The Critical Importance of Aircraft Control Cable Inspection

Why Control Cable Inspection is Critical

The environment within an aircraft's structure is harsh. Control cables are subjected to constant tension, friction, vibration, and environmental factors like moisture, temperature fluctuations, and even chemical exposure. Over time, these stresses can lead to degradation, posing severe risks:

1. Fatigue and Wear: Repeated flexing and tension cycles can cause individual wires within a cable to break. This "fatigue" significantly weakens the cable, making it prone to sudden failure under stress.

2. Corrosion: Moisture, condensation, and chemical residues can lead to corrosion, especially in areas where cables pass through fairleads or pulleys, or are exposed to differing metals. Corrosion degrades the cable material, reducing its strength.

3. Friction and Chafing: Cables constantly move over pulleys and through fairleads. If these components are worn, misaligned, or improperly lubricated, they can cause friction, leading to chafing and rapid wear of the cable.

4. Improper Tension: Both too much and too little tension are problematic. Excessive tension can overstress the cable and its attachment points, while insufficient tension can lead to excessive slack, flutter, erratic control response, and even cables jumping off pulleys.

5. Contamination: Accumulation of dirt, debris, or foreign objects can interfere with cable movement, cause premature wear, or conceal underlying damage.

Any of these issues can lead to partial or complete loss of control, endangering the aircraft, its occupants, and those on the ground.

General Steps for Aircraft Control Cable Inspection

Control cable inspection is a thorough, systematic process typically performed by certified aviation mechanics according to the aircraft's maintenance manual (AMM) and regulatory guidelines. While specific procedures vary by aircraft type, the general steps involve:

1. Preparation and Access:

   • Consult the AMM: Always begin by reviewing the aircraft maintenance manual for specific instructions, torque values, tension specifications, and access panel locations.

   • Gain Access: Remove all necessary inspection panels, fairings, and covers to expose the control cables, pulleys, turnbuckles, and attachment points. This often requires working in confined spaces.

   • Cleanliness: Thoroughly clean the inspection area to ensure all components are free of dirt, grease, and debris that could obscure defects.

2. Visual Inspection (The "Look and Feel"):

   • Full Length Scan: Carefully inspect the entire visible length of each cable for signs of fraying, broken wires, nicks, kinks, or corrosion. Pay close attention to areas passing over pulleys, through fairleads, or near sharp edges.

   • Attachment Points: Examine cable terminals, thimbles, swaged fittings, and cotter pins for security, deformation, cracking, or wear.

   • Pulleys and Fairleads: Check pulleys for freedom of rotation, excessive wear in the groove, cracks, or damage to bearings. Ensure fairleads are intact, properly aligned, and not causing the cable to chafe.

   • Turnbuckles: Inspect turnbuckles for proper safety wiring, thread engagement (ensure no more than 3 threads are exposed at either end), corrosion, and damage.

   • Guard Pins and Stops: Verify that all guard pins, cable stops, and other protective devices are in place and secure, preventing cables from leaving their tracks or over-travelling.

3. Functional Checks (The "Move and Measure"):

   • Tension Measurement: Using a calibrated cable tensiometer (like the one seen in the image), measure the tension of each control cable. Compare these readings to the specifications in the AMM. Adjust turnbuckles as needed to achieve the correct tension, followed by proper safety wiring.

   • Freedom of Movement: Move the flight controls (stick, rudder pedals) through their full range of motion. Observe the cables for any binding, sticking, excessive slack, or interference with surrounding structures or other cables.

   • Control Surface Travel: Verify that the control surfaces (ailerons, elevator, rudder) move smoothly and achieve their full and correct deflection angles as specified in the AMM. This often involves using a protractor or specific rigging tools.

4. Documentation and Reassembly:

   • Record Findings: Document all inspection findings, measurements, adjustments made, and any discrepancies discovered in the aircraft's maintenance logbook.

   • Reassembly: Once all inspections and adjustments are complete, carefully reinstall all inspection panels, covers, and fairings according to the AMM, ensuring all fasteners are properly secured.

   • Functional Check (Final): Perform a final functional check of the flight controls to confirm proper operation before releasing the aircraft for service.

In aviation, there's no room for complacency. The meticulous inspection of control cables underscores a fundamental principle: constant vigilance and adherence to detailed procedures are the bedrock upon which the miracle of flight safely depends.