Japan's biggest airliner ANA has started grounding some of its Boeing 787 Dreamliner jets for checks on the Rolls-Royce engines on them for corrosion.

The airline, with a fleet of 50 Dreamliners, cancelled nine flights using the aircraft on Friday and may have to cancel more than 300 through the end of September, Takeo Kikuchi, a deputy senior vice president of engineering and maintenance, was quoted as saying by a Bloomberg report.

ANA is replacing medium pressure turbine blades on the planes, Kikuchi said. ANA is the world’s biggest operator of Dreamliners.

The 787-related flight cancellations are the largest for ANA since 2013, when Boeing and regulators grounded the global Dreamliner fleet while fixing a fire issue with the plane’s lithium-ion battery. About 38 percent of the 787s in service are powered by Rolls-Royce’s Trent 1000 turbines, while the rest are outfitted with General Electric engines.

The latest issue came to the fore as ANA investigated why a 787 engine overheated during a February flight. That jet returned to Kuala Lumpur airport after receiving a warning that the temperature of the exhaust gas from its right engine was very high. ANA has encountered the issue of corrosion in turbine blades three times since February, Kikuchi said.

Rolls-Royce said it had notified other airlines that use the same type of engine, adding that it would make an improved part available by the end of the year.