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.
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.
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.
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.
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".
The risk of falling debris actually killing someone pales in comparison to the risks of it perhaps doing more damage onboard the aircraft. A loose part near/inside an engine is no longer doing its job and could cause more damage where it is. And the ground is a big place. Drop a random pin in google maps. Then zoom in to see if it is actually on someone's head. This is lottery odds territory.
Objects drop from aircraft all the time, daily. It isn't generally newsworthy unless part of a larger story. And even then, only if the object is found and recognized as being from an aircraft. Small rocks also fall daily from space, probably more by weight than aircraft-related objects, yet virtually nobody ever gets hit by space rocks.
To add to that, 100 tons of spacerocks hit eath every day. I dont think 100 tons of parts fall of airliners daily.
That being said, there was a russian spacecraft that disintegrated and hit someone house, in the middle of siberia bo less. So it does happen, but its freak ecen3ts territory.
Oh, if you are going to include manmade space-related objects there have been many deaths. Dig into how many Chinese rocket stages have landed on villages. If we include such things as "aviation" I would retract my above statements re debris. Rockets do sometimes fall on people.
"It has happened many times before, including most infamously in 1996 when a Long March 3B rocket veered off course shortly after a launch and crashed into a village. Chinese officials reported six dead from the accident, although Western sources have speculated that hundreds of Chinese citizens may have died in the accident."
I didnt. I only said that rockets sometime crash on people and gave an example. Nobody is comparing countries in this thread. Aviation is about as international as any industry can be.
False equivalency. 100 T of diffuse material reaching Earth, likely burning up, isn't the same as or even remotely comparable to parts falling off aircraft due to man-made negligence. Jettisoning honeycomb cowling sections because a particular model of engine is relatively unreliable, through design, manufacturing, or maintenance, isn't an excuse for not fixing it or not using a better engine if it cannot be fixed economically.
Could you proofread and type correctly so we understand what you're saying? I can't read all of what you're saying.
"Bad things will always happen" is a despicable shrug mentality. Bad things happen when people don't have their acts together in design, engineering, manufacturing, maintenance, and operation. The failure rates should be striving for zero, unlike the stunts Boeing has pulled on 737NG, MAX, and the 787.
Totally agree with you on the recent laxness in design and the regulatory capture that allowed it. But treating zero as a feasible goal is unrealistic. I've done code inspections for safety of flight code and making sure you have 100% coverage and branch coverage not just in the high level code but in assembler still doesn't get everything. You try to make sure that redundancy saves you (seriously boeing!) But common mode errors and just human fallibility to see all the possibilities mean we miss stuff. And all this is so much easier in software than in mechanical designs where redundancy sometimes just isn't doable. We shouldn't give up best practices, but we shouldn't have unreasonable expectations of them either. And not every engineering failure implies a failure in engineering process.
I wanted to clarify my last statement. Even when best practices are followed bad stuff happens, and that doesn't necessarily mean best practices need to change.
Of course not. Make improvements rather than knowingly shove-in bad Ducommun parts on the line or crappy MCAS. Also, hold manufacturers responsible when they take cost-shortcuts, sacrifice safety, and kill people. Boeing routinely gets a slap for doing so since it's also considered a strategic defense contractor, part of the MIC that greases palms in DC.
