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Electrical Wire Splices in High Vibration Environments.
3

Electrical Wire Splices in High Vibration Environments.

Electrical Wire Splices in High Vibration Environments.

(OP)
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.

RE: Electrical Wire Splices in High Vibration Environments.

Can they not just wrap and solder? or a couple of mechanical connectors with Bellville washers or similar non loosening screws? or, maybe crimp? Don't know, I'm not a sparky.

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

-Dik

RE: Electrical Wire Splices in High Vibration Environments.

Typical failures of wires is from cutting or abrasion. Secondary failures are from flexing, particularly if the flex is at a change in stiffness. A great way to create that change is to solder stranded wire. So, if the wires are constrained against flexing they shouldn't fail. This is why bundles are often tightly wrapped and supported at short intervals and nearby structure is provided with grommets to prevent cutting and abrasion. The better splices seem to be those done with crimped shells inside of heat-shrink that includes a hot-melt adhesive that seals against corrosion and provides a strain relief for the wires.

RE: Electrical Wire Splices in High Vibration Environments.

(OP)
At a large airline we defer to the OEMs wiring standard practice manuals as often as possible. Those are part of the instructions for continuous airworthiness. These documents range anywhere from 2000 to 10,000 pages long and attempt to provide repair practices, part numbers and tooling for restoring and repairing every wire and connector anywhere in the aircraft.

These airplanes are all built with many thousands of crimp wire splices and connections brand new. There is a huge range of wire types and wire situations, some involve flammability areas, high heat areas, high vibration areas, areas that require lightning and HIRF protection etc. So there are a lot of challenging wiring situations.

Having said all that. Soldering is a really intriguing idea. The last two times I dealt with this it was relatively straight forward twisted shielded wire pairs in the wing near the pylon. We wanted to use a spare wire pair that ran the 20 ft down the wing, through the pressure seal and to an equipment bay. Last time, the airplane was on the ramp with a non-deferrable fault in JFK with harsh weather.

I see we have something called solder splices I'm not sure why we don't use them more. We operate 5 fleet types, I have to dig through the manuals and see what the restrictions for each manufacturer.

Trying to think like a ME, crimped wire splices have a transition from the rigid splice to (most often) annealed copper, and I have no idea how that would be different to the transition from a stiff solder joint. It could get clumsy in a 5 conductor shielded wire situation. Still, it would work in a lot of situations and it would eliminate any worries related to splice loosening or intermittent connections. All there would be is how long before the wire strands break. I could schedule a follow up wire replacement before then, maybe 3-4 years down the road at a heavy check.



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

RE: Electrical Wire Splices in High Vibration Environments.

K99...

What kind of wires do You want to repair?

This is not a trick question. Tread Lightly.

IF not strictly per an OEM maintenance document/procedure, then best You can hope for is 'no technical objection' and FAA and/or DoD supplemental approval.

AC? DC?
Analog signal/control wires?
Analog signal/control/power wires?
Digital-communications/computing quality signal wires?
Ground wires?
Low-amp and/or voltage and/or cycles?
High-amp and/or voltage and/or cycles?
Ground-power/APU/starter-generator?
HIRF/TREES/EMP/EMI/lightning/Static shielded-critical, unshielded-not-critical?
Low temp/cryogenic?
High Temp/Fire/engine-heat exposure?
High vibration clamping/mounting/connector issues?
Fail-safe/emergency/critical system?
Bone-Dry? Moist-humid? Rain/ice/snow/slush/deicing/wash water critical/saturated?
etc...
My head hurts...

BE VERY CAREFUL!

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]

RE: Electrical Wire Splices in High Vibration Environments.

Quote (A great way to create that change is to solder stranded wire.)


so soldering is out.

Quote (I see we have something called solder splices I'm not sure why we don't use them more.)


or maybe not...

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

-Dik

RE: Electrical Wire Splices in High Vibration Environments.

