Before the jets can fly again, the large, titanium hollow fan blades at the front of each engine must be removed and shipped to a Pratt Whitney facility where they will undergo a “thermal acoustic image” inspection, according to the F.A.A. Under that technique, a fan blade is bombarded with high-frequency vibrations, raising its temperature. A thermal image of the blade is then recorded and analyzed for unusual readings that may signify a potential crack.
In 2018, a United flight involving the same plane-and-engine combination suffered a similar failure, prompting the F.A.A. to order engine inspections every 6,500 flights. In its statement on Tuesday, the agency said it might still adjust that inspection frequency.
Also on Saturday, a Boeing 747 equipped with a relative of that engine suffered a similar fate, shedding parts in the Netherlands. Europe’s aviation authority has said it does not believe that episode is related to the other failures. None of the four engine failures resulted in deaths. Two people were reported to have suffered minor injuries in the Netherlands.