Boeing's troubles with its newest airplane got worse on Wednesday after an emergency landing prompted Japan's two biggest airlines to ground all their 787s for safety checks.
It was the second fire-related incident in two weeks involving the 787's lithium-ion batteries.
All Nippon Airways said pilots detected a burning smell and received a cockpit message showing battery problems. They made an emergency landing at Takamatsu airport in western Japan, and passengers rode emergency slides off the plane.
ANA said an inspection found leaking electrolyte from the battery and burn marks around it. The lithium ion battery is below and slightly behind the cockpit, and experts have said its electrolyte is flammable.
Japan's transport ministry categorized it as a "serious incident" that could have led to an accident.
The ministry said it received notices from ANA, which operates 17 of the jets, and Japan Airlines, which has seven, that all their 787s would not be flying. The airlines grounded the planes voluntarily. It was unclear how long the Dreamliners would remain grounded.
The two airlines are major customers for the jet.
ANA was especially proud of its 787s. Its executives' business cards and the top of its website read "We fly 1st." Even when the 787 ran late, they expressed confidence in it. ANA got the first one that Boeing delivered in late 2011.
On Wednesday, ANA executives apologized, bowing deeply at a hastily called news conference in Tokyo.
"We are very sorry to have caused passengers and their family members so much concern," said ANA Senior Executive Vice President Osamu Shinobe.
Boeing has delivered 50 of the new 787s so far, so the groundings of 24 planes represents nearly half of the world's fleet of what is meant to be the most technologically advanced plane in the skies.
The 787 relies more than any other modern airliner on electrical signals to help power nearly everything the plane does. It's also the first Boeing plane to use rechargeable lithium ion batteries, which charge faster and weigh less than other airplane batteries. Most of the 787 is made from lightweight composites instead of aluminum.
Boeing said it is aware of the latest incident and is working with ANA and regulators.
Other airlines stuck with the 787. United Airlines checked all six of its 787s overnight and was flying them as scheduled on Wednesday, spokeswoman Christen David said.
LOT Polish Airlines was beginning regular 787 flights between Chicago O'Hare and Warsaw on Wednesday, and it said its plans have not changed.
Its planes are among the later ones built by Boeing, meaning it received "proper modifications which reduce technical problems" seen in the 787s of other airlines, a statement from the airline said. A spokesperson declined to say more about which technical problems had been fixed.
Boeing was already under scrutiny after last week's fire, which was also tied to a lithium-ion battery in a different part of the plane.