Last week, a fire on a Japan Airlines Boeing 787 Dreamliner parked in Boston prompted American regulators to launch a comprehensive review of the new jet program. But they maintained the plane was safe and allowed it to keep flying during their unusual if not unprecendented re-examination.

Flight line

Boeing Co. has delivered 50 of its new 787s to airlines around the world. A look at which carriers are flying them:All Nippon Airways17Japan Airlines7Air India6*United Continental6Qatar Airways5Ethiopian Airlines4LAN Airlines (Chile)3LOT Polish Airlines2 *Four were made in North Charleston.Sources: Boeing, airlines

That changed Wednesday after pilots on an All Nippon Airways 787 had to make an emergency landing after another smoky battery malfunction. Before the day was over, the FAA had grounded Boeing’s technologically advanced jetliner, declaring that it won’t fly again until the onboard batteries are proven to be safe.

“Before further flight, operators of U.S.-registered Boeing 787 aircraft must demonstrate to the Federal Aviation Administration ... that the batteries are safe and in compliance,” the U.S. agency said in a statement accompanying its emergency airworthiness directive.

United Airlines is the only U.S. carrier with 787s, but aviation authorities in other countries usually follow the lead of the country where the manufacturer is based. The groundings already had begun early Wednesday, with Japan’s two major airlines halting flights. By Wednesday night, Reuters reported, Air India had grounded its six Dreamliners.

In a statement, Boeing CEO Jim McNerney said the Chicago-based aerospace giant is committed to the safety of its planes and those who fly in them.

“We are confident the 787 is safe and we stand behind its overall integrity,” the statement read. “We will be taking every necessary step in the coming days to assure our customers and the traveling public of the 787’s safety and to return the airplanes to service.”

Boeing South Carolina’s spokeswoman would not comment when asked whether the news would affect local test flights.

Boeing has delivered 50 Dreamliners to airlines around the world, including four assembled in the Boeing factory in North Charleston to Air India. Most were officially grounded as of Wednesday evening.

The groundings also potentially affect future deliveries, including the three 787s parked along the flight line of the local planemaking complex. The twin-aisle, composite-bodied 787 also is assembled in Everett, Wash.

The FAA’s order is the latest setback for a plane that was supposed to set a new standard for jet travel but has been beset by one issue after another, ranging from fires to a July engine failure in North Charleston to fuel leaks.

The latest battery incident raises the risk that the jet’s electrical problems are more dangerous than previously thought. So far, no one has suggested that the plane’s fundamental design can’t be fixed. But it is unclear how much will need to be changed.

The remedy could range from relatively quick-and-easy improvements to more extensive changes that could further delay deliveries just as Boeing is trying to double its 787 production to 10 planes per month. The company’s local factory, where more than 6,000 people work, is aiming to turn out at least three 787s a month by the end of the year.

Latest incident

All Nippon Airways said its pilots smelled something burning and received a cockpit message warning of battery problems Wednesday morning while flying from Yamaguchi Ube airport in western Japan to Tokyo.

The flight crew made an emergency landing at Takamatsu airport in western Japan, and passengers evacuated using inflatable slides.

An inspection found that a flammable liquid had leaked from the main lithium-ion battery, which is below and slightly behind the cockpit. Investigators found burn marks around the damage.

“Anytime you have a fire on board — whether it’s the battery that has caused it or a passenger that caused it or another electrical component — that’s a very serious situation on an aircraft and something not to be taken lightly,” said Kevin Hiatt, president of the Flight Safety Foