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According to Bloomberg:
Boeing Co. told U.S regulators on Friday that it didn't see the need to undertake a potentially costly fix for a wiring issue on the company's grounded 737 Max, according to two people familiar with the briefing.
The planemaker found in an audit last year of the 737 Max that wires were bundled improperly in a way that could trigger a failure similar to what happened in two crashes of the plane in which a total of 346 people died.
U.S. law requires wiring that could cause a hazardous condition in a failure to be separated from other wires. [...]
The wiring issues have been found in more than a dozen locations on the 737 Max.
From The Seattle Times [May require that Ad-Blockers be switched off, or at least disable style sheets]:
During the original design and certification of Boeing's 737 MAX, company engineers didn't notice that the electrical wiring doesn't meet federal aviation regulations for safe wire separation. And the Federal Aviation Administration (FAA) failed to detect Boeing's miss.
The wiring vulnerability creates the theoretical potential for an electrical short to move the jet's horizontal tail uncommanded by the pilot, which could be catastrophic. If that were to happen, it could lead to a flight control emergency similar to the one that brought down two MAX jets, causing 346 deaths and the grounding of the aircraft.
Because this danger is extremely remote, the FAA faces a dilemma over what to do about it. The issue has complicated the return of the MAX to service after a grounding that is edging close to one year. [...]
"There are 205 million flight hours in the 737 fleet with this wiring type," a Boeing official said. "There have been 16 failures in service, none of which were applicable to this scenario. We've had no hot shorts."
In addition, Boeing says pulling out and rerouting wires on the almost 800 MAXs already built would pose a potentially higher risk of causing an electrical short, because insulation could chafe or crack in the process of moving the wires.
However, an FAA safety engineer familiar with the issue, who asked not to be identified because he spoke without agency permission, said agency technical staff have been clear that the wiring doesn't comply with regulations and have told their Boeing counterparts it has to be fixed.
(Score: 5, Insightful) by sjames on Sunday February 16 2020, @09:18AM (11 children)
That's why a properly designed conduit has access points anywhere you might need to make a turn and at mid poinys for long runs.
Part of me can't help snickering just a little. For once it's the manufacturer of something that experiences the pain of repairing something that wasn't designed to be repaired.
(Score: 2) by Runaway1956 on Sunday February 16 2020, @09:50AM (1 child)
Just two weeks ago, I left a note for my boss, with a sentence to that effect. "Call the manufacturer, and tell them that we want their engineers to come out here and DEMONSTRATE how this is done!"
Odd that I didn't make that connection here. ;^)
Abortion is the number one killed of children in the United States.
(Score: 4, Insightful) by sjames on Sunday February 16 2020, @10:11PM
I would love to see more of that sort of thing.
Perhaps even as a reality TV sort of challenge. The engineering teams from the major auto manufacturers are forced to perform routine maintenance and common repairs on the car they designed live in prime time. They each get a set of standard tools that a well equipped shade tree mechanic might have.
If they have to call for a specialty tool, they lose points. If the tool is restricted by licensing or only available from the manufacturer, they get paddled with a shop manual by a select group of angry mechanics.
(Score: 0) by Anonymous Coward on Sunday February 16 2020, @02:26PM (1 child)
conduit weight reduces payload weight.
Incidentally the wiring spec isn't for how the wire performs when new. It is there because of how the wire performs after 20 years of chafe.
(Score: 2) by sjames on Sunday February 16 2020, @09:13PM
Where there isn't a conduit, access points are far more important.
And yes, the danger is that you might badly damage the insulation on installation such that at some future point it will fail due to further vibration and chafing while in service.
(Score: 2) by RS3 on Sunday February 16 2020, @08:54PM (6 children)
Absolutely agree. I've installed a few feet of conduit here and there. I'm a freak for deburring things, especially conduit ends. It only takes 2 seconds per end. Wires pull much easier, and without chafing.
NEC rules (not airplane obviously) limit a conduit run to a total of 360 degrees of curves, bends, elbows, etc., before you have to put in a "pull box" or some kind of access box.
I keep hearing about wiring problems in planes and I don't understand why they don't use conduit for all wiring.
(Score: 3, Interesting) by anubi on Monday February 17 2020, @12:50AM (5 children)
If anything, like a length of wire, is loose, it will vibrate and chafe. I had that problem show up on some oil tankers. Premium Teflon wire, too. Did not last a year. Failed by chafing against anything else by relentless vibration.
We had to rewire the whole engine circuits of those tankers. And this time, using lots of anti chafing and anti vibration measures.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by sjames on Monday February 17 2020, @01:54AM
I remember something from years ago that a U.S. fighter plane frequently had that same problem (also with teflon wireing) but I don't remember which model.
(Score: 2) by RS3 on Monday February 17 2020, @03:02AM (3 children)
Good points. How about multi-conductor cables? I know some are designed for lots of flexing and vibration.
(Score: 1) by anubi on Monday February 17 2020, @08:21PM (2 children)
I did not see this in multiconductor cables, where the cable jacket secured the internal wires from rubbing against each other.
What got us was several individual wires, say 12 Gauge, stranded, in a half inch steel conduit They bounced around in there and the insulation began failing.
We replaced the wiring with some sort of neoprene armored ship rated cabling, and I never heard of any more problems. Sure taught me a lesson. After seeing what an expensive mess was made, I paid a lot more attention to detail from then on.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by RS3 on Monday February 17 2020, @11:44PM (1 child)
Thank you, good to know!
Interesting about the wire (THHN?) in steel conduit problem. Again, possibly sharp edges?
I'm very particular about sharp edges- I hate them and remove them generally, and conduit is no exception- fitting, boxes, connectors, conduit itself. I notice people being lazy / negligent about using plastic bushings on fitting threads.
I've noticed many multi-conductor cables often have some kind of white powder everywhere inside. It seems to be a little slippery. I doubt it's talcum, but maybe something similar.
Anyway, maybe Boeing / other aircraft mfgrs. should plan harness design / layout based on multi-conductor cables which might be much more reliable.
(Score: 1) by anubi on Thursday February 20 2020, @02:39AM
You nailed it on the sharp edges. On disassembly and inspection of the failing wiring, it seemed every sharp edge and bend had left damage in the insulation.
I was a green engineer fresh out of college, working for Chevron at the time, and I was with a far more experienced engineer. I hold Chevron responsible for training me to be so perfectionist, by showing me what huge expensive messes we make when we ignore little details.
Seems like everyone learns this lesson the same way I did, and by that time, we are considered to be too set in our ways to be an obedient employee under some leadership type that has never experienced a good screwup. Types that emphasize shortcuts to maximize a bonus. If one thinks experience and education are expensive, try ignorance.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]