Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Rolls-Royce plc (RR) RB211-535E4-37, RB211-535E4-B- 37, and RB211-535E4-B-75 series turbofan engines. That AD requires initial and repetitive ultrasonic inspections of installed low pressure compressor (LPC) fan blade roots on-wing and during overhaul, and relubrication according to accumulated life cycles. That AD also introduces an alternative technique to ultrasonically inspect installed fan blades on-wing using a surface wave ultrasonic probe. Also, that AD introduces application of Metco 58 blade root coating as an optional terminating action. This proposed AD would require the same actions but would add compliance paragraphs to relax the compliance schedule for repetitive inspections for RB211-535E4 engines operating in flight profiles A and B, if certain requirements are met. This proposed AD results from RR issuing Mandatory Service Bulletin (MSB) No. RB.211-72- C879, Revision 5. That MSB introduces a relaxed repetitive compliance schedule for RB211-535E4 engines operating in flight profiles A and B, if certain requirements are met. We are proposing this AD to detect cracks in LPC fan blade roots, which if not detected, could lead to uncontained multiple fan blade failure, and damage to the airplane.