Summary
The Federal Aviation Administration (FAA) proposes to supersede an existing airworthiness directive (AD), applicable to Rolls-Royce plc. (RR) models RB211-535E4-37, RB211-535E4-B-37, and RB211-535E4-B-75 turbofan engines, with certain part number (P/N) low pressure (LP) turbine stage 2 discs installed. That AD currently requires establishing new reduced LP turbine stage 2 disc cyclic limits. That AD also requires removing from service affected discs that already exceed the new reduced cyclic limit, and removing other affected discs before exceeding their cyclic limits, using a drawdown schedule. This proposal would require changing certain cyclic limits, changing the effective date of certain disc cyclic lives, and would allow intermix of Flight Plan A and Flight Plan B intermix calculations. This proposal is prompted by a reassessment of the thermal and stress data from recent operational experience and comments received from operators on the current AD. The actions specifiedby the proposed AD are intended to prevent LP turbine stage 2 disc failure, which could result in uncontained engine failure and possible loss of the airplane.