The agency ordered operators to inspect the blades “before further flight.”
More than 100 Boeing 777s are either temporarily grounded, banned, or removed from service worldwide in response to the incident.
The agency is not increasing the frequency of these blade inspections yet, but the FAA said it will review the results on a rolling basis and it may revise the directive to set a new inspection interval.
“The FAA anticipates that further AD action will follow,” the directive said.
During United Flight 328, one blade broke off mid-flight and struck another, causing significant damage to the front of the engine.
The National Transportation Board (NTSB) said Monday that the damaged blades showed signs of metal fatigue based on preliminary evidence. The NTSB has still not shared when this aircraft or engine was last inspected or how often it required inspection.
The FAA’s order, called an “AD” or airworthiness directive, comes after multiple suspected similar failures. One occurred in 2018 when pieces of the same Pratt and Whitney series engine broke loose after a fan blade failure on a United 777. Another occurred in December 2020 when a fan blade broke in the same engine and debris hit the fuselage of a Japan Airlines 777.
Engine manufacturer Pratt & Whitney released a statement on Sunday stating that it “is actively coordinating with operators and regulators to support the revised inspection interval of the Pratt & Whitney PW4000 engines that power Boeing 777 aircraft.”
ABC News’ Sam Sweeney, Jeffrey Cook, and Amanda Maile contributed to this report.