Summary
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 foreignmaterial, 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.