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novarupta
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 12:56 am

Spetsnaz55 wrote:
Can some more Captains or Pilots chime in on which way to turn with a failed engine?


It’s been answered a few times up-thread already, but generally with multi-engined airplanes (not using centreline thrust), you’d want to avoid turning into the dead side as far as practicable. That’s due to the higher risk of getting into an unrecoverable situation when turning to the side of the failed engine.
 
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SumChristianus
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 1:03 am

The satirists have gotten hold of the story... saying UA had it all planned as a successful fuel-saving customer-experience enhancing test flight ;) : https://babylonbee.com/news/united-airl ... boeing-777
 
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SEPilot
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 1:55 am

sgbroimp wrote:
So to me the ETOPS question: Would this bird have made it halfway to HNL (or half way back to land) in this condition? If not, was this the one in ______ (fill in the number if you know it) flights that ETOPS theory was based on? Maybe silly me, but over water I like lots of engines.

I did some research a number of years ago about crashes caused by engine problems. I compared the number of engine caused crashes in twins to the number with more than two engines. The result? They were exactly the same number. And since there are far more twins flying than planes with more than two engines it turns out that the chance of an engine caused crash is much greater with more engines. And when you think about it it makes sense. A simple engine failure never leads to a crash. But an uncontained failure can, as can an inboard engine on a quad falling off and striking the outboard engine. Both of these scenarios are more likely the more engines you have. There has never, to my knowledge, been two unrelated engine failures on the same jet aircraft on the same flight, not even on the B-52 with 8 first-generation jet engines. So it turns out theat the safest number of engines is two.
 
bigb
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Re: UA328 engine explosion

Wed Feb 24, 2021 2:09 am

novarupta wrote:
Spetsnaz55 wrote:
Can some more Captains or Pilots chime in on which way to turn with a failed engine?


It’s been answered a few times up-thread already, but generally with multi-engined airplanes (not using centreline thrust), you’d want to avoid turning into the dead side as far as practicable. That’s due to the higher risk of getting into an unrecoverable situation when turning to the side of the failed engine.


Yes this true in regards to Multi-Engine Prop aircraft due to the amount of Drag on the Dead engine. Jet aircraft, generally speaking, you just need to limit bank turns and not get slow.
 
DualQual
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:24 am

novarupta wrote:
Spetsnaz55 wrote:
Can some more Captains or Pilots chime in on which way to turn with a failed engine?


It’s been answered a few times up-thread already, but generally with multi-engined airplanes (not using centreline thrust), you’d want to avoid turning into the dead side as far as practicable. That’s due to the higher risk of getting into an unrecoverable situation when turning to the side of the failed engine.


In 10000 hours of handling airliners and having been through multiple rating courses and recurrent training I’ve never heard of the dead engine being a consideration for direction of turn. Granted this time has all been accrued in jet aircraft so that may differ from a multi engine GA aircraft but dead engine doesn’t even rate when considering which way to turn. Do I have an engine out procedure to follow? If not then runway heading to minimum safe altitude before any turns. After that my turn consideration doesn’t really change from any other scenario. Does the turn keep me away from terrain and weather? Otherwise do I have time or do I need to get back on the ground ASAP? That’s it.
 
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flee
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:26 am

I think the bottom line is that no lives were lost - so talking about how well or how badly the pilots performed is not top priority at the moment. What is important is that this is not repeated - three engine failures of similar nature seems to be a bit too much!
 
CriticalPoint
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:32 am

Blimpie wrote:
mm320cap wrote:
CaptainHaresh wrote:

Talking about the communications in this incident, I also thought back to US1549 and just listened to the recordings.
That is professionalism at its finest, efficient, concise.
Sully truly is a good pilot.

The UA328 pilot on the radio said his callsign wrong 2 times before the engine failed...and when it failed he was all over the radio instead of on his checklist.
I expect pilots paid 300K a year to show a little more focus than that, I'm certainly not going to applaud for not screwing up a very manageable situation.


Are you an airline pilot? What’s your profession “Captain”?


Upthread, he stated he flies for UA B787

I will leave it at that, and am staying out of it.


No I said that I am a retired United 787 CA don’t give this individual any credit they don’t deserve.
 
BEG2IAH
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 5:18 am

nm2582 wrote:
The -112 engine is quite a bit more than 3 tons.


Exactly. It's more than double, i.e., about 7 tons.

United Tech Ops has a reputable engine shop at SFO that's been handling PW4000s for quite a while. https://www.unitedtechops.com/engines It will be interesting to find out how the metal fatigue went undetected.
 
Max Q
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 7:18 am

This crew handled the emergency efficiently and with great competence



The initial radio transmission stumbles are irrelevant, they got the job done. Interestingly this is a very common reaction when you’re put under high stress


When BA 38 lost both engines approaching LHR the pilot used the call sign he’d just used on a previous flight, as stated earlier similar call sign confusion happened on ‘Sully’s’ flight


I remember, after shutting down an engine in the MD80 inadvertently using ‘Continental one’ as our call sign when initially declaring an emergency with ATC, that’s the call sign we commonly used in the simulator!


