[Retric]

Critically the material is still titanium. Some of the paperwork is counterfeit so there’s concerns around quality control etc not what it is.

> Spirit is trying to determine where the titanium came from, whether it meets proper standards despite its phony documentation, and whether the parts made from the material are structurally sound enough to hold up through the projected life spans of the jets, company officials said. Spirit said it was trying to determine the most efficient way to remove and replace the affected parts if that ended up being necessary.

[_moof]

Unfortunately it's not enough for it to just be titanium. A hard alpha inclusion in an ingot used to make turbine blades was the root cause of the deaths of 112 people aboard United Airlines 232.

[dgoodell]

Technically it was in the fan disc, and not a turbine blade. And while there was a defect, a big part of the problem was that an inspector most likely missed a crack during overhaul. The crack was present at a previous inspection, which they knew because there some fluorescent penetrant remaining in the defect.

I worked in a turbine engine component repair shop for 8 years. We had an NDT inspector fall asleep a lot in his booth and miss cracks. I’m pretty sure they ended up firing him. But maybe not as quick as they should have.

[ThePowerOfFuet]

I disagree.

Poor design leading to the loss of all flight control surfaces in the event of an uncontained engine failure is what led to their deaths.

[_moof]

I said the root cause. There is always more than one factor in an air accident. But if the ingot hadn't had an inclusion, none of the other factors would've mattered.

[stoperaticless]

A bit offtopic. Nitpick regarding definition of “root cause”.

Let’s say there are two conditions X and Y. Neither sole-X nor lonesome-Y, cause the disaster, but when X+Y happen together, they produce a very negative outcome.

It would seem that both are equally “root” of the cause. But human brain desires to declare one as primary.

In situation where disaster was “human died”, with conditions X=“bullet was shot at the human”, Y=“humans are squishy”, we naturally would lean towards X being the root cause, while Y would be treated as ”that’s just the way it is”.

On the other hand we could construct ”human died” situation with reverse root cause assignment, ie. X=“bullet was shot at human” is taken as a constant, while root cause is Y=“ humans are squishy” (employing some grotesque reader can construct a better one, but something like “The journalist should have followed the process and used a bulletproof vest. It is a war zone after all” seem to work)

“Root case” usually is the smallest and most easily changable part of situation that can prevent disaster.

Though the “ease of change” is not fixed. (“People must follow process” vs “invest milions to change process”)

I just wanted to ramble a bit on the concept of “root cause”. To highlight that on precision-of-terminology-spectrum that spans between mathemathics and astrology, “root cause” falls somewhere in the middle. (probably bit to the right of engineering)

[Retric]

If that specific part was fine an effectively identical accident would likely have happened later.

[kube-system]

> The National Transportation Safety Board determines that the probable cause of this accident was the inadequate consideration given to human factors limitations 1n the inspection and quality control procedures used by United Airlines' engine overhaul facility which resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the stage 1 fan disk that was manufactured by General Electric Aircraft Engines.

https://www.ntsb.gov/investigations/AccidentReports/Reports/...

[Retric]

Cropping the cause is misleading, this is all under cause:

> determines that the probable cause of this accident … Aircraft Engines. The subsequent catastrophic disintegration of the disk resulted in the liberation of debris in a pattern of distribution and with energy levels that exceeded the level of protection provided by design features of the hydraulic systems that operate the DC-10's flight controls.

Under recommendations:

> Encourage research and development of backup flight control systems ·for newly certificated wide-body airplanes that utilize an alternative source of motive power separate from that source used for the conventional control system. (Class II, Priority Action) (A-90-168)

> Conduct system safety reviews of currently certificated aircraft as a result of the lessons learned from the July 19, 1989, Sioux City, Iowa, DC-10 accident to give all possible consideration to the redundancy of, and protection for, power sources for flight and engine controls. (Class II, Priority Action) (A-90-169)

>Analyze the dispersion pattern, fragment size and energy level of released engine rotating parts from .the July 19, 1989, Sioux City , Iowa, DC-10 accident and include the results of this analysis, and any other peripheral data available, in a revision of AC 20-128 for future aircraft certification. (Class II, Priority Action) (A-90-170)

Etc. So calling this a design issue rather than an inspection issue is quite reasonable. Inspections are guaranteed to eventually fail, the aircraft being 100% dependent on them is a recipe for future disasters.

[kube-system]

In aviation safety investigations, all contributing factors are considered, and there are usually multiple factors involved in any incident.

My purpose of quoting that wasn't to be a wholly inclusive description of the situation (that's what the full report is for), it was to refute the above idea that engine defect was not the root cause.

> So calling this a design issue rather than an inspection issue is quite reasonable. Inspections are guaranteed to eventually fail, the aircraft being 100% dependent on them is a recipe for future disasters.

Likewise, we don't just require "good designs" instead of inspections, because even a "good design" will experience failures. In the swiss-cheese model of safety, all of the slices are important. In this case, the inspection was the first failed slice.

[Retric]

> was to refute the above idea that the engine defect was not the root cause

You misunderstand what a root cause is. An accident has multiple root causes in the swiss cheese model.

Each process update is supposed to address a root cause.

This is separate from contributing factors. IE: It happened at night.

[ThePowerOfFuet]

If the QC is unknown, then so is the metal.

[Retric]

The point is verifying that the parts are titanium is insufficient to ensure safety.