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United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

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Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#471

Post by pdonis »

sandworm101 wrote: post #462
pdonis wrote: post #454

Earlier quoted context omitted.

> These failures are anticipated Sort of. The possibility of some types of failure is anticipated in the design of other parts of the engine. But there are also inspection procedures in place to ensure that engine parts that might fail are replaced before they fail. A report on a previous incident in Feb 2018 (referred to upthread) says that the root cause was a cracked engine fan blade that should have been detected…

fan blade failures are expected. Engines are designed to contain failed blades. There is a huge test that is done whereby a blade is "failed" at full throttle. Engine dies but damage is to be contained. https://youtu.be/j973645y5AA (A380 "blade off" test, rare footage of giant engine failing)

> fan blade failures are expected.

No, they're not. Fan blade cracks are expected; and fan blades are inspected for cracks so that the blades can be replaced before they fail.

Yes, it's also true that, as a second line of defense, engine housings are designed to contain failed blades. But the overall risk of the system is calculated on the assumption that that is a second line of defense, not the only line of defense. In other words, it's calculated on the assumption that a fan blade failure in flight will not be due to a crack that could have been detected at the last inspection but wasn't. It's calculated on the assumption that a fan blade failure in flight will be due to some other root cause that nobody has ever seen before. In other words, we have second lines of defense because we don't presume that we know about all possible root causes for a given failure. We don't expect fan blades to fail, but just in case one does due to some root cause we didn't know about, we design an extra layer of protection.

But what happened here is that an inspection regime designed to catch a root cause we do know about, failed to catch it. That's not within the design parameters of the system.

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#472

Post by dredmorbius »

colechristensen wrote: post #371
underseacables wrote: post #336

Earlier quoted context omitted.

Is that what happenes when The fan blades fly off and hit the airplane?

Pieces on the inside of jet engines are spinning between 2,000 and 12,000 rpm. They should all be properly contained in an airliner, but before that was the case of one fan blade broke and hit the plane it could look like a bomb blew an enormous hole in the side of the plane. These small pieces have a huge kinetic energy because they’re spinning so fast. Nothing bad happening, everyone uninjured and a plane making an…

Hull penetration at altitude can lead to explosive decompression, and, depending on the specifics of the penetration, complete hull loss.

Airplanes are big fragile inflated sausages, and it takes relatively little by way of explosive to down one. An early model (the de Havilland Comet, operated by BOAC and South African Airways in the 1950s) was downed due to a design flaw leading to metal fatigue around the windows, with three aircraft lost in 12 months due to in-flight break-ups, 99 souls lost.

Even at lower altitudes, an uncontained fan or turbine failure can be rough on the cargo or passengers, either from direct shrapnel, decompression, or (partial or full) egress.

https://www.bbc.com/news/world-us-canada-43803340

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#473

Post by sandworm101 »

pdonis wrote: post #471
sandworm101 wrote: post #462

Earlier quoted context omitted.

fan blade failures are expected. Engines are designed to contain failed blades. There is a huge test that is done whereby a blade is "failed" at full throttle. Engine dies but damage is to be contained. https://youtu.be/j973645y5AA (A380 "blade off" test, rare footage of giant engine failing)

> fan blade failures are expected. No, they're not. Fan blade cracks are expected; and fan blades are inspected for cracks so that the blades can be replaced before they fail . Yes, it's also true that, as a second line of defense, engine housings are designed to contain failed blades. But the overall risk of the system is calculated on the assumption that that is a second line of defense, not the only line of defens…

The requirement came after several blades left their engines, severing vital systems on a couple flights. So the requirement is that new engines be able to contain blade failures regardless of the cause. Inspections can save a blade failure from happening, but they cannot be relied upon to prevent failures, necessitating the reliance on containment of eventual non-prevented failures.

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#474

Post by ZeKZ »

moltenguardian wrote: post #84

Probably a dumb question, but why don't the pilots cut the fuel to the right engine after they know it's on fire?

See this video where he explains what the pilots probably did during the checklists : https://www.youtube.com/watch?v=q5Wler87pwY

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#475

Post by throw0101a »

bredren wrote: post #312
throw0101a wrote: post #222

Earlier quoted context omitted.