I corrected myself, point is it really doesn’t matter, the adrenaline is flowing, a lot is going on that almost never happens outside of the sim where you expect it (90% of airline flying is uneventful) and it takes a few minutes to take stock, look at the big picture, switch gears from the normal routine and start dealing with the problem


This crew did all that and an excellent job, any criticism of their radio procedure is derived from ignorance and a total lack of comprehension regarding the job
 
gcb5196
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 8:11 am

Polot wrote:
ContinentalEWR wrote:
The fan blades and metal fatigue are increasingly the focus of the investigation. While older airplanes are not inherently a risk issue, they can be with improper, incomplete maintenance routines. This plane was 26 years old. The 4th or 5th 777 to roll off the assembly line. These frames (222As at UA) were repurposed years ago into higher density, domestic trunk route rotations (hub to hub, mainland to Hawaii, principally). The incident does beg the question as to whether aircraft should have a shelf life and whether the cost of upgrading and meticulously maintaining older fleets is worth it vs. acquiring new aircraft, particularly now when the industry is in a tough squeeze.

Fan blades and metal fatigue are not new threats to commercial aviation safety. They've been an issue for decades. Plenty of incidents of the past, not limited to engines have highlighted this risk. Aloha Airlines, UA 811, to name a few.

The airframe is 26 years old. That doesn’t mean the engine (the thing that failed, not the airframe) is 26 years old-those get swapped around and replaced all the time. I’m not sure if the age of the engine has been released yet-for all we know the engine could only be 10 years old.


I am almost certain that that engine is not original to that airframe. Like Polot said, they get swapped around all the time. The blades and components get swapped all the time. It is highly unlikely that the engine, let alone the blades, were delivered with that aircraft. It will be interesting to see what comes from this, and I am glad that no one was seriously injured or worse. Props to all the professionals out there for getting this one safely back on the ground.
 
wjcandee
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 8:56 am

In general, these engines are aging and growing time and probably cycles-relative-to-hours given the repurposing of the older (nearly-original) 777s. It's a good observation to make that engines don't typically stay with their original airframe. There has been nothing released about the age, hours or cycles on the incident engine. It could be new, old, recently partially-overhauled, recently-fully-overhauled, nearing a planned overhaul. It could have recently had its blades inspected, or be nearing a required inspection. It could have been worked on at UA. It could have been inspected at Pratt. We don't know.

What we do seem to have is a couple of data points about what happens as these engines age, and the necessary frequency of inspection and perhaps inspection method and procedure, and maybe we will learn something about the training required for the Pratt and other techs who will do these inspections. We also may have some info that will be useful in designing to account for the possibility that blades will project forward and possibly damage parts thought not to be as vulnerable as perhaps they are.

But what we also have is evidence that the containment ring in now several severe blade-off events worked as designed, that the engines didn't do anything materially-unexpected after such a serious event, that the attachment design functioned properly, that no sequelae of the original event harmed any other system, and that the aircraft remained controllable and that a good crew was able to respond to the event and execute a safe landing. Whether human factors, checklists, procedures, warnings, etc., can be improved to make things even safer, whether there are maneuvers to add to AQP, etc., we will see down the line.

But from where I sit, if there wasn't a photo of a 15-foot Hula Hoop leaning against a tree branch in somebody's yard, and pax video of some fuel burning off in the rear of the engine after the shroud departed, the public wouldn't have had as much interest in this incident. Most things functioned as designed, and the crew did a good job, and everybody lived. And for the most part, that outcome wasn't seriously in-doubt at any point in the incident sequence.

So while we probably will and should see a revised inspection and perhaps replacement schedule on these blades, the engine series in question seems to remain an extremely-reliable, well-designed product that performed largely as expected after the initial anomaly. As did the airframe. As did the crew.
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 9:43 am

It isn’t the public who have grounded this fleet but the Authorities and for very good reason. The outcome could have been very different if the random departure direction of the separating intake had been different and it had gone over the wing and hit the tailplane or fin. The Kevlar wrap did its job with regards to radially containing the blades but the design allowed a blade to migrate forward still with enough kinetic energy to slice through the intake and cause it to separate.

On a new engine in development, this wouldn’t constitute a fan blade off test pass. I’m not sure how they will argue these engines are airworthy without a design change to the fan casing. A fan blade off needs to be a non-hazardous failure due to the frequency being above the allowable threshold for a hazardous failure. Disc burst on the other hand can’t be contained so has to have a frequency less than the hazardous failure threshold.
 
Max Q
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 11:48 am

Just to be clear, right now the entire P&W powered triple 7 fleet has not been grounded except in Japan


The FAA has issued an AD requiring inspections and that’s the only mandatory action for other operators at this time


As more is learnt further action may be required and additional AD’s in fact this is expected
 
StTim
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 12:13 pm

Max Q wrote:
Just to be clear, right now the entire P&W powered triple 7 fleet has not been grounded except in Japan


The FAA has issued an AD requiring inspections and that’s the only mandatory action for other operators at this time


As more is learnt further action may be required and additional AD’s in fact this is expected



As far as I remember I saw a notice that the UK have banned and aircraft with these engines from UK airspace.
 
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747classic
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 12:16 pm

- The PW4000-112 was the first PW engine with a snubberless, wide chord fan with hollow titanium fan blades, to counter the increased weight of this enlarged fan blade..

