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

avherald.com

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

#451

Post by pdonis »

terramex wrote: post #113

Almost identical incident happened 3 years ago - the same type (B777-200), the same engine (PW4077), the same operator (United Airlines), the same side (right engine), the same failure (unconfined engine failure). https://avherald.com/h?article=4b4e8ca7&opt=0 I would not be surprised if the whole fleet of this type/engine gets grounded for some time.

From the report on the previous incident (Feb 2018), it looks like NTSB determined that the root cause was a cracked fan blade in the engine that should have been spotted on a previous inspection but wasn't. That doesn't just implicate this type/engine; it implicates the inspection procedures in general.

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

#452

Post by donarb »

dzhiurgis wrote: post #382
throwawayboise wrote: post #306

Earlier quoted context omitted.

Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basically the entire aircraft is taken apart and inspected, looking for among other things anything like stress fractures, corrosion, unusual wear, etc. https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#D_... A commercial aircraft does not just accumulate…

> basically the entire aircraft is taken apart How is that safe unless you've got a production line doing it? Seems impossible to re-assemble it in the same way as it was done in factory...

It's not taken totally apart, but it is stripped of the interior down to the bare metal, all wiring is checked/replaced as needed. All mechanical parts like the flaps and landing gear are removed and checked for wear. The skin is checked for cracks. This is done every 5 years for planes, taking about 5-6 weeks to complete.

Here's https://www.youtube.com/watch?v=WLil1MZmchI

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

#453

Post by avh02 »

dmoy wrote: post #134

That quoted ground observer. Do they work for the NTSB or something? I am 110% certain that if I saw a plane on fire in the sky, I would not have the presence of mind to remember the term "cloud deck", let alone the rest of those details. Ground observer: "Good sir, I do say that the cloud deck was quite low so I didn't get a good look, but the engine was mildly louder than usual, and possibly had smoke, but perhaps…

I recently listened to one of the radio correspondents (Herbert Morrison) [1] that was observing the hindenberg coming in - and it amazed me the things he thinks of while he's talking about it (how the people waiting for the passengers will be distressed) and the eloquent language used. ("Oh, the humanity!")

That said, he definitely also got distressed, but mostly remembered to describe.

[1] https://www.youtube.com/watch?v=DJ2qP4wd4LE

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

#454

Post by pdonis »

sandworm101 wrote: post #420
Kye wrote: post #412

Earlier quoted context omitted.

If I were an airline's insurer, I wouldn't want to gamble on the good luck lasting.

Not luck. Design. These failures are anticipated. That they can be handled so well is testimony to the energy and regulation put into engine safety over decades. Whereas once such failures could down an airline, killing all on board, they can now be handled safely.

> 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 on a previous inspection but wasn't. Failures that are supposed to be prevented by inspection and replacement of parts are not necessarily also allowed for in other parts of the design. So it's quite possible that luck is involved here as well and that a future failure of this type could have much worse consequences.

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

#455

Post by pdonis »

throwawayboise wrote: post #306
codingdave wrote: post #169

Earlier quoted context omitted.

Another way of looking at it is that after flying and accumulating 25 years of wear and tear without major incident, we now have seen a repeatable flaw that these aircraft may encounter due to their age.

Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basically the entire aircraft is taken apart and inspected, looking for among other things anything like stress fractures, corrosion, unusual wear, etc. https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#D_... A commercial aircraft does not just accumulate…

> Aircraft undergo regular preventative maintenance checks

And in a similar incident in February 2018 on a 777 (referred to upthread), one of those checks was found to have failed: the NTSB determined that the root cause was a cracked engine fan blade that should have been detected on a previous inspection (and that would have resulted in the blade being replaced), but wasn't. If this incident turns out to have a similar root cause, that means there are issues with the preventive inspection and maintenance process.

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

#456

Post by acvny »

terramex wrote: post #113

Almost identical incident happened 3 years ago - the same type (B777-200), the same engine (PW4077), the same operator (United Airlines), the same side (right engine), the same failure (unconfined engine failure). https://avherald.com/h?article=4b4e8ca7&opt=0 I would not be surprised if the whole fleet of this type/engine gets grounded for some time.

Also, the same destination: Honolulu. And only 1 digit difference in registration number (N773UA in 2018 vs N772UA in 2021).

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

#457

Post by donarb »

lisper wrote: post #146
tialaramex wrote: post #140

Earlier quoted context omitted.

"Mayday" is the internationally agreed code, so that's one reason to use that - but US accident investigators also noticed a pattern that American pilots are often too reluctant to declare emergency status when it's appropriate as it is here, because they feel it's "not that bad" yet. Having them say it's an emergency without saying "Mayday" is good enough and might mean a few more cases that should have been emergen…

Listening to the audio, the pilot first says, "We've experienced an engine failure, need a turn." ATC does not respond, so he calls again and says "Mayday" in order to unequivocally get their attention. There are actually two different emergency calls. There is "mayday", and there is "pan-pan", which is a less urgent version of "mayday", but that is hardly ever used.

Pan-pan is used for maritime distress calls when a ship is sinking.

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

#458

Post by MauranKilom »

silvestrov wrote: post #364
laurent92 wrote: post #214

Earlier quoted context omitted.

Random = clusters happen. In fact, mathematicians were hired during the Battle of England to estimate whether the Germans were aiming for specific buildings (“why is there a cluster of bombs around this church???” or around some secret offices) or just spreading randomly. Verdict: They weren’t aiming, it was random chance that bombs made some clusters onto some buildings. This is what random looks like: No even distr…

I've tried to find a non-clustering pseudo-random function. Anybody knows the name or urls of those?

This is my go-to: http://extremelearning.com.au/unreasonable-effectiveness-of-...

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

#459

Post by Sn0wCoder »

andrewflnr wrote: post #55
chrisseaton wrote: post #20

Earlier quoted context omitted.

They could go faster with a single larger engine. Why do you think they went with two engines instead of a single larger engine? Redundancy.

Citation needed. It's not at all obvious that a single huge engine is in any way better than two for a given speed.

Note sure this is reliable source but “ In general, twin engine aircraft allow for faster speeds, and faster pickup...”[1]

1 - https://www.vikingair.com/twin-otter-information/twin-otter-...

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

#460

Post by nyolfen »

gamegoblin wrote: post #269
nyolfen wrote: post #244

Earlier quoted context omitted.

how would this apply to disparate aircraft on different maintenance cycles?

It has nothing to do with aircraft, and everything to do with random chance. Basically, it is more likely for time-series data to have clumps than to be perfectly even. Imagine you throw a three darts a board. Which is more likely: all darts are equidistant, or 2 of the darts are closer to each other than the 3rd? Now imagine it's 3 events in time rather than 3 darts on a board. And the same logic applies to an arbit…

it seems to me that there is a lot of room between "perfectly even" and "twice on the same day"
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