(OP)
dik,

Help me understand this. Crimp splice stranded wires and you have a stress riser at the crimp. How is that different than the stress riser where you have soldered stranded wire?

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

RE: Electrical Wire Splices in High Vibration Environments.

I can't make an explanation. My first posting indicated means of splicing that I have seen, I missed using heat shrink tubing. I don't know the merits of each kind of connection. For high voltage stuff, I've seen heavy duty clamping devices... but that's it. I've also seen cadweld splices... the thread is a bit of a learning process for me.

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

-Dik

RE: Electrical Wire Splices in High Vibration Environments.

I guess you have tried digging though your existing data stack for OEM field mod's / STC's that resulted in wiring splices in similar areas with similar wires, and using the "its no worse than what the OEM did there".

When supporting 20 year old plus 737 classics I don't recall anyone complaining about bad splices, plenty of bad rack pins, brunt earths & mechanical damage.

My Electrical knowledge is pretty rough but I seem to recall the mantra of reliable wiring looms is something like "Strain Relief, Strain Relief,& more Strain Relief", how was the strain relief incorporated in the factory looms near factory splices, hand tied lacing or did they do something fancy?

RE: Electrical Wire Splices in High Vibration Environments.

OK - when a bunch of fine wires is soldered together they form a rigid rod of whatever the original diameter of the overall wire was. This means that the outer wires of that rod see the entire tension load from any bending that happens.

With a crimp the bundle of wires is deformed so it's no longer rod shaped and allows a more even distribution of the strain of bending. In addition, the crimp normally also contains an integral strain relief that prevents bending at the crimp.

To help out solder splices have the outer shell of the adhesive heat shrink extend 5-10 wire diameters on either side of the solder volume easing the strain transition. If one simply takes wires, lays them side by side and solders, and then uses a typical shrink sleeve, it doesn't provide nearly that amount of strain relief that a solder splice does. A worse condition - soldering into a connector pin for which no strain relief at the pin can be created.

A feature of stranded wire to pay attention to is that it is usually twisted inside the jacket. The twist is what allows the wire to be flexible - it continuously shifts each strand from being under tension to under compression throughout a bend, equalizing the load. Crimping or soldering stops the ability to shift at that spot by fixing the strands, hence the importance of strain reliefs.

Further, it's important in cables that are intended to flex to repeat that twist. I've seen parallel strand cable that, when a shrink sleeve is applied becomes as stiff as a baseball bat and, if flexed, will destroy the connections or just fatigue the outer fiber wires. So, get the cable layout engineers to ensure that wires have some amount of twist if flexure for shipping/storage or installation is going to be required.

Why are solder splices so popular? Only one tool is required to install them - a heat gun (or a butane lighter for the truly daring.) And they can be installed in places where a crimping tool would be really inconvenient. They aren't necessarily bad, but they do require a little more care than crimps in terms of fixing the rest of the wire and potentially the cable bundle to keep it from flexing.

RE: Electrical Wire Splices in High Vibration Environments.

Sigh... another area I am all-to-familiar with...

WindWright...

Your reference links [19 Jan 22 03:44] are old/marginal... and relate to a study-group/program ended by the FAA.

K99...

Aging aircraft wiring is has been fairly-well studied and there are several good reports for inspection/detection/evaluation of aged/deteriorated wiring. Still You MUST KNOW/UNDERSTAND the system to REPAIR any element of the system. Electrical/electronic interconnect-wire damage can be insidious... it can be at one discrete location... or a hundred places on the same physically damaged or age-deteriorated wire(s)

'Generic' wire repairs are well-established... but not necessarily appropriate... especially with 'deteriorated' or overloaded/damaged wires.

Often the best repair for damaged wires are to simply disconnect/dyke them... IE: remove them from connector pin arrays [make them 'dead'] in large wire bundles... and over-lay new/replacement wires on the harness, connector-to-connector.

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]

RE: Electrical Wire Splices in High Vibration Environments.

