The Federal Aviation Administration is ordering airlines to replace fuel manifolds on some GE Aviation GEnx-2B67 engines, which power Boeing 747-8s, due to the risk of an engine fire.
An airworthiness directive that takes effect on 4 January comes in response to an engine fire caused by "low-cycle fatigue cracking of the fuel manifold".
The order requires airlines to replace the manifolds during the next shop visit.
The issue affected 424 GEnx-2B engines worldwide, but GE already issued a service bulletin and only 140 engines still require fixes, the company says.
Those 424 engines compose the bulk of engines on the worldwide in-service fleet of 123 747-8s and 747-8Fs, according to Flight Fleets Analyzer.
US airlines operate only two affected engines, the directive says.
The US aviation regulator has previously issued airworthiness directives addressing problems with fuel manifolds on GEnx-1A engines, which power 787s.
In 2017, the FAA required airlines to replace some GEnx-1A fuel manifolds in response to an in-flight engine shutdown caused by a fuel manifold fracture.