Electrical Wire Splices in High Vibration Environments. 3

[kontiki99]

I'm looking for information on electrical wire splices in high vibration environments (aircraft wings, engine pylons, and engines).

Sometimes wire splice repairs are an operational necessity. Some OEMs consider all wire splice repairs “temporary.” I’ve seen very conservative hard limits on engine harness wiring splices. I’ve seen where the OEM built in spare wiring that ran from wing pylons to fuselage electronic bays, but didn't allow permanent wire splices in the wings or pylons.

Has anyone really studied how wire splices fail? Is it loosening or broken wiring strands? Are there designs that are better for high vibration environments? Are there electronic methods for security verification or failure detection. Maybe there are good rules for estimating how long they last before failure.

This is kind of a fishing trip. I'm really hoping for something to hang my hat on to extend wire replacement to a heavy maintenance visit a few years down the road while we fly the daylights out of them.

Thanks in advance.


My posts reflect my personal views and are not in any way endorsed or approved by any organization I'm professionally affiliated with.

 

[Sparweb]

Hi Wil,
I confess I'm an opportunist. I'm seeing a lot more valuable information about wire harnessing than I ever expected to see on this forum. As a long-time ET member it's still a pleasant surprise. Kontiki is being generous and I'm enjoying the stories, so I thought I'd ask for more. An Oliver Twist moment.

Don't take my little "burr" personally. In real life I've been delivered an unpleasant surprise and I will soon find myself re-engineering an aircraft already compliant with EWIS requirements to make it "more" compliant with EWIS. It won't be fun and will have only a vague contribution to safety. Do you have a copy of the FAA TAIL list? I have stepped in one of those little quagmires.

 

[dik]

Great thread... not my area, but very interesting. Thanks, everyone.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WKTaylor]

FAA TAIL list??? No clue... I ONLY work MIL Acft [and some civ=>MIL derivatives]… a whole different/murky world.

NEVER take any of this lightly. In the very early 1980s I took a fire and explosion investigators course [after the basic mishap investigators' course]. Over many years, I've investigated many aircraft ground and inflight incidents/mishaps/tragedies... with most-all starting from EE-EL root-failures [a few others were catastrophic turbine-engine, or bleed-air duct, failures]. Electrical components and systems are insidious: many ways to start small failures/fires which result in confusing circumstances for the crews/mechanics... and often induce cascading failures and ferocious fires. Regardless of outcome, ALL can be perplexing, terrifying and devastating.

All Energized wires and many components are scary to me and are worthy of great respect/concern... especially in tropical/oceanic environments...especially Kapton insulated wires, buss-bars/junctions, airframe grounds, all conventional circuit breakers, solenoids and electric fuel pumps... to name a few, coming immediately to mind.

OH, YEAH... and static-lightning-corona-EMP-EMI-TREES-CME are truly unique hazards to aviation and space vehicles that need added consideration. Often what is done to 'combat' these effects seem excessive... but lessons have been learned... especially in vehicles carrying huge quantities of liquid-flammables [fuel] and pressurized hot-air sources [bleed-air] and energized EE-EL systems.

ELECTRONIC FAILURE ANALYSIS HANDBOOK: TECHNIQUES AND APPLICATIONS FOR ELECTRONIC AND ELECTRICAL PACKAGES, COMPONENTS, AND ASSEMBLIES, ISBN 9780070410442

FAILURE ANALYSIS: A PRACTICAL GUIDE FOR MANUFACTURERS OF ELECTRONIC COMPONENTS AND SYSTEMS ISBN 0470748249

WRDC-TR-90-4075 FAILURE ANALYSIS TECHNIQUES FOR THE EVALUATION OF ELECTRICAL AND ELECTRONIC COMPONENTS IN AIRCRAFT ACCIDENT INVESTIGATIONS

AFAPL-TR-73-73 FIRE AND EXPLOSION MANUAL FOR AIRCRAFT ACCIDENT INVESTIGATORS

AFWAL-TR-85-2057 AIRCRAFT MISHAP FIRE PATTERN INVESTIGATIONS

AFWAL-TR-85-3006 ATMOSPHERIC ELECTRICITY HAZARDS PROTECTION CONCEPTS

AC25-16 ELECTRICAL FAULT AND FIRE PREVENTION AND PROTECTION

AC120-80 IN-FLIGHT FIRES

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[kontiki99]

WW,

The point I was making with my statements was that I wasn’t here seeking advice on approval strategy. When I post here, I’m looking for data and technical knowledge.

