Summary
This action revises an earlier proposed airworthiness directive (AD), applicable to certain RR RB211-524 series turbofan engines. That proposal would have required initial and repetitive borescope inspections of the head section and meterpanel assembly of the combustion liner, and replacement if necessary with serviceable parts. That proposal was prompted by an inquiry submitted by an operator, which resulted in RR performing a complete review of the affected front combustion liner part numbers (P/Ns). This action revises the proposed rule by clarifying the applicability paragraph (c) of the proposed AD. We are proposing this AD to prevent deterioration of the engine combustion liner, which can result in combustion liner breakup, case burn-through, engine fire, and damage to the airplane.