FAA Issues Emergency AD To Inspect PW4000-112 Fan Blades

 - February 24, 2021, 8:32 AM

The FAA issued an emergency airworthiness directive Tuesday night requiring inspection of all fan blades from certain Pratt & Whitney PW4000 turbofans for cracking after investigators found signs of metal fatigue in the engine that failed in a United Airlines Boeing 777-200 on September 30. The interim action mandates that operators perform a thermal-acoustic imaging (TAI) inspection of the hollow titanium fan blades on each engine. TAI can detect cracks on the interior surfaces of the hollow fan blades or in areas that cannot be seen during a visual inspection.

As the required inspections proceed, the FAA will review the results on a rolling basis, said the agency. Based on the initial results and other data gathered from the ongoing investigation, the FAA might revise the directive to set a new inspection interval. Previous requirements called for inspection every 6,500 flight cycles.

The FAA mandated the 6,500-cycle interval following the December 2018 fan blade failure involving a PW4000-112 in another United Airlines 777-200. Last year the NTSB determined that insufficient training for the TAI inspection process developed by Pratt & Whitney led to technicians misdiagnosing a problem with the fan blade that ultimately failed in the 2018 incident. Since then Pratt developed a formal training curriculum for the inspections, and the FAA issued an airworthiness directive in March 2019 requiring the repetitive inspections of all PW4000-112s in service. 

In a statement, Pratt & Whitney said the latest directive applies only to PW4000-112s—the model of PW4000 found in some 125 Boeing 777s—and that it would perform the needed TAI inspections at its FAA-authorized repair station.

“Pratt & Whitney is coordinating all actions with Boeing, airline operators, and regulators,” said the Connecticut-based engine company. “The safe operation of the fleet is our top priority. Pratt & Whitney commends the flight crew operating United Airlines flight 328 for their professionalism.”