Airworthiness Directives; Bombardier, Inc. Airplanes

We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model CL-600-2B19 (Regional Jet Series 100 & 440) airplanes. This proposed AD was prompted by results of a design review indicating that the burst pressure of the flexible hose, used to vent oxygen from the high-pressure relief valve of the oxygen cylinder overboard, was lower than the opening pressure of the high-pressure relief valve, which could cause the flexible hose to burst before it can vent the excess oxygen overboard. This proposed AD would require replacing the oxygen hose assembly with a new, improved assembly. We are proposing this AD to prevent the accumulation of oxygen in an enclosed space, which could result in an uncontrolled oxygen-fed fire if an ignition source is nearby.