Just Plain Broken

While in process of checking the individual oxygen masks during an annual inspection and five-year O2 bottle re-certification, a technician heard a very faint sound of a gas leak in the overhead interior paneling of the aircraft. After pulling the headliner for a closer inspection and plumbing in low-pressure nitrogen for troubleshooting, the technician narrowed down the "hiss" to a line just forward of the cabin door (p/n 5100107-46). To access this line, which passes through a structural beam in the overhead, it was necessary to drill out approximately 40 rivets securing a thin honeycomb panel to the overhead (structure). Above the panel is the ducting supplying the cabin Wemac vents. The line as pictured has been cleaned up and the corrosion removed for clarity. The corrosion occurred where the ducting passed under it. The ducting was removed to facilitate line removal, and was found to be totally deteriorated.

Key Takeaways:

• A Cessna 421C revealed a corroded oxygen line, hidden by deteriorated ducting, emphasizing the risk of concealed wear during inspections.
• Piper PA28 aircraft are experiencing recurring cracks in flap handle support mounts, attributed to fatigue and air loads, requiring careful inspection.
• A newly installed oil cooler on a Robinson R22-A helicopter cracked shortly after use, leading to rapid oil loss and an unscheduled landing.
• Continental IO-520 C engines have shown a pattern of new through-bolts snapping post-torquing, suggesting a manufacturing or design issue with specific replacement parts.

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