Airworthiness Directives; Rolls-Royce plc RB211 Series Turbofan Engines

The FAA is superseding an existing airworthiness directive (AD) for Rolls-Royce (RR) plc RB211-535E4-37, RB211-535E4-B-37, and RB211-535E4-B-75 series turbofan engines. That AD currently requires initial and repetitive ultrasonic inspections of installed LPC fan blade roots on-wing and during overhaul using a surface wave ultrasonic probe, and relubrication, according to accumulated life cycles. That AD also adds the application of Metco 58 blade root coating as an optional terminating action. This AD requires the same actions, but changes the reference to Mandatory Service Bulletin (MSB) No. RB.211-72-C879 from Revision 3 to Revision 4. This AD results from RR issuing MSB No. RB.211-72-C879, Revision 4, which contains revised Accomplishment Instructions and consumable materials list. We are issuing this AD to detect cracks in low pressure compressor (LPC) fan blade roots, which if not detected, could lead to uncontained multiple fan blade failure, and damage to the airplane.