Japan said it is still unclear what caused a main battery on a Boeing 787 Dreamliner operated by ANA to overheat last month.
Investigators may widen their probe of the battery problems to other equipment on the technologically advanced aircraft, Japan Transport Safety Board (JTSB) chairman Norihiro Goto said.
All Boeing's 787s are out of action as investigators in Japan and the United States try to find the cause of two incidents with the plane's lithium-ion batteries - a battery fire on a Japan Airlines 787 at a U.S. airport and the emergency landing on a domestic ANA flight after battery problems triggered a smoke alarm.
Goto also said CT scans showed six of the main battery's eight cells on the ANA Dreamliner were badly damaged, charred and deformed.
Boeing asked the Federal Aviation Administration (FAA) for permission to conduct Dreamliner test flights, suggesting it is making progress in finding a solution to the battery problems.
Boeing said it has submitted an application to conduct test flights, confirming a report in the Seattle Times.
The newspaper reported that the FAA might grant permission this week, citing sources with knowledge of the matter.
The FAA did not immediately respond to a request for comment.
Boeing would test a potential fix for the problem that caused two batteries to burn on 787s last month, the paper said.
But passenger flights would still be weeks if not months away, the paper said, citing two sources.
Goto said Boeing had not discussed its test flight request with the Japanese agency, and he did not know if the planemaker had found clues as to the cause of the battery problems.
The test flights "could mean they have made progress," he said.
Launch customer ANA is the world's biggest Dreamliner operator with 17 of the jets.
With local rival JAL owning seven, Japan accounts for almost half the 50 787s that have been grounded since Jan. 17.
U.S. officials said last week they are making progress in their investigation into the battery fire on JAL's jet, although they have yet to set any timetable for completing their work.
ANA said last week it lost around $15 million in revenue as a result of the Dreamliner grounding, while JAL said the halting of 787 flights would shave $7.6 million from its operating profit in the year to end-March.
Both companies have said they will discuss compensation for the losses with Boeing.
GS Yuasa, the Japanese firm that makes batteries for the Boeing 787, said its April-December net profit fell 3.6 percent to 5.52 billion yen ($59.55 million) on revenue that slipped 4.6 percent to 196 billion yen.
The company forecast its full-year net profit would drop by almost a third to 8 billion yen, while sales would be up a touch at 288 billion yen.