All Nippon Airways Co. and Japan Airlines Co. announced Monday they have begun installing modified batteries into their grounded Boeing 787 Dreamliners.

ANA began swapping batteries in five jets grounded at Narita, Haneda, Okayama and Matsuyama airports, while JAL worked on jets at Narita and Haneda airports. ANA has 17 Dreamliners in its fleet, while JAL has seven.

According to ANA, each jet will take about five days to modify, and all 17 of its Dreamliners will be ready in about a month. It expects to start flying passengers in June after several weeks of test flights.

The move comes after the U.S. Federal Aviation Administration’s announcement Friday that it had approved Boeing’s design for modifications to the troubled battery system of the 787 jet.

The Japanese airlines received manuals for the procedures from Boeing on Sunday, they said.

Both airlines still need permission from the Land, Infrastructure, Transport and Tourism Ministry before they can fly the planes. The ministry’s Civil Aviation Bureau is in its final stages of the Dreamliner probe, Shigeru Takano, the agency’s director in charge of air transport safety, said last week in Tokyo.

ANA, whose All Nippon Airways unit is the biggest operator of Dreamliners, said in January the grounding of the fleet cut sales by ¥1.4 billion that month. The Tokyo-based carrier canceled 3,601 flights through May, affecting 167,820 passengers.

The carrier is targeting June to restart commercial flights with Boeing’s most advanced jet, President Shinichiro Ito said this month.

JAL, the second-biggest operator with seven planes, said last month that flight cancellations would cut sales for the Tokyo-based company by ¥1.1 billion through the end of March. A spokesman declined to comment on the repairs.

A total of 50 Dreamliners worldwide have been grounded after one operated by ANA made an emergency landing on Jan. 16 at an airport in western Japan due to smoke in the cockpit. JAL and ANA together operate almost half the 50 787s delivered around the world.