US regulators announced extra inspections on Boeing Co 777 jets using the same type of engine that shed debris over Denver on Saturday, while Japan went further and suspended their use while it considers what action to take.
The regulatory moves involving Pratt & Whitney 4000 engines came after a United Airlines 777 landed safely at Denver International Airport on Saturday after its right engine failed.
United said on Sunday it would voluntarily and temporarily remove its 24 active planes of the type from its schedule.
Images posted by police in Broomfield, Colorado showed significant plane debris on the ground, including an engine cowling scattered outside a home and what appeared to be other parts in a field.
The National Transportation Safety Board (NTSB) said its initial examination of the plane indicated most of the damage was confined to the right engine, with only minor damage to the airplane.
It said the inlet and casing separated from the engine and two fan blades were fractured, while the remainder of the fan blades exhibited damage.
Japan's transport ministry ordered Japan Airlines Co Ltd (JAL) and ANA Holdings Inc to suspend the use of 777s with P&W4000 engines while it considered whether to take additional measures.
The ministry said that on December 4, 2020, a JAL flight from Naha Airport to Tokyo International Airport returned to the airport due to a malfunction in the left engine about 100 kilometres north of Naha Airport.
That plane is the same age as the 26-year-old United Airlines plane involved in Saturday's incident.
United is the only US operator of the planes, according to the Federal Aviation Administration (FAA). The other airlines using them are in Japan and South Korea, the US agency said.
"We reviewed all available safety data following yesterday's incident," the FAA 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."
Japan said ANA operated 19 of the type and JAL operated 13 of them.
Pratt & Whitney, owned by Raytheon Technologies Corp, was not available immediately for comment.
Boeing said its technical advisers are supporting the US National Transportation Safety Board with its investigation.
A spokeswoman for South Korea's transport ministry said it was monitoring the situation but had not yet taken any action.
In February 2018, a 777 of the same age operated by United and bound for Honolulu suffered an engine failure when a cowling fell off about 30 minutes before the plane landed safely. The NTSB determined that incident was the result of a full-length fan blade fracture.
Because of that 2018 incident, Pratt & Whitney reviewed inspection records for all previously inspected PW4000 fan blades, the NTSB said. The FAA in March 2019 issued a directive requiring initial and recurring inspections of the fan blades on the PW4000 engines.