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.
On Jan. 7, the battery near the rear of a Japan Airlines 787 burned shortly after the plane landed at Boston Logan and passengers had gotten off. It took firefighters 40 minutes to put it out.
That fire prompted investigations by the U.S. National Transportation Safety Board and the Federal Aviation Administration, and the FAA later said it would review the design and manufacture of the plane, focusing on its electrical systems.
The NTSB said on Wednesday that it is sending an investigator to Japan to join the newest probe.
Other 787s have recently had problems with certain electrical panels on the 787 and fuel leaks.
ANA canceled a domestic flight to Tokyo on Jan. 9 after a computer wrongly indicated there was a problem with the Boeing 787's brakes. Two days later, the carrier reported two new problems with the aircraft — a minor fuel leak and a cracked windscreen in a cockpit.
The earliest manufactured jets of any new aircraft usually have problems and airlines run higher risks in flying them first, said Brendan Sobie, Singapore-based chief analyst at CAPA-Center for Aviation. Since about half the 787 fleet is in Japan, more problems are cropping up there.
GS Yuasa Corp., the Japanese company that supplies all the lithium ion batteries for the 787, had no comment as the investigation was still ongoing. Thales, which makes the battery charging system, had no immediate comment.
Boeing has said that various technical problems are to be expected in the early days of any aircraft model.
"Boeing is aware of the diversion of a 787 operated by ANA to Takamatsu in western Japan. We will be working with our customer and the appropriate regulatory agencies," Boeing spokesman Marc Birtel said.
United frequent flier Josh Feller said he changed his plans to fly a United 787 from Los Angeles International to Houston next month because of the 787's troubles.
"I've been following the 787 news closely and the latest incident finally spooked me into changing my flight," he said by e-mail. "It's an unnecessary risk and since I was going out of my way to fly the plane in the first place, decided to change flights." He also wanted to avoid any disruptions if United eventually grounds the 787.
Aviation safety expert John Goglia, a former National Transportation Safety Board member, said the ANA pilot made the right decision.
"They were being very prudent in making the emergency landing even though there's been no information released so far that indicates any of these issues are related," he said.
But much remains uncertain about the problems being experienced by the 787, said Masaharu Hirokane, analyst at Nomura Securities Co. in Tokyo.
"You need to ensure safety 100 percent, and then you also have to get people to feel that the jet is 100 percent safe," Hirokane said.
Associated Press Writers Elaine Kurtenbach and Yuri Kageyama in Tokyo, Kelvin Chan in Hong Kong, Scott Mayerowitz in New York and Joan Lowy in Washington contributed to this report.