Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 767-200 and 767-300 series airplanes. This proposed AD would require reworking certain duct assemblies in the environmental control system (ECS). This proposed AD results from reports of duct assemblies in the ECS with burned Boeing Material Specification (BMS) 8-39 polyurethane foam insulation. This proposed AD also results from a report from the airplane manufacturer that airplanes were assembled with duct assemblies in the ECS wrapped with BMS 8-39 polyurethane foam insulation, which is a material for which the fire retardant properties deteriorate with age. We are proposing this AD to prevent a potential electrical arc from igniting the BMS 8- 39 polyurethane foam insulation on the duct assemblies of the ECS, which could propagate a small fire and lead to a larger fire that might spread throughout the airplane through the ECS.