The other engines two engines, offered at the early 777's had the following fan blades installed :

- Trent 800 : The 280 cm (110 in) fan has 26 diffusion bonded, wide chord titanium fan blades
This engine had also a fan blade failure in 2001, see : https://www.atsb.gov.au/media/33974/tr200100445_001.pdf

-GE90 : Composite fan blade
GE introduced the composite fan blade—the first-ever in commercial aviation. Measuring more than four feet long and weighing less than 50 pounds, the GE90 fan blade is made from carbon fiber and a toughened epoxy matrix that delivers double the strength and one-third the weight of titanium. AFAIK no fan blade has failed up to now.

Questions : Could the increased loads at the snubberless wide chord fan blades of the PW4000-112 and RR Trent 800 be handeled properly with legacy titanium fan blades (hollow or diffusion bonded) for reducing blade weight. Both seem to be operating at the max load (due weight) and higher vibration levels (no snubber), leading to titanium fatigue issues
Last edited by 747classic on Wed Feb 24, 2021 12:21 pm, edited 1 time in total.
 
hamiltondaniel
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 12:40 pm

Amp1 wrote:
The outcome could have been very different if the random departure direction of the separating intake had been different and it had gone over the wing and hit the tailplane or fin.


Exactly. I don't know how heavy the intake ring is, but it's certainly heavy enough to do some serious damage if it goes flying in the wrong direction. Saying that, "Well, it's no big deal because the plane didn't crash," is a pretty serious mistake.

It makes me think of Feynman's response to Challenger managers' decision to launch even knowing there were problems with O-rings but they had never caused a massive failure before:

"When playing Russian roulette, the fact that the first shot got off safely is little consolation to the next."
 
btfarrwm
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 1:53 pm

Amp1 wrote:
On a new engine in development, this wouldn’t constitute a fan blade off test pass. I’m not sure how they will argue these engines are airworthy without a design change to the fan casing. A fan blade off needs to be a non-hazardous failure due to the frequency being above the allowable threshold for a hazardous failure. Disc burst on the other hand can’t be contained so has to have a frequency less than the hazardous failure threshold.


How would a new-build engine be tested differently? Are they now tested with the cowlings on? Is it reasonable to assume that the physics of a blade failure may be different on an engine within a cowling that is travelling in a 200kt+ airstream?
 
slider
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:07 pm

Okcflyer wrote:
This was a 772 (non-ER) model. Max thrust is ~ 77klbs. The engines on it should be ER spec later models capable of ~92klbs thrust, derated down to the 77klbs required for the early frame model.

Fan speed (rpm), and thereby thrust, for this 77A application is slower than if the same engine was installed on a 77E.

RPM largely determines the tensile loading of the blades. Brittle fatigue fracture occurs in metal subject to tensile stress.

As the engine was "not at it's limits" in this case, I'm a bit surprised that this failure on a 77A (non-ER) frame, rather than on one of the 77E with full engine rating available.

- Does P&W increase the life expectancy of the fan blades in the lower thrust rated models? Fatigue failure is a function of stress (load) and load cycles, and increasing life is reasonable to do so. Did their models overestimate the life remaining? If so, why?
- Maybe there is a dynamic load issue, likely from a resonance case, that increases the stress (load) and/or increases the number of cycles? These tend to be pretty easy to test and measure for, so it seems highly unlikely to find such a situation this late in product maturity level.
- Material composition issue?
- Record keeping issue?


The 92k derated thrust is on the GE90s (which for UA, are the pmCO shells).

Good questions about fatigue.
 
Cubsrule
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:12 pm

hamiltondaniel wrote:
Amp1 wrote:
The outcome could have been very different if the random departure direction of the separating intake had been different and it had gone over the wing and hit the tailplane or fin.


Exactly. I don't know how heavy the intake ring is, but it's certainly heavy enough to do some serious damage if it goes flying in the wrong direction. Saying that, "Well, it's no big deal because the plane didn't crash," is a pretty serious mistake.

It makes me think of Feynman's response to Challenger managers' decision to launch even knowing there were problems with O-rings but they had never caused a massive failure before:

"When playing Russian roulette, the fact that the first shot got off safely is little consolation to the next."


From an aerodynamic perspective, is it possible for that piece to get to the wing or empennage in flight?
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:14 pm

btfarrwm wrote:
How would a new-build engine be tested differently? Are they now tested with the cowlings on? Is it reasonable to assume that the physics of a blade failure may be different on an engine within a cowling that is travelling in a 200kt+ airstream?


When you say cowlings do you include the intake ring? If so, no engine is ever run without an intake. Development engines do run with slave intakes during some tests but fan blade off tests have to be run with the production flight intake fitted. The cowling doors are not usually fitted for fan blade off tests but these are very different components to the intake.
 
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Revelation
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:22 pm

wjcandee wrote:
But what we also have is evidence that the containment ring in now several severe blade-off events worked as designed, that the engines didn't do anything materially-unexpected after such a serious event, that the attachment design functioned properly, that no sequelae of the original event harmed any other system, and that the aircraft remained controllable and that a good crew was able to respond to the event and execute a safe landing.

I think there will be room to question the containment system. It seems the blades escape forward of a large part of the structure. Is this something the ground testing is taking into account? What if the fragment that appears to hit the side body fairing hit the main fuselage itself, could it have caused rapid decompression, or did the blade lack the energy to do any meaningful damage?

