Oct 1, 2025
You can win or lose a certification on the length of a wire and the choice of a connector.
You know the stakes when you design wire harnesses for aircraft de-icing systems. These harnesses carry high currents, survive thermal shocks, sit where fluids and abrasion take their toll, and must pass strict certification checks. Small mistakes early on become big rework later, and you end up juggling safety, schedule, and budgets.
What if you could avoid the seven technical mistakes that most often trip teams up? What would happen to your lead times, your test cycles, and your warranty claims if you caught these risks before fabrication? Which rule, if enforced at the start, would save you the most risk and cost?
This article walks you through the errors that happen at each stage of the design lifecycle, in the order you are likely to make them. You will get pragmatic fixes, test protocols, and real examples to help you deliver harnesses that pass certification, survive de-icing operations, and remain maintainable in service. You will also see where digital tools like Cableteque’s Quoteque reduce human error and speed decisions by extracting BOMs, mapping alternates, and flagging single-source risk during quoting, which can shorten quoting from days to minutes, according to Cableteque internal product materials ([Quoteque overview].
Table of contents
Preparation: underestimating thermal loads, inrush currents, and ampacity
Preparation: choosing non-qualified connectors or contacts
Preparation: ignoring compatibility with de-icing fluids and extreme temperatures
Execution: poor EMI and EMC management near avionics and sensors
Execution: inadequate routing, support, and chafe protection
Finalization: insufficient documentation, traceability, and test planning
Finalization: failing to plan for supply chain variability and part substitution
1) Preparation: underestimating thermal loads, inrush currents, and ampacity
Why this is problematic
You often start by sizing wires to the steady current of the heater element, because that is what the spec sheet highlights. That feels logical, until the unit cycles on and drags large inrush currents. Relays, terminals, and fuses that were selected for continuous current overheat or trip. Voltage drop over long runs weakens heating effectiveness at the skin, and overheating at a connector can go unnoticed until it causes damage.
Tips and workarounds
Model both steady state and transient loads. Include inrush duration and duty cycles in your calculations, not just average power. Use circuit simulation or bench measurements to capture real waveforms during start-up.
Size conductors and contacts for peak currents, then apply derating for bundling and ambient temperature using recognized guidelines such as SAE wiring derating tables and installation practices [SAE AS50881].
Introduce staged switching or soft-start circuits to limit peak stress on switching devices, or use inrush-limiting resistors or NTCs where appropriate.
Validate with thermal soak tests. Measure contact temperature rise under load and document results for certification evidence, following environmental test planning in DO-160 guidance [RTCA DO-160 overview].
Real example
A Contract Manufacturing partner reported a boot-style electrothermal system that drew multiple times the steady-state current at turn-on. The team upsized a few critical legs and added an inrush limiter, which stopped repeated fuse trips during ground checks. That case study and tool-driven quote workflow are discussed in Cableteque materials [Cableteque case examples].
2) Preparation: choosing non-qualified connectors or contacts
Why this is problematic
You may be tempted to reuse a lower-cost connector family to hit a delivery date. In the field, those connectors might corrode from de-icing fluids, loosen under vibration, or develop high contact resistance that heats and accelerates wear. A marginal connector can be the single point failure in an otherwise robust harness.
Tips and workarounds
Pick aerospace-qualified connectors and terminals with appropriate environmental, vibration, and thermal ratings. Request vendor qualification data up front.
Check contact plating and retention specifications, to prevent fretting corrosion and intermittent contact.
Specify sealing measures like O-rings or grommets when the harness sees glycol or water spray.
Require vendor test data, mating cycle life, and shock and vibration test records in the approval package.
Include connector verification in your lab qualification sequence. Do not rely solely on datasheet claims.
Real example
An OEM experimented with a lower-cost commercial connector to avoid a six-week lead time. During qualification humidity and fluid exposure tests failed, forcing a chassis redesign and an eight-week delay. The premium for aerospace-grade connectors would have been lower than the cost of rework and schedule slip.
