(CNN Business) -
United Airlines recalled all of its currently in-service Boeing 777s powered by Pratt & Whitney 4000 series engines after the Federal Aviation Administration (FAA) ordered more intensive inspections.
The airline announced Sunday that it would immediately recall the planes "as a precaution."
The 24 aircraft are part of the 52 Boeing 777s in United's fleet.
The other 28 remain in storage.
The move is voluntary and temporary, United said, and should only affect "a small number of customers."
The announcement came after the FAA issued an emergency order saying it would intensify inspections of Boeing 777s equipped with certain Pratt & Whitney PW4000 engines.
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"We reviewed all the available safety data after yesterday's incident," said FAA Administrator Steve Dickson.
He was referring to the United Airlines flight that was forced back to Denver International Airport on Saturday after suffering an engine failure shortly after takeoff, causing debris to fall in Denver.
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"Based on the initial information, we concluded that the inspection interval should be increased for hollow blades that are unique to this engine model, which is used only in Boeing 777 aircraft," said Dickson.
The National Transportation Safety Board (NTSB) said Sunday that an initial examination of the Pratt & Whitney PW4077 engine on United Airlines Flight 328 showed that two blades were fractured and the remaining blades had damage "to the tips and edges ”.
These are preliminary findings and should not be taken as conclusive of what went wrong on Saturday, but they are still significant.
Investigators believe a blade on the engine of the Boeing 777 that experienced a catastrophic failure on Saturday broke loose and took another blade, a source familiar with the situation told CNN.
United Airlines plane engine failure, debris falls outside Denver
On Sunday night, Boeing recommended suspending all its 777s that have Pratt & Whitney 4000 engines.
"While the NTSB investigation is ongoing, we recommend suspending operations of the 69 777s in service and 59 in storage powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol," read the statement from Boeing.
Countries that use the Boeing 777
According to the most recent registration data, the only airlines operating the affected engines are in the United States, Japan and South Korea.
United is the only US operator with this type of engine in its fleet.
Japan's Ministry of Transportation said it ordered domestic airlines to halt operations of Boeing 777 jets equipped with Pratt & Whitney PW4000 engines.
“Boeing supports yesterday's decision by the Japanese Civil Aviation Bureau and today's action by the FAA to suspend operations of 777 aircraft powered by Pratt & Whitney 4000-112 engines.
We are working with these regulators to take action while these planes are on the ground and Pratt & Whitney conducts further inspections, "the company said in its statement Sunday.
The NTSB said the "investigator in charge of this event along with a power plant specialist" traveled from Washington to Denver Sunday morning to assist local NTSB investigators.
The agency said it will examine "the engine, the plane and the photographs and videos taken by the passengers aboard United Flight 328".
The NTSB will also review flight data and cockpit voice recorders.
Boeing 777United Airlines
