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DocLightning
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Wiring/controls and uncontained failures

Mon Mar 09, 2020 8:19 pm

Obviously, this question is inspired by the recent FAA directive to move certain wiring bundles in the 737MAX to provide more safety in the event of an uncontained failure, but my question is more general.

Consider an uncontained failure involving a turbine disk (high-temperature, high-speed, high-stress, no way to contain, fragments depart engine at very high energy). The area of potential impact comprises a plane passing through the turbine disk's location and transecting the entire fuselage. How is it possible to protect any fore-to-aft wiring bundles (or cables in aircraft so rigged) when anywhere in the fuselage is at risk of being struck?
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AirKevin
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Re: Wiring/controls and uncontained failures

Mon Mar 09, 2020 8:25 pm

That I have no idea, but if I remember, Qantas 32 had the issue where parts of the engine went right through the wing, so....
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Web500sjc
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Re: Wiring/controls and uncontained failures

Mon Mar 09, 2020 8:44 pm

DocLightning wrote:
Obviously, this question is inspired by the recent FAA directive to move certain wiring bundles in the 737MAX to provide more safety in the event of an uncontained failure, but my question is more general.

Consider an uncontained failure involving a turbine disk (high-temperature, high-speed, high-stress, no way to contain, fragments depart engine at very high energy). The area of potential impact comprises a plane passing through the turbine disk's location and transecting the entire fuselage. How is it possible to protect any fore-to-aft wiring bundles (or cables in aircraft so rigged) when anywhere in the fuselage is at risk of being struck?



Redundency? Instead of 1 bundle of wiring carrying all the signals for critical functions, separate it into different bundles that are strategically place around the fuselage.
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DocLightning
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Re: Wiring/controls and uncontained failures

Tue Mar 10, 2020 2:45 am

Web500sjc wrote:

Redundency? Instead of 1 bundle of wiring carrying all the signals for critical functions, separate it into different bundles that are strategically place around the fuselage.


Good point. What about cables?
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Starlionblue
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Re: Wiring/controls and uncontained failures

Tue Mar 10, 2020 3:06 am

DocLightning wrote:
Web500sjc wrote:

Redundency? Instead of 1 bundle of wiring carrying all the signals for critical functions, separate it into different bundles that are strategically place around the fuselage.


Good point. What about cables?


Three separate runs of cables running at radially equidistant points around the inside of the fuselage is the best you can do. Yes, all three could theoretically be severed by debris, but you can't completely eliminate risk.
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basspaul
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Re: Wiring/controls and uncontained failures

Tue Mar 10, 2020 9:03 pm

It's called PRA: Particular Risk Analysis. For a rotor burst PRA, the engine manufacturer will provide the "burst cone" geometry for un-containable failures (disk). The debris will always move outward and aft of the engine, that's why it's a cone. Disk fragments are considered to have infinite energy for the analysis.

You place this cone geometrically across your airframe and see what it hits (much easier after 3D model became standard). For electrical, hydraulics and controls, you ensure redundancy and that a single piece of debris will not defeat those redundancies. For other critical system components, you either get them out of the burst cone or create a redundancy for it.

Similar PRA's are done for tire failure, runway debris kicked up by the tires, wheel rim failure (another infinite energy case), RAT blade off, etc.

As for things hitting passengers: for the infinite energy cases, too bad (statistically very rare).

About the Qantas flight mentioned: stuff going through the wing is "acceptable risk". From what I've read about that incident is that the crew were overwhelmed dealing with the all the error messages they had to deal with from the impacted systems. The plane was still able to fly (with difficulty) and land. The one total failure was not being able to shutdown the engine once landed. Fortunately there was no fire and the engine running did not cause any additional injuries.

Supposedly, Airbus has change the logic on how to clear errors on the HMS so that pilots will get the big picture when there are multiple simultaneous system failures. Previously, the pilots would have to troubleshoot the entire system reporting the failure, then move on to the next failed system. Now they are supposed to see something like a list of what system(s) have failed and then the pilots use their judgment or another checklist as to what system to prioritize for troubleshooting.
 
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CALTECH
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Re: Wiring/controls and uncontained failures

Sat Mar 14, 2020 12:03 am

DocLightning wrote:
Web500sjc wrote:

Redundency? Instead of 1 bundle of wiring carrying all the signals for critical functions, separate it into different bundles that are strategically place around the fuselage.


Good point. What about cables?


Cable runs are as straight as possible to lower complexity of their runs and really the only place for them is under the cabin floor / cargo pit ceiling.

Image

Wire runs are already separated. They run in the ceiling and in raceways around the fuselage. It gets crowded.

Image

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