3) Preparation: ignoring compatibility with de-icing fluids and extreme temperatures
Why this is problematic
Insulation, gaskets, and seals can degrade quickly when exposed to glycol-based de-icing fluids, hydraulic fluids, or aggressive cleaning agents. Materials that perform well at room temperature might crack, swell, or lose dielectric properties after repeated exposure and thermal cycling.
Tips and workarounds
Select materials with proven chemical resistance to the actual fluids in service. Ask suppliers for compatibility data and certificates of analysis.
Use high-temperature insulations, such as PTFE or polyimide, near heater elements or exhaust paths.
Run fluid-exposure and thermal cycling tests on candidate materials, and document the outcomes for certification records. Incorporate DO-160 environmental categories into your test plan [RTCA DO-160 overview].
List approved material families in your specifications to prevent unauthorized substitutions during build.
4) Execution: poor EMI and EMC management near avionics and sensors
Why this is problematic
De-icing circuits switch high currents and can create conducted and radiated noise. If you route power harnesses near sensitive avionics or sensor runs, you increase susceptibility risk. EMI can be intermittent and hard to trace, and it can appear only under certain flight regimes or power conditions.
Tips and workarounds
Plan harness segregation from the start. Keep high-power runs separate from signal and communications cables.
Use shielded cables and drain wires for sensitive signals. Ensure shields are terminated properly to structural grounds.
Add suppression devices like TVS diodes, RC snubbers, and common-mode chokes at switching nodes.
Include conducted and radiated emission and susceptibility tests in your qualification plan, and perform ground checks with representative loads.
Document bonding and grounding strategies, including chassis tie points and bonding strap locations, so maintenance does not inadvertently remove a required connection.
Authoritative guidance
EMC and emissions tests are covered under DO-160. Practical design guidance and examples of virtual routing to test EMI separation can be found in industry articles [Assembly Magazine harness design dos and donts].
5) Execution: inadequate harness routing, support, and chafe protection
Why this is problematic
Routing and clamp decisions during the harness assembly stage determine long-term survivability. Poor clamp spacing, insufficient strain relief, and lack of chafe protection create wear points that fail in service, often under vibration and thermal cycling. These errors are frequently the dominant cause of mid-life harness failures.
Tips and workarounds
Define routing rules in your harness specification: clamp spacing, minimum bend radii, separation from moving parts, and required service loops.
Add abrasion protection at pass-throughs and near sharp interfaces using sleeving, convoluted tubing, or abrasion pads.
Plan strain reliefs at connectors and provide access panels or removable fairings for inspection and maintenance.
Use virtual routing tools during the design phase to capture actual geometries, get accurate lengths, and validate clamp locations before fabrication. Teams that adopt virtual routing report fewer build errors and more accurate length estimates, reducing scrap and late changes [Zuken harness routing guidance].
Standardize labeling and documentation to make maintenance faster and error free.
6) Finalization: insufficient documentation, traceability, and test planning
Why this is problematic
A harness that is not documented with clear build sheets, terminal lists, and test plans becomes a liability. Troubleshooting takes longer, certification records are incomplete, and assembly shops make mistakes when revisions are not properly controlled.
Tips and workarounds
Produce complete harness build sheets, connector pin lists, and step-by-step assembly instructions.
Develop and run a comprehensive test plan, including continuity, contact resistance, insulation resistance, hipot, and functional thermal tests.
Include environmental tests required by DO-160 where applicable: vibration, thermal cycling, humidity, and fluid exposure [RTCA DO-160 overview].
Implement traceability for parts, including lot numbers and supplier certificates. Keep version control for drawings and BOMs.
Perform a design FMEA for the harness to capture likely failure modes and mitigation plans.
Practical step
Make your test protocols part of the release criteria. No harness leaves the factory without passing the documented acceptance tests and being traceable to component lot numbers. Systems that enforce release gating in software reduce human workarounds and lost records.
7) Finalization: failing to plan for supply chain variability and part substitution
Why this is problematic
A single obsolete terminal or long-lead connector can pause production. Worse, an unauthorized substitution can introduce a new failure mode. Supply chain shocks are routine, and engineering teams must design for resilience.
Tips and workarounds
Maintain approved alternates in the BOM, with source preference rules and qualification status documented.
