Airworthiness Directives; Rolls-Royce plc RB.211-524 Series Turbofan Engines

This amendment adopts a new airworthiness directive (AD), applicable to Rolls-Royce plc RB.211-524 series turbofan engines, that requires initial and repetitive borescope inspections of the head section and meterpanel assembly of the combustion liner, and replacement, if necessary, with serviceable parts. In addition, this AD allows an optional installation of a front combustion liner with a strengthened head section as a terminating action to the inspection requirements. This amendment is prompted by reports of engine fires due to premature engine combustor distress. The actions specified by this AD are intended to prevent engine combustor liner deterioration due to thermal fatigue, which can result in combustor liner and case burn- through and engine fire.