferentially then the cowl becomes limited in vibration. looking at the various video feeds on the nws, the shiny front lip of the cowl can be seen after the initial event still attached. Later on in the flight it is now missing.

It is not good that the engine nacelle (reverser) caught fire. The smoke behind the engine does not match a fuel fire and neither does the flame color in the videos. Quite possibly the non-metallic vanes in the reverser are what is burning. The ability to extinguish this in flight is challenging, but at least the slip stream keeps it away from the wing spar. I would be interested to know how the fire fighters addressed this on the ground.

I suspect there will be a few lessons learned here

[MLHeliwrench]

https://youtu.be/G7-zh7Sebr8

VAS aviation video

[Mike_UEM]

I don’t see any hole in the casing. Don’t see any report of debris hitting the fuselage. Is it really an uncontained failure?

[phylosocopter]

if bits fall off its uncontained!

[568]

TD,

Was the vibration levels the same on all engine types?
Thanks.

[CCA]

Technically contained vs uncontained for certification is only concerned with rotor parts inside the engine. So while the severe vibration causes nacelle parts to fail they are not proof of an uncontained failure.

The fan parts are allowed to impact up to +/- 15 degrees forward / aft radially but must not exit the fan other than out the back after they’ve been stopped so to speak.

[Mike_UEM]

Don’t have the books here. But last time I read it, uncontained, meant blades coming out at high energy sideways with risk of serious damage to the remaining aircraft.
bits coming through the back or low energy is a successful blade failure containement.

[tdracer]

568

No, it's a function of the engine. The GE90 was the worst - not coincidentally it also has the largest diameter fan (~120 inches, vs. ~112 for the PW4084 - the GE90-115B is ~122 inches).

It was the FBO test of the GE90 that was the real eye-opener. The blade debris was completely retained, but the vibration was so great that the inlet fell off, with several bits of the engine accessories. FBO is always tricky due to the uncertainties. It's a hugely expensive test to run (basically destroying a highly instrumented engine in the process), so they only want to run it once (assuming it passes) - so you have the statistical uncertainty of a single data point. It's also run statically, so you don't get the effect of the forward speed aero loads (which must be estimated). As Lomo noted, on the 737NG events, the fan blade debris moved forward beyond the containment ring and got into the inlet - I don't think we've ever seen that during a FBO static test so there are apparently other dynamics at play due to forward speed of the aircraft.
Lomapaseo, IIRC correctly the reverser cascades are carbon composite for all the 777 engine installations - so I presume hydraulic fluid (from the T/R actuators) started burning, which then ignited the resin in the carbon composite cascades.

[B2N2]

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1200x692/image_ff0eef8846a7b4d4993c4c443417affd07cfa7b7.jpeg

The tan covering around the fan casing is acoustic dampening and also intended to capture smaller parts almost like a bulletproof vest. Behind is the accessory case/gearbox which contains or drives (amongst other things) electrical generator, hydraulic pump and engine oil pumps.
So even with the fuel valve shut off there is still plenty of hydraulic oil and engine oil that will burn. Composite materials may have been covered in fuel or oil during the initial failure.
In short, there’s plenty to burn for at least a short period of time.
Engine fire suppression bottles may be less effective with that much cowling missing.
So it may just have to burn itself out.

* This is an exceptionally rare and spectacular failure but it’s not as potentially catastrophic as it looks.
If you’re an ER doctor this is a shallow wound with lots of blood if you will.

No damage to the wing or fuel tanks, no damage to the fuselage, no explosive decompression, no damaged flight controls.
Just really spectacular :}

[tdracer]

That's not the definition of an uncontained failure.
The definition of an uncontained failure is high energy debris exiting tangential to the engine (within a few degrees).
Bits coming out the front or back, or the inlet/nacelle falling off, is not considered an uncontained failure. That being said, large bits of the inlet and nacelle coming off is a big no-no since it can do damage to the tail surfaces or to people/structures on the ground.

[568]

TD,

Great information as always, sure appreciate that!
Regarding the 737-700, did the Southwest 1380 engine episode also exhibit debris moving forward?

[tdracer]

B2N2

The tan covering is the fan containment ring - probably Kevlar. It provides no meaningful acoustic dampening - it's only purpose is to catch and contain fan fragments.
The gearbox is in the core area of the engine (PW4000 and GE90 - Rolls Trent has the gearbox on the fancase), however the oil tank is on the fan case. The fire appears to be in the reverser cascades which as I noted are a carbon composite structure. Likely oil or hydraulic fluid started burning which then ignited the resin the the composite construction.
There is no fire suppression system for the fan case on the PW4000 and GE90 installations - only on the core.

[WHBM]

tdracer

27 year old aircraft (though engine may not be), 777 number 5. It even spent its first year flying in the development programme It's taken a good while to show up.

[Machdiamond]

I agree with the comments that the thread title seems inappropriate, as video evidence so far points to a brilliant example of a successful containment.

[lomapaseo]

Following from a few posts above

The engine test is just that, nothing more. The idea is to demonstrate the engine capabilities and provide enough load data to the various installers to use in estimating the loads on their nacelle and their pylon mounts. This goes along way in later analysis to demonstrate to t the FAA that the engine has the capability to be safely installed on multiple aircraft designs. It's then up to the Boeings and Airbus to design their parts to remain safe,

The last thing the engine guy wants is to have some sort of test apparatus that screws up the engine to demonstrate itself and to generate useful load data. Hence interface parts like inlets and nacelles are chosen simply as end-loading attachments. The inlets must operate at zero static speed and max power so they really don't look like flight inlets and then ejected blade pieces just screw themselves forward and out the inlet rather than through the side (just like a turbine exhaust pipe)
The FAA is quite tolerant of the measured load capability in the presence of containment and rundown of the engine debris. Some of us like numbers more than just a one-off test..

On the engine side the worst loads to the mounts and fan bearing supports etc. occur in about 5 rev of the fan, after that it's just run-down loads and changing frequencies to the stuff hung off the engine. This quite often shows up in large oscillations as the plane slows down for landing. Typically nothing to worry about except for passenger comfort

Obviously there are some lessons to be learnt here that will have to wait for the investigation to complete

[BFSGrad]

Well...I just watched an interview with aviation gadfly, Greg Feith, who clearly stated that this event was an "uncontained engine failure," so take that for what it's worth.

[nonsense]

More media (https://www.theage.com.au/world/north-america/debris-falls-from-plane-into-denver-suburbs-during-emergency-landing-20210221-p574dx.html):

Former National Transportation Safety Board Chairman Jim Hall called the incident another example of “cracks in our culture in aviation safety [that] need to be addressed”.
Hall, who was on the board from 1994 to 2001, has criticised the FAA over the past decade as “drifting toward letting the manufacturers provide the aviation oversight that the public was paying for.” That goes especially for Boeing, he said.

Seems Pprune writers aren't the only ones who have the answers long before the investigators...

[tdracer]

That's pretty rich, given this was certified over 25 years ago - when he was the chair of the NTSB...

[krismiler]

With the size of the fan blades on modern high bypass jet engines, we are reaching the stage where a failure will have similar consequences to losing a propellor blade on a piston or turbo prop. If the pitch isn't bought into feather immediately then the engine will do its best to shake itself out of the wing.

[lomapaseo]

Lockhart

Are you sure here was a fire light?

It depends on where the pick-ups were installed and where the extinguishing is directed. I don't believe there would be much annunciated for a fire in the reverser

[Big Pistons Forever]

The whole engine was vibrating pretty badly. Was there any danger of the engine attach points failing and the whole engine coming off the wing ?

[Dave Therhino]

The area where the visible part of that fire is located is not a fire zone. The fire detectors on that engine are limited to the core compartment.

[tdracer]

lomapaseo

For the PW4000 installation, reasonably sure there isn't any fire detection in the fan cowl - and I'm certain there is no fire extinguishing ability (not that it would help with the cowl missing). Fire detection/overheat/extinguishing is all in the engine core - not the fan cowl. For engines where the gearbox is located on the core, the fan cowl is a "flammable leakage zone" (oil and hydraulic fluid) - by design there are no ignition sources, so no fire detection needed.
Edit - I see Dave T beat me to it...

[ACMS]

WHBM

Its not like a car where the Engine will most likely stay with the chassis for life. Aircraft Engines get swapped out and replaced during their life cycle. Also now days the Engines are leased by the operator and its separate to the Airframe.

[Big Bad D]

Strictly by definition it seems not to be an uncontained engine failure (I rely on the experts to review engine, ot in speculation). However such size of parts departing aircraft is itself an issue both for risk of damage to aircraft and on ground below. From an operational point of view seems to have been well managed.

[Dannyboy39]

nonsense

I really don't understand this logic in relation to this incident. Yes, BOE clearly have had it too easy in recent years and processes needed a significant tightening, but I'm not sure how an engine failure relates to this? The B777 family have proven over 25 years that it's probably the most reliable and safest aircraft in history - the GE90 equally the most reliable engine in history (I know this is the PW option)... we see this in the reliability data - 1 IFSD per 1,000,000 FH. This may be overtaken by the A350 after being in service that long.

For what it's worth, as more aircraft are removed from long term storage, I can forsee more incident rearing their ugly heads, but not on the scale of this.

As for being line #5 - so what? The engines will be serviced every few years (I don't know the typical MTBR on a GE90 / PW4000). but over 25 years, I'd have expected at least 6 SVs.

[clareprop]

I agree with the comments that the thread title seems inappropriate, as video evidence so far points to a brilliant example of a successful containment.

You can play with words as much as you all like - technically. Now tell these people it was a contained engine failure.

https://www.bbc.com/news/world-us-canada-56141673

[rmiller4292]

At 1:10 in the VAS video above you can hear the fire warning aural annunciation in the background.

[fox niner]

Is there anyone who can find out whether this engine or airframe has been in long term storage during the pandemic?

[KingKoopa]

lomapaseo

I'm pretty sure they got a fire indication of some type when the failure occurred -- when you listen to the ATC audio, you can clearly hear the fire bell in the background. This would have been accompanied by FIRE ENG R on the EICAS and a master warning.

You're correct in saying that there's no fire detection installed where the fire is visible in the video, though.

[daelight]

fox niner

From FR24 records, she's been flying pretty much 2 sectors a day, since ~1 month hiatus in Febuary 2020 -

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/895x312/ual_e6d38b24db72f15621dd08d81b382ef06af5ec1d.png

[WHBM]

ACMS

I'm aware of that, and in fact alluded to it. However it's the same engine design that was on the original certification. You haven't been able to get a P&W on a new 777 for many years now (which might be an interesting point to start reviewing things).

[DaveReidUK]

flynerd

Freezing the video would suggest a fan blade and a half missing. Looks like a carbon copy of UA1175 (https://www.pprune.org/rumours-news/605391-ua1175-emergency-landing-honolulu.html) three years ago.

[Fursty Ferret]

Having listened to the ATC it highlights the clear problem in the USA of controllers handling multiple frequencies without band-boxing. It's almost impossible to make a radio call without stepping on someone because you can't tell if someone else is transmitting. My policy in the USA is that if I need to make an emergency turn I'll do it and wait for ATC to contact me. Not being able to get a call in clearly added significantly to the crew's workload in this instance which isn't ideal in a terrain heavy airport with the performance issues associated with being single-engine on departure at high elevations.

[Fursty Ferret]

lomapaseo

In the ATC broadcast you can hear the fire warning. Not sure why people are saying that the fire detection is in the the engine core - there's no point having fire detection there, that bit of the engine is always on fire... You put fire detection around the core, not in it, the purpose being to detect a leak in the hot gas path.

[B2N2]

tdracer

Well pardon my artistic liberties in explaining this. We said 90% the same, good enough for government work.

[Less Hair]

Parts hit the house and fell right into the kitchen and living room.

[rb14]

I was quite surprised how often ATC was communicating. Of course there were the initial exchanges but then we reached a "OK we're running some checklists". From that point it felt like some of the ATC comms might have been a little distracting?

[fdr]

Mike_UEM

That took longer to arise as a comment than was expected.... :}

25.903(d)(1) Design precautions must be taken to minimize the hazards to the airplane in the event of an engine rotor failure or...

and that doesn't seem to fully answer the question, but, AC20.128A ?DESIGN CONSIDERATIONS FOR MINIMIZING HAZARDS CAUSED BY UNCONTAINED TURBINE ENGINE AND AUXILIARY POWER UNIT ROTOR FAILURE of 25 MArch 1997 states in para 6 (c) of definitions:

Uncontained Failure: For the purpose of airplane evaluations in accordance with this AC, uncontained failure of a turbine engine is any failure which results in the escape of rotor fragments from the engine or APU that could result in a hazard. Rotor failures which are of concern are those where released fragments have sufficient energy to create a hazard to the airplane.

That was put out by the Mangler of TAD-ACS out of Seattle, Mike Kaszycki... for "harmonization".

The inlet looks like it would make a great paddling pool while the engine was an excellent cigar lighter.

[N707ZS]

If the parts land on your property are they still the property of the airline.

[3Greens]

yes. If someone enters your house, you don’t then take ownership of their wristwatch and wallet etc...

[unmanned_droid]

Big Pistons Forever

FBO and UERF loads should have been part of the load cases so will have been covered in the static analysis of the pylon attachments and wing structure (my experience is with stress analysis of A wings and this is true of the aircraft I have worked on so feel confident it would have been the case for B wings). In my experience we mix the engine failure loads in with the other groupings so the design is covered for some fairly nasty concurrent situations.

The FBO loads are likely to produce the peak engine failure loads as alluded to elsewhere in this thread simply because of the size of blades. This does not appear to be an FBO event so the peak design loads were likely not reached.

The amount of movement isn't cause for concern and the attachments can stand that kind of cycling for the time taken to get back to the ground. It doesn't look like there is any damage to the pylon structure in the video and the vibration to me looks to be consistent and well damped suggesting that all wing and engine attachments are still operating as normal. I would say the risk of losing the engine was minimal in this specific situation. The engine probably moves that much in strong winds anyway - but you don't notice it because it's an oscillation or 2 (for example there's a video of an A380 landing in Manchester with all 4 engines moving around and pointing in different directions during a winter storm/gales).

[bsieker]

clareprop

Nobody argues that it was not a catastrophic failure, but "uncontained" vs. "contained" have specific technical meanings for a good reason. No matter what the press calls it, we should not muddle those terms.

[silverstrata]

The flames are coming out of the thrust-reverser matrix.
Which might suggest a failure between the HP compressors and the turbine section.
Perhaps in the combustion chamber itself.
I imagine an exploding combustion chamber might be powerful enough to take out all the cowlings.

[Maninthebar]

fdr's quote (above) would indicate that this event might well be classified as 'uncontained'
"Uncontained Failure: For the purpose of airplane evaluations in accordance with this AC, uncontained failure of a turbine engine is any failure which results in the escape of rotor fragments from the engine or APU that could result in a hazard. Rotor failures which are of concern are those where released fragments have sufficient energy to create a hazard to the airplane."

[WingNut60]

I am somewhat surprised at the seemingly gentle landing of the inlet ring, a bit of bark off the tree branch seems to be about the limit of the damage.
Am I right in thinking that it may have descended parachute fashion?

[bsieker]

It is not a structural part, and as such is a very lightweight honeycomb structure and has a large surface area. So yes, rather parachute-y.

[bsieker]

blancolirio channel said that the fire continued on the ground. Assuming all shutoff valves worked, all fuel in the engine should have burned off by the time and/or been flushed out, so I think it may have been an oil fire.

The imbalance of a fan-blade-off event will be violent enough to shake the cowling to pieces. Combustion chambers are not known to explode; they are designed to contain an extremely fierce fire, and are open on both ends.

[silverstrata]

Why do ATC always ask stupid questions about fuel and souls on board..?

Look, ATC paper-shufflers, the aircraft has only just taken off, so it has enough fuel to hang around for ages.
And the number of souls is on the loadsheet. Why the ... do you think we leave a copy of the loadsheet behind?
Oh - and by the way: I am dealing with a ***** emergency here, and my hands (and brain) are full....

In addition, dear ATC - please stop thinking of Sully landings, will you?
Contrary to what the FAA were promoting on the Hudson, we are not supposed to do a split-arrse ‘turn-n-return’ back onto the same runway. We are supposed to take up the hold and secure the engine, before calmly returning in a composed and ordered manner. That is the approved SOP. And from experience, the pattern this aircraft took is the absolute minumum flight time to get everything done.

As you can see from the video, the engine was happily smouldering away to itself, and not endagering the aircraft. That is why podded engines were invented. Podded engines with the N1 and compressors well in front of the leading edge, so that an N1 failure will not disrupt the wing systems or fuel tanks.

It all worked as designed and planned, and there was no need for a panic-return. So please stop offering immediate returns to land - unless specifically requested. (If a turn-n-retrn had. een executed, I can just imagine the request for fuel-load and souls onboard on 1/2 mile finals....)

[silverstrata]

bsieker

Here is a Bae146 engine with an exploded combustion chamber, that also took out the cowlings.

The vibration we can see on the B777 failure may be aerodynamic, as the slipstream runs around the decidedly non-aerodynamic N1 fan. Those fat cowlings are not there for normal flight - they are designed to allow smooth airflow around the engine after it fails (and the airflow spills out around the front of the engine). Take the cowling away, and the resulting turbulence is bound to make it shake, rattle, and roll...

Bae146 combustion chamber failure:
https://news.aviation-safety.net/2016/05/02/report-avro-rj100-engine-fire-incident-due-toe-incorrect-engine-repairs

The ALF507 was not the best of engines, and had a variety of N1, compressor, combustion-chamber, and turbine-section failures. Which is why the aircraft was unfairly known as the Bring Another Engine 146. Or the Cockroach, for short.

[fdr]

I am somewhat surprised at the seemingly gentle landing of the inlet ring, a bit of bark off the tree branch seems to be about the limit of the damage.
Am I right in thinking that it may have descended parachute fashion?


Think it converted the Ram roof to low rider.. :}

As far as terminal velocity goes, would be interesting to see if it was rotating around its radius like a Flettner lifting surface.

[fdr]

silverstrata

One of the happy snaps on CNN shows at least one fan blade is a shorty.

[DaveReidUK]

unmanned_droid

"This does not appear to be an FBO event so the peak design loads were likely not reached."

How do you account for the gap where you would expect a fan blade to be, in the photos ?

[Starbear]

Lockhart

You're presuming that the pilots' actions actually caused the SOVs to close, they may not have. QANTAS A380 2010 could not shut down No 1 engine (undamaged). It ran for about 3 hours after the landing, until fuel exhaustion. EK A340 on the ground in Toulouse, engines ran for about 9 hours (?) until fuel exhaustion, but that was very different reasons. i.e. lack of access to flight deck.

[Capn Bloggs]

Silver, ATC probably ask for the POB because they are required to.

As for the rest, ATC's reaction was prompted by the chaotic radio calls and lack of information provided by the crew. The crew would have done this in the sim every 6 months for years. To blurt out a panicked "we need to turn" without giving a direction is mind-boggling. No wonder ATC thought the situation was dire and that they might need an immediate reland. What about "Mayday Mayday Mayday, UAXXXX, engine fire, tracking direct Zimmr until advised, standby for further information".

As for the fire bell still ringing during the radio calls...

[Pilot DAR]

Why do ATC always ask stupid questions about fuel and souls on board..?

They're asking on behalf of the crash/fire/rescue, who think that information is smart to know. ATC should not guess, and do not have time to go find the paper elsewhere at the airport of departure.

[silverstrata]

fdr

Link?
Image?
The N1 fan appears to be intact, as does the containment-ring.
So which blades can you see, other than the N1?

[silverstrata]

Capn Bloggs

Yeah - we know that.
But every aircraft has left a loadsheet behind, for the last 80 years.
And with modern comms, it is not difficult to get that information from the handling agent or airline.
(Who are not dealing with an engine fire...)

As for the ‘we need to turn’ call, it is natural to ask ATC for a turn, because only ATC know where all the other traffic is. The number of times a commercial pilot will tell ATC they are turning, can be counted on one hand in an entire career. Perhaps with a storm-cell ahead, or the like.

The request for an ATC-determined turn was natural and logical, and for ATC to then overload the pilots with a “which way” request was stupid in the extreme. The crew may not even instantly know where the airport is (it being behind them), nor where any prohibited areas, terrain restrictions, or conflicting traffic may be.

ATC should have kept things simple, and just given a normal traffic pattern back to the departure runway: “this will be a left-hand circuit for rwy 26”. And perhaps for reassurance added: “other options available, if you require”.

(Remember, the crew need to know the runway to set up the ILS - they don’t need a guessing-game for which approach, while dealing with an engine fire.)

[DaveReidUK]

silverstrata

"The N1 fan appears to be intact"

Really?

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/530x465/ua3a_794677f7447ce912eedd75c77b455182ec92b90f.jpg

[silverstrata]

DaveReidUK

If you has posted the pic, we would know.
This is not a guessing-game.

P.S. The reason the containment-ring appears intact, is the blade-tips often fly off forwards, hitting the front cowl rather than the ring. The blades are under extreme forwards pressure, especially during the low-airspeed high-rpm climb.

I am presuming the different colour of the broken blades is due to reflections from sunlight, with the Sun being behind the camera position.

[ivor toolbox]

Bits of the rotating group or engine casing as opposed to cowl, inlet lipskin etc.

[lomapaseo]

correct on the blade tips going forward. but it isn't the aereo loads which might only move the tip about a few mils in the time before it is laying down against the casings. Also you forgot to mention the much heavier inner blade portion which is pumped aft and imbed itself in the Kevlar belt. The rest of the engine response eats up the engine innards and that's where most of the interest will point

[fergusd]

P.S. The reason the containment-ring appears intact, is the blade-tips often fly off forwards, hitting the front cowl rather than the ring. The blades are under extreme forwards pressure, especially during the low-airspeed high-rpm climb.


Really ?

https://youtu.be/wcALjMJbAvU?t=20

[Winemaker]

You're presuming that the pilots' actions actually caused the SOVs to close, they may not have. QANTAS A380 2010 could not shut down No 1 engine (undamaged). It ran for about 3 hours after the landing, until fuel exhaustion. EK A340 on the ground in Toulouse, engines ran for about 9 hours (?) until fuel exhaustion, but that was very different reasons. i.e. lack of access to flight deck.
In the Qantas incident the wing was penetrated multiple times by debris; this severed wiring and made shut off impossible. This is a totally different scenario, as the wing is intact.

[Del Prado]

ATC always train not to turn in to dead engine if possible although that’s not so important with modern jet aircraft direction of turn is still a reasonable question (although I’d welcome any other views on this, particularly about non jet types).

SOB - Aircraft was probably 8/10 mins from touchdown so why ask someone else to try and get through to an ops department to find someone that will give the upmost priority to a request for souls on board?
If the fire service need that info best to get it from the flight deck.

I’d also want to know which engine was out to pass that to fire service too.

Good to hear UAL say “Mayday” I realise US procedures are different but nothing catches the attention quite like the M word.

While overall I thought it was really well handled on both sides the ATC didn’t know if the fire was still burning (endangering wing/control surfaces/falling out of the sky) or fire was out and a ‘normal’ return.
On that basis, any criticism about circuit or questioning seems pretty harsh in my view.

[Longtimer]

Contained or not? Note damage to fuselage just under the wing root.
https://theairlinewebsite.com/uploads/monthly_2021_02/152844002_10224369972578942_3558511734802398052_n.jpg.408c76 b8aacee918be91e74583773472.jpg

[FlightCosting]

lomapaseo

when the airframe manufacturer sets up an engine selection process they always require the powerplant supplier to provide an engine /nacelle that provides the performance to meet the spec. If the engine supplier fails to meet the spec they do not get on the airframe. Only the Russians build an airframe around an engine as they dud with the IL62 and IL76. I spent years negotiating with GE on the SF340 powerplant.

[Dave Therhino]

I think we will find that damage was from the separated thrust reverser outer wall, fan cowl door, or inlet pieces. That damage is to the composite wing-to-body fairing parts. No penetration of the wing plank or spar. There was no high energy uncontained rotor debris from the initial reports and photos I have seen.

[MLHeliwrench]

is that an ‘exit wound’ at three o’clock (from this view) lined up with the ‘entry wound’ at the wing root!

[Longtimer]

NDI Process Failures Preceded B777 PW4077 Engine FBO - Aerossurance (http://aerossurance.com/safety-management/ndi-failures-b777-pw4077-fbo/)

[mnttech]

silverstrata

Based on the weather in the video/and what it was like yesterday here, they had a pretty good view of the front range that was right in front of them before the turn. Lots of rough stuff in the 12K or higher range in front of them. The ground track shows them turning before reaching the front range. Dont disagree with the rest of the post.
Interesting they came within a couple of miles of my place!

[Feathers McGraw]

MLHeliwrench

The in-flight footage didn't indicate anything in the fan cowl area on the fuselage side.

[silverstrata]

fergusd

Yes, really.
Engine manufacturers test a whole blade separation, as that is the worst case scenario for the containment-ring. But a blade tip has much more forward pressure when it breaks, than the whole blade, and can spin out to the front of the engine. And then return and perhaps hit another blade.

I note in another image that there is wing-root damage on the aircraft, so a blade must have spun out of the engine somehow. If there is no breach of the containment-ring (difficult to see), then it must have gone through the forward cowling, taking the whole cowling with it.

Even a blade tip has a lot of energy. I saw a turbine blade from an ALF507, which is only 2 cm long, go straight through the back of the engine and embed itself in the fuselage (over 2 m away).

Update: Looking again at the video, I see no breach of the containment ring on the port side (nearest the fuselage). And I cannot believe that a piece of cowling could stray so far as to hit and damage the wing root. Thus the most likely scenario at present, is the blade missed the containment ring, took out the cowling, and penetrated the wing-root.

An unusual result for sure. But when you set this high velocity debris in motion, it is like making a forceful break on a billiards table - you have no idea where the balls will go...

[Alpine Flyer]

ACMS

As a maintenance guy recently put it, to them the aircraft is more of a formation of valuable components (engines, APU, gear, other swappable spares) held together by the airframe.

