E - Electronics (Avionics)Chapter 9 · 25 practice questions

Chapter 9: EWIS - Zonal Inspections, Chafing, Degradation, Aging Aircraft

Includes 7 animated diagrams — view them live in the interactive theory reader.

Diagram — EWIS - Zonal Inspections, Chafing, Degradation, Aging AircraftSkydrol fluidChemical insulation degradationClean with approved solvent;inspect for damage; replace ifdegradedGreaseChemical attack; dirtattractionClean with approved solvent;inspect insulationSalt depositsElectrical tracking;accelerated corrosionClean with distilled water;inspect for damageSticky residues fromnon-approved tapeConductive paths; chemicalattackRemove residue; inspectunderlying wires

Regulatory Framework and Standard Practices

CARs Standard 571 Requirements

Standard 571.02 - Maintenance Standards:

  • All maintenance must be performed to a standard that ensures continued airworthiness
  • Work must follow manufacturer's recommendations or standard industry practices
  • Non-approved repairs or modifications are not acceptable regardless of mechanical soundness

Standard 571.06 - Repairs and Modifications:

  • Repairs must use approved data (manufacturer's instructions, AC 43.13-1B, STC data)
  • Modified areas require EWIS compliance verification with approved installation data
  • Fire zone repairs require appropriate fire-resistant materials

AC 43.13-1B Guidance

Chapter 11 - Wire Installation:

  • Wires must be protected from chafing against sharp edges
  • Tie-wraps should be snug but not deform insulation
  • Proper support spacing and routing clearances required
  • Grommets required for wires passing through bulkhead holes

Chapter 12 - Corrosion Cleaning:

  • Light surface corrosion may be cleaned using approved methods
  • Wire brushes can damage plating and should be avoided
  • Terminal corrosion requires replacement

Insulation Repair Standards:

Insulation Repair — Approved Repair Decision Insulation Repair — Approved Decision Tree AC 43.13-1B Chapter 11 — EWIS Cable Repair Standards INSULATION INSPECTION Damage detected during zonal inspection Conductor damaged? YES NO APPROVED SPLICE Mandatory Requirements: • Approved crimp connector • Per AC 43.13-1B • De-energize source INSULATION ONLY Minor damage Conductor intact Heat-shrink sleeving available? YES ✓ HEAT-SHRINK SLEEVING Acceptable permanent repair NO ✗ TAPE OR LIQUID Not approved as permanent repair Temporary repair Only while awaiting harness replacement Source: AC 43.13-1B Ch.11 §11-86 — CAR 571.02 / 571.06 — Splices must use approved crimp connectors
  • Minor insulation damage (conductor undamaged): Heat shrink tubing is acceptable
  • Tape or liquid tape are not approved permanent repairs
  • Conductor damage requires approved splice installation

Inspection Techniques and Tools

Visual Inspection Limitations

Visual inspection is the primary method but cannot detect:

  • Internal conductor damage (strand breakage beneath intact insulation)
  • Insulation breakdown not visible to the unaided eye
  • Hidden chafing in bundle interiors

Advanced Detection Methods

Insulation Resistance Testing (Megger):

  • Applies higher-than-normal voltage to identify weak insulation
  • Detects chafing and damage not visible externally
  • Primary tool for identifying hidden insulation degradation

High-Potential Testing:

  • Similar principle to insulation resistance testing
  • Identifies insulation breakdown points

Thermal Imaging:

  • Detects hot spots from high-resistance connections
  • Secondary tool for chafing detection

Common Defects and Corrective Actions

Chafing-Related Defects

Chafing — Critical Zones and Inspection Chafing — Critical Zones and Inspection DANGER: No grommet Sharp metal edge Cut insulation = Arc Vibration Zone Repeated structure contact Abrasion wear (Chafing) Action: Sleeve or Re-route Clamp COMPLIANT Grommet installed Protective sleeving Adequate clearance Immediate risk (Short/Arc) Progressive degradation (Inspect) Compliant EWIS protection (AC 43.13-1B) Ref: CAR 571.02 / AC 43.13-1B Ch.11

Insulation Damage

Contamination and Corrosion

Insulation Contamination — Chemical Agents and Treatment Insulation Contamination — Chemical Agents and Treatment INSULATION DEGRADING AGENTS SKYDROL HYDRAULIC FLUID Effects: • Softening of insulation • Swelling of PVC/nylon • Chemical degradation degraded insulation GREASES AND OILS Effects: • Attract dust and debris • Create a conductive path • Long-term chemical attack conductive path SALT DEPOSITS (COASTAL) Effects: • Hygroscopic (absorb moisture) • Current leakage (tracking) • Accelerate corrosion current leakage CORRECTIVE SEQUENCE 1. CLEANING Approved solvent: • Isopropyl alcohol • Removes contamination • Thorough harness cleaning 2. INSPECTION Check insulation condition: • Softening? • Swelling? • Cracking? 3A. REPLACEMENT If insulation degraded: • Affected wire section • Approved splice • Per AC 43.13-1B Healthy insulation → no action References: CAR 571.02 · CAR 571.06 · AC 43.13-1B Ch.11 — Protection against chafing, clamps, splices Skydrol Greases Salt
Wire Degradation — Causes and Aging Cable Degradation — Causes and Aging 1. Mechanical wear by chafing Vibration Cause: Repeated contact with sharp edges, metal clamps or pipes. Visible Effect: Thinned insulation, shiny marks, exposed conductor or shield. 2. Thermal degradation Heat Source Cause: Proximity to engine, exhaust or natural aging. Visible Effect: Hardened, discolored insulation (brown/yellow), cracking, brittle to the touch. 3. Chemical contamination Skydrol / Fuel Cause: Hydraulic fluids (Skydrol), fuel, oils, solvents. Visible Effect: Swollen, softened, sticky insulation, delamination or dissolution. 4. Corrosion (Connectors/Lugs) 💧 Humidity/Salt Cause: Humidity, salt, electrolysis, dissimilar metals. Visible Effect: Green/white deposits, pitting, high resistance, overheating. Ref: AC 43.13-1B Ch.11 | CAR 571.02 | EWIS Zonal Inspection Standards