747classic wrote:
- The PW4000-112 was the first PW engine with a snubberless, wide chord fan with hollow titanium fan blades, to counter the increased weight of this enlarged fan blade..

The other engines two engines, offered at the early 777's had the following fan blades installed :

- Trent 800 : The 280 cm (110 in) fan has 26 diffusion bonded, wide chord titanium fan blades
This engine had also a fan blade failure in 2001, see : https://www.atsb.gov.au/media/33974/tr200100445_001.pdf

-GE90 : Composite fan blade
GE introduced the composite fan blade—the first-ever in commercial aviation. Measuring more than four feet long and weighing less than 50 pounds, the GE90 fan blade is made from carbon fiber and a toughened epoxy matrix that delivers double the strength and one-third the weight of titanium. AFAIK no fan blade has failed up to now.

Questions : Could the increased loads at the snubberless wide chord fan blades of the PW4000-112 and RR Trent 800 be handeled properly with legacy titanium fan blades (hollow or diffusion bonded) for reducing blade weight. Both seem to be operating at the max load (due weight) and higher vibration levels (no snubber), leading to titanium fatigue issues

Also worth considering: the GP-7200 engine used the same style blades as PW4000:

The GP7200 engine features a 116-inch (295-cm) hollow titanium fan blade with “swept” aerodynamics
...
GP7200 benefits from the heritage of the GE90 and PW4000 families
...
Derived from three million hours of service experience on the PW4000-powered Boeing 777, the GP7200 hollow titanium fan blade with swept aerodynamics will have the same durability as the PW4000 fan blade.

Ref: https://www.enginealliance.com/news/ge- ... 00-design/
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:26 pm

Cubsrule wrote:
From an aerodynamic perspective, is it possible for that piece to get to the wing or empennage in flight?


I would say yes, everything in that area is fairly axisymmetric so it will depend on the circumferential position of the blade when it releases, which will be random. The intake ring separates in one piece, if it goes in a vertical or near vertical direction, it will go over the main wing, and could then very easily hit the tailplane or fin. More likely it would go under the wing as the engine is mounted under the wing, in which case it would most likely go under the tailplane as well. However, as hamiltondaniel says, it’s like playing Russian roulette.
 
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Revelation
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:38 pm

Max Q wrote:
Just to be clear, right now the entire P&W powered triple 7 fleet has not been grounded except in Japan

The FAA has issued an AD requiring inspections and that’s the only mandatory action for other operators at this time

As more is learnt further action may be required and additional AD’s in fact this is expected

I agree, but inspecting all the fan blades on the fleet is not a simple task, and it's not clear what such inspections will find. I suspect not a lot, but you never know till you do the work.

https://www.faa.gov/news/updates/?newsId=96858 says:

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.


The AD itself ( https://rgl.faa.gov/Regulatory_and_Guid ... rgency.pdf ) refines that to:

This AD requires performing a TAI inspection for cracks in certain 1st-stage LPC blades and removal of those blades that fail inspection


And lists them by part number:

This AD applies to Pratt & Whitney Division (PW) PW4074, PW4074D, PW4077, PW4077D, PW4084D, PW4090, and PW4090-3 model turbofan engines, with a 1st-stage low pressure compressor (LPC) blade, with part number 52A241, 55A801, 55A801-001, 55A901, 55A901-001, 56A201, 56A201-001, or 56A221, installed.

So the task is to inspect each blade that matches these part numbers. It doesn't say what percentage of the fleet has those blades installed or how much time it will take to do the inspection. I thought ADs used to require a cost estimate, but I don't find one here.
 
kalvado
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:41 pm

Amp1 wrote:
Cubsrule wrote:
From an aerodynamic perspective, is it possible for that piece to get to the wing or empennage in flight?


I would say yes, everything in that area is fairly axisymmetric so it will depend on the circumferential position of the blade when it releases, which will be random. The intake ring separates in one piece, if it goes in a vertical or near vertical direction, it will go over the main wing, and could then very easily hit the tailplane or fin. More likely it would go under the wing as the engine is mounted under the wing, in which case it would most likely go under the tailplane as well. However, as hamiltondaniel says, it’s like playing Russian roulette.

There is also a case for failure with flaps out, which may become another target to hit.
 
btfarrwm
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 2:50 pm

Amp1 wrote:
When you say cowlings do you include the intake ring? If so, no engine is ever run without an intake. Development engines do run with slave intakes during some tests but fan blade off tests have to be run with the production flight intake fitted. The cowling doors are not usually fitted for fan blade off tests but these are very different components to the intake.


It is interesting that the blade-off tests all seem to be performed on a test stand and not a wind-tunnel. The expense of doing so would be huge, but an intake ring may be perfectly capable of absorbing shrapnel in a static situation, but become dislodged or fall apart and become a projectile during flight conditions.
 
889091
Posts: 595
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:00 pm

747classic wrote:
- The PW4000-112 was the first PW engine with a snubberless, wide chord fan with hollow titanium fan blades, to counter the increased weight of this enlarged fan blade..

The other engines two engines, offered at the early 777's had the following fan blades installed :

- Trent 800 : The 280 cm (110 in) fan has 26 diffusion bonded, wide chord titanium fan blades
This engine had also a fan blade failure in 2001, see : https://www.atsb.gov.au/media/33974/tr200100445_001.pdf

-GE90 : Composite fan blade
GE introduced the composite fan blade—the first-ever in commercial aviation. Measuring more than four feet long and weighing less than 50 pounds, the GE90 fan blade is made from carbon fiber and a toughened epoxy matrix that delivers double the strength and one-third the weight of titanium. AFAIK no fan blade has failed up to now.

