Engineers have developed a rework procedure which resolves the problem of Rolls-Royce Trent 1000 gearboxes affected by a recent corrosion issue.
The European Aviation Safety Agency had previously required replacement of the transfer gearboxes after corrosion was blamed for failure of the crown wheel gear.
But it says that this directive has since been superseded following development of a rework procedure which "corrects the unsafe condition".
EASA has issued a new directive stating that a reworked external gearbox assembly is "eligible for installation".
Japanese carrier All Nippon Airways temporarily grounded some of its Trent-powered Boeing 787s as a result of the problem, which affected a specific batch of gearboxes following a change in the manufacturing process.