Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model BD-700-1A10 and BD-700-1A11 airplanes. This proposed AD was prompted by a design review, which found that the burst pressure of the flexible hose used to vent oxygen from the high- pressure relief valve of the oxygen cylinder overboard is lower than the opening pressure of the high-pressure relief valve. This pressure difference could cause the flexible hose to burst before it is able to vent excess oxygen overboard. This proposed AD would require replacement of flexible relief hoses for the crew oxygen bottles with new metal design relief hoses. We are proposing this AD to prevent the accumulation of excess oxygen in an enclosed space, which could, if near a source of ignition, cause an uncontrolled oxygen-fed fire.