Questions : Could the increased loads at the snubberless wide chord fan blades of the PW4000-112 and RR Trent 800 be handeled properly with legacy titanium fan blades (hollow or diffusion bonded) for reducing blade weight. Both seem to be operating at the max load (due weight) and higher vibration levels (no snubber), leading to titanium fatigue issues


If a titanium blade can cause so much damage, I'd hate to see the damage caused by a wayward carbon fibre blade from a GE90.

Modern F1/Indy cars and exotic supercars have their cockpit 'tubs' made of carbon fibre, which is very strong.
 
dragon6172
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:09 pm

Amp1 wrote:
fan blade off tests have to be run with the production flight intake fitted.

This isn't true.... there are videos of blade off tests and I don't think I have seen one with a production flight intake installed. Not saying they don't do it, but it certainly isn't a requirement.
 
hamiltondaniel
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:10 pm

889091 wrote:

If a titanium blade can cause so much damage, I'd hate to see the damage caused by a wayward carbon fibre blade from a GE90.



Someone more knowledgeable correct me if I'm wrong, but the difference between titanium and CFRP is weight for a given strength. In general, for a given weight, titanium will be isotropically stronger, but CFRP can be anisotropically stronger (i.e. stronger in a given axis). On that axis, a given strength of CFRP will weigh less than titanium but it will be weaker in other axes.

Since a fan blade mostly needs to be strong along its long axis, composites work well.

If I understand this correctly, then, a CFRP fan blade will weigh less, and thus have less kinetic energy, than a titanium blade. Uncontained failure will then be less dangerous, not more dangerous, with CFRP than with titanium.

This is without taking into account fracture strength on impact, where I assume that the titanium would also be more dangerous (less likely to fracture).
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:21 pm

dragon6172 wrote:
This isn't true.... there are videos of blade off tests and I don't think I have seen one with a production flight intake installed. Not saying they don't do it, but it certainly isn't a requirement.


Well if you know different, that may be the source of this problem. There’s no point in doing a fan blade off test with an intake that’s different mass, stiffness and construction to the flight intake. As shown here it all forms part of the containment system that has to perform as intended during a fan blade off event.
 
nikeherc
Posts: 686
Joined: Thu Sep 13, 2012 8:40 pm

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:37 pm

Amp1 wrote:
dragon6172 wrote:
This isn't true.... there are videos of blade off tests and I don't think I have seen one with a production flight intake installed. Not saying they don't do it, but it certainly isn't a requirement.


Well if you know different, that may be the source of this problem. There’s no point in doing a fan blade off test with an intake that’s different mass, stiffness and construction to the flight intake. As shown here it all forms part of the containment system that has to perform as intended during a fan blade off event.


I can't recall a video of an engine in ground testing for certification where the engine is in the flight nacelle. Usually a bell-shaped inlet is used. It may be that this is necessary because a stationary engine can't draw enough air through the flight nacelle.
 
dragon6172
Posts: 1140
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:44 pm

Amp1 wrote:
dragon6172 wrote:
This isn't true.... there are videos of blade off tests and I don't think I have seen one with a production flight intake installed. Not saying they don't do it, but it certainly isn't a requirement.


Well if you know different, that may be the source of this problem. There’s no point in doing a fan blade off test with an intake that’s different mass, stiffness and construction to the flight intake. As shown here it all forms part of the containment system that has to perform as intended during a fan blade off event.

"production flight intake" is what you said.

https://www.youtube.com/watch?v=YFu8SyP ... annel=HJTV

Around 1:30 or so

The intake in the linked test is shaped like a bell.... not an intake used for flight.
 
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Aaron747
Posts: 17787
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:47 pm

Revelation wrote:
I think there will be room to question the containment system. It seems the blades escape forward of a large part of the structure. Is this something the ground testing is taking into account? What if the fragment that appears to hit the side body fairing hit the main fuselage itself, could it have caused rapid decompression, or did the blade lack the energy to do any meaningful damage?


Yeah - it seems to me perusing the NTSB report from UA 1175 in 2018 that they already looked into the containment system and did seemingly identify an issue AND location that could initiate inlet separation. While the Kevlar fan case performed admirably, that wasn't enough to hold the entire assembly together.

On pg. 10 of the report they note that Boeing FBO failure modeling showed a clear difference in materials performance between CFRP and aluminum in the inlet bulkheads. The aft portion of the PW4000-112 bulkhead is CFRP while the portion ahead of the fan is aluminum. Modeling revealed failure of the CFRP leading to a displacement wave that could initiate failure of the inlet/fan case interface. The production inlet aft bulkheads use CFRP while the aft bulkheads in the test inlets used for engine certification were all-aluminum. This seems rather significant - on page 6 they cite the above while also pointing out a regulatory gap between FAR 33 engine certification and FAR 25 inlet/fan cowl certification by Boeing:

The engine is certified under FAR part 33 regulations. To comply with the regulations, the engine successfully demonstrated containment and safe shutdown of an engine after intentional fracture of a fan blade at redline speed. Although it is necessary to install an inlet for proper engine operation during these tests, it is not required that this inlet meet production standards. The test inlet used was of a different design which included an aluminum aft bulkhead instead of the production CFRP aft bulkhead. Additionally, these tests are conducted without the fan cowls attached. The inlet and fan cowls are certified under FAR Part 25 of which Boeing was responsible for.

https://data.ntsb.gov/carol-repgen/api/ ... /96738/pdf

It seems one of the holes in the swiss cheese here is the engine certification process itself - where the regs don't require a production inlet to be installed. In this case, the PW inlet in service uses a different mix of materials and testing seemed to show the installed CFRP is inadequate to absorb and redistribute FBO loads.

Incidentally, the powerplant group report also features a number of findings that look quite similar to UA 328, though there was more high velocity exit damage to various parts of the aircraft:

https://data.ntsb.gov/Docket/?NTSBNumber=DCA18IA092
 
Amp1
Posts: 17
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:53 pm

dragon6172 wrote:
Amp1 wrote:
dragon6172 wrote:
This isn't true.... there are videos of blade off tests and I don't think I have seen one with a production flight intake installed. Not saying they don't do it, but it certainly isn't a requirement.


Well if you know different, that may be the source of this problem. There’s no point in doing a fan blade off test with an intake that’s different mass, stiffness and construction to the flight intake. As shown here it all forms part of the containment system that has to perform as intended during a fan blade off event.

"production flight intake" is what you said.

https://www.youtube.com/watch?v=YFu8SyP ... annel=HJTV

Around 1:30 or so

The intake in the linked test is shaped like a bell.... not an intake used for flight.


That is a very close to flight intake. It’s been painted to help with visualisation and the cowel C doors aren’t fitted but functionally it’s as the flight intake.
 
dragon6172
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 3:58 pm

Amp1 wrote:

That is a very close to flight intake. It’s been painted to help with visualisation and the cowel C doors aren’t fitted but functionally it’s as the flight intake.

Agreed. But you are the one that said "have to be run with production flight intake installed".... which is what I responded to.

For reference from AC 33-5 Turbine Engine Rotor Containment Testing

"A typical aircraft inlet and typical aircraft exhaust nozzle/ducting, or equivalent (i.e., having the same attachment loads and reactions which influence engine case deflections, containment capability, and engine vibratory response), should be used"
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 8:07 pm

dragon6172 wrote:
Amp1 wrote:

That is a very close to flight intake. It’s been painted to help with visualisation and the cowel C doors aren’t fitted but functionally it’s as the flight intake.

Agreed. But you are the one that said "have to be run with production flight intake installed".... which is what I responded to.

For reference from AC 33-5 Turbine Engine Rotor Containment Testing

"A typical aircraft inlet and typical aircraft exhaust nozzle/ducting, or equivalent (i.e., having the same attachment loads and reactions which influence engine case deflections, containment capability, and engine vibratory response), should be used"


Now you’re splitting hairs, earlier you said it was a bellmouth intake!!

Anyway enough, it should be a flight intake or something functionally equivalent. It appears from Aaron747’s excellent piece of detective work above, the PW4000-112 FBO test didn’t use a functionally equivalent intake. If true, and the reason for the intake separations on the 3 FBO aircraft, this is a major drop-off. 3 bullets dodged but can they afford to pull the trigger again?
 
gobears19
Posts: 11
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 9:04 pm

So is the theory that the blade(s) went into the engine and then came back out the front (i.e. passed back through the fan) and sliced the cowling on the way out? How would it not damage other blades when passing back through the fan?
 
Amp1
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 9:29 pm

gobears19 wrote:
So is the theory that the blade(s) went into the engine and then came back out the front (i.e. passed back through the fan) and sliced the cowling on the way out? How would it not damage other blades when passing back through the fan?


No, the blade never went rearwards, only forwards and out the front, slicing the intake on the way. There are high forward aerodynamic forces acting on the blades which send them forwards when they break free. A fan case requires an axial catcher to prevent the blade moving from underneath the containment zone while it still has high circumferential velocity. If there’s nothing to stop it getting forward of the containment zone it will slice through the thin intake possibly leading to separation as seen here.
 
btfarrwm
Posts: 181
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Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 9:29 pm

gobears19 wrote:
So is the theory that the blade(s) went into the engine and then came back out the front (i.e. passed back through the fan) and sliced the cowling on the way out? How would it not damage other blades when passing back through the fan?


I think the fan blade separated and was ejected forward, damaging the inlet ring and causing it to separate. The exposure of the remainder of the engine casing to the airstream caused it to come apart. There were likely fragments of the shielding and other damaged fan blades that were ingested into the engine.
Last edited by btfarrwm on Wed Feb 24, 2021 9:31 pm, edited 1 time in total.
 
OldB747Driver
Posts: 176
Joined: Tue Mar 12, 2019 11:40 pm

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 9:30 pm

gobears19 wrote:
So is the theory that the blade(s) went into the engine and then came back out the front (i.e. passed back through the fan) and sliced the cowling on the way out? How would it not damage other blades when passing back through the fan?

I believe you may have misinterpreted the information at least as far as how I've read it; there was no "back and forth", only "forth" - as the blade failed, the culmination of physical forces impinging upon it caused its direction of travel to be outward AND forward, "missing" the containment shroud and slicing through the inlet structure forward of the containment shroud.

