Aviation safety officials investigating the Boeing's 787 Dreamliner have visited the headquarters of the plane's battery maker.
A spokesman for GS Yuasa, which makes batteries for the 787, said the company was fully cooperating with the investigation, and its engineers were working with the officials from the U.S. Federal Aviation Administration (FAA) and Japan's Civil Aviation Bureau (CAB) at the company's compound in Kyoto, where it makes airplane batteries.
CAB official Tatsuyuki Shimazu told reporters the investigating team had been briefed by GS Yuasa and had toured the plant, looking at battery design, production and quality.
The Japanese investigation at the plant will continue this week on a more detailed level, including tracking battery batch numbers and production dates, he said.
Authorities around the world last week grounded the new lightweight Dreamliner, and Boeing halted deliveries after a problem with a lithium-ion battery prompted an All Nippon Airways 787 into the emergency landing at Takamatsu airport during a domestic flight.
Earlier this month, a similar battery caught fire in a Japan Airlines' 787 parked at Boston Logan International Airport.
U.S. safety investigators have ruled out excess voltage as the cause of the Boston battery fire on Jan. 7, and said they were expanding their probe to look at the battery's charger and the jet's auxiliary power unit.
The battery is one part of the 787's complex electrical system, built by French company Thales.
"Results have shown the battery was abnormal in both the Boston and Takamatsu (incidents).
They were the most damaged," Shigeru Takano, a senior safety official at the CAB, told reporters ahead of the on-site visit to GS Yuasa.
"We will look into if the work that took place, from design to manufacturing, was appropriate."
Shares in GS Yuasa, valued at close to $1.5 billion, rose 1 percent on Monday, having dropped nearly 10 percent since the Boston fire.
The benchmark Nikkei fell 1.5 percent.
The company, which employs nearly 12,300 staff, expects revenue of 288 billion yen ($3.2 billion) in the year to end-March - with only around 1 percent of that coming from its aircraft battery business.
The company's batteries are used primarily in motorbikes, industrial equipment and power supply devices.
GS Yuasa, in which automaker Toyota has a 2.7 percent stake, reported an operating profit of around $160 million in the year to last March.
The grounding of the Dreamliner, an advanced carbon-composite plane with a list price of $207 million, has forced ANA to cancel 151 domestic and 26 international flights scheduled for Jan. 23-28, affecting more than 21,000 passengers, the airline said on Monday.
The cancellations add to the 72 flights scheduled for Jan. 19-22 that ANA called off last week.
ANA, which flies the most Dreamliners of any airline, said it will announce on Thursday its plans on flight cancellations for dates from Jan. 29.
ANA said it had not yet decided whether to seek compensation from Boeing for losses as a result of the 787's grounding.
"At this point we're concentrating on getting the Dreamliner back in service, rather than considering requesting compensation," said spokesman Ryosei Nomura.
Rival JAL said it cancelled four flights on its Tokyo-San Diego route for Jan. 27-28, adding to the 8 flights originally scheduled for Jan. 19-25 on the same route it called off last week. It said it had yet to decide changes for flights slated for Jan. 26.
"We've been able to rearrange routes originally scheduled to use the Dreamliner with alternative aircraft," said JAL spokeswoman Sze Hunn Yap, adding there was no talk about compensation at this stage.
Japan is the biggest market to date for the Dreamliner, with JAL and ANA flying 24 of the 50 passenger jets that Boeing has delivered.