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How to Inspect Aviation Cable for Wear and Fray: A Safety-Critical Gu...

Aviation cable (also known as aircraft cable or wire rope) is the silent workhorse of aircraft control systems, landing gear, lift mechanisms, and countless other critical applications. Its failure can have catastrophic consequences. Regular, meticulous inspection is non-negotiable for safety. Here’s how to do it correctly:

Why Inspection is Vital:

Cables are subject to fatigue, abrasion, corrosion, and overload, often in hard-to-see areas.
Even minor damage significantly reduces strength.
Failure in flight or under load is unacceptable.

Tools You’ll Need:

Clean, lint-free white cotton cloths or shop towels
Bright, adjustable light source (flashlight or task light)
Magnifying glass or loupe (10x magnification is often recommended)
Ruler or caliper (for measuring diameter)
Mirror (for inspecting hard-to-reach areas)
Good Recordkeeping: Pen/paper or digital log.

The Inspection Process: Step-by-Step

Preparation is Key:
- Ensure Safety: Follow all lockout/tagout (LOTO) procedures if applicable. Ensure the system is isolated and under zero tension or load during inspection.
- Clean Thoroughly: Wipe the entire length of the cable section you’re inspecting with a clean, white cloth. Dirt, grease, or grime can hide defects. Examine the cloth afterward – red dust (iron oxide) indicates rust forming inside the cable. This is a serious red flag.
Visual Inspection – The Foundation:
- Look Closely: Under bright light, slowly and methodically run the cable through your fingers while visually examining its entire surface.
- Check the Full Length: Pay special attention to:
  - Terminations: Swages, sockets, nicopress sleeves, thimbles. Look for cracks, deformation, slippage, or corrosion at the entry/exit points where the cable enters the fitting.
  - Contact Points: Anywhere the cable runs over pulleys, fairleads, guides, or through conduits. These areas suffer the most abrasion.
  - Bends: Cable subjected to tight bends or frequent flexing points.
- Key Defects to Spot:
  - Broken Wires: The most critical finding. Run the cloth slowly over the cable – broken wires will often snag the cloth or be readily visible as sharp ends sticking out. Any broken wire is grounds for immediate replacement. Pay extra attention near fittings and contact points. A magnifying glass is essential here.
  - Wear (Loss of Diameter): Measure the cable diameter periodically at points known to experience wear (e.g., over pulleys) and compare it to the cable’s original specified diameter. General Rule: Replacement is mandatory if wear reduces the diameter by more than 5-10% below nominal size (Consult your specific aircraft/service manual or component manual for the exact tolerance – NEVER GUESS).
  - Corrosion: Look for rust stains, pitting, or discoloration. White powder can indicate zinc corrosion on galvanized cable. Severe pitting drastically reduces strength. Internal corrosion (shown by the red dust on your cleaning cloth) is especially dangerous.
  - Kinks or Crushing: Sharp bends that permanently deform the cable cross-section create stress risers and significantly weaken it. Never straighten a kinked cable – replace it.
  - Birdcaging: Where outer wires splay outwards from the core, often due to torsional overload or improper swaging. Looks like a partially opened birdcage. Requires replacement.
  - Core Protrusion: Where the inner core pushes out past the outer strands, indicating core damage or failure.
  - Fraying: Visible unraveling or separation of individual strands or groups of strands. Distinct from normal strand lay.
  - **”Peening” or Flattening:** Wires flattened by repeated impact against guides or fairleads.
  - Heat Damage: Discoloration (blue/brown hues) or annealing (loss of temper, wires become softer), usually from excessive friction or proximity to heat sources.
  - Distortion of Strand Lay: Irregularities in the uniform helical pattern of the strands along the length.
  - Excessive Stretching: Permanent elongation (not to be confused with normal elastic stretch under load). Compare to cable length at installation (good records are vital).
Tactile Inspection:
- Carefully run your fingers (wearing clean gloves if possible to avoid snags) along the cable. Feel for bumps, depressions, changes in texture, or broken wires that might be visually obscured. Listen for any rustling or grating sounds that might indicate internal corrosion or broken wires.
Document Everything:
- Record the date, inspector name, specific cable location/identification, measurements taken, condition observed, and any defects found.
- Sign and date the log entry. This creates a vital maintenance history.

The Golden Rules:

If in Doubt, Throw it Out: Aviation cable is relatively inexpensive compared to the safety risk. Erase any doubt by replacing a suspect cable. Never take a chance.
Follow the Manual: Always adhere to the specific inspection procedures, criteria, and replacement intervals outlined in your aircraft’s maintenance manual, component maintenance manual (CMM), or the equipment manufacturer’s instructions. Their criteria override any general guidelines.
No Repairs: You cannot effectively splice or repair a damaged section of a critical aviation cable assembly. Replacement is the only acceptable course of action for any significant defect.
Qualified Personnel: While basic visual checks can be performed by many, formal inspections, especially Non-Destructive Testing (NDT) like Magnetic Particle Inspection (MPI), must be done by certified technicians.
Replace Hardware: When replacing a cable, always replace the corresponding fittings (thimbles, shackles, swage sleeves, etc.) with new parts approved for that assembly.

When Replacement is Non-Negotiable:

ANY broken wire.
Diameter reduction beyond manual limits (typically >5-10%).
Significant corrosion (surface pitting, or any evidence of internal corrosion).
Kinks, birdcaging, core protrusion.
Evidence of heat damage.
Excessive permanent stretch.
Fraying compromising strand integrity.
Damage to or slippage at terminations.
Reaching the service life limit specified in the manual.

Conclusion:

Inspecting aviation cable isn’t just a checklist task; it’s a crucial safeguard. Diligence, thoroughness, and an unwavering commitment to replacing suspect cables are paramount. By consistently performing these detailed inspections and adhering strictly to replacement criteria, you ensure the reliability and safety that aviation demands. Remember, that thin cable might be the only thing standing between smooth operation and disaster. Treat it with the respect it deserves.