[Dave Therhino]

MLHeliwrench

No. That's a remnant of the aft bulkhead of the inlet still attached to the fan case front flange. Other views clearly show no penetration of the containment ring by blade fragments.

[Alpine Flyer]

The request for an ATC-determined turn was natural and logical, and for ATC to then overload the pilots with a “which way” request was stupid in the extreme. The crew may not even instantly know where the airport is (it being behind them), nor where any prohibited areas, terrain restrictions, or conflicting traffic may be.

Stupid is a bit of an overstatement. As they said "turn" rather than "return" it is not entirely obvious to ATC where they need to go and having stated an engine failure and depending on the circumstances there might be a preferential side to turn. In a perfect world they might have said "return" or said "turn right or left" but calling ATC stupid for asking feels inappropriate


ATC should have kept things simple, and just given a normal traffic pattern back to the departure runway: “this will be a left-hand circuit for rwy 26”. And perhaps for reassurance added: “other options available, if you require”.

(Remember, the crew need to know the runway to set up the ILS - they don’t need a guessing-game for which approach, while dealing with an engine fire.)


I've never been to Denver but with the number of runways they seem to have according to the Radar display, it seems a bit unlikely that the departure runway would also be the arrival runway. They might have briefed a different runway for an eventual return and in any case they need to calculate landing figures. ATC offered them a runway and added that they could have any other. I'd say that's what you want to hear in a case like this.

[Alpine Flyer]

silverstrata

I'd say because their procedures require them to ask and while it's on a load sheet somewhere retrieving that load sheet for a flight originating in a different country may take some time (or will have taken some time when these procedures were devised in the age of telex). And there are lots of GA planes around that don't have a load sheet filed somewhere.

As for the fuel it might be useful for the fire department to know whether to prepare equipment for a fully loaded 777 or a Dash 8 fuelled for 90 minutes.

[silverstrata]

I have never been to Denver either. But at most airfields you can expect a left-right split between take-off and landing. That is pretty axiomatic, but it gives you an idea of the circuit pattern.

And Billy Boeing (and Andy Airbus) have a helpful generalisation - if you can take off from a runway (whatever the performance figures), you can do a single-engine landing on the same runway. (Presumably post fuel-dump if fitted, but not flown those types.). So no calculations required. Although the landing performance figures don’t give you much margin for error.

[Chris2303]

Is "Aviate, Navigate, Communicate" no longer relevant?

[Zeffy]

NTSB Docket (https://data.ntsb.gov/Docket/?NTSBNumber=DCA18IA092)
N773UA, BOEING 777 222
Date of Accident: 02/13/2018

[DaveReidUK]

And Final Report: DCA18IA092 N773UA Boeing 777-222, Honolulu (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/96738/pdf)

[lomapaseo]

So what changes were made or not justified to address the engine nacelle cowl?

and that leaves the latest failure with a fire issue in the reverser much farther aft

Personally I can't get very excited with an engine alone fire as long as it doesn't threaten the pylon and has limited fuel

[JPJP]

The only indication of a uncontained engine failure to the flight crew, is when they rotate the fire switch a second time to release the squib.
If the fire light remains on for approximately 30sec, then the engine is considered uncontained then you need to return ASAP.
If the light goes out it's an engine severe damage as per the QRH, though sometimes you need to look outside the square to asses the situation.
They did declare a mayday so that fire light would of stayed on or if it went out then a CC member only need to communicate a fire is still visible.

I’m curious about your statement above. Do you have some form of reference, from anywhere ? I’ve never heard of it, and it doesn’t make much sense. Caveat - I don’t know everything and I haven’t heard everything.

The fire light remaining illuminated on a Boeing, indicates that the temperature at the sensor remains above a specified threshold.

[visibility3miles]

https://www.youtube.com/watch?v=XnSjAdvKp8k&ab_channel=ThePeople%27sElixir

The video you mentioned was also posted on YT few moments ago

What struck my phone savvy spouse immediately when watching this video is that although the engine is in rock steady focus, the edge of the window in the picture is moving around.

It is the smart feature of the phone camera that makes it look like a steady view out the window, when in fact the plane and the passengers were bouncing due to engine vibration.

If you don’t believe me, watch the video again and focus your eyes on the lower right corner of the photo which shows the edge of the window.

[Zeffy]

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/2000x1316/ais_japan_notam_5e7f0fff6ba317b8a725e0765515f934d6ea366a.png

[GlobalNav]

Breaking news

[WillowRun 6-3]

Multiple news outlets reporting FAA has ordered inspections.
From WSJ website this evening:

The Federal Aviation Administration said late Sunday it was ordering immediate inspections of Boeing Co. 777 aircraft equipped with the type of engine that broke apart in the air and scattered debris over a Colorado town over the weekend.

“This will likely mean some airplanes will be removed from service,” FAA Administrator Steve Dickson said in a statement.

The move comes as safety investigators in the U.S. are looking into why the Pratt & Whitney-made engine of a United Airlines Holdings Inc. 777-200 jet failed shortly after the Honolulu-bound flight took off Saturday, forcing the plane to return to the airport.

“We reviewed all available safety data following yesterday’s incident,” Mr. Dickson said. “Based on the initial information, we concluded that the inspection interval should be stepped up for the hollow fan blades that are unique to this model of engine, used solely on Boeing 777 airplanes.”

United is the only affected airline in the U.S. the FAA said. Regulators in Japan have ordered airlines to stop flying aircraft with the same engine type until further notice, the FAA said.

[Zeffy]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1200x670/img_0352_561d370792222832a2f4f11454ae5cec7f8774eb.jpg

[Zeffy]

NTSB Update (https://www.ntsb.gov/news/press-releases/Pages/MR20210221.aspx)

[lomapaseo]

visibility3miles

It's mostly a forcing function generated by off center a windmilling rotors at frequencies in a narrow band of RPM tied to windmill conditions. When this excitation tunes with other parts of the aircraft those parts start vibrating. All this is nicely damped down to very low stress even though the seat shakes them a little bit. (lots of history never a critical problem)

[Zeffy]

Boeing Statement (https://boeing.mediaroom.com/news-releases-statements?item=130829&sf243254140=1)

Boeing Statement on United Airlines Flight 328

CHICAGO, Feb. 21, 2021—Boeing today released the following statement:


"Boeing is actively monitoring recent events related to United Airlines Flight 328. While the NTSB investigation is ongoing, we recommended suspending operations of the 69 in-service and 59 in-storage 777s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol.

Boeing supports the decision yesterday by the Japan Civil Aviation Bureau, and the FAA’s action today to suspend operations of 777 aircraft powered by Pratt & Whitney 4000-112 engines. We are working with these regulators as they take actions while these planes are on the ground and further inspections are conducted by Pratt & Whitney.

Updates will be provided as more information becomes available."

[Pin Head]

Direction of turn when single engine Captain Joe FB said that the crews request for L turns was based on being single engine.

20yrs of flying jets I have never been told that direction and preferred direction of turn in a jet is important assuming clear both sides and still air. Excellent training providers.

Have I missed something ?

[finfly1]

Loaded with enough fuel to reach Hawaii, and returning only minutes after departure, why was fuel dumping never mentioned or involved?

[Veruka Salt]

Because fuel jettison takes time - based on assessment of the situation, crew may have (rightly) decided to do an overweight landing & get back on the ground PDQ.

[MLHeliwrench]

maybe if fire still visible after pulling the handle, checklist may say to land as soon as possible even if overweight?

[krismiler]

Japan is very concerned about things falling from planes. Pilots operating to Japan have to complete an online course titled “Parts Departing from Aircraft” which shows areas to be checked. Certain runways even require an early extension of the landing gear in case any ice falls off.

[B-757]

​​​​​​.. Because this was an experienced crew.. The engine was in fire..

[fdr]

is that an ‘exit wound’ at three o’clock (from this view) lined up with the ‘entry wound’ at the wing root!

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/464x248/152844002_10224369972578942_3558511734802398052_n_jpg_408c76 b8aacee918be91e74583773472_7239299d951651ceef9fdcf388c63ef07 ddb6536.jpg

probably not. The blade components do not look like they have punctured any of the remaining structure of the acoustic liner and did not look like they penetrated the ballistic wrap. The blade failure will be interesting to look at in-depth, but I would expect that the missing blade immediately in front of the partial blade failed near the blade root, and as it has departed the fix, has impacted the following blade and torn the LE, leading to it liberating the outer 1/3rd of that blade. The liberated blade is under radial acceleration to the point of release, and aerodynamic bound vortex flow giving lift, so is going to come out at a rate and forward. The full blade looks like it is what went into the #2 pack fairing, and the area around the fuel drip drains aft of that point. 90.4% is 3255 RPM... D=112"; so at climb thrust, it's going to be a bit higher than that, and that is a fair old radial acceleration. Wouldn't be surprised if the full blade that is missing never punctured the cowling, and departed out front and then back to hit the pack. An engine failure & pack failure was on the cards, but, at least the failure didn't look like an impact on the #1 engine. (in LAX, that occurred via a ricochet of a fragmented and liberated disk, but it is not going to happen airborne unless you really have not been living cleanly)

(the white bit at 3 OClock is the fill layer, outside of the ballistic wrap, and it looks like it has flopped forward. It extends forward further than it would with the nacelle annulus... the detail inspection will show what it did better than this musing).

[hitchens97]

I'm assuming Denver Hawaii is perhaps only ~half range of this aircraft. Also flights are not going anywhere near full, so guessing nowhere close to full fuel load.

[BoeingDriver99]

The initial comms from the cockpit is cringeworthy.... they got on the ground safely but to be a fly on the wall in that cockpit would be eye-opening I reckon.

And silverstrata; your lack of knowledge about procedures on the other end of the radio is the same.

[cncpc]

Question...what is fueling that fire? Surely it must be possible to shot fuel off to that engine?

[Dannyboy39]

hitchens97

Over 200 passengers on board with all their bags.

[DaveReidUK]

Zeffy

The proposed AD covers PW4000 models with the 112" fan (PW4074 to PW4098) and apart from United will primarily affect JAL, ANA, Asiana and Korean.

[fruitflyer]

Anyone got a link to the EAD? I can't seem to find it on the FAA website, thank you.

[Fursty Ferret]

BoeingDriver99

How joined up would your radio call be if you got a fire warning while making it, while at the same time trying to figure out if someone else is transmitting on the forty other frequencies in use that you can't hear?

[sky9]

A couple of comments refer to engine Fire rather than Severe Damage. When you listen to the ATC recording the flight crew reported an Engine Failure, not Fire which would be correct because the cowling separated from the engine so the fire warning light would not be triggered.
How would that affect the 777 checklist items after pulling the fire switch?

[Capn Bloggs]

When you listen to the ATC recording the flight crew reported an Engine Failure, not Fire which would be correct
It sounds like fire bell was going in the background of the first two calls.

[davidjohnson6]

Is there anything in SOP after an engine failure that includes a task like "Ask somebody in cabin crew to go and look through the window at the dodgy engine and report back to flight deck what they see" ? I know pilots will have their hands full at the time, but wondering if a description from somebody who is likely to give a non-exaggerated and accurate description might be a useful thing for the future.
I was going to suggest cabin crew taking a photo on their phone - but thought this would probably just create panic, along with encouraging pax to get out of their seats and pose for selfies which is probably undesired :)

[Zeffy]

https://newsroom.prattwhitney.com/2021-2-21-Pratt-Whitney-Statement-on-United-Airlines-Flight-328



https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1058/7073d34f_1fab_47c0_a89a_9da814b9e5af_75f17619c1026aff6aaa286 7ddc41b529e4c5c93.jpeg

[rickyricks]

Given the similarity between the latest B777 P&W engine failure over Denver and this incident in 2018 I was curious to find out more about the earlier engine failure. The report on the examination of the failed fan blade makes for some interesting reading. Apparently after 5000 cycles (take-off and landing) all fan blades must be examined at P&W by thermal acoustic imaging (TAI) in which ultrasound vibrates the fan blade and if any cracks are present frictional heating at the crack can be thermally imaged. Some sort of paint has to be painted on the fan blade surface to allow TAI and this paint can affect the resultant thermal image. All paint is removed after TAI inspection. Anyway, the failed fan blades were inspected in 2010 and 2015 and this is straight from the report.

“The installed set of fan blades, including the fractured fan blade, had undergone two overhauls at which time the blades underwent a thermal acoustic imaging (TAI) inspection. At the initial TAI in 2010, there was a small indication at the location of the origin of the crack. The review of the records from the 2015 TAI show that there was a larger indication in the same area as where there was an indication in 2010 and from where the crack originated. At the time of each TAI, the inspectors attributed the indication to a defect in the paint that was used during the TAI process and allowed the blade to continue the overhaul process and be returned to service”.

So two inspections, five years apart, showed an indication of a growing fatigue crack in the same place and yet the thermal image was attributed to a paint defect in two different paint coatings.

[Glide Landing]

At last there has been a serious a/c incident and no one has died or been injured. Has any noticed the fact that the crew got the aircraft safely back on the ground which is what they were trained to do and did do. The fractured fan blade did not damage the a/c fuselage, some cowling dropped away, the engine pylon remained intact despite serious vibration due to the unbalanced rotor shaft. Now you are all blathering on about a ‘turn’ or a ‘return,’ and souls on board. Stick to the point – the cockpit crew got on with the job and 6 hrs later the pax were on another a/c and on their way to Hawaii. Congratulations to all the crew - cockpit and cabin - for a job well done in an unenviable situation.

