The Federal Aviation Administration (FAA) said on Tuesday it was ordering immediate inspections of Boeing 777 planes with Pratt & Whitney PW4000 engines before further flights after an engine failed on a United flight on Saturday. The engines are used on 128 older versions of the plane accounting for less than 10% 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. Operators must conduct a thermal acoustic image inspection of the large titanium fan blades on each engine, the FAA said. The National Transportation Safety Board said on Monday that a cracked fan blade from the United Flight 328 engine that caught fire was consistent with metal fatigue. “Based on the initial results as we receive them, as well as other data gained from the ongoing investigation, the FAA may revise this directive to set a new interval for this inspection or subsequent ones,” the FAA said. In March 2019, after a 2018 United engine failure attributed to fan blade fatigue, the FAA ordered inspections every 6,500 cycles. A cycle is one take-off and landing. South Korea’s transport ministry on Wednesday ordered the grounding of all local airlines’ Boeing 777s with PW4000 engines and would ban foreign carriers with those planes from entering its airspace from Thursday. A day earlier it instructed airlines to inspect the fan blades every 1,000 cycles following guidance from Pratt. An airline would typically accumulate 1,000 cycles about every 10 months on a 777, according to an industry source familiar with the matter. The U.S. FAA said in 2019 that each inspection was expected to take 22 man-hours and cost $1,870. It did not provide updated estimates on Tuesday. A spokeswoman for Pratt, owned by Raytheon Technologies, said fan blades would need to be shipped to its repair station in East Hartford, Connecticut, for the latest inspections, including those from airlines in Japan and South Korea. Boeing said it supported the FAA’s latest inspection guidance and would work through the process with its customers. It had earlier recommended that airlines suspend the use of PW4000-powered planes while the FAA identified an appropriate inspection protocol, and Japan imposed a temporary suspension on flights. Japan’s transport ministry said on Wednesday it was examining the FAA directive and had not yet decided what action to take. ANA Holdings and Japan Airlines (JAL) said they would comply with any directives from the Japanese regulator. The FAA spent the last two days discussing the extent of the inspection requirements, according to sources with knowledge of the matter. On Monday, the FAA acknowledged that after a JAL engine incident in December it had been considering stepping up blade inspections. United, the only U.S. operator of the older PW4000-powered 777s, had temporarily grounded its fleet before the FAA announcement. The airline said on Tuesday it would comply with the airworthiness directive. United has warned of possible disruptions to its cargo flight schedule in March as it juggles its fleet after its decision to ground 24 Boeing 777-200 planes, according to a notice sent to cargo customers. Another 28 of United’s 777-200 planes were already grounded before the incident on Saturday, amid a plunge in demand.