Installation Discrepancies

Aging Aircraft Considerations

Key Indicators of Aging Wiring

Aircraft with over 20 years in service require specific attention to:

Insulation Condition:

  • Hardening and embrittlement
  • Cracking, especially at bend points and supports
  • Loss of flexibility
  • Discoloration from thermal exposure

Common Problem Areas:

  • Engine fire zones (thermal degradation)
  • Wheel wells (vibration, debris, fluid contamination)
  • Wing roots (corrosion, fluid contamination)
  • High-vibration areas (chafing, loose supports)
  • Areas near heat sources (exhaust pipes, bleed air ducts)

Progressive Failure Mechanisms

Work Hardening at Sharp Bends:

Chafing — Progressive Failure to Conductor Break Friction — wear progression until failure Animated sequence of the three stages of conductor degradation under vibration — EWIS / Chapter 9 STAGE 1 — Insulation wear thinned • Insulation compressed, marked, or thinned • Conductor not exposed • Dielectric integrity compromised STAGE 2 — Conductor exposed • Insulation breached — bare conductor visible • Risk of short circuit and electrical arc • Possible stray bonding STAGE 3 — Strand failure OPEN • Strands severed by metal fatigue • Work-hardening at tight bends • Intermittent open circuit FAILURE MECHANISM — Vibration + tight bend + friction max stress vibration sharp edge friction Work-hardening: Cyclic vibration deforms the strands. The metal hardens, becomes brittle and cracks. Failure occurs at the point of max flexure. VISUAL INSPECTION AND CORRECTIVE ACTIONS Signs to look for: • Bright marks, indentations, thinned insulation • Visible conductor, fluid residue, cracks • Discoloration (yellowing) — thermal sign Corrective actions: • Eliminate the source: grommet, conduit, re-routing • Replace metal clamp with plastic clamp • Exposed conductor → approved splice (AC 43.13-1B) Canadian Aviation Regulations (CAR) 571.02 / 571.06 — AC 43.13-1B Chapter 11 — EWIS
  • Stress concentration at bend point
  • Vibration and thermal cycling cause strand fatigue
  • Internal conductor breaks while insulation remains intact
  • Results in intermittent or open circuit failures

Insulation Crack Propagation:

  • Small cracks grow under vibration and thermal cycling
  • Eventually expose conductor
  • Particularly critical in fuel tank and fire zones

Safety-Critical Considerations

Fuel Tank Areas

  • Exposed conductors are potential ignition sources
  • First action: De-energize the circuit
  • Repairs must ensure no sparking potential
  • Approved sealing and splicing methods required

Fire Zones

  • Insulation degradation is critical
  • Replacement with fire-resistant wire required
  • No temporary repairs acceptable

High-Vibration Areas

  • Missing supports create chafing hazards
  • Both wire and adjacent systems (hydraulic lines) at risk
  • Proper support restoration required

Relationships Between Concepts

Cause and Effect Chains

EWIS — Cause and Effect Chains EWIS — failure cause-and-effect chains Missing grommet sharp edge of bulkhead exposed → Friction repeated abrasion on the insulation Insulation wear thinning, marks dielectric integrity compromised Exposed conductor shielding or bare copper visible Short circuit / arc → failure or fire Chemical contamination Skydrol, greases, salt, fuel Degradation softening, swelling of the insulation Cracks surface crazing exposing the conductor Electrical fault current leakage, electric arc Clamp too tight excessive tightening of the wire bundle Compression deformation of insulation and wire strands Strand breakage fatigue rupture of the metal Open circuit loss of continuity Corrosion of connectors, lugs and bus bars High resistance pitting, oxidation of contact surfaces Heat localized heating at the connection point Failure Failure chains — overview Failure progression Mechanical / Chemical
  1. Missing grommet → Chafing → Insulation wear → Conductor exposure → Short circuit/arcing → System failure/fire
  2. Chemical contamination → Insulation degradation → Crack formation → Conductor exposure → Electrical fault
  3. Over-tightened tie-wrap → Insulation compression → Internal conductor stress → Strand breakage → Open circuit
  4. Corrosion on terminal → High resistance → Voltage drop → Heat generation → Further degradation → Connection failure

Inspection Priority Relationships

  • Zonal location determines risk: Wheel wells and engine bays have higher chafing and contamination risk than avionics bays or passenger cabins
  • Aircraft age increases inspection scrutiny: Older aircraft require more attention to insulation condition and progressive damage
  • Environmental factors compound degradation: Coastal operations increase corrosion risk; high-temperature operations accelerate insulation aging

Regulatory Compliance Relationships

  • Mechanical soundness ≠ Airworthiness: Non-approved repairs must be corrected regardless of apparent functionality
  • Root cause correction required: Addressing symptoms without eliminating the cause (e.g., taping over a sharp edge) is not acceptable
  • Documentation accompanies correction: Defects must be corrected AND properly documented

Summary of Critical Actions

This comprehensive approach to EWIS zonal inspections ensures that aircraft wiring systems maintain their integrity throughout the aircraft's service life, preventing electrical failures that could compromise safety.

Diagram

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