[NutLoose]

SD-2021/002: Limitation of Operations of Boeing 777 Aeroplanes Following Serious Incident of Engine Failure on 20 February 2021This SD is made in the interests of continued safety of operation and to protect the public following a serious incident on 20 February 2021 involving a United Airlines Boeing 777 aeroplane, Flight 328, where the right-hand engine failed in flight following a suspected fan blade failure. A similar engine failure occurred to a Japanese Airlines Ltd Boeing 777 on 4 December 2020.

http://publicapps.caa.co.uk/docs/33/SafetyDirective2021002.pdf

[kenparry]

Equivocal: if your read the CAA Directive, it's completely unequivocal. All B777 ops with that engine banned worldwide if G- reg, for other reg banned in UK airspace.

[GrandPrix]

Fan blades fail. That’s a known and acceptable risk. Containment rings are failing when they shouldn’t. With the cowling gone and the vibration causing a separation, the damaged engine will not depart the wing in a controlled manner and possibly destroying the airframe. Flinging shrapnel into the fuselage is a big concern as well.

[JonnyH]

Grant Schapps working with the CAA on this. 777 with Pratt & Whitney engines now temporarily suspended from flying in UK airspace.

[DaveReidUK]

kenparry

To be fair, it is slightly confusing given that there aren't, nor have there ever been, any PW-powered 777s on the UK register.

[mnttech]

fruitflyer

I wanted to read it too. We will have to wait until someone else posts it (probably about 30 seconds after I post this)
Found out they don't have to post it there, from the FAA web site Emergency Airworthiness Directives

An Emergency AD is issued when an unsafe condition exists that requires immediate action by an owner/operator.

Who is affected by an Emergency AD?

An Emergency AD may be distributed by Fax, letter, or other methods. It is issued and effective to only the people who actually receive it. This is known as “actual notice.”

Who will receive an Emergency AD?

All known owners and operators of affected U.S.-registered aircraft or those aircraft that are known to have an affected product installed will be sent a copy of an Emergency AD.

Is an Emergency AD published in the Federal Register?

To make the AD effective to all persons, follow up publication of the Final Rule AD in the Federal Register is critical. This Final Rule AD must be identical to the Emergency AD, and is normally published in the Federal Register within 30 days of the Emergency AD issue date.

[FLCH]

davidjohnson6

Last thing you need is cabin crew coming up and giving you their two cents worth, work the problem then let them know what's happening, many moons ago I experienced an inflight emergency, F/A was a horrible distraction asking irrelevant questions, while I had 10 other things on my mind. Drama drama drama just when you don't need it......

[WHBM]

Grant Schapps working with the CAA on this. 777 with Pratt & Whitney engines now temporarily suspended from flying in UK airspace.
I think this is only (some of) United's, who are stopped by the FAA notice anyway, so a bit of a non-event. All the Far East operators of the variant have moved on to the -300ER for European flights.

[traveler24]

Hello all. A quick question here, Does Boeing manufacture or contract an outside vendor that produce the engine cowlings or is the a P&WC or GE part that accompanies the engine?

[paulross]

SLF here but given we are in the era of instant photographs would these be useful in informing the crew during the event? And how might that fit into the crew's workflow?
I'm minded of the incident report from G-VROM https://www.gov.uk/aaib-reports/aaib-investigation-to-boeing-747-443-g-vrom

"It would have been a useful facility to have been able to send and receive photographs from on-board the aircraft. This facility might also have been useful for the crew, as photographs were available in the public domain several hours before the eventual landing, showing the position of the landing gear."

[Gipsy Queen]

Grant Schapps working with the CAA on this.

I'm sure they will welcome his wide experience and technical expertise.

[lomapaseo]

traveler24

any of the above, but the installer is responsible for its approved use

[Nil by mouth]

Just out of interest, would either a RR Trent 1000 or GE GEnx be an alternative engine?

[tdracer]

Hello all. A quick question here, Does Boeing manufacture or contract an outside vendor that produce the engine cowlings or is the a P&WC or GE part that accompanies the engine?
The engine nacelle for the 777 - all engine types - was designed and (initially) built by Boeing (although it was nearly all outsourced for the 787). Most of this work was at Boeing Wichita - which is no longer a part of Boeing (now Spirit Aerosystems) but still done to Boeing specs.

As others have noted, the evidence so far indicates that the fan blade failure was contained - that part of the system worked.
The nacelle coming apart is not supposed to happen - design intent is that the nacelle is designed to withstand the forces of a FBO event without failing. Further, large parts departing the aircraft is a no-no - corrective action should be taken whenever it happens.
I am rather surprised that apparently no action was taken with regard to the nacelle structure after the similar UAL event in 2018.

[Una Due Tfc]

The fractured fan blade did not damage the a/c fuselage.

Well something punctured the fuselage below the wing root.

Got annoyed watching the 6pm news on the national broadcaster here in Ireland earlier. Anchor said on the intro “New crisis for Boeing after seven seven seven aircraft type is grounded after engine explosion”. I mean, less than 10% of 777s built are affected? But don’t let facts get in the way of some hysteria.

They did also cover the failure on the 744F out of Schipol the same day too. “a smaller version of the same engine was involved”.
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/480x853/9485c0f0_5982_4586_a5fa_fff4d6272496_d767618b96da82ea7922ab8 e696f1873eabe080d.jpeg

[hr2pilot]

According to CBC news (Canada Broadcasting Corp):

“Boeing said there were 69 777’s with the PW 4000-112 engines in service and another 59 in storage. United is the only U.S. airline with the engine in it’s fleet, according to the FAA, and it had 24 of the planes in service. Two Japanese airlines had another 32 in service.”

FAA:


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1604x1289/674162cb_2c11_432e_933c_bee9b48d7c82_d63bbf2f4c5ab55793bda34 cbc4c3db9aaf136e5.jpeg

[keesje]

Okay so if we’re talking semantics, the pressure vessel was left intact (that we know of), but the fuselage was still penetrated.

It worries when people are so determined to downplay, generalize. Safet first? Clearly an uncontained engine failure that could have hit the cabin too.

A quick search showed there were Pratt 777 blade seperations in 2018 and 2020 also. So Japanese authorities pulled the plug and then FAA and Boeing.

Would love to see Boeing/FAA take innitiatives to ensure safety after incidents, instead of denial and only look bold when things became inevitable.

[Seat4A]

Source: https://twitter.com/aviacionhr_info


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/496x886/1u_17b470fd9024c2e39aeaf86323d57e492a30bf32.png


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/498x886/1u1_c50ced2b0b4999bf2970170c2b6aa08344d076ee.png


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/499x886/1u2_d6a48031180a1de7f7f39fea4aedf9a24bfb4e19.png

[Zeffy]

https://www.bloomberg.com/news/articles/2021-02-22/jet-engine-explosion-over-denver-rings-alarms-about-shielding


Jet Engine Explosion Over Denver Rings Alarms About Shielding
By Alan Levin
February 22, 2021, 2:20 PM EST

Damage to front of engine was similar to fatal 2018 event
NTSB has called for review of engine design in prior failures


The mid-air disintegration of a jet engine over suburban Denver Saturday is the latest in a string of failures that has raised alarm among regulators about debris evading shielding that’s supposed to keep broken parts from hitting aircraft.

The incident aboard the United Airlines flight 328, which showered neighborhoods with metal debris, appears to have been the fifth in five years in which a fan blade broke and destroyed the front section of the engine, according to accident reports and safety experts. That portion of the engine isn’t as protected as the core areas around the jet turbines that are built to contain material in a failure.

“It’s getting more attention with each fan-blade-out event, resulting in these dramatic pictures showing the core of an engine hanging from a wing,” said Jeffrey Guzzetti, the former head of accident investigations for the U.S. Federal Aviation Administration.

No one was hurt in Saturday’s incident and the Boeing Co. 777 safely landed. But a similar episode above Pennsylvania in 2018 killed a woman on a Southwest Airlines Co. jet after a metal chunk from the engine struck the window where she was seated and sucked her partially out of the jet.

On Sunday, regulators in the U.S., Japan and elsewhere said they are concerned that a crack on a fan blade in the Pratt & Whitney PW4077 was allowed to grow to the point that caused it to break off, triggering the failure. They ordered emergency inspections on the hollow titanium blades, which effectively grounded several dozen older 777-200s. Pratt is a division of Raytheon Technologies Corp.

The PW4077 front fan section, which is more than nine feet (2.7 meters) wide, spins at several thousand revolutions per minute, so a broken blade can cause extensive damage to the mechanism and nearby structures.

The failure raises questions about engine designs that are supposed to prevent debris from escaping out the sides of an engine when a fast-spinning fan blade fails. The FAA told the NTSB last year that it planned to order a design change to prevent such incidents, according to a previously unreported letter last year to the NTSB.

“We are working with Boeing to ensure that the corrective action, in the form of a design change, will address the most critical fan blade impact locations,” FAA Administrator Steven Dickson said in a March 9, 2020, letter.

Both FAA and the European Aviation Safety Agency are conducting reviews of their aircraft certification rules to determine whether the standards for engine and aircraft design need to be updated, they have each told the National Transportation Safety Board. The safety board recommended such a review after its earlier investigation of the Southwest fatality.

Engine manufacturers go to great lengths to demonstrate that a broken fan blade won’t shower a jet with dangerous shrapnel. Modern turbine engines are encased in Kevlar to prevent high-velocity debris from escaping to protect vulnerable fuel tanks, equipment and passenger areas.

But the guiding theory in ensuring safety was that blades and other debris wouldn’t bounce too far forward through the onrushing air. As a result, the curved structure at the front of the engine -- known as a nacelle and engine cowl -- aren’t built as strongly.

The five recent events show that debris can, in fact, damage those areas. The result is that the existing engine standards have a gap that may not offer adequate protections during violent fan-blade failures, said a person who has participated in accident investigations. The person wasn’t authorized to speak about the issue and asked not to be named.

The issue has been getting quiet attention in recent years, but Saturday’s highly publicized failure over Denver -- in which videos on social media showed a burning engine beneath the wing and metal chunks thumping to the ground -- means “it’s now reaching a crescendo,” Guzzetti said.

The United plane was headed for Hawaii and was certified to fly long distances on a single engine over the ocean. But heavily damaged engines cause more drag, raising questions about what might have happened if the failure had occurred hours from an airport, he said.

In 2016, a Southwest jet was forced to make an emergency landing in Pensacola, Florida, after suffering a similar failure. Parts of the left engine broke apart, damaging the fuselage, wing and tail, the NTSB found. The plane lost cabin pressure and passengers had to don oxygen masks.

That engine was made by CFM International Inc., a joint venture between General Electric Co. and France’s Safran SA. They power the popular 737 Next Generation family of airliners.

A similar situation occurred on another United 777-200 on Feb. 13, 2018, as it was preparing to descend to Honolulu. Chunks of the front of the engine tore loose after a fan blade failed, the NTSB said. Metal fragments struck the fuselage, wing and tail sections. The jet flew about 120 miles on one engine and landed safely.

On April 17, 2018, another fan blade failed on a Southwest flight, also a 737-700 using CFM56-7B engines. In this case, a latch mechanism near the front of the engine was flung into the side of the jet, causing a window to break open, killing the woman seated next to it. Pilots landed safely and nobody else was seriously hurt.

The NTSB issued five recommendations to the FAA and its European counterpart, EASA, as a result of the 2018 failure. The safety board called on the regulators to require Boeing to redesign the front of the engine to prevent debris from escaping in the future.

Investigators also sought a broader review of how engines and aircraft are designed to ensure future designs aren’t vulnerable.

A Japan Airlines Co. Ltd. 777-200 suffered similar damage on Dec. 4 after a fan blade broke. In this case, a door on the exterior of the engine broke loose and the plane’s fuselage and tail section were hit by debris, according to a preliminary report by Japanese investigators.

All three of the 777s were powered by Pratt & Whitney PW4077 engines.

Pratt said last June that it had taken corrective actions to address the cause of the 2018 failure. After that incident, Pratt re-inspected all 9,600 fan blades and didn’t find any others with potential safety problems, the NTSB said.

The violent failure on the engine above Denver destroyed most of the relatively unprotected areas at the front of the turbine. At least some debris struck the plane itself, causing minor damage, the NTSB said Sunday in a press release.

One fan blade broke off at the root where it was mounted to a spinning rotor, according to a person familiar with the preliminary investigation who wasn’t authorized to speak about it. A second blade broke off, apparently after it was struck by the first, the person said.

While details of the failure haven’t been provided by the investigation, the violent loss of the blades caused the entire structure at the front of the engine to break loose, according to photos of the remains of the engine. Pilots returned to Denver for an emergency landing.

Both Guzzetti and the person who participated in engine investigations cautioned that the planes in each of the incidents were able to land safely, suggesting that other layers of safety had helped protect against a catastrophe.

The inspections of fan blades ordered by FAA and other regulators also will help lower the chances of a similar failure in the future.