While on this subject... two books by a Lufthansa Avionics engineer are well worth reading. Here are my book reviews of his unique experiences, that are documented in 'short story format'.

[A] I, AVIONICS ENGINEER, MARIJAN JOZIC, 2007
[B] YOU, AVIONICS ENGINEER, MARIJAN JOZIC, 2012

https://www.lulu.com/shop/search.ep?keyWords=marij...=
MARIJAN JOZIC IS A HIGHLY RESPECTED AIRLINE AVIONICS-MOD ENGINEER/MANAGER. HE LOVES THE AVIONICS-MOD BUSINESS [FOR MANY REASONS] AND IT SHOWS… EVEN WHEN SITUATIONS ARE HEAD-SHAKING CRAZY AND EXHAUSTING TO ENGINEERS AND TECHNICIANS. THESE BOOKS ARE NOT ON THE SCIENCE AND TECHNOLOGY OF AVIONICS ENGINEERING: THAT’S 'THE EASY STUFF'!! THESE BOOKS RELATE TO THE REAL-WORLD BUSINESS-DRAMA, ART AND HUMAN-FACTORS INVOLVED WITH AVIONICS ENGINEERING: THE MAKE-OR-BREAK INTRICACIES, FALLICIES/REALITIES, FRUSTRATIONS, ETC OF TRYING TO GET ‘AVIONICS MODS DONE’. IN THE MANY SHORT CHAPTERS [ACTUALLY ARTICLES PUBLISHED IN MAGAZINES THRU THE YEARS], MARIJAN RELATES REAL-WORLD SITUATIONS AND THEIR CONSEQUENCES AND OUTCOMES… AND SOMETIMES POST-MORTEMS… LIKE NO-ONE-ELSE. THE 'AH-HA' LESSONS-TO-BE-LEARNED FROM THESE TWO BOOKS WILL MAKE A DEEP IMPRESSION AND WILL PROBABLY STAY WITH YOU A LIFETIME… AND MIGHT JUST HELP YOU HAVE A LONGER, MORE-SATISFYING CAREER!!!
OBVIOUSLY MARIJAN IS SPEAKING IN A FOREIGN LANGUAGE THAT WAS SOME-WHAT ROUGHLY TRANSLATED TO ENGLISH: HOWEVER THE WRITING STYLE ‘WORKS’ TO DELIVER CLEAR/PRECISE INTENT THRU WELL-TOLD, VERY PERSONAL, STORIES

NOTE. One of the 'experiences' Marijan related was a serious in-flight electrical/electronics problem, that could Not Be Duplicated [CND] on the ground by any conventional testing. It wasn't until an engineer was so frustrated with troubleshooting... with the test equipment hooked-up/running... that he 'slammed' the avionics rack where the 'system boxes' were mounted... and OMG... got a defect response. He repeated the 'rack-slamming' exercise several times... from different directions, at different places... and finally determined approximately were the defect [component/wiring?] was located for further/carful teardown and detailed inspections!

EE-EL/AE LL = when all-else fails 'give it a solid thump'.

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]

RE: Electrical Wire Splices in High Vibration Environments.

(OP)
I appreciate everyone’s comments. As an engineer that supports the maintenance division at a part 121 operator, we know what we can legally do and not do. Our job is providing 24x7 support globally. There are always at least 4 engineers on duty: structures, systems, avionics, and power plants. Large parts of the policy manuals that describe what our engineering group can and cannot do are FAA approved.

We of course understand the signals. For us that is not as much an issue, all we have to do is follow the OEMs standard wiring practices. We have all the specs though. The only newish thing are the fiber optics cables and we ran them on our own.

Usually, the make or break question is how critical a wire is to the operation of a system from a flight safety standpoint. A lot of the approvals we get into are to supplement our use of FAA Minimum Equipment Lists which are FAA STCs (FAR 91.213). We don’t have the authority to change any FAA data or make any FAA Major Alterations or Repairs.

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.

