By Yoko Kubota
TOKYO (Reuters) - All Nippon Airways <9202.T> (ANA), the biggest customer for Boeing Co's
U.S. regulators approved on Friday a revamped battery system for the Dreamliner, a crucial step in returning the high-tech jet to service after it was grounded in January because its lithium-ion batteries overheated.
Boeing engineers will start to refit each of the 50 jets owned by airlines around the world with the battery system and regulators are expected to lift the ban on passenger flights as early as next week, for the jets that have been fixed.
But ANA will conduct about 100 to 200 round trip test flights in May, before it starts carrying passengers again on scheduled flights in June, sources knowledgeable about ANA's operations told Reuters.
They declined to be identified as they are not authorized to speak to the media about the matter.
The test flights are aimed at checking the safety of the aircraft, as well as having about 200 of ANA's Dreamliner pilots get accustomed to flying it again after more than a three-month break, one of the sources said.
For some pilots, the test flights will allow them to renew their qualifications that have expired while the jet was grounded, the source said.
ANA plans to conduct the test flights between Tokyo's Haneda airport, or nearby Narita airport, and Chitose in northern Japan, the sources said.
ANA said final details had yet to be set.
"We haven't come up with a schedule yet," said ANA spokesman Ryosei Nomura, adding that ANA employs 180 pilots to fly the Dreamliner.
One source said that before carrying passengers, ANA could use the repaired Dreamliners for cargo flights.
ANA has not said how much the 787's grounding has cost it to date, though it has said it lost $868,300 in revenue per plane in the last two weeks of January.
Friday's approval by the Federal Aviation Administration (FAA), the U.S. regulator, all but ends a grounding that has cost Boeing an estimated $600 million. Nearly half of the planes in service are owned by ANA and rival Japan Airlines <9201.T>.
Boeing has 10 teams already in place worldwide and it takes them five days to refit each jet with the new battery system, including a "containment and venting" system, the company said.
The FAA said it would issue an airworthiness directive next week that formally lifts the U.S. ban on passenger flights. Its Japanese counterpart, the Civil Aviation Bureau, said its revised directive could come on or after April 25.
(Additional reporting by Tim Kelly and Maki Shiraki; Editing by Robert Birsel)