Airworthiness Directives; Rolls-Royce plc Models RB211 Trent 768-60, Trent 772-60, and Trent 772B-60 Turbofan Engines

The FAA is superseding an existing airworthiness directive (AD) for Rolls-Royce plc (RR) models RB211 Trent 768-60, Trent 772-60, and Trent 772-60 turbofan engines. That AD currently requires initial and repetitive surge margin testing of engines. This AD requires the same actions but at updated intervals. This AD also requires installation of updated software for the engine electronic controllers (EECs), and adds a terminating action for the surge margin testing requirement. This AD supersedure results from RR requiring EEC software to be revised, and extending the repetitive interval for surge margin testing for engines that have incorporated the software update for the EECs. This AD also results from RR introducing a stage 1 high pressure (HP) compressor casing and intermediate case outer location ring with wear-resistant coating, to reduce wear to prevent reduction in surge margin. We are issuing this AD to prevent a possible dual-engine in- flight surge, which could result in dual engine power loss.