I’m a big fan or all the aging wire activity that took place, all the SFAR 88 activity, and all the EWIS attention. It was overdue. I saw it firsthand in my early carrier as a mechanic for Eastern airlines many years ago. The very worst I saw was working out of Miami’s corrosion corner after Eastern. To be perfectly frank the aging wire problem is better described as neglected wiring. It was not uncommon to see layers of dirt and sheet metal shavings on wiring raceways that had been undisturbed for years.

Some of those problems still persist in General Aviation today. I rewired a lot of my own airplane because of it. Time and again I’ll see someone doing something like an engine change where they have it opened up and I’ll take a look at the wring. All too often it looks like the blazes. The individual doing the work doesn’t want to hear about it. Often the owner/pilot is part of the problem.

I met Marijan Jozic, years ago. The maddening troubleshooting efforts he describes are the situations we assist with weekly. We’re working on one today. No idea what caused the alerts. We banged away at it for a few weeks last month. It flew fine for a dozen times, now it’s back.

I remember years ago, we taxied a Jetstream 32 out to the Miami run-up area. I was still assembling something in a panel just behind the cockpit to save time. I moved a bundle of wires, one of the guys in the cockpit got real excited and shouted back asking me what I had just moved. Working with the guys in the cockpit and pushing on various wire bundles in the panel we located a bundle that, when pushed would fix a long standing problem. We taxied back and took it apart to find a pin not completely locked in it’s connector that had partially worked it’s way out. A lot of times, you just keep banging away until someone on the plane gets lucky.

Back on topic, It would be great if someone had real data on splices. Has anyone tested splices to failure? How do they fail?

I suspect the OEMs now build an airplane making sure there are very few splices if any in certain areas because they are likely a source of problems a couple decades in the future. I just want something to hang my hat on to get labor intensive wire replacements off a check that can’t be accomplished in reasonable time if we need to take power off the airplane for a week.




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

RE: Electrical Wire Splices in High Vibration Environments.

2
My Go-to's for wiring knowledge, inspections, repairs etc... Can't help myself...

USAF T.O.s
1-1A-14 Installation and Repair Practices - Volume 1 - Aircraft Electric and Electronic Wiring
1-1A-14-2 Installation and repair practices. Vol. II, Aircraft circular electrical, connectors and accessories
1-1A-14-3 Installation and repair practices. Vol. III, Aircraft rectangular electrical connectors and accessories
1-1A-14-4 Installation and repair practices, aircraft fiber optic cabling

ARMY TM
1-1500-204-23-4 AVIATION UNIT MAINTENANCE (AVUM) AND AVIATION INTERMEDIATE MAINTENANCE (AVIM) MANUAL FOR GENERAL AIRCRAFT MAINTENANCE (ELECTRICAL AND INSTRUMENT MAINTENANCE PROCEDURES AND PRACTICES

FAA
AC43.13-1 ACCEPTABLE METHODS, TECHNIQUES, AND PRACTICES - AIRCRAFT INSPECTION AND REPAIR
AC43.13-2 ACCEPTABLE METHODS, TECHNIQUES, AND PRACTICES – AIRCRAFT ALTERATIONS
FAA AC120-94 AIRCRAFT ELECTRICAL WIRING INTERCONNECTION SYSTEMS TRAINING PROGRAM
FAA AC120-102 INCORPORATION OF ELECTRICAL WIRING INTERCONNECTION SYSTEMS INSTRUCTIONS FOR CONTINUED AIRWORTHINESS INTO AN OPERATOR’S MAINTENANCE PROGRAM
FAA-H-8083-6 ADVANCED AVIONICS HANDBOOK
DOT/FAA/AR-04-14 SHIELD DEGRADATION EFFECTS OF LOOSENED CONNECTOR BACKSHELLS OF AIRCRAFT WIRING HARNESSES
DOT/FAA/AR-04-15 COMPARISON OF VARIOUS IMPEDANCE MEASUREMENT TECHNIQUES FOR ASSESSING DEGRADATION IN WIRING HARNESS SHIELD EFFECTIVENESS AND A FIELD
DOT/FAA/CT-TN94/55 ELECTRICAL SHORT CIRCUIT AND CURRENT OVERLOAD ON AIRCRAFT WIRING
FAA AIRCRAFT EWIS PRACTICES JOB AID 2.0 AIRCRAFT ELECTRICAL WIRING INTERCONNECT SYSTEM (EWIS) BEST PRACTICES - JOB AID
FAA AIRCRAFT WIRING PRACTICES - AN INTERACTIVE TRAINING AND SELF-STUDY COURSE (25827)
FAA FSAW 2-10 ELECTRICAL WIRING INTERCONNECTION SYSTEM (EWIS) PROTECTIONS AND CAUTIONS DURING MAINTENANCE AND ALTERATION

