AD FAA-2013-0766

We are revising airworthiness directive (AD) 2014-17-08 for all Pratt & Whitney Canada Corp. (P&WC) PT6A-114 and PT6A-114A turboprop engines. AD 2014-17-08 required initial and repetitive borescope inspections (BSIs) of compressor turbine (CT) blades, and the removal from service of blades that fail inspection. This new AD adds an additional single crystal CT blade, reduces the affected population, and corrects the Credit for Previous Action paragraph. This AD was prompted by P&WC development of an additional single crystal CT blade that corrects the unsafe condition. We are issuing this AD to prevent failure of CT blades, which could result in damage to the engine and damage to the airplane.