GE spokesman Perry Bradley said it was more appropriate for Boeing to answer questions about the design of the front of the engines since it’s the planemaker’s responsibility under FAA regulations, not the engine manufacturer. Boeing and Pratt & Whitney didn’t immediately respond to a request for comment on the issue.

By contrast, the failure of a Pratt & Whitney engine on a Longtail Aviation 747-400 cargo jet on Saturday in the Netherlands didn’t allow debris to fly out and hit the plane, according to Longtail Aviation Chief Executive Officer Martin Amick.

The failure prompted metal shards to fall to the ground, injuring two people, according to local news reports. The metal debris escaped out the rear of the engine, which is how they are designed to fail.

— With assistance by Ryan Beene, and Siddharth Vikram Philip

[Una Due Tfc]

WHBM

Quite. Fire was burning away happily in the airflow and one presumes after fire bottle deployment. Same thing happening 3 hours from nearest alternate? Concerning.

[lomapaseo]

good photo!. Now at least one can see where the problem is coming from. Looks like a fire shield to cover 30 sec of time would get rid of the reverser ignition source. The upper nacelle parts seemed to stay out of it and even in the air it would probably go out by itself without the need for extinguisment. We'll see what Boeing does other than lean on Pratt

[Tango and Cash]

WHBM

Right--ETOPS is completely relevant here. An ETOPS aircraft departing on an ETOPS flight with an engine failure...

But then if anyone seriously questions ETOPS, the long-haul aviation world would come to a complete halt.

[Droop Snoot]

What is the on wing periodic inspection interval and method for the fan blades? :confused:

[Una Due Tfc]

Every 5000 cycles for fan blades I read elsewhere after the 2018 event.

[PAXboy]

lomopeso

My cynical guess is: Zero.

They will say that P&W designed it and said it was good and that the engines are not the aircraft. We'll get the "We are working closely with our friends and colleagues in P&W and FAA to ..." to ensure where the blame goes. Then you can discuss the, "Who asked for engines that could go further/faster on less fuel and be reliable for ages? Well, ultimately, the passengers!

[armagnac2010]

The nacelle coming apart is not supposed to happen - design intent is that the nacelle is designed to withstand the forces of a FBO event without failing. Further, large parts departing the aircraft is a no-no - corrective action should be taken whenever it happens.Well, it all depends upon the actual unbalance load. The normal assumption is one full fan blade, including the retainer portion which fits in the fan disk, a rather big chuck of material. From the pictures it seems the first blade ruptured just above the spinner so this portion of the blade stayed in place. The departing ('liberated') blade probably took away the adjacent one, at mid span. Not sure if it results in unbalance loads are higher or lower than the nominal case. The engine RPM is also an important parameter.

The FBO demonstration during engine certification typically demonstrates only one fan blade will depart. This is a big deal, because it directly drives the sizing of the containment ring and dermines the unbalance loads used to siez the airframe, nacelle included. The data I remember on such engines is that the separation of 3 adjacent fan blades, at 100% RPM, will result in loads well above the front spart capability of the wing, resulting an instant catastrophic failure of the aircraft structure.

Compared with the certification test involving a full fan blade, in service events with partial blade separation often result in multiple blade damage (and eventually rupture), because the cinematic is different, but the certification case is expected to be the envelope. This will be confirmed (or not) by the investigation.

It is interesting this involves a hollow titanium fan blade design. A similar material is used on the Trent and it resulted in various events with ruptures just outboard of the spinner.

[silverstrata]

Looks like I was right - the blade-tip went forwards, and sliced through the cowling ring, eventually destroying the entire cowling (and then hitting the wing-root). There was a lot of push-back to this explanation here, but it has been known as a possibility for decades.. Indeed, the only fan-failure I have had, left impact marks all across the front cowling noise suppression ring.

Unlike the whole blade, the tip has much more forward force on it and a lot less weight, and it can easily spin out the front of the engine. And it appears that this is what happened.

Take a look at the Blancolirio channel.
https://youtu.be/EwNCCrjMmeg

[WillowRun 6-3]

Amidst many entries here (and other subject areas ongoing) this SLF/atty has noticed some references to the NTSB incident report about the 2018 incident of the same or substantially similar nature appear to base inferences, or innuendo, on the fact that nothing actually was changed after that incident, that is to say, after the pertinent report was published.

While not having read the full docket of items in the 2018 Board record, one item which has been noted is that the inspection process left a number of things to be desired. (To avoid misstating these, I'm not summarizing the findings of the report here.)

What became of those findings, in context of initiatives to dig deeper into the gaps or evident traps for the unwary, in the inspection area? Just one example: attributing apparent findings to the coating or paint used to facilitate the inspection process (if I understood correctly). That gap having been noted by NTSB, what became of any action steps? Or less non-cynically, were there any action steps?

(Somewhat related, as a member of the traveling-by-air public, to be told that Denver to Honolulu doesn't quite definitely fall within ETOPS, I dunno, I'd have to ask some dumb, non-aviator questions.)

[DaveReidUK]

There were no Safety Recommendations made as a result of the above investigation, so I'm not sure what changes could reasonably be expected.

[WillowRun 6-3]

DaveReidUK

The report did point to areas of the inspection process which could be improved, specifically areas which were implicated (if not formally found as a factual matter) to have led to the failed blade flaw(s) going unaddressed - is that not correct?

If that is correct, then is it the case that only formal Safety Recommendations can be predicates for re-examination and improvement of processes?

I'm not being formalistic - I'm not relying on the prior post not referring to "Safety Recommendations". Instead, having identified aspects of the inspection process overall which appeared directly involved in the problem blade continuing in service to failure, is that not a sufficient predicate to ask how to close those gaps? or at least to start to address it?

[Euclideanplane]

WillowRun

Assuming you refer to the SWA1380 accident in April 2018, an AD was issued to effect inspection of possible fatigue cracking in CFM56-7B engine fan blades specifically [FR Doc No: 2018-09338]. It is a reasonable question whether much was done towards similar precautions targeted at other engine types or products.

[lomapaseo]

armagnac2010

It does not demonstrate only one blade will depart. It demonstrates a safe shutdown for all the consequences of the intentional release of a single fan blade. So if that single released blade takes out a couple more blades then the engine must still be capable of being safely shutdown. Mostly nobody cares about all the other engine damage as long as it doesn';t catch fire or break its mounts

Of course there will be unbalance loads including even at windmill conditions. However once shutdown most of the rules govern the aircraft .

Some other poster presented a video which opinioned that windmill vibration loads will break things, including the inlet nacelle. It is important to understand that the greatest load condition across al the engine flanges including the inlet are at the instance of about 5 rev of the fan in rundown.. the windmill unbalance loads loads are minor. Of course aero loading to seriously compromised surfaces must be considered

[WillowRun 6-3]

Sorry Euclideanplane no, it was:
N773UA, BOEING 777 222
Date of Accident: 02/13/2018

Earlier posts (95) had the NTSB docket; 96 had the final report.

[armagnac2010]

Of course the safe shut down has many more aspects than the single blade. But the unbalance loads are important, because they drive the aircraft structure compliance. If the engine lose say 5 blades and has a safe shut down, it can be certified, but will remain the most expensive fan ever, because nodoby can install it and certify an airplane able to withstand the FBO loads.

With modern, wide chord fan blades, unbalance loads have increased. As pointed out above, in the 90s FAA and JAA became aware of the issue and drafted AC25-24. The airframer have to demonstrate safe 3-hour diversion with a windmilling engine, covering strcuture, system, structure and human factors. The recent USAF E-11 (Global Express) accident report shows that vibrations are such that flight crew can barely read instruments to the point of shutting down the 'good' engine...

[OldLurker]

Tango and Cash

The failure occurred on climbout - not in ETOPS - presumably on high power. Does the power state affect the probability of blade separation? In other words, if an engine doesn't fail on climbout, is it likely to fail in cruise?

The engine burned but the fire doesn't seem to have compromised the wing above, so I guess the fuel shutoff was effective and as stated earlier in this thread, what was burning was 'only' engine oil and maybe hydraulic oil, and if this had happened in ETOPS it would have burned itself out in a relatively short time.

OTOH, as shown in the photo in post #142, something punctured the fuselage below the wing root and, in cruise, would presumably have caused decompression.

How many ETOPS flights take place every day? In the many years since ETOPS was introduced, how many engine failures endangering the aircraft have occurred in ETOPS flight? Of course, there's always got to be a first time ...

[tdracer]

A few comments - I won't bother quoting the exact posts since the mods have been removing much of the quoted posts.

ETOPS - part of the ETOPS equation is that most engine failures occur during takeoff or initial climb, not during the ETOPS portion of the flight. Failures - particularly catastrophic failures - are very rare at cruise. This is also true of FBO events. While a FBO can happen anytime, it's most likely to occur during takeoff or climb since that's when the fan blades experience the highest loads.
As I've posted previously, it was discovered during the 777 development program that some of the assumptions that had been used for FBO loads to the nacelle and engine structure were not valid - at least not for the (then) new generation of very large, very high bypass engines. As a result, higher FBO loads were used during for the 777 and subsequent programs. Recent experience suggests those loads need to be re-evaluated.

The PW4000/112" engine and the associated installation is out of production - and has been for about 15 years. That results in different treatment of things like these FBO events than would have resulted if it was still being produced (expanding fleet). Instead, analysis is done of the probability of a future, catastrophic event given the size of the existing fleet and how long it will remain in service. Hence, a relatively small fleet such as the PW4000/777 will be treated differently than a large fleet such as the 737NG/CFM56. No first hand experience (retired before the first PW4000/112" FBO event), but the process will look at the probability of a future PW4000/112" FBO event - presumably with some mitigation factor for more frequent, improved inspections - with additional probabilities assigned for the chances of a future event becoming catastrophic (remember, as dramatic as this event was, no one was hurt and the aircraft did not suffer serious damage - granted the next one may not be so lucky, there is a good chance it would). That process will determine what - if any - additional steps are required to maintain the expected level of safety. Now, before anyone starts in on their criticisms, know that while there are some Boeing specifics in the process that will be applied - the process itself is used throughout the industry, with a high level of FAA and other regulatory involvement.

Not privy to details, but the recent 777/PW4000 and 737NG events appear to share a common theme - fan debris is going forward of the containment ring and damaging the inlet/nacelle - leading to structural failure of the inlet and nacelle. This is something new - I don't recall that ever been seen before a few years ago. There had been cases where fan debris impacted the inlet forward of the containment ring, but it was low enough energy that it didn't do meaningful damage. For some reason that's changed (my guess is it's related to the higher bypass ratios of the newer engines, but that's just a guess). However I believe that's where the focus need to go, since I doubt any engine installation out there is going to deal gracefully with high energy debris impacting the inlet/nacelle forward of the engine containment ring - the inlet and nacelle are simply not designed for that.

[tdracer]

OTOH, as shown in the photo in post #142, something punctured the fuselage below the wing root and, in cruise, would presumably have caused decompression.
No, the impact damage is to the wing root fairing - that is for aero purposes and is not structural (and is technically not part of the fuselage).
Now that being said, it doesn't mean the next time it won't penetrate the fuselage and cause a decompression - but that didn't happen on this event.

[OldLurker]

BTW, one of the longest ETOPS engine-out diversions ever was ... yes, a United 777-200 with PW engines. They landed safely.
www.pprune.org/showthread.php?p=2560874 (http://www.pprune.org/showthread.php?p=2560874)

[WHBM]

OldLurker

You can't just say "Oh, it happened less than 180 minutes time from an airport, so that's not ETOPS". It covers the whole flight, including procedures before departure.

My understanding was that the ETOPS cert was dependent on some certain, notably high, reliability standards. With the relatively modest numbers of Pratt-powered 777s, and the two events which have now afflicted the type in recent times (and bear in mind the other one did happen in cruise, out over the Pacific), has the type fallen below the required ETOPS standard ?

This seems to be the third Boeing grounding in eight years, when I don't believe any other manufacturer has had one. A bit disappointing.

[Droop Snoot]

td:
That's fascinating. Because the blade separation is due to static overload, it requires a higher flight load to do so. So even though takeoff and climb represents a pretty small portion of the overall flight spectrum, the much larger time spent in the remaining portions of flight is not enough to allow the crack to propagate further and fail at a cruise flight load. It almost seems like that's been borne out in some of the incidents I remember, is it an industry wide trend? Sounds indeed like it could be used to support ETOPS certification.

Your explanation of the quantitative risk assessment is right on.:ok:

[darobstacraw]

With the failure of a P & W engine on a 747, do you folks think they will change the inspections \ groundings to cover more airframes? Will the USAF ground the KC-46's?

article on the 747 engine failure: simpleflying.com/boeing-747-engine-parts-rain-down-on-dutch-village-after-engine-fire/

[lomapaseo]

Quite often the key stress component is a vibratory mode superimposing on static stress. One thing to check is the clock position of where the blade first strikes the casing.. across multiple events

[pilotguy1222]

It does not even matter if it was an ETOPS flight. ETOPS is an aircraft AND operator certification. You just don’t buy a 777 and automatically have ETOPS capability.
All ETOPS types are easily flown on one engine, and the aircraft systems required have plenty of redundancy, so it really comes down to engine reliability.
3 failures in 3 yrs doesn’t sound so bad. 3 failures that are nearly identical in 3 yrs sounds a bit worse. 2 of those failures in 3 months. Fatigue cracks found in 2010 and 2015, yet covered up with some pure BS. Ouch.
Now add in all the Pratt 4000 series issues (ex. 747-400 of of AMS the same day).

