Even prior to the engine failure on a United Airlines Boeing 777 on February 20, 2021, on flight UA328 caused, Boeing was reportedly already planning on how to strengthen engine cowlings on the Boeing 777.

Boeing was in active discussion with the FAA for about two years, prompted by two engine failures in 2018, reported the Wall Street Journal, citing sources familiar with the matter. The first failure involved another United Airlines Boeing 777. The aircraft, registered as N773UA, suffered an engine failure, which resulted in debris penetrating the fuselage, while operating flight UA1175 from San Francisco International Airport (SFO) to Honolulu International Airport (HNL) on February 13, 2018. The Triple Seven was also powered by an engine from the Pratt & Whitney PW4000 family. The flight landed safely in HNL without any injuries onboard.

The second failure was that of a Southwest Airlines Boeing 737-700 on April 17, 2018. The aircraft was operating flight WN1380 from New York LaGuardia Airport (LGA) to Dallas Love Field (DAL), when the engine failed, broke the cowl and penetrated the 737’s fuselage. As a result, one passenger passed away and eight more were injured. The aircraft diverted to Philadelphia International Airport (PHL).

Following the two failures, in addition to another PW4000-powered Boeing 777 suffering an engine failure in Japan in 2017, Boeing decided to “redesign the fan cowl instead of trying to modify existing fan cowls to address both the structural strength concerns” and moisture issues, read an internal FAA document, examined by the Wall Street Journal. The document, dated August 6, 2020, also outlined that the plane maker would manufacturer “new fan cowls and providing service instructions for operators to remove and replace the fan cowls.”

The latest incident in February 2021 prompted the FAA to issue an emergency AD for the PW4000 engine that powers the Boeing 777, obligating operators to inspect the engine’s fan blades for cracks utilizing the thermal acoustic image (TAI) method.

While no passengers were injured on the United Airlines flight UA328 incident on February 20, 2021, debris once again penetrated the fuselage. The Boeing 777 safely returned to its origin point, Denver International Airport (DEN).

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The NTSB said the damage to one of the Pratt & Whitney engine blades of a United Boeing 777 that failed in Denver appeared consistent with metallic wear.