Summary
We propose to adopt a new airworthiness directive (AD) for certain Model 747 airplanes. This proposed AD would require inspecting to verify the part number of the low-pressure flex-hoses of the crew oxygen system installed under the oxygen mask stowage boxes in the flight deck, and replacing the flex-hose with a new non-conductive low- pressure flex-hose if necessary. This proposed AD results from reports of low-pressure flex-hoses of the crew oxygen system that burned through due to inadvertent electrical current from a short circuit in the audio select panel. We are proposing this AD to prevent inadvertent electrical current, which can cause the low-pressure flex-hoses of the crew oxygen system to melt or burn, causing oxygen system leakage and smoke or fire.