Map customer part numbers to manufacturer numbers and track availability in real time. Digital part mapping reduces errors and speeds procurement decisions, and automated alerts can flag long lead or EOL conditions early.
Qualify alternate vendors for critical parts well before they are needed.
Require procurement and engineering to collaborate on long-lead and single-source parts early in the project.
Consider stocking critical long-lead components where allowed by program economics.
How tools help
Digital solutions that capture part mappings, supplier availability, and tribal knowledge reduce the chance of an unqualified substitution. Cableteque’s Quoteque automates BOM extraction from PDFs, maps customer and manufacturer part numbers, and applies rules for alternates and single-source risk during quoting, which helps you catch supply issues before they affect build schedules [Quoteque overview], [Cableteque supply chain article].
Key takeaways
Size conductors for peak and transient currents, and apply derating for bundling and ambient temperature, using recognized standards [SAE AS50881].
Choose aerospace-qualified connectors and verify sealing and contact plating with vendor test data.
Test materials for compatibility with de-icing fluids and thermal cycles, and document acceptance according to environmental test categories in DO-160 [RTCA DO-160 overview].
Plan EMC segregation early, and include suppression and bonding in the harness design to reduce intermittent failures.
Formalize routing and chafe protection rules, and use virtual routing tools to validate lengths and clamp locations before committing to tooling.
Require full build documentation, traceability, and a complete test plan as release criteria.
Maintain approved alternates and real-time vendor visibility to avoid supply chain-driven delays, and use digital quoting tools to surface risks before procurement commitments.
You will avoid the most common errors if you build discipline into three phases: preparation, execution, and finalization. Catching misconceptions in the preparation phase saves rework during execution. Validating routing and test plans during execution prevents escapes into service. Locking down documentation and supply resilience during finalization stops production interruptions.
Would you like a one-page harness checklist tailored to your de-icing architecture? Would a demo showing how Quoteque extracts BOMs from PDFs and maps alternates save your next program weeks? Which mistake on this list would you tackle first to cut risk on your current project?
Faq
Q: What standards should I consult when designing de-icing harnesses?
A: Start with RTCA DO-160 for environmental testing and SAE AS50881 for wiring installation practices. These documents define test categories and installation rules that affect material selection, derating factors, and harness routing. Also consult FAA advisory circulars and the aircraft type certificate holder’s wiring requirements early, because program-specific rules can supersede general guidance ([FAA advisory circulars](https://www.faa.gov/regulations_policies/advisory_circulars)).
Q: How do I size a wire for a heater with high inrush current?
A: Model both the steady-state current and the turn-on inrush, including duration and duty cycle. Size the conductor and switching contacts for the peak current, then apply derating for bundling and ambient temperature. Consider soft-start or staged switching to reduce peak stress. Validate choices with thermal tests and contact temperature measurements.
Q: How can I reduce EMI risks from heating circuits?
A: Maintain physical separation from sensitive signal harnesses, use shielded cables where needed, and add suppression components such as TVS diodes and common-mode chokes at power entries and switching nodes. Ensure proper bonding of shields to structure and include conducted and radiated EMC tests in your qualification plan.
Q: What documentation should leave the factory with each harness?
A: Each harness should have build sheets, wire and terminal lists, connector pin-outs, inspection records, and test certificates. Include supplier lot numbers and test results for critical parts, and archive test logs for certification evidence. Use revision control so assembly teams always work from the correct documents.
Q: How do I guard against part obsolescence causing production stops?
A: Maintain an approved alternates list in your BOM and qualify secondary vendors early. Map and track customer part numbers to manufacturer part numbers and watch supplier inventories. Where program economics allow, hold safety stock for single-source long-lead items. Use digital tools that alert you when a part becomes long lead or obsolete.
Q: When should I bring manufacturing and procurement into design reviews?
A: Bring them in early, during conceptual and preliminary design. The biggest mistakes are translation errors from functional requirements to manufacturing reality. Including manufacturing and procurement in design reviews reduces late ECOs, clarifies lead-time risks, and surfaces alternates before you commit to a single source.