Your comment does exactly illustrate the confusion I was talking about though. I’ve had the general counsel at a vendor try to tell me what we at the airline I work for could or could not legally do. My only guess is that her understanding of what’s legally possible for us was based on what they can legally do as a manufacturer of approved parts and STC holder. It doesn’t work that way. If we buy the rights to use an STC and later make changes to our airplane; I’ve never seen anything that says we must notify the STC holder. I don’t think anyone cares if the wire connection is made at a specific terminal block. When a terminal block is completely occupied, we make the connection someplace else or upgrade the block. It's functionally equivalent. This is how it is with old airplanes.

I suspect some vendors never even read much less understand the FARs that govern the airlines they sell parts to. I doubt most know which branches of the FAA their customers do business with. I doubt most have any idea which FAA certificates their customers hold. I doubt they have any idea what operation specifications they are approved for. All that anyone really knows is how the FARs affects them.

The aviation and airline regulatory environment is hugely complex and oddly mercurial. All it takes is one incident, one disclosure, one remedial agreement with the FAA inspectors that monitor us and our procedures and job duties change in unpredictable ways.

In my opinion, the thing that saves us at an airline is that fact that the FAA really doesn’t expect every employee to understand the maze of regulations that affect us.

The airlines are required to develop manuals that describes the procedures we will use to comply with all the relevant regulations. Some or all of those procedures are approved by the FAA. I believe FAR § 121.9 Fraud and falsification is a law that requires us to follow our approved policies. If we comply with our approved policy manuals, we’re good.

FAR § 121.379 does give an airline the authority to perform and approve maintenance, preventive maintenance, and alterations, gives us the ability to make minor changes to the airplanes we operate.

I don’t know that an airline necessarily needs to get involved with Parts Manufacturing Approvals we can manufacture repair parts for airplanes we operate without them. I don’t know that an airline necessarily needs to get involved with an FAA Aircraft Certification Office if they choose not to develop their own STCs.

As far as an FAA Tail List goes, there is a registry lookup on the FAA’s website. You can probably still look up all the registry numbers used or reserved by a company, though all may not be active. Most airline customized manuals that I’ve seen do have an aircraft effectivity cross reference in the front matter. An airline that assigns their own tail number/ effectivity codes will list them there. It’s easier to use than the OEMs master manual serial number format.

See For Registry Lookup->

https://registry.faa.gov/aircraftinquiry/Search/NNumberInquiry

I do appreciate everyone's help and ideas. I've got my work cut out for me looking through all the references. It's a busy night for me.





My posts reflect my personal views and are not in any way endorsed or approved by any organization I'm professionally affiliated with.

 

[debodine]

kontiki99:

In one of your earlier posts, you included the paragraph below:

It's sometimes not obvious to non-operators, but someone that holds a Supplemental Type Certificate for an aircraft modification cannot make a minor change to the STC without FAA approval, where as an operator we are allowed to make FAA minor changes to the airplanes. We often change the plane to make the STC work.

You made two separate statements, both accurate and for those of your readers that may not understand, I would like to add a bit of clarification. I live in the world you describe, being in an organization that develops and obtains approval for STC configuration changes to Part 25 Transport category aircraft, normally operated by Part 121 airlines.

We do make minor changes to an STC after the original approval and yes that minor change must follow the same approval path that the STC did. What I mean is that the same level of scrutiny (design review, substantiation, FAA approval typically by FAA-DER or ODA-UM) happens. The only real difference is that the minor change is not immediately reported to the FAA, but gets reported with all other minor changes on a six month cycle. So your statement is accurate that such minor changes still require the same level of FAA scrutiny and approval as the original STC program.

As far as changing the airplane to make the STC work, that is definitely the case. I will give a fictitious example that illustrates a number of real-life projects I have worked. Assume we are issuing an STC for ten aircraft and aircraft number seven has a repair that will not allow our STC to be incorporated correctly. Sometimes the operator will contract with us to develop an alternate repair that works with our STC, or to develop a deviation to the STC that works with the existing repair. But as you accurately stated, sometimes the operator will develop their own alternate repair that allows the STC to be incorporated on aircraft seven, just the same as the other nine aircraft.

So both of your statements were spot on as written. I just thought there may be a few readers who would like to understand how the situations described in your statements are resolved.