AG CASA AC 21-99 AIRCRAFT WIRING AND BONDING

ASTM F2639 STANDARD PRACTICE FOR DESIGN, ALTERATION, AND CERTIFICATION OF AIRCRAFT ELECTRICAL WIRING SYSTEMS [GA ACFT]
ASTM F2696 STANDARD PRACTICE FOR INSPECTION OF AIRCRAFT ELECTRICAL WIRING SYSTEMS [GA ACFT]
ASTM F2799 STANDARD PRACTICE FOR MAINTENANCE OF AIRCRAFT ELECTRICAL WIRING SYSTEMS [GA ACFT]

MIL-HDBK-522 GUIDELINES FOR INSPECTION OF AIRCRAFT ELECTRICAL WIRING INTERCONNECT SYSTEMS
MIL-HDBK-525 ELECTRICAL WIRING INTERCONNECT SYSTEM (EWIS) INTEGRITY PROGRAM
MIL-HDBK-535 GUIDELINES FOR TROUBLESHOOTING OF AIRCRAFT ELECTRICAL WIRING AND INTERCONNECT SYSTEMS (EWIS)

NASA-STD-8739.4 WORKMANSHIP STANDARD FOR CRIMPING, INTERCONNECTING CABLES, HARNESSES, AND WIRING

AFRL/MLSA [SLENSKI] AIRCRAFT WIRING SYSTEM INTEGRITY INITIATIVES http://wire.nasa.gov/participating_orgs/RTO%20BF%2...

NIAR-ASP AGING AIRCRAFT WIRING FAULT DETECTION SURVEY http://citeseerx.ist.psu.edu/viewdoc/summary?doi=1...
NPGS THESIS AGING AIRCRAFT WIRING: A PROACTIVE MANAGEMENT METHODOLOGY
MASTERS THESIS EVALUATION OF DETERIORATION OF THE AIRCRAFT ELECTRICAL WIRING SYSTEM DUE TO UNDETECTED ARCING EVENTS [HAU T. BUI]

RESEARCHGATE PAPER A SURVEY ON ARC FAULT DETECTION AND WIRE FAULT LOCATION FOR AIRCRAFT WIRING SYSTEMS
RESEARCHGATE PAPER ARC FAULT SIGNATURES DETECTION ON AIRCRAFT WIRING SYSTEM

AIAA
91-3137 AIRCRAFT WIRING DAMAGE - DEVELOPMENT OF A COMPUTERIZED ASSESSOR AID

SAE
AIR6808 AEROSPACE VEHICLE WIRING, LESSONS LEARNED
AIR6820 ELECTRICAL WIRING FUEL COMPATIBILITY
ARP6216 EWIS WIRING INSULATION BREAKDOWN TESTING
AS50881 WIRING - AEROSPACE VEHICLE
SAE/TP 2006-01-2410 WIRING ASSESSMENT OF AGING COMMUTER CLASS AIRCRAFT [NIAR]
SAE/TP 2008-01-2870 A SURVEY ON ARC FAULT DETECTION AND WIRE FAULT LOCATION FOR AIRCRAFT WIRING SYSTEMS
SAE/TP 2008-01-2932 INTERMITTENT FAULT LOCATION ON LIVE ELECTRICAL WIRING SYSTEMS

OK I'm tired, gotta-go.

