Summary
We propose to revise airworthiness directive (AD) 2014-17-08 that applies to all Pratt & Whitney Canada Corp. (P&WC) PT6A-114 and PT6A-114A turboprop engines. AD 2014-17-08 requires initial and repetitive borescope inspections (BSIs) of compressor turbine (CT) blades, and the removal from service of blades that fail inspection. Since we issued AD 2014-17-08, P&WC developed an additional single crystal CT blade that corrects the unsafe condition. This proposed AD would retain all the requirements of AD 2014-17-08, add an additional single crystal CT blade that corrects the unsafe condition, reduce the affected population, and correct the Credit for Previous Action paragraph. We are proposing this AD to prevent failure of CT blades, which could result in damage to the engine and damage to the airplane.