Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 757 airplanes. This proposed AD would require inspecting to verify the part number of the low-pressure flex-hoses of the flightcrew and supernumerary oxygen system installed under the oxygen mask stowage box at a flightcrew and supernumerary oxygen mask location, and replacing with a new non-conductive low-pressure flex- hose of the oxygen system if necessary. This proposed AD results from reports of a low-pressure flex-hose of a flightcrew oxygen system that burned through due to inadvertent electrical current from a short circuit in an adjacent audio select panel. We are proposing this AD to prevent inadvertent electrical current which can cause the low-pressure flex-hose of a flightcrew or supernumerary oxygen system to melt or burn, resulting in oxygen system leakage and smoke or fire.