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]

RE: Electrical Wire Splices in High Vibration Environments.

Nice list... you deserve a nap...

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

-Dik

RE: Electrical Wire Splices in High Vibration Environments.

(OP)
WK, I appreciate the list. Some of course, I've already clawed to pieces, many are intriguing and new to me.

I have have more tales from the crypt. Seems like once you tap into that, they just flow. Couple doozies; tripping breakers due to fuselage flex that happened within a few hundred feet of the same altitude consistently. Fuselage chafing issues require hand over hand inspections to locate. It can make a lot of work and ground time on big airplane with a tight cockpit. One time we did install 5 temporary breakers and flew a non-rev test flight to narrow the work down. It worked great.

A megger will detect chaffed wire laying close to a fuselage. We have a lot of group calls. On one such call I heard the tech say, something is wrong with the megger after megging one particular wire run to ground. I suggested that was the megger telling us that was where we need to look. They didn't want to open that area up, and warned us about the lengthy ground time we were suggesting. They finally did check and found the chafing within a couple hours. With the megger, on an airplane, if you don't see infinite resistance, replace the components. Don't use too high a test voltage though.

We had an airplane with altimeters that always seemed to go crazy at a certain altitude. Understand, Above 18000 ft, pilots stop using MSL altitudes and start using flight levels (FL). That is under 18000 ft, the crew needs to adjust baro offset to local pressures. Above, it just stays at 29.92 in hg.

The baro offset signal from the altimeter to the air data computer was a synchro output. The Air Data Computer ADC used the synchro input to develop a corrected altitude which was sent back to the indicator on a 429 bus. At a certain altitude the altimeters would flag and unwind a turn or two. We flew a couple Mx test flights with a bus reader and a scope and could see the bus data change mid flight for no apparent reason. We were at it for weeks. Finally we replaced all the associated wiring.

Just before the 10th-11th? test flight, the window heat controller flagged. We all assumed it was a don't care for this flight, we were thinking pressure related changes. So that window heat was deactivated, the crew flew it, we stayed at warmer altitudes, it passed no altimeter faults. We RTB, got our stuff and climbed on for the ride home.

Between flights Mx had done a bite check on the window heat controller that flagged earlier and it passed, so they left it in. Half way home the crew called me into the cockpit to show me that the altimeters flagged when window heat was turned on. When we landed at home field, we went through every gyration we could to make it happen on the ground. Ice on the window wouldn't do it. Turns out that unit has a high heat mode that kicks on below a certain OAT. No way to get it into high heat mode on the ground. I believe it was activation of that high current mode and some internal filter fault that introduced noise on the 115 VAC power bus and that noise passed through to the 26VAC(?) corrupting the synchro reference signals .

What the altimeter needles were doing was fluctuating between FL and MSL because the ADC defaults to FL altitudes if the offset is lost. That was literally weeks of TS on site and more MX test flights than I have ever seen.

We also have a long running office joke on the "lucky relay" fixes. Some of those I could never piece together after the fact. Still, it's the engine guys that have the best Hall of Fame stories. I wont try to steal their thunder here.




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

RE: Electrical Wire Splices in High Vibration Environments.

In the 'for-what-its-worth' column...

Many Years ago [~mid-1990s] I recognized that most enginerds... service, liaison, design, stress and [oddly/sadly] EE/EL/AE... like me at that time... were woefully ignorant on this topic. Even basic go-to 'Duhhhh' references seemed obscure and unknown to us.

