A new Airworthiness Directive (AD) will require initial and repetitive borescope inspections of some 300 PT6A engines and potentially cost operators as much as $18,106,200. Following reports of compressor turbine (CT) blade failures causing engine power loss, the FAA issued an AD Wednesday that requires replacement of blades that fail inspection with a newly developed blade. The purpose of the AD is to prevent failure of CT blades, which the FAA said “could result in damage to the engine and damage to the airplane.” It becomes effective Oct. 8. Affected engines are Pratt & Whitney Canada (P & W) PT6A-114 and PT6A-114A engines.
According to the FAA, “There have been a number of reported incidents where Compressor Turbine (CT) blade failures have caused power loss on PT6A-114 & PT6A-114A engines, resulting in in-flight shutdown.” The FAA went on to say that Pratt & Whitney’s investigation revealed that high-power and high-temperature operations could cause the CT blades to crack or break because of “creep” or sulfidation. P & W developed a new CT blade that is less affected by creep and published specific inspection requirements for engines with affected CT blades. The engines are most commonly installed on Cessna 208 Caravans, where an inflight shutdown means a forced landing. The FAA estimates the inspection will require four hours-with eight hours to replace blades, if required. Should all of the old-style blades require replacement, the cost is estimated to be about $59,334 per engine.
