All Nippon Airways Co. on Thursday started modifying the battery system on the Boeing 787 Dreamliner jet that made an emergency landing in Takamatsu, Kawagawa Prefecture, in January.

ANA, which owns more 787s than any other carrier in the world, is planning to conduct a test flight of the fuel-efficient aircraft next Thursday night after Boeing's technical staffers finish installing an improved lithium-ion battery.

ANA has modified six of the 17 Dreamliners in its fleet and is hoping to resume commercial operations involving the plane in June. The 787s were grounded worldwide after the emergency landing Jan. 16 at Takamatsu Airport.

On April 26, U.S. and Japanese aviation authorities gave the green light for 787s to resume service, following a redesign of the aircraft's battery system.

In a related development, United Airlines said Wednesday it will resume flying 787s on May 20, earlier than planned, with a flight from Houston to Chicago. Ethiopian Airlines resumed Dreamliner operations on April 27.