Action
Supplemental notice of proposed rulemaking (NPRM); request for comments.
Summary
We are revising an earlier proposed airworthiness directive (AD) for all Pratt & Whitney Canada Corp. (P&WC) PT6A-114 and PT6A-114A turboprop engines. The NPRM proposed to require initial and repetitive borescope inspections (BSIs) of compressor turbine (CT) blades, and the removal from service of blades that fail inspection. The NPRM was prompted by several incidents of CT blade failure, causing power loss and in-flight shutdown of the engine resulting in four fatalities. This action revises the NPRM by adding a mandatory terminating action. We are proposing this supplemental NPRM (SNPRM) to prevent failure of CT blades, which could lead to damage to the engine and damage to the airplane. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on this proposed change.