It will be interesting to follow.

[Zeffy]

https://youtu.be/-VfGJsfS13g



WASHINGTON (Feb. 22, 2021) NTSB Chairman Robert Sumwalt conducted a virtual media briefing Monday, Feb. 22, 2021, to provide an update on the agency’s investigation of Saturday’s engine failure incident on United Airlines flight 328. United Airlines flight 328 experienced a right engine failure after takeoff from Denver International Airport Feb. 20, 2021. The airplane returned safely to Denver; none of the 229 passengers or 10 crewmembers were injured.

[WillowRun 6-3]

WSJ article for tomorrow's dated edition refers to an FAA AD issued in March 2019 in the wake of a similar occurrence (United 1175) in February 2018. Finally SLF/atty realized AD cite should be in NTSB report on that 2018 incident - report DaveReidUK had posted earlier.

So, link to AD 2019-03-01 pertaining to blade inspections and related:
2019-03-01.pdf (faa.gov) (https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/bb315c3fce9e8c75862583a2005079f0/$FILE/2019-03-01.pdf)

[kenish]

Anyone know what this part is? The entire part is approximately 6 feet (2m) long and there is video on the usual news outlets of it hitting the pavement with quite a bit of force. FYI the miscellaneous photos on this site are interesting:
https://www.denverpost.com/2021/02/21/united-airlines-engine-failure-debris-colorado-denver/

https://www.denverpost.com/wp-content/uploads/2021/02/TDP-L-PLANE-ENGINE-EXPLOSION_JAC7742x.jpg?w=620

[Zeffy]

High res photos avail at
NTSB Flickr

[fdr]

tdracer

The PW4000 112, GE90 etc have low examples of fan blade release, as is the case for the CFM-56-7's. These have larger chord blades in general compared to earlier fan designs, which may be helping in the path of the liberated part.

general comment not related to tdr... :). Was queried on. my post #113 on the wording I used, and it needs clarification, and that is related to your observation so here goes...

I commented on the release dynamics, noting the radial accelerations. This is more correctly stated as centripetal acceleration but has the same meaning, well at least in my limited language skills.

The fan disk transfers torque to the blade root, to counter the aerodynamic drag of the blade. The blade root transfers loads to the disk and VV through the fir tree root fittings for radial, in-plane loads. the root also absorbs the out-of-plane bending loads and also torsional loads. The blade has inertial and aerodynamic moments, and these all come to play in a failure. On the release of the blade it is free to depart the scene, and follows Nootin's 1st, translating outwards and along the tangent of the in-plane path, for a poofteenth of a second, until the tip contacts the inner wall of the annulus/rub strip, whereupon drag forces slow down the outer end of the blade, and inertia starts a rotation out of the radial alignment of the blade as built. The blade tip is a light structure, (designers are smart... ). the tip hitting anything including ice will deform, hitting the engine annulus is going to collapse the blade structure and leave a witness mark. That impact slows down the blade's outer end... at the same time, drag is moving the blade rearwards, and it approaches the following blade. Coincidentally, the lift force twists the blade out-of-plane, and the pitching moment gets a say on it's alignment, and it will start rotating LE downwards. About now, it gets the kick in the pants from the following blade, and gets pushed forward for a short while, while damaging the following blade LE at part span. rotating around its length, the blade develops Flettner style lift and gets carried forward for a short period of time.

Does the blade need to hit the intake lip to sever it? Probably not.... my guess... the out-of-balance of losing 1 1/2 blades on one arc of the fan is going to be quite impressive. Happy snaps will show if contact occurred, but I'm thinking Arby's... that the light structure will fail under high oscillatory loads. Maybe...

Then again, the blade may work like a chainsaw and chew its way through the structure, but, I doubt that is the case.


Sunil K. Sinha and Sreekanth Dorbala wrote an interesting paper on "Dynamic Loads in the Fan Containment Structure
of a Turbofan Engine" J. Aerospace Engineering July 2009, and stated in part:

"A typical fan blade-out event involves very complex nonlinear transient dynamics with large deflection of the release blade and rigid body rotation of the trailing blade as well as progressive failure and fragmentation of various components. Due to the nature of the impact type loading, the solution to the problem should also address dependence of the material behavior such as yield strength as a function of strain rates. In short, the transient dynamic analysis of a fan blade-out event highlights the complexity of the numerical technique, which includes all the nonlinearities of structural dynamics: plastic behavior of the materials, large displacements, and contact interaction between structural elements. In this paper, we present the results of a LS-DYNA simulation of a FBO event on a full-engine analytical model, which covers both the primary as well as secondary damages."

These guys did a neat analysis, however even using the LS-DYNA code it is a simplification of the dynamics of the release, and as far as I am aware, that remains the case to this day. The last time I looked at this was when we were doing some weird $&*T on fan blades doing a POC, and wondering where the stuff was gonna go fly. (in the end, our assumptions happened to be OK on the day, luckily, and we didn't blow up the test engine, the test cell, or the building).

Page 264, upper right paragraph under figure 4 "Comparison of von Mises stresses between ANSYS and LS-DYNA" has comments that say in a high tech manner what is stated above in lyrical prose. The 5th happy snap below tells a story of the engine response, why it pretty much disassembles itself. the image before that with the graphs indicates what is missing in the analysis and should be considered in relation to the observation of the paragraph mentioned on page 264 of their report.

Now, it could well be that the LS-DYNA code is absolutely correct, and if so, then we can expect to see plastic deformation at one particular point of the containment ring, and then we would come up with a new trajectory for the blade parts.... how do they get from point A to entry point X. My suspicion is that there is no penetration of the containment, and that should give a hint as to what to add to the code.

Gotta say I'm a bit miffed, I quite liked the 4094 donk, I would hope the failure is from an isolated cause such as inclusions or similar rather than a design of the blade, presuming that the 112" has a common blade P/N... which is probably the case.

Zeffy, thanks for the NTSB photos, that blade root is telling a story. The future of the 4000-112 series rides on the close-ups of that picture.





https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/850x362/fan_blades_rubbing_differently_at_two_different_times_after_ fbo_showing_nonlinear_effect_77ad4d4de4499004a228c0d9a86fe50 d1cfcc592.png
https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/850x1458/a_fringe_pattern_showing_bulge_formed_in_casing_due_to_impac t_of_release_blade_b_local_a3ab1b789e0df6ae30639122dff63ffb8 91fc8e1.png
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/850x525/fragmented_release_blade_inside_containment_analysis_8331707 ecbb8b5fffb755b22f6f3660b2579f59e.png
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/850x1144/time_history_of_first_following_fan_blade_and_containment_st rain_energy_energy_values_31c98305cc8cad0c161c04389ac96b5a7a a9c3c4.png
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/850x762/fan_lpt_rotor_orbit_at_two_different_axial_locations_of_roto r_a_fan_disk_center_b_7259c10520eccd46ffa502d169012097a474ea 0a.png
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/850x628/normalized_acceleration_time_history_of_auxiliary_gear_box_a fter_fbo_event_on_engine_dbb532d3ecef56c68290743ae160a8b5401 f46aa.png
https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/850x598/effect_of_rubbing_action_highlighted_by_contact_stresses_bei ng_generated_in_shaft_in_rub_72985ca83573d1ee2af0f6a6973aa4f 5f7e79191.png
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/850x619/time_history_of_load_in_bearing_no_1_support_cone_analysis_v ersus_test_bf8980b5f8860a99d82b271f0fb6f7a7587909be.png

[fox niner]

The NTSB has concluded that this engine failure “was contained”. Probably semantics, but that is stretching it quite a bit.

[DaveReidUK]

Are you suggesting that the NTSB's definition is wrong, or that the term is meaningless ?

Either way, it might be quite useful to have a term that's shorthand for "no rotating part of the engine was ejected radially", which is a bit of a mouthful but accurately describes this event.

[wiggy]

Not really, as DR UK points out what happened/didn't happen means objectively the event meets the definition of being contained.

[Less Hair]

So it is called contained while the airplane got hit and damaged by high energy fragments?

[bsieker]

darobstacraw

The PW4077 as used on the 777-200 is a unique sub-variant as it is the only one to use hollow titanium alloy fan blades (similar to many RR Trent engines).

The 744 case in Maastricht was a completely different failure mode and a different variant of the engine. It seems to have suffered some catastrophic turbine blade failure, for reasons yet unknown, but also contained.

[sprite1]

The home pic on this link https://aviationtribune.com/airlines/middle-east/pratt-whitney-to-support-el-al-pw4000-engines/
is of the PW4000 series. On the bottom of the engine, in the 6 o’clock position, running length-wise are two similar piping ducts with matching insulation.

Going by the other pictures up thread of the engine damage/severe burns on the bottom half of the engine, parked on stand, it appears they’re the same ducts.

If so, I’d say they’re engine anti-icing ducts.

[bsieker]

Less Hair

The airplane was not hit by high-energy fragments. Those would have gone straight through. A non-structural fairing was hit by a low-energy fragment. Not something you want, but not a catastrophic (arguably not even "major") failure from the point of view of the aircraft.

[Gizm0]

Less Hair

As previously mentioned (but removed by Mods) this WAS CONTAINED. An uncontained failure involves bits flying off radially - and at very high speed - that very much do have the capability to seriously wound an aircraft. The worst that was going to happen in this instance (assuming a competent crew) was a relatively low energy fragment penetrating the pressure hull and causing a decompression. No worse than a blown door or window - although still not pleasant of course. However there is / was significant risk to persons on the ground. In this case they were lucky.
I know this is a rumour forum but please, guys & girls, try to stay calm & accurate!
(Beaten to it by bsieker)

[SLF3]

'Sumwalt (NTSB) said the United incident was not considered an uncontained engine failure because the containment ring contained the parts as they were flying out. There was minor damage to the aircraft body but no structural damage, he said.'

[Less Hair]

https://images.app.goo.gl/XvuYCgnyRvgg5oG99

Looks like the wing got at least scratches.

[ivor toolbox]

cncpc

probably engine oil, from engine lubrication system,


sprite1

Looking at the lagging, and insulated coupling I would agree with that observation

[WOTME?]

silverstrata

To be fair the Bring Another Engine 146 was for the BAe 146 which had the much less reliable LF502.The damage on the RJ100 LF507 in your example was caused by incorrect maintenance not an unreliable engine,although there have been examples of LF507 turbine failures.

[WHBM]

But didn't the "other" United 777/PW fan blade failure in 2018 happen in cruise, at FL360, over the Pacific ?

[billovitch]

Question for the engines, structures and certification guys:

Instead of planning future engines for x- number of fan blade separation failures and constructing appropriate static containment surrounding the fan disk -

- how would it be to support the blades themselves with an integral peripheral band or cord, providing a centripetal force and opposing the separation loading?

This solution, while increasing the inertia of the rotor could be quite a bit lighter than all the present external measures and would tackle the problem at source tending to prevent separation (and by the way to damp vibration) in the first place and easing certification requirements.

Worth a try?

[DaveReidUK]

WHBM

"But didn't the "other" United 777/PW fan blade failure in 2018 happen in cruise, at FL360, over the Pacific ?"

Yes, shortly before ToD.

[bsieker]

Less Hair

Possible damage to some bolts and some superficial scratches. This will undergo a very detailed and careful inspection but my first guess would be that the airframe structure was not compromised in any way. Which is precisely the point of the fan containment ring. It worked as designed, and it is there precisely because a fan blade failure is not one of those "extremely improbable" (10^-9 per hour) failures (not expected during the lifetime of the fleet), but merely "extremely remote" (not anticipated during the lifetime of each individual airframe, but may occur a few times during the lifetime of the fleet".

[unmanned_droid]

unmanned_droid

When I posted this I had only seen the passenger video, which, to me did not show fan blades missing. Since I posted this I have seen the pictures showing 1 blade broken at the root and an adjacent blade missing the outer quarter. I still feel that design peak loads would not have been reached so a failure of the pylon or wing structure leading to a loss of an engine would not have happened in this case.

[NutLoose]

https://edition.cnn.com/2021/02/23/us/boeing-aircraft-engine-fail-tuesday/index.html


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/780x438/210222211840_02_boeing_aircraft_engine_failure_ntsb_exlarge_ 169_2d5c840ec413100ede43af9c05b91b3388a29caa.jpg


https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/780x438/210222212002_03_boeing_aircraft_engine_failure_ntsb_exlarge_ 169_33c32817a8154dc3f34c70f61ea134621aedc967.jpg

[dragon6172]

silverstrata

I'd guess the wing fairing damage was caused by cowling bits or the inlet ring itself. The slice/slash that goes through the inlet ring is outboard between 2-3 o'clock.

[Dan Winterland]

Sometimes in fan blade failures, the blade flies out the front of the engine due to the aerodynamic force on it. In this case, it appears to have struck the belly fairing. This is very similar to a incident an airline I flew for experienced.

