Even before two battery failures led to the grounding of all Boeing 787 jets this month, the lithium-ion batteries used on the aircraft had experienced multiple problems that raised questions about their reliability.
Officials at All Nippon Airways, the jets’ biggest operator, said in an interview Tuesday that it had replaced 10 of the batteries in the months before fire and smoke in two cases caused regulators around the world to ground the jets.
The airline said it had told Boeing of the replacements as they occurred but was not required to report them to safety regulators because they were not considered a safety issue and no flights were canceled or delayed. National Transportation Safety Board officials said Tuesday that the replacements were now part of their inquiry.
The airline also, for the first time, explained the extent of the previous problems, which underscore the volatile nature of the batteries and add to concerns over whether Boeing and other plane manufacturers will be able to use the batteries safely.
In five of the 10 replacements, All Nippon said that the main battery had showed an unexpectedly low charge. An unexpected drop in a 787’s main battery also occurred on the All Nippon flight that had to make an emergency landing in Japan on Jan. 16.
The airline also revealed that in three instances, the main battery failed to operate normally and had to be replaced along with the charger. In other cases, one battery showed an error reading and another, used to start the auxiliary power unit, failed.
All the events occurred from May to December 2012. The main battery on the plane that made the emergency landing was returned to its maker, GS Yuasa, and 10 other batteries involved in mishaps were sent to the airline’s maintenance department.
Kelly Nantel, a spokeswoman for the NTSB, said investigators had only recently heard that there had been “numerous issues with the use of these batteries" on 787s.
She said the board had asked Boeing, All Nippon and other airlines for information about the problems.
“That will absolutely be part of the investigation," she said.
Boeing, based in Chicago, has said repeatedly that any problems with the batteries can be contained without threatening the planes and their passengers.
But in response to All Nippon’s disclosures, Boeing officials said the airline’s replacement of the batteries also suggested that safeguards were activated to prevent overheating and keep the drained batteries from being recharged.
Boeing officials also acknowledged that the new batteries were not lasting as long as intended. But All Nippon said that the batteries it replaced had not expired.
A GS Yuasa official, Tsutomu Nishijima, said battery exchanges are part of the normal operations of a plane but would not comment further.