Airlines in Japan and the US have grounded dozens of Boeing 777 aircraft after the dramatic engine failure that United Airlines flight 328 experienced over Denver this weekend. According to the National Transportation Safety Board’s ongoing investigation, two fan blades on the plane’s number 2 engine had developed fractures.

The Federal Aviation Administration issued an emergency airworthiness directive that requires “immediate or stepped-up inspections of Boeing 777 airplanes equipped with certain Pratt & Whitney PW4000 engines.” The administration noted that this was likely to result in aircraft being removed from service.

“We reviewed all available safety data following yesterday’s incident,” FAA administrator Steve Dickson said in a statement. “Based on the initial information, we concluded that the inspection interval should be stepped up for the hollow fan blades that are unique to this model of engine, used solely on Boeing 777 airplanes.”

United Airlines says it’s voluntarily grounding 24 Boeing 777 aircraft that use the 4000-series Pratt & Whitney engines and expects “only a small number of customers to be inconvenienced.” Japan’s Civil Aviation Bureau ordered Japan Airlines and All Nippon Airways to remove their aircraft with the same engines from service; JAL operates 14 and ANA has 19, according to Reuters.

No-one was injured on United flight 328, which was bound for Honolulu but safely returned to Denver after encountering the engine failure shortly after takeoff.