Then I had to assist some EE/EL/AE shop techs [MIL-NCO and civilians]... and just/only was barely able to help with the basics of interconnect wiring in-aircraft: black boxes 'and other stuff' were [are still mostly] a 'mystery meal' to me. BUT I knew back-shop guys in the local 'depot' and the flying wing... and of course most 'wrench-turners/crew-dogs'... and became a go-between to solve odd problems. These shop-guys [men/women, actually] took pity-on-me-over-the-years and taught me a lot of basics... including finer-aspects of workmanship... especially for signal-critical areas/wiring/connectors/etc of ANALOG control system elements [F-15A-thru-Ds, F-16s, etc]. I became 'just smart-enough' so I could back-them-up against in their struggle with NOT-SO-supportive [stateside] Depot engineers/techs who... often failed to grasp need for rapid-response to 'short-fuse' field issues to keep the fleets flying FMC, safely.

Sigh.... These were some truly smart/talented/dedicated techs! I miss them all... well, maybe not ALL of them.

I started a short cheat-sheet-list of useful USAF T.O.s and MIL-documents at that time... which lingered in obscurity/who-cares to most all-others. Then I left USAF-CS and went to work at my current company... and began stumbling-over/onto/around amazing EE-EL-AE-and-related-stuff... everywhere in my searches for mechanical and structural stuff. I couldn't ignore what I was seeing... So I started growing my list. Just imagine some of the odd topics EE-EL-AE's butt-up-against. Hmmmmmmm???? The 'list' is now 3xx-pages long in WORD... and NO I won't publish this full list outside of want/need-to-know within my company.

OH YEAH... I've started similar lists for mechanical and structural and fuels... but the EE/EL/AE list is still my 'most-challenging one'.

My 'most favorite/fun' list is 'Quotes, Truisms, Humor, Native Wisdom, etc...Worth-Remembering' [now almost 600-WORD pages after +20-years].

I can relate to Einstein when he said... "I have no special talent. I am only passionately curious."

I promise I'll never repeat this litany again. Gotta go back to work.

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]

RE: Electrical Wire Splices in High Vibration Environments.

Quote (kontiki99)

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.

It's not that cut-and-dried. I can do it all, not because I work for an operator, but because I work with an engineering organization with authority delegated to make the approval, hold the approval, and change the approval. We don't skirt supervision of the regulator, but it's a "keep informed" relationship. This is the privilege that a certain company named "B" abused, and serves as a lesson to me in particular.

Quote (kontiki99)

Back on topic, It would be great if someone had real data on splices. Has anyone tested splices to failure? How do they fail?

Don't the Mil-spec splices have a "spin test"? That suggests one method to demonstrate the life of a splice. Even if it's not necessarily what typically causes them to fail.

Thank you for the accounts of wire neglect and troubleshooting. Do you write about your observations in media other than this forum? Give me something I can use professionally and I can motivate people here with stories like these.

RE: Electrical Wire Splices in High Vibration Environments.


WW...

OK, I have access to a lot general MIL EE-EL wire repair procedures... as I have PARTIALLY detailed, above... which has been quit useful to ME solving wiring problems.

ALSO, I have access to a lot of military and corporate 'confidential and proprietary' data [all kinds] that I can never reveal. GOOD LUCK getting someone to send proprietary data Your way. That kind of stuff is hard-earned and tightly held for MANY good reasons.

Quote (Thank you for the accounts of wire neglect and troubleshooting. Do you write about your observations in media other than this forum? Give me something I can use professionally and I can motivate people here with stories like these.)


NOTE. Just because You are frustrated at the lack of 'hard/substantive data' for EWIS repairs... which we are not serving you on a silver platter... don't get testy... this really is a tough and somewhat obscure subject.

BTW... WW I am curious...

Kontiki99 was the 'one who presented this topic/issue/question to this forum... but you are now suddenly HOT about it... what burr got under Your collar?

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]

RE: Electrical Wire Splices in High Vibration Environments.

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.

RE: Electrical Wire Splices in High Vibration Environments.

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

RE: Electrical Wire Splices in High Vibration Environments.

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]

RE: Electrical Wire Splices in High Vibration Environments.

(OP)
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/NN...

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.

RE: Electrical Wire Splices in High Vibration Environments.

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.

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