Notable for now, while we know there were two blades that were dislodged/fractured, until those fragments are collected, we don't know if either of those blades became further fragmented, which in turn presents a much higher number of "culprits" responsible for both the cowl separation as well as downstream engine damage.
 
2175301
Posts: 2292
Joined: Wed May 16, 2007 11:19 am

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 10:46 pm

The FAA met days before the UA 328 engine failure on reducing the engine inspection interval for the P&W 4000 series engines from 6500 cycles to less than that - with a recommendation from P&W to inspect the fan blades every 1000 cycles.

https://www.cnn.com/2021/02/24/politics ... index.html
 
889091
Posts: 595
Joined: Sat Apr 06, 2019 7:56 pm

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 11:05 pm

2175301 wrote:
The FAA met days before the UA 328 engine failure on reducing the engine inspection interval for the P&W 4000 series engines from 6500 cycles to less than that - with a recommendation from P&W to inspect the fan blades every 1000 cycles.

https://www.cnn.com/2021/02/24/politics ... index.html


Less than 1/6th of the original planned inspection cycle. That's gotta hurt...

Article states:

"The FAA announced Tuesday evening that it would require seven versions of Pratt & Whitney 4000 engines to be inspected before flying again. The thermal inspections involve removing the fan blades from the engine and transporting them to a Pratt & Whitney facility where each blade is pelted with high-frequency vibrations to expose possible flaws."

I assume the seven versions will cover the 94, 100 and 112 inch variants?
 
OldB747Driver
Posts: 176
Joined: Tue Mar 12, 2019 11:40 pm

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 11:16 pm

It is interesting to me that in the UA1175 metallurgy report by P&W (pg 29) there had been 5,500 cycles since the origination of the flaw, and even more interesting that ~4,100 cycles at the time it was TAI inspected and attributed to 'paint' (whatever that means) and therefore dismissed as a potential failure point.
 
codc10
Posts: 3380
Joined: Sat Jul 08, 2000 7:18 am

Re: UA328 engine explosion at DEN

Wed Feb 24, 2021 11:35 pm

889091 wrote:
2175301 wrote:
The FAA met days before the UA 328 engine failure on reducing the engine inspection interval for the P&W 4000 series engines from 6500 cycles to less than that - with a recommendation from P&W to inspect the fan blades every 1000 cycles.

https://www.cnn.com/2021/02/24/politics ... index.html


Less than 1/6th of the original planned inspection cycle. That's gotta hurt...

Article states:

"The FAA announced Tuesday evening that it would require seven versions of Pratt & Whitney 4000 engines to be inspected before flying again. The thermal inspections involve removing the fan blades from the engine and transporting them to a Pratt & Whitney facility where each blade is pelted with high-frequency vibrations to expose possible flaws."

I assume the seven versions will cover the 94, 100 and 112 inch variants?


Only the 112” fans, just various thrust ratings.
 
iamlucky13
Posts: 1522
Joined: Wed Aug 08, 2007 12:35 pm

Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 1:12 am

OldB747Driver wrote:
It is interesting to me that in the UA1175 metallurgy report by P&W (pg 29) there had been 5,500 cycles since the origination of the flaw, and even more interesting that ~4,100 cycles at the time it was TAI inspected and attributed to 'paint' (whatever that means) and therefore dismissed as a potential failure point.


There is some kind of paint they apply to the blade for the thermal acoustic inspection, but it is difficult to work with. There are notes in the report that I skimmed, but didn't read in detail about issues with it cracking and flaking off. There was some alternative tried, but it had other issues. One of the planned resolutions on P&W's side was to continue working on identifying a paint that works better for this inspection process.

So apparently the inspector of the UA1175 blade saw an area of interest in inspection, but for unclear reasons thought he was seeing a surface issue with the paint, not the early stages of crack formation.

If I understood right, the size of that TAI indication was a good match for what investigators believe the size of the crack would have been at the time, based on the apparent progression of the fatigue.
 
catiii
Posts: 3974
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Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 1:42 am

Max Q wrote:
This crew handled the emergency efficiently and with great competence



The initial radio transmission stumbles are irrelevant, they got the job done. Interestingly this is a very common reaction when you’re put under high stress


When BA 38 lost both engines approaching LHR the pilot used the call sign he’d just used on a previous flight, as stated earlier similar call sign confusion happened on ‘Sully’s’ flight


I remember, after shutting down an engine in the MD80 inadvertently using ‘Continental one’ as our call sign when initially declaring an emergency with ATC, that’s the call sign we commonly used in the simulator!


I corrected myself, point is it really doesn’t matter, the adrenaline is flowing, a lot is going on that almost never happens outside of the sim where you expect it (90% of airline flying is uneventful) and it takes a few minutes to take stock, look at the big picture, switch gears from the normal routine and start dealing with the problem


This crew did all that and an excellent job, any criticism of their radio procedure is derived from ignorance and a total lack of comprehension regarding the job


You shut down an engine inadvertently? Or did you inadvertently use the wrong call sign.

If the former I want to hear that story!
 
Amp1
Posts: 17
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Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 9:45 am

OldB747Driver wrote:
It is interesting to me that in the UA1175 metallurgy report by P&W (pg 29) there had been 5,500 cycles since the origination of the flaw, and even more interesting that ~4,100 cycles at the time it was TAI inspected and attributed to 'paint' (whatever that means) and therefore dismissed as a potential failure point.


