A United Airlines plane with a Pratt & Whitney engine that failed on Saturday had flown fewer than half the flights allowed by US regulators between fan blade inspections, two sources with knowledge of the matter said.
The Boeing Co 777 plane had flown nearly 3,000 cycles, equivalent to one take-off and landing, which compares to the checks every 6,500 cycles mandated after a separate United engine incident in 2018, said the sources.
They sought anonymity as they were not authorised to speak publicly. United Airlines declined to comment.
Pratt, the maker of the PW4000 engines, advised airlines on Monday to step up checks to every 1,000 cycles, in a bulletin seen by Reuters. It did not immediately respond to a request for comment.
On Tuesday, the US Federal Aviation Administration (FAA) said it was ordering immediate inspections of 777 planes with PW4000 engines before they could return to flight, going further than Pratt.
The engines are used on 128 older versions of the plane, accounting for less than 10 per cent of the more than 1,600 777s delivered and only a handful of airlines in the United States, South Korea and Japan were operating them recently.
Japan and South Korea have also grounded the planes for fan blade checks.