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CD-10 – Aerospace Secondary Seal Cap Plug
Available now on the Airparts.aero Marketplace.
The CD-10 is a high-visibility, precision-molded protective cap plug designed for the temporary sealing of aerospace fluid lines, electrical connectors, and threaded fittings. Manufactured from high-density, non-shredding polyethylene, the CD-10 is an essential component of Foreign Object Debris (FOD) prevention programs. Its primary function is to protect critical male-threaded fittings or open tubing from environmental contamination, moisture ingress, and mechanical damage during aircraft maintenance, shipping, or long-term storage.
Unlike standard industrial plugs, the CD-10 is engineered with a "tapered" design, allowing it to function as either a cap (over a fitting) or a plug (inside a port). This dual-functionality makes it a versatile staple in A&P (Airframe and Powerplant) toolkits for sealing fuel, hydraulic, and pneumatic lines during component removal.
Key Features
Tapered Dual-Use Geometry: Features a calculated draft angle that allows the unit to be pressed firmly onto the outside of a tube or into the inside of a threaded boss, providing a friction-fit seal.
Non-Shredding Polyethylene: Formulated to resist "flaking" or tearing, ensuring that no plastic particles enter the fluid system—a critical requirement for high-pressure hydraulic and fuel systems.
High-Visibility "Aviation Red/Orange": Brightly colored to ensure the technician can easily identify that a temporary seal is in place, preventing the "forgotten plug" scenario during reassembly.
Chemical Resilience: Resistant to common aerospace fluids, including Jet-A, Skydrol, and de-icing over-spray, preventing the plug from softening or bonding to the fitting over time.
Ergonomic Lift Tab (Optional on some variants): Often features a reinforced rim or knurled edge to allow for easy removal even when the technician is wearing flight-line gloves.
Technical Specifications
Part Number: CD-10
Manufacturer: Caplugs / Niagra (Standard Aerospace Supply)
Material: Low-Density Polyethylene (LDPE)
Color: Red (Standard)
Temperature Range: -94°F to 175°F (-70°C to 79°C)
Fitment Range: Designed for approximately 5/8" (0.625") nominal diameter fittings (Verify specific taper dimensions for your application).
Standard: Meets NAS837 and MIL-C-5501 requirements for protective closures.
Aircraft Compatibility
Universal Application: Found in the maintenance kits for all major airframes, including Boeing, Airbus, Bombardier, and Gulfstream.
General Aviation: Used extensively during annual inspections for Cessna, Piper, and Beechcraft aircraft to seal brake lines and fuel strainers.
Rotary Wing: Critical for protecting open gearbox vents and hydraulic actuators on Bell and Sikorsky helicopters.
Applications
The CD-10 is utilized for System Integrity and FOD Protection. Its primary roles include:
Hydraulic System Maintenance: Sealing open lines during actuator or pump replacement to prevent Skydrol spills and air ingestion.
Engine Storage: Plugging open bleed-air ports or fuel nozzles to prevent insect nesting and dust accumulation.
Electrical Protection: Capping open circular connectors (MIL-DTL-38999 style) to protect pins from bending or oxidation.
Why Choose CD-10?
Choosing the CD-10 over "shop-made" solutions (like tape or rags) is a matter of Safety and Airworthiness. Rags can leave lint, and tape can leave adhesive residue that causes valves to stick. The CD-10 provides a clean, mechanical barrier. Its tapered design ensures that as the plug is pushed further into a port, the seal becomes tighter, accommodating slight variations in thread pitch or tube diameter.
The CD-10 operates on the principle of Interference Fit. Because polyethylene has a lower Modulus of Elasticity than the aluminum or steel fittings it protects, the plug deforms slightly to match the surface irregularities of the threads. This creates a Hermetic-style barrier against atmospheric dust. The physics of the taper ($\theta$) allow the CD-10 to distribute its radial force evenly, ensuring that even if the system experiences a minor pressure "burp" due to thermal expansion, the plug remains securely in place.
Note: This is a ground-support and maintenance item. It is NOT for flight use. All CD-10 plugs must be removed and accounted for before the aircraft is returned to service. Failure to remove protective plugs can lead to catastrophic system failure. Always follow your "Remove Before Flight" checklist and tool-control procedures.