Yes good spot and it will be even more interesting to hear why this latest one wasn’t picked up as presumably the inspection lessons learnt from UA1175 were implemented.

As they don’t have a non-hazardous containment system it looks like they will rely on the blade failure becoming an extremely improbable event. This would require a blade failure probability of less than 10e-9 per engine flying hour as they apply to discs. It’ll be interesting to hear how they plan to achieve this with the previous history.
 
User avatar
Aaron747
Posts: 17787
Joined: Thu Aug 07, 2003 2:07 am

Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 10:33 am

Amp1 wrote:
OldB747Driver wrote:
It is interesting to me that in the UA1175 metallurgy report by P&W (pg 29) there had been 5,500 cycles since the origination of the flaw, and even more interesting that ~4,100 cycles at the time it was TAI inspected and attributed to 'paint' (whatever that means) and therefore dismissed as a potential failure point.


Yes good spot and it will be even more interesting to hear why this latest one wasn’t picked up as presumably the inspection lessons learnt from UA1175 were implemented.

As they don’t have a non-hazardous containment system it looks like they will rely on the blade failure becoming an extremely improbable event. This would require a blade failure probability of less than 10e-9 per engine flying hour as they apply to discs. It’ll be interesting to hear how they plan to achieve this with the previous history.


Would reducing the identified material weaknesses in the inlet / fan casing interface help?
 
Max Q
Posts: 9193
Joined: Wed May 09, 2001 12:40 pm

Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 10:36 am

catiii wrote:
Max Q wrote:
This crew handled the emergency efficiently and with great competence



The initial radio transmission stumbles are irrelevant, they got the job done. Interestingly this is a very common reaction when you’re put under high stress


When BA 38 lost both engines approaching LHR the pilot used the call sign he’d just used on a previous flight, as stated earlier similar call sign confusion happened on ‘Sully’s’ flight


I remember, after shutting down an engine in the MD80 inadvertently using ‘Continental one’ as our call sign when initially declaring an emergency with ATC, that’s the call sign we commonly used in the simulator!


I corrected myself, point is it really doesn’t matter, the adrenaline is flowing, a lot is going on that almost never happens outside of the sim where you expect it (90% of airline flying is uneventful) and it takes a few minutes to take stock, look at the big picture, switch gears from the normal routine and start dealing with the problem


This crew did all that and an excellent job, any criticism of their radio procedure is derived from ignorance and a total lack of comprehension regarding the job


You shut down an engine inadvertently? Or did you inadvertently use the wrong call sign.

If the former I want to hear that story!



I didn’t write that very well did I ?

No we shut down the engine deliberately due to a complete loss of oil and subsequent oil pressure

I used the wrong call sign inadvertently
 
Amp1
Posts: 17
Joined: Wed Apr 03, 2019 7:42 pm

Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 10:43 am

Aaron747 wrote:
Amp1 wrote:
OldB747Driver wrote:
It is interesting to me that in the UA1175 metallurgy report by P&W (pg 29) there had been 5,500 cycles since the origination of the flaw, and even more interesting that ~4,100 cycles at the time it was TAI inspected and attributed to 'paint' (whatever that means) and therefore dismissed as a potential failure point.


Yes good spot and it will be even more interesting to hear why this latest one wasn’t picked up as presumably the inspection lessons learnt from UA1175 were implemented.

As they don’t have a non-hazardous containment system it looks like they will rely on the blade failure becoming an extremely improbable event. This would require a blade failure probability of less than 10e-9 per engine flying hour as they apply to discs. It’ll be interesting to hear how they plan to achieve this with the previous history.


Would reducing the identified material weaknesses in the inlet / fan casing interface help?


Yes that would be another way to solve the problem but it would be prohibitively expensive. An intake could never be a containment zone so the blade would have to be prevented from moving forward. This would require a new fan case with a feature to catch the blade, it would have to be FBO tested and certified and then a new case manufactured and fitted to all engines. The cost would be astronomical.
 
User avatar
Aaron747
Posts: 17787
Joined: Thu Aug 07, 2003 2:07 am

Re: UA328 engine explosion at DEN

Thu Feb 25, 2021 10:48 am

Amp1 wrote:
Aaron747 wrote:
Amp1 wrote:

Yes good spot and it will be even more interesting to hear why this latest one wasn’t picked up as presumably the inspection lessons learnt from UA1175 were implemented.

As they don’t have a non-hazardous containment system it looks like they will rely on the blade failure becoming an extremely improbable event. This would require a blade failure probability of less than 10e-9 per engine flying hour as they apply to discs. It’ll be interesting to hear how they plan to achieve this with the previous history.


Would reducing the identified material weaknesses in the inlet / fan casing interface help?


Yes that would be another way to solve the problem but it would be prohibitively expensive. An intake could never be a containment zone so the blade would have to be prevented from moving forward. This would require a new fan case with a feature to catch the blade, it would have to be FBO tested and certified and then a new case manufactured and fitted to all engines. The cost would be astronomical.


I follow re cost and containment, but I meant in reference to the UA 1175 report suggesting that the underperforming CFRP in the inlet bulkhead could initiate inlet separation.

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