Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Rolls-Royce plc (RR) RB211 Trent 700 series turbofan engines. That AD currently requires initial and repetitive borescope inspections of the high pressure-and-intermediate pressure (HP-IP) turbine internal and external oil vent tubes for coking and carbon buildup, and cleaning or replacing the vent tubes if necessary. This proposed AD would require the same actions, but would add additional inspections of the vent flow restrictor. This proposed AD results from further analysis that the cleaning of the vent tubes required by AD 2007-02-05 could lead to loosened carbon fragments, causing a blockage downstream in the vent flow restrictor. We are proposing this AD to prevent internal oil fires due to coking and carbon buildup that could cause uncontained engine failure and damage to the airplane.