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Comment by 4cao | Hacker News Reader

Specifically, it concerns some variants of the Pratt & Whitney PW-40xx engine (the affected model was a PW-4077). Japanese carriers also grounded their affected planes earlier, and so did United.

Japanese authorities issued a NOTAM requesting airlines not to fly the affected planes over its territory. The US FAA is about to issue an emergency directive soon but only expected to decrease the inspection intervals of the affected parts rather than ground the planes completely.

The Aviation Herald has all the updates: http://avherald.com/h?article=4e35503b

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CNN for comparison focused on "right engine failures" rather than engine type, citing 2 failures in three years. In related news, for two coin flips there's a 1/4 chance of two heads in a row.

To be fair they did mention that the engine type was the same, along with the fact that both aircraft were headed for Hawaii.

[1] https://www.cnn.com/2021/02/22/us/united-airlines-2018-engin...

Korean Air had a similar incident in 2016 where a PW4000 on a Boeing 777 disintegrated during takeoff.

https://en.wikipedia.org/wiki/Korean_Air_Flight_2708

and UAL in '18

http://avherald.com/h?article=4b4e8ca7&opt=0

...Decrease them to zero, aka ordered an immediate inspection.

The fan blade had a stress fracture. So they'll need to do an immediate ultrasonic scan of the blades, which should clear the engines for flight, and then figure out why the maintenance schedule didn't catch the fracture.

Which, to pinpoint the insanity of the FAA, the failure seen over denver actually involved an uncontained blade exiting the engine, something it was clearly not designed to allow to happen. It's a mess.

But the engine did contain the failure. No pieces of the engine caused any functional damage to the rest of the aircraft. The housing is designed to prevent shrapnel damage, not to prevent stuff from falling out altogether.

What's insane about the FAA's approach? They are ordering immediate inspections of all fan blades in these engines for cracks like the one that apparently brought this one down.

There certainly was shrapnel damage to the plane. http://avherald.com/img/united_b772_n772ua_denver_210220_8.j...

Not fully contained. See https://twitter.com/breakingavnews/status/136379347594735616... for damage to wing to body fairing.

Contained vs uncontained turbine failures relate to the damage from the blades being contained, which in this case they were. Contained failures still result in engine parts exiting the engine, but not through the engine case, which is reinforced to contain the turbine blades in a failure. The unexpected issue here is that the cowling was knocked off, which is not supposed to happen, but in recent years it seems to be happening.

It was not contained. A blade went though the lower wing root.

https://twitter.com/breakingavnews/status/136379347594735616...

decrease? increase?

Decrease the interval, increase the frequency.

As a non-native I would've used `increase the interval` -- but I understand now this is incorrect. TIL..

indeed, it would have been clearer to say 'increase the frequency of inspection'

My bad, I could have worded it clearer: "have the parts inspected more often" would do, I think.

Alas, can't edit the comment anymore, and probably shouldn't anyway, considering the discussion it sparked.

sorry for nitpicking, but as a non-native speaker I can understand the confusion

> As a non-native

i am a native and this confuses me constantly.

the windshield wipers in my car change their speed based on a UX showing an in increasingingly long bar. i can never tell if it represents time or 1/time until i futz with it.

Huh? The lowest setting (the one closest to off or auto) is the one for the least rain, and it goes up to handle more rain, i.e. the further you are from off/auto the faster the windshield wipers wipe.

> Huh?

Yes, you are right to be confused. You dont know the UX of car. Why did you think this was worth commenting?

> (the one closest to off or auto)

the on/off toggle is separate from the speed dial. there is no obvious (to me) directionality.

Only on hacker news can a discussion about an airplane engine end up about windscreen wiper UX.

Yeah that's one thing European cars do wrong. They have two separate controls: one for on off the other one for interval.

American cars in contrast have just one control: it starts with off, then does intervals, finally the shortest interval, then low speed and then high speed.

Welcome to downvote hell with me. God damn, sanctimonius know-it-all HN jerkoffs do piss me off (yeah, go ahead reader, downvote me).

But your classification of European/American cars isn't accurate either. I drive an Italian car (well, but surprise, it's Fiat Chrysler) and the wiper controls makes sense, like what you refer as "American cars". Search for Mercedes Benz wiper controls on Youtube, that also makes sense. BMW's one is strange, the Ford one looks confusing but I didn't bother to look for a video.

I’ve been living in Europe for a couple of decades and I have never seen a on/off control separate from the speed.

>> UX showing an in increasingingly long bar

I have driven car where the pictogram meant "amount of rain", the longer bar meaning more rain and therefore a shorter interval.

If it counts only time on air, can we call it wavelength?

Thank you. I'll show myself out.

Yes!

When inspection frequency gets too low, airplanes fail, leading to more frequent inspections.

When inspection frequency gets too high, airlines and authorities decide to save money, leading to less frequent inspections.

So the inspection schedules (somewhat) satisfy Hook's Law, and thus we should expect wavelike oscillations.

[Edit: The system also requires momentum. That's provided by labor unions agreements, maintenance contracts, and the time needed to change regulations.]

Thanks, I'll be waiting for you at the pub.

We should write a paper on this. I know quite a few (dis)reputable journals that would readily take it.

>> When inspection frequency gets too high, airlines and authorities decide to save money, leading to less frequent inspections.

More often such aircraft are just retired. One defining difference between upstart airlines and "legacy" airlines is that the upstarts generally have new aircraft with lower inspection requirements. An interesting paper would address the inevitable evolution of new airlines as as their airframes age. When do they first try to transition to higher-profit services? When do they hit their first period of labor unrest? I theorize it is a function of aircraft age.

At least a few airlines don't ever buy aircraft. Instead they lease them with the intention of returning them moment they require more frequent inspections.

Upstart airlines frequently lease used aircraft because they're cheaper.

This whole business is so capital-intensive the decisions often follow non-obvious patterns. There are advantages in keeping a fleet uniform, even if a newer plane lease is cheaper than another model you already have a bunch of just because of the costs of training ground and air crews. Some leases may end up cheaper for you - and only for you - because of some tax break you got from one government that, for now, wasn't questioned by the WTO (and, since it's the manufacturer who'll pay the fines, it's not a concern).

It's... complicated. Very complicated.

When the interval decreases the frequency increases

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