Animated recreation with audio: * https://www.youtube.com/watch?v=G7-zh7Sebr8 * Via: https://forums.liveatc.net/atcaviation-audio-clips/ual-328-u...

How come the discrete audio on 120.15 was not available?

LiveATC uses volunteers to record well-known frequencies at various airports. 120.15 may have been stood-up in an ad hoc fashion, so there was no radio configured to record it.

* https://en.wikipedia.org/wiki/Airband

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#476

Post by eddof13 »

alistairSH wrote: post #53
mrfusion wrote: post #23

Earlier quoted context omitted.

How do you account for oceans?

By staying as close to land as required to ensure safety. until fairly recently, flights to Hawaii were largely served by 3- or 4-engine jets. It's only in the last several decades that ETOPS regulations have shifted enough to allow regular twin-engine service to Honolulu. See the 3rd response... https://www.airliners.net/forum/viewtopic.php?t=119921

Thanks for the recommendation on that 3rd response, it was an excellent reply

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#477

Post by pdonis »

sandworm101 wrote: post #473
pdonis wrote: post #471

Earlier quoted context omitted.

> fan blade failures are expected. No, they're not. Fan blade cracks are expected; and fan blades are inspected for cracks so that the blades can be replaced before they fail . Yes, it's also true that, as a second line of defense, engine housings are designed to contain failed blades. But the overall risk of the system is calculated on the assumption that that is a second line of defense, not the only line of defens…

The requirement came after several blades left their engines, severing vital systems on a couple flights. So the requirement is that new engines be able to contain blade failures regardless of the cause. Inspections can save a blade failure from happening, but they cannot be relied upon to prevent failures, necessitating the reliance on containment of eventual non-prevented failures.

> Inspections can save a blade failure from happening, but they cannot be relied upon to prevent failures

You still are not addressing my point.

Of course inspections cannot be relied upon to prevent failures due to root causes that are not known prior to the incident.

But inspections are relied upon to prevent failures due to root causes that are known. And that's what failed to happen in this case.

Put it this way: by your argument, the NTSB's final report on this should be something along the lines of "this was an expected failure and the containment worked, so no corrective action needs to be taken". Do you really think that's what will happen?

Whereas by my argument, the NTSB's final report on this will be something along the lines of "the inspection process failed to properly catch a cracked fan blade, and corrective actions A, B, and C need to be taken to fix the process".

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#478

Post by bredren »

throw0101a wrote: post #475
bredren wrote: post #312

Earlier quoted context omitted.

How come the discrete audio on 120.15 was not available?

LiveATC uses volunteers to record well-known frequencies at various airports. 120.15 may have been stood-up in an ad hoc fashion, so there was no radio configured to record it. * https://en.wikipedia.org/wiki/Airband

When control described it as "discrete" was it because they know that listeners wouldn't be prepared to monitor it? I find it odd that a public frequency would be described as discrete without some greater barrier to listening in.

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#479

Post by pintxo »

beervirus wrote: post #470
pintxo wrote: post #463

Earlier quoted context omitted.

If there is only one sensor, how do you know it’s reporting wrong data?

One sensor failed. If one sensor gives readings that don’t jibe with all the others, maybe the software shouldn’t react by pushing the nose down.

Didn't they have only 2 angle-of-attac sensors to begin with, and then decided, that only one would be fed into the software? So the software part had zero chance to even detect a problem with the sensor.

Re: United B772 at Denver on Feb 20th 2021, engine inlet separates from engine

#480

Post by xvf22 »

snuxoll wrote: post #138
xvf22 wrote: post #126

Earlier quoted context omitted.

Fair enough and my memory may be fuzzy but I see quite a few references to V1 as being the minimum single engine takeoff speed. https://skybrary.aero/bookshelf/books/493.pdf (page 2)

It's kind of poorly worded. Hitting V1 means you are committed to taking off, single engine failure or not - but you HAVE to reach V2 to safely climb on one engine. This should happen within moments of hitting Vr, but being single-engine after V1 means you went from hitting Vr halfway down the runway to potentially doing so at the ass-end of your minimum runway length. This means you have basically no room for any pi…

Not sure where the original disagreement came from. I never said an aircraft should be able to take off at V1. Perhaps you took the "fly" literally which is fine but that was certainly not the intention.
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