[bsieker]

billovitch

There are several fundamental problems with that idea: what would hold such a band or cord in place? If it is attached to the blades, it only increases the weight of the blades, and thus increases the force on the blade's attachment point. It would need, in turn, to be anchored to something else, but to what? If you anchor it to the fan disk (the "hub"), it just creates additional structures that could break and fly off, and if you anchor it to the case, you basically have a containment ring, which is just what we already have. Any way you turn it, it makes no sense.

I'm also not sure you have a grasp of the stupendous magnitude of the centripetal force required to make these blades turn in circles. Assuming an effective radius of 0.5 m, a blade weight of 20 kg and 3000 rpm fan speed at takeoff, that would come out to roughly 1 MN ("100 tonnes") per blade! Show me the cord or band that can hold even just a substantial fraction of that.

[Speed of Sound]

billovitch

Not exactly the same thing but in Formula 1 the F.I.A. mandated a similar system to stop wheels coming off the cars in a crash. This system uses three separate Zylon tethers each bonded to a different part of the car to provide redundancy if one of those parts fails in a crash.

Despite each tether being designed to take 10x the weight of a car, they still fail fairly often in high speed crashes.

[bsieker]

Dan Winterland

What makes you think it was a part of the fan blade that struck the fairing? Lots of other pieces fell off from the nacelle.

And is that really true about forward ejection? It certainly never looks like that in blade-off tests I have seen. And the maths also doesn't work out:

Even full forward load is tiny compared to the centripetal load, so any forward acceleration would not move it forward any significant amount in the time it would reach (a) the following blade trying to shove it backwards and (b) the containment ring, deflecting it unpredictably. So (b) could possibly deflect it forwards, but the talk about aerodynamic load is a red herring.

Look at the numbers: centripetal load per blade: 1 MN. Maximum forward aerodynamic load: 16 kN (rough numbers: 350 kN of thrust distributed over 22 blades). In the fraction of a second that blade would need to reach the containment ring, it would only accelerate to single-digit m/s forward speed component, and would have perhaps a 50th of a second to move. It wouldn't move more than a few centimetres forward.

TL;DR: yes, blades could be ejected forward, but not from aerodynamic loads, but from being deflected erratically by the containment ring.

[fitliker]

Have they ruled out bird strike or drone strike ? Or would more blades be damaged from such an event ?

[tdracer]

What I'm hearing is that they found evidence of metal fatigue at the fracture surface of the failed blade - just like on the previous two PW4000/112" FBO events (presumably the trailing blade that failed mid-span due to overload due to impact with debris from the leading blade).

Metal fatigue is pretty obvious when you know what to look for at the facture surface.

[WHBM]

Bear with me for some notes that possibly should be in the Nostalgia section, but as I understand it the fan blades of the P&W engines here are hollow, whereas on other 777 engine types they are solid.

If Boeing care to go back 70 years in their archives they will find that the P&W piston-engined Boeing Stratocruiser also offered a choice of propellers, hollow or solid, and that well into the aircraft's life the hollow ones began to give significant problems from internal fatigue and internal corrosion. Eventually, 10 years into the aircraft's operation, an AD was issued that prohibited the hollow units.

AD 58-19-02, if Boeing would care to look it up.

Discussed on a PPRuNe thread here (post #43 in particular) 12 years ago Propellors on DC6/7, Stratocruiser, Constellation & Britannia - PPRuNe Forums (https://www.pprune.org/aviation-history-nostalgia/361812-propellors-dc6-7-stratocruiser-constellation-britannia.html)

[Droop Snoot]

billovitch

The same basic concept is applied in the H-60 main rotor spindle tie rod. Redundant load paths are always desirable.

[horizon flyer]

The AN124 uncontained engine failure a few posts earlier shows I think is what one really looks like.
From this I believe the containment ring worked.
The hole in the hull looks fairly low energy compared to the AN124, which went straight through destroying things on the way.

[billovitch]

bsieker

Hi bsieker and others,

Probably I didn’t explain the idea very well - think of the band as a rim and the fan blades as spokes of a rigid or semi rigid wheel.

This rim looks a bit like the metal tyre round a wagon wheel and is attached directly to the all blade tips.

In this way the blades are stabilised and supported by each other. There may even be an aerodynamic benefit due to the fencing effect at the tips.

Now imagine you are a blade, hanging on to the disk hub but also being held in there by this band. Before you can fly off you have to compress all the opposite blades which are supporting the band in turn. The band doesn’t have to take the 100 tons - the hub does that and the band provides support to stop it getting ideas.


It is the sum of the forces working like wagon wheel spokes in compression but like bicycle wheel spokes in tension. (Wagon sits on its spokes - a bicycle hangs from them)

So the blade doesn’t get much chance to get fatigued and won’t want to depart. If the blades expanded there would be a bending moment so the rim material should be the same as the blade material. If composite, then composite too.

A tight cord around the blade tips would be lighter and have a similar effect but could be more difficult aerodynamically.

[DType]

I am VERY out of date on jet engine design, but I do not think there is any practical material that could exist as a hoop at the relevant speed and radius without bursting.
Unless I dropped a 0 or two in my calcs.
So the blades would be holding on to the hoop, not vice versa.
That is why engine discs concentrate the material near the hub, where it is best value.

[Zeffy]

Originally posted July 2020 - updated a number of times - including as recently as today.

NDI Process Failures Preceded B777 PW4077 Engine FBO (http://aerossurance.com/safety-management/ndi-failures-b777-pw4077-fbo/)

[Winemaker]

DType

Yes, I ran some rough numbers for thin wall hoop stress with a 120" diameter and some rough guess as to load; a hoop 'retainer' sort of device does not look realistic. Any serious load would quickly over stress it.

[tdracer]

WHBM

The fan blades on the GE90 series are carbon composite construction, with a TI leading edge (GEnx uses the same basic fan blade design). The GE90 blades have proved to be amazingly durable - I can't recall a single fan blade release or failure on a GE90. I don't know if it's still true, but back in the early 2000's GE had a sign in their training center stating that a GE90 fan blade had never needed to be scrapped due to in-service damage.
Memory says the Trent engine uses a TI skin over a TI honeycomb matrix material - and I believe they use the same construction on all their wide-cord fan blades. Rolls has had issues with fan flutter with their fan blades - the RB211-524G/H, Trent 800 (777), and Trent 1000 (787) have all had to implement fan 'keep out zones' which prevent engine operation in a defined RPM range without forward airspeed. I recall a Trent 800 FBO event back around year 2000, although IIRC it wasn't the blade that failed - the blade 'dovetail' root failed due to improper lubrication.

[Feathers McGraw]

WHBM

From what I read, this particular PW4000-112 series engine (PW4077?) is the only hollow-bladed version. I don't know about the GE90 engine (except that it has part composite blades in the larger variants at least), but RR Trents nearly all have hollow titanium blades. These are made of three pieces which are placed in a mould, heated to very high temperature and are then internally inflated with high pressure gas to form them to the shape of the mould. The third piece between the two halves of the outer blade faces is corrugated and it stretches into shape with the vertices of the corrugations melting into or fusing with the outer pieces effectively forming a one-piece finished structure.

[DaveReidUK]

Feathers McGraw

"From what I read, this particular PW4000-112 series engine (PW4077?) is the only hollow-bladed version."

All PW4000 series engines with the 112" fan (PW4074 to PW4098) have the hollow blade.

[Zeffy]

https://youtu.be/jh4727krwH4

Juan Browne spoke with the CA of the 2018 777 near HNL.

Very interesting comments about the hazards downstream of the fan blade release -- not just with 777s and PW4000-series engines.

Big pieces of departed cowlings can introduce serious aerodynamic and flight control issues.

[Feathers McGraw]

DaveReidUK


Right, I see, I didn't realise that the thrust rating of the PW4000-112 varied so widely, but I now realise that it's the 112 that decides the fan size and blade construction, the 40xx gives the thrust rating. Engines now seem to come in many flavours while all aircraft have become twins with few real differences, just the wingtips.

[Seat4A]

Didn't see this one posted:


"Page last modified: February 23, 2021 8:13:59 PM EST

The FAA issued an Emergency Airworthiness Directive (AD) (https://www.faa.gov/news/media/attachments/Emergency%20AD%20Document%20AD-2021-00188-E.pdf) (PDF) tonight that requires U.S. operators of airplanes equipped with certain Pratt & Whitney PW4000 engines to inspect these engines before further flight.

The FAA is taking this action as the result of a fan-blade failure that occurred Saturday on a Boeing 777-200 that had just departed from Denver International Airport. Although the aircraft landed safely, the failure resulted in damage to the engine, an in-flight engine fire, and damage to the airplane.

After reviewing the available data and considering other safety factors, the FAA determined that operators must conduct a thermal acoustic image (TAI) inspection of the large titanium fan blades located at the front of each engine. TAI technology can detect cracks on the interior surfaces of the hollow fan blades, or in areas that cannot be seen during a visual inspection.

As these required inspections proceed, the FAA will review the results on a rolling basis. Based on the initial results as we receive them, as well as other data gained from the ongoing investigation, the FAA may revise this directive to set a new interval for this inspection or subsequent ones.

The previous inspection interval for this engine was 6,500 flight cycles. A flight cycle is defined as one takeoff and landing.

This AD is effective immediately upon receipt. The FAA will share this information with other international civil aviation authorities."

https://www.faa.gov/news/updates/?newsId=96858&omniRss=news_updatesAoc&cid=101_N_U

[DaveReidUK]

Seat4A

"The FAA issued an Emergency Airworthiness Directive (AD) (https://www.faa.gov/news/media/attachments/Emergency%20AD%20Document%20AD-2021-00188-E.pdf) (PDF) tonight that requires U.S. operators of airplanes equipped with certain Pratt & Whitney PW4000 engines to inspect these engines before further flight.

The FAA is taking this action as the result of a fan-blade failure that occurred Saturday on a Boeing 777-200 that had just departed from Denver International Airport. Although the aircraft landed safely, the failure resulted in damage to the engine, an in-flight engine fire, and damage to the airplane."

It's curious that while the FAA (and everyone else) correctly refer to the event as a fan blade failure, the authors of the AD quaintly describe it as the "1st stage LP compressor", as if we've somehow jumped back 60 years in time.

[Flightmech]

All air carriers opr (taking-off/landing) within the territory of Japan are requested to avoid using aircraft equipped with PW4000-94 series engines until further notice applicable engine types are as follows


PW4052 PW4056 PW4060 PW4062 PW4062A PW4152 PW4156A PW4156 PW4158 PW4460 PW4462 RMK : EXC MIL ACFT

[DaveReidUK]

Flightmech

"All air carriers opr (taking-off/landing) within the territory of Japan are requested to avoid using aircraft equipped with PW4000-94 series engines until further notice applicable engine types are as follows

PW4052 PW4056 PW4060 PW4062 PW4062A PW4152 PW4156A PW4156 PW4158 PW4460 PW4462 RMK : EXC MIL ACFT"

That doesn't seem to have made it into any of the mainstream or aviation media. What's your source, and what does it say is the reason ?

[Flightmech]

It's a NOTAM. Effective today. Already affecting our own MD11PW operation into Japan.

[Flightmech]

I believe the 777PW is banned along with aircraft powered by the engines above.

[DaveReidUK]

Thanks - yes, we learned about the Japan PW4000-112 ban 3 days ago (see post #100).

The new ban on the PW4000-94 (B744, MD11) doesn't seem to have any obvious connection to that, unless anyone knows otherwise.

[Flightmech]

Yes. That's why I didn't mention the 777 in my original post.

[bsieker]

DaveReidUK

That is probably related to the Netherlands incident, which was a PW4000-powered B744. There is little information available, but it looks like multiple turbine blades and/or vanes (and not much else) were ejected. Nothing to do with the fan.

[iranu]

Feathers McGraw

This process is known as superplastic forming and diffusion bonding (SPF/DB).

[iranu]

DaveReidUK

Probably because that's the part description as per the drawing as well as what's in the engine/overhaul manual.

The PW4000 series is a 2 spool engine with a fan (LPC 1) and 4, 5, 6 or 7 additional LPC stages depending on model:


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/713x470/screenshot_2021_02_24_pratt_whitney_pw4000_wikipedia_9cab72b bbff36612881753d94ce356fe98b1bc40.png

Historically LPC blades have been labelled with the fan being number 1. Not sure if that's the case with modern high bypass ratio engines, but it makes sense.

[WillowRun 6-3]

The confidence of the flying public always is a background factor, at least, in how safety incidents are handled. In this time of repressed demand for air travel, and aftermath of debacles with Boeing MAX (and other bad news about another type), perception of the traveling public can be interesting thing to watch, to an SLF/atty anyway.

So reading a good solid reporting piece in the Wall Street Journal today, by-line of Alison Sider, with headline, "Probes of Faulty Jet Engine Intensify" yields some confidence that despite other sources of less reliable repute, there is some good reporting out there. Article covers relation of past incidents to the current one, as well as good laypeople's explanation of some of the operational or design characteristics involved.

[DaveReidUK]

iranu

"Historically LPC blades have been labelled with the fan being number 1. Not sure if that's the case with modern high bypass ratio engines, but it makes sense."

