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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

#411

Post by davrosthedalek »

Stupulous wrote: post #356
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 think it depends on how frequent the thing in question is. If an engine losing parts is something that happens yearly, twice in one day is still pretty rare. But then you have to deal with degrees of freedom as well. If your search space is just 'two uncorrelated ~yearly events', there's enough of them that you'll always find false positives.

For independent, random occurrences, the probability distribution for delta-T follows an exponential decay. I.e. the most likely time is "right after". Of course, that "most likely" can still be small. Fun fact: This is true for any chosen point in time, i.e. the prob that this happens exactly one day after your birthday is higher than that it happens two days later.

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

#412

Post by Kye »

djmips wrote: post #389
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.

2020: (JAL 777 same engine) https://www.youtube.com/watch?v=O-_IAKCBTxc&t=10s 2018: United 777 same PW engine (seems very similar but without fire) https://www.youtube.com/watch?v=O-_IAKCBTxc&t=10s 2016: KAL 777 same PW engines (aborted takeoff after engine failure) https://www.youtube.com/watch?v=9bHrW_34kAk All planes had zero casualties.

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

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

#413

Post by will_asouka »

ufo wrote: post #100
jrockway wrote: post #28

Earlier quoted context omitted.

By having airports on islands, or by pushing up the number of minutes that the engines/operator are certified for.

For transatlantic flights, two important "backups" are in Iceland and in the Azores. I wonder how often airplanes actually have to detour to these airports...

Happens fairly regularly but for passenger issues rather than technical- medical emergencies and disruptive passengers usually.

Airlines have contracts with companies who provide a sat phone link to doctors who have the flight information and medical facilities at possible diversion airfields. Eg MedAire.

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

#414

Post by archi42 »

just_steve_h wrote: post #65
Dirlewanger wrote: post #46

Earlier quoted context omitted.

One thing that sets software apart from other engineering disciplines is that they are grounded in physics (bits running on a semiconductor doesn't matter for this discussion) and have been around (in some form) for thousands of years. How do we know if a design is sound? We can check it by doing the math. How do we know if a program is sound (what does that even mean? There's our first problem)? Well, we rely on a l…

I'm wading into waters that are way over my head here, but my understanding is that it is possible for software to be provably correct, in the mathematical sense of "proof." I'm well aware of the admixture of folklore, experience, and caffeine-fueled inspiration that constitutes much of the software that runs our world.

Source: I work on static analyzers, so I'm biased to that.

We can not prove everything, as others pointed out the fundamental issue here is the "halting problem". However, this doesn't mean we can't prove anything. Wikipedia says:

> In computability theory, Rice's theorem states that all non-trivial, semantic properties of programs are undecidable.

I often feel like the "trick" is to push the trivial stuff to be as useful as possible. You can work from several vectors: 1. You build better static analyzers (difficult and computationally expensive the further you push it - but that's what we're doing) 2. reduce the complexity of the "analyzed thing" (high level language, assembly,...) to allow for easier analysis, while still being useful (a assembly language only supporting 'nop' is trivial to analyze, but pretty useless overall; otoh you can disallow some constructs in C to make the language easier to analyze).

There are of course other forms of "provably correct". E.g. programming in a language that has proofs attached to it, like coq [which is the name of a proof assistant]. Disclaimer: I've never used coq myself, but know plenty who do. I think that's something that might interest you. [And thanks to the genius who christened that tool: No, seriously, I'm not trying to be rude!]

[edit] Didn't check that link, but maybe you find it interesting https://www.cs.princeton.edu/courses/archive/spring13/cos510... There are of course other approaches than coq, e.g. Isabelle is often mentioned. See the "See also" on https://en.wikipedia.org/wiki/Coq

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

#415

Post by benhurmarcel »

underseacables wrote: post #336
colechristensen wrote: post #329

Earlier quoted context omitted.

The plane landed and didn’t blast enormous holes with ejected compressor blades. That’s a successful failure.

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

To add to the topic, aircraft structure and systems are made to withstand the projection of those debris hitting with "infitite" energy. That means for every trajectory possible, it's considered that a part flies through everything in its path. The aircraft still has to land.

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

#416

Post by benhurmarcel »

jabl wrote: post #366
iawix wrote: post #287

Earlier quoted context omitted.

It's good airmanship to turn into your "good" engine.

Why? Surely it's easier to turn the other way? Then again, it's not a dogfight, so maybe less chance of losing control if turning into the working engine?

> Surely it's easier to turn the other way?

That's exactly why. Because then it helps you getting out of your turn, instead of fighting against it.

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

#417

Post by dtgriscom »

hazeii wrote: post #406
colechristensen wrote: post #329

Earlier quoted context omitted.

The plane landed and didn’t blast enormous holes with ejected compressor blades. That’s a successful failure.

Plenty of youtube videos of a blade-off test - here's a short one [0] of an A380 Rolls Royce engine testing. That's about £9,000,000 of engine being destroyed in this (successful) test. [0] https://www.youtube.com/watch?v=5-8_Gnbp2JA

At the beginning of the video the blades seem to be spinning at about 2RPS, but after the explosion they're spinning much faster. I presume the former was an artifact of the camera's frame rate.

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

#418

Post by tantalor »

EvangelicalPig wrote: post #340
tantalor wrote: post #245

Earlier quoted context omitted.

Why is that suprising? Serving static content is easy

I mean. How much is classic Perl used in web applications these days?

0.1%, not much!

https://w3techs.com/technologies/overview/programming_langua...

But concatenating strings together is the same in any language, right?

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

#419

Post by ghaff »

dehrmann wrote: post #173
chrisseaton wrote: post #52

Earlier quoted context omitted.

The idea that the engines need to sit on the wings like they do is something seems important, because it's so often done, but is actually not necessary. You can put a single engine in the tail, or on top of the cabin, or on the top of the cockpit, or underneath. They go on the wings because when you need two (for redundancy) it's a good place to put them for balance, and because it makes them nicely accessible for ma…

> it's so often done The MD-80 had two rear engines and was a fairly popular plane. A lot of smaller jets still have rear engines, too.

The MD-80 (and 727) were old turbojets though. Probably a lot harder to come up with a practical tailmounted design with a turbofan although I'm open to it being possible to mount one turbofan above the fuselage.

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

#420

Post by sandworm101 »

Kye wrote: post #412
djmips wrote: post #389

Earlier quoted context omitted.

2020: (JAL 777 same engine) https://www.youtube.com/watch?v=O-_IAKCBTxc&t=10s 2018: United 777 same PW engine (seems very similar but without fire) https://www.youtube.com/watch?v=O-_IAKCBTxc&t=10s 2016: KAL 777 same PW engines (aborted takeoff after engine failure) https://www.youtube.com/watch?v=9bHrW_34kAk All planes had zero casualties.

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.
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