AD FAA-2015-0827

We propose to supersede Airworthiness Directive (AD) 2011-07- 10, for certain Bombardier, Inc. Model BD-100-1A10 (Challenger 300) airplanes. AD 2011-07-10 currently requires revising the Airworthiness Limitations section of the Instructions for Continued Airworthiness; doing detailed visual inspections; removing discrepant material; cleaning the surfaces of the valves, the plug of the sensing port, and the cabin pressure-sensing port plug; securing the insulation; installing a new safety valve, and replacing certain cabin pressure-sensing port plugs. Since we issued AD 2011-07-10, we have received reports of in-flight loss of cabin pressurization that was attributed to partial blockage of a safety valve cabin pressure-sensing port in conjunction with a failed safety valve manometric capsule. This proposed AD would retain all requirements of AD 2011-07-10. This proposed AD would also require a detailed visual inspection of both safety valves and the surrounding area for foreign material, room temperature vulcanizing (RTV) silicone, contamination, foam on the bulkhead structure, tape or insulation, and loose material; and corrective actions if necessary. We are proposing this AD to detect and correct blockage of a safety valve cabin pressure-sensing port, which could result in loss of cabin pressure.