Correct - I asked the FAA earlier today and this was the response:

"1st-stage LPC compressor blade" is what P&W uses to refer to their fan blade. I am required to use the nomenclature P&W uses in their engine manual (EM) and service bulletins (SB) for all ADs that are written. This is mainly because the maintenance personnel will use the EM and SB to accomplish the AD. Using fan blade in the AD would cause confusion.

[Arydberg]

This seems to be the fifth time this has occured.

see,

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW4000

[DaveReidUK]

Two of those five incidents were not fan failures, so it's not clear what you mean by "the fifth time this has occurred".

[Arydberg]

Perhaps even 3 are cause for concern.

see:
1) left engine, PW4098-112 engine suffered an uncontained failure

2) 45 minutes before landing, suffered a fan blade failure, which caused much of the inlet and cowl to separate from the engine.

3) left hand engine (PW4074) failed and its access doors ripped of
also see "The ministry reported one of the fan blades of the left hand engine was damaged at the root". from the source https://avherald.com/h?article=4e011c3a

4) On February 20, 2021, a Boeing 777-200 with PW4077-112 engines performing United Airlines Flight 328 from Denver to Honolulu suffered a fan blade failure shortly after takeoff

5) engine failure above the village of Meerssen, shortly after taking off from Maastricht Aachen Airport on the way to John F. Kennedy International Airport. Falling turbine blades lightly injured two persons on the ground.

[DType]

Compressor stage numbering:-
In pre-bypass days, RR would sometimes stick a 0 stage on the front, and even a 00 stage in front of that.

[Gauges and Dials]

If the parts land on your property are they still the property of the airline.
If memory serves me correctly, this is may be a weird and ancient corner of real estate law: If fruit from your neighbor's tree falls onto your property, you can't eat it, but then again you aren't obligated to let your neighbor onto the property to retrieve it, either.

[WillowRun 6-3]

Boeing Moved to Replace 777 Engine Covers Before Recent Failures - Wall Street Journal:

First few paragraphs of article (by-line Andrew Tangel and Alison Sider):
_________________
Boeing was planning to strengthen protective engine covers on its 777 jets months before a pair of recent serious failures, including one near Denver last weekend, according to an internal Federal Aviation Administration document.

The plane maker and regulator had been discussing potential fixes even longer—for about two years, according to people familiar with the matter. The talks began after two failures in 2018, one on a 777 operated by United Airlines Holdings Inc. and the other on a Southwest Airlines Co. 737.

Because potential modifications to 777 external engine covers, commonly known as cowlings, had various shortcomings, “Boeing has decided to redesign the fan cowl instead of trying to modify existing fan cowls to address both the structural strength concerns” and moisture issues, according to the internal FAA document reviewed by The Wall Street Journal.

“Boeing will be manufacturing new fan cowls and providing service instructions for operators to remove and replace the fan cowls,” according to the document, part of a routine Aug. 6, 2020, update on efforts under way at the agency’s Seattle-area offices. Boeing and the FAA declined to comment on the engine-cover plan’s status Wednesday.
_____________________

No clue on where or how the internal document emerged.... an interesting set of issues in and about FAA to greet the new Secretary of DOT, methinks.

[maxxer1977]

Lomon

Well spoken. The atc controller has also to get all the hospitals on standby based on the number; they do not all create a crater

[ex-EGLL]

Good Response, ATC aren't asking these questions to make you're life more difficult! Admittedly trying to find the right time to ask these questions is a problem.

[lomapaseo]

Some first hand knowledge here. In some cases the suspected owner denies ownership ( few hundred pound piece found in woods, never claimed) Seems to match the maintenance reports that get filed months later of parts missing upon walk-round before next flight
A few cases where new owner demanded significant money for parts that fell before giving them back. Problem solved by immediate confiscation by the likes of the NTSB et.al. Not sure about new owner reusing the parts as long as they meet all air-regulations. One guy simply displayed the parts (fell off a truck0 in his front yard for all to see that he was within his rights.

[Lomon]

WillowRun 6-3

Are Boeing (or Airbus for that matter) actually responsible for engines manufactured by Pratt and Whitney, Rolls Royce, GE, CFM International etc?

[lomapaseo]

best to define your interpretation of "responsible"
Each side is responsible to the regulator for meeting their side of providing safety

come to think of it I've never heard of an engine getting grounded, but only the plane

TD ought to be able to add some wisdom here

[tdracer]

It depends. The engines are the responsibility of the engine manufacturer, but the actual cowling (nacelle) can either be done by the airframer, outsourced, or sourced from the engine manufacturer.
On the 777, Boeing did most of the nacelle in-house for all three engine types. On the 787, nearly all the nacelle was outsourced (which didn't go very well). On the 747-8, the nacelle was something of a joint venture between Boeing and GE (Middle River).
But the specific mater in hand - the PW4000/112" engine as installed on the 777 - Boeing did the nacelle.

[GlobalNav]

Boeing owns the type design and was the pt 25 certification applicant. The type design includes installation of the particular engine. So Boeing certainly has responsibility from nose to tail and wingtip to wingtip. The engine manufacturer also had its engine type design certified under cognizant regulations and also has responsibility.

[ChicoG]

So the media are into their usual frenzy I see. Headlines everywhere about a B777 emergency landing at Moscow due to an "engine sensor problem".

They sort of mention halfway down their articles that it was a GE engine mind you.

[Nil by mouth]

I recently watched with interest an item showing very high tolerance metal parts being formed by a "3D Printer" that did away with the the injection mould method that was used on these hollow fan blades that failed in this thread discussion.

Are there any engineers that can comment on this process that could or are being used in the aerospace industry, and may be attending the AM Industry Summit below?

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1263x512/3dparts_9a973b3740487a06bad9223f8f52d40cc2f5aca5.jpg

[daved123]

Can't comment on these kinds of parts in Aerospace industry but Porsche are using this 3D printing technique.
They have been re-manufacturing parts that have been out of stock for a long time and for which the original tooling is worn out.
Such parts include clutch-operating levers and even pistons for their top sport models using, IIRC 'adaptive-laser-fusion' tech both of which would be high-stress parts, so I can't see why fan blades would be too far of a stretch .

[Droop Snoot]

From the NTSB Powerplants Group Chairman's Factual Report, UAL 1175, https://data.ntsb.gov/Docket/?NTSBNumber=DCA18IA092

"The PW4000 112-inch fan blade has a hollow core airfoil. The blade is made from two titanium-alloy flat plates that have the airfoil’s external and internal features machined out. The airfoil halves then undergo dimensional and material inspections prior to being bonded together. The bonded halves undergo further machining and another material inspection prior to being formed into the fan blade’s final shape. After the blade is formed into the final shape, the blade’s root is machined as are the leading and trailing edges and the blade tip. The blade then undergoes a visual and another material inspection before undergoing several surface finish treatments. The blade then undergoes a dimensional inspection and a final inspection."

Not a very good or complete description :ugh:, but apparently diffusion bonded and superplastic formed.

[tdracer]

I doubt you'd find many if any "injection molded" parts in a modern turbofan engine. The technologies used to make the parts are pretty universally high-tech and often state of the art. In the hot section, you'll find some pretty amazing technology used for both the turbine blades and nozzles - things like single crystal or directionally solidified part to eliminate or minimize grain boundaries in the parts. Fan blades used to be forged/machined solid titanium - however with the introduction of wide cord blades, the weight of solid TI became prohibitive - which lead to developments like the hollow fan blades used by Pratt and Rolls and the carbon composite used by GE.
3d printing is advancing rapidly, but I suspect we are still a ways from widespread use of 3d printed parts in commercial turbofan engines. When things like grain boundary's become critical to the performance and life of the part, 3d printing has a long way to go.

[spangzilla]

The GE9X has a lot of 3D printed parts, including some LP turbine blades made from TiAL powder

(can't post links)

[Turbine D]

You may want to take a look at GE's 3-D printing sites on the internet. For example, the new GE90X engine for the Boeing 777X contains numerous 3-D printed parts including 3-D printed LPT blades. The engine has passed its initial certification to enable full flight testing this year. GE bought a company in Italy that developed the machines and processes for producing larger components such as the GE90X LPT blades now being produced. The developed processes have the same capability to produce LPT blades as rapidly as if they were cast, but with much more in terms of initial design freedoms.

[Turbine D]

When things like grain boundary's become critical to the performance and life of the part.
Consideration of the chemical composition of the alloy being used when producing single crystal turbine blades should be determined and how it is managed. The choice is deciding to leave grain boundary strengthening elements in the single crystal alloy when producing single crystal blades or removing those elements completely simplifying the alloy composition. Leaving the strengthening element in the single crystal turbine blade can produce the strength of an equiax blade in the undetected grain boundary while providing additional time to detect the growing defect prior to failure.

[lomapaseo]

I don't believe the thread subject fan blade stretch-fits into single crystal discussions, perhaps the inlet cowl? :)

[Airbubba]

Today's NTSB media release with some pictures from the NTSB Flickr album.

The link to the latest NTSB Investigative Update: DCA21FA085 (ntsb.gov) (https://www.ntsb.gov/investigations/Pages/DCA21FA085.aspx)

NTSB News Release

National Transportation Safety Board Office of Safety Recommendations and Communications
NTSB Issues Investigative Update for United Airlines Flight 328 Engine Failure Event
3/5/2021

​​WASHINGTON (March 5, 2021) — The National Transportation Safety Board published an investigative update Friday for its ongoing investigation of the Feb. 20, 2021, United Airlines flight 328 engine failure event.

UAL flight 328 experienced a failure of the right Pratt & Whitney PW4077 engine shortly after takeoff from Denver International Airport, Denver. There were no injuries reported, and the airplane sustained minor damage.

The investigative update does not contain analysis and does not discuss probable cause in this ongoing investigation. As such, no conclusions regarding the cause of the engine failure should be made based on the information contained in the update. The information in the update is preliminary and subject to change as the investigation continues.

Facts gathered to date in the investigation, and provided in the update, include:

Initial examination of the right engine fire damage found it was primarily contained to the engine's accessory components, thrust reverser skin, and composite honeycomb structure of the inboard and outboard thrust reversers.

The spar valve, which stops fuel flow to the engine when the fire switch is pulled in the cockpit, was found closed – there was no evidence of a fuel-fed fire.
Initial examination of the right engine fan revealed the spinner and spinner cap were in place and appeared undamaged.
All fan blade roots were in place in the fan hub, two blades were fractured.

One fan blade was fractured 7.5 inches above the base at the trailing edge. The fracture surface was consistent with fatigue.

The second fractured blade exhibited indications of overload failure, consistent with secondary damage.

Initial review of maintenance and inspection data for the blade with the fatigue fracture, revealed it had experienced 2,979 cycles since its last inspection. This blade underwent thermal acoustic image inspections in 2014 and 2016. Inspection data collected from the 2016 inspection was examined again in 2018 because of a Feb. 13, 2018, incident involving a Boeing 777 with Pratt & Whitney PW4077 engines.

The engine fan blade with the fractures consistent with fatigue was sent to the metallurgical laboratory at Pratt & Whitney for further examinations led by a senior NTSB metallurgist. Preliminary findings from the scanning electron microscope examination identified multiple fatigue fracture origins on the interior surface of a cavity within the blade. Efforts to further characterize the fracture surface, including identifying the primary origin and counting striations, are ongoing. Additional work is underway to further characterize secondary cracks identified through fluorescent penetrant inspection. The NTSB metallurgy group also plans to analyze the blade's chemical composition and microstructure near the fracture surface.

The full investigative update is available online​.

​
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/ntsb_51006517771_0972f7f08c_o_7dc87ff331cbb50c091777a0cdfa35 8eab9fef61.jpg
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1440x1080/ntsb_51006404401_2e8351e3ae_o_large__5d7a6a1e66ec9e577b44750 0d2b5bde443389373.jpg
https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1440x1080/ntsb_51006404791_6f6c068089_o_large__a0d190e312a7d6e39831480 2e69c6c3fa7bd63d8.jpg
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1080x1440/ntsb_50970654253_8ab98eb8a9_o_large__448bb892c7b72af46aed979 3cc7799ba959018cd.jpg
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1440x1080/ntsb_50970664463_0fa84aca4e_o_large__00d178a15e2e4f2c26c2841 a8ad2d4a34cc1fdef.jpg

[Lomon]

Thanks

So although the fan blade failed (possibly prematurely) would be for P&W to investigate Boeing are looking into why the fan blade was able to remove the cowling and nacelle parts.

[Droop Snoot]

Fatigue origins are in similar location in the cross section on UAL 1175 and UAL 238 fractures.

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/717x446/ual1175_54f6377ce5cbb09d5c9f4a158c4cf77fcf5736af.jpg
UAL 1175



https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/747x449/ual238_9b3e768da3296f874bd43f8a2ad71f59d20c1197.jpg
UAL 238

[etudiant]

So these hollow blades fatigue from the inside, which makes finding the flaw really challenging. It would be informative to see the pictures of the fluorescent dye penetration tests done on these blades which indicated the incipient failure.

[infrequentflyer789]

May be some selection bias there - if the flaws we don't find are the ones on the inside which then lead to big news failures it doesn't follow that they always (or even mostly) fail that way, it may be that the other failure modes are more common but tend to get found on inspection so don't result in in-flight failure. We'd need to know the rate of prevented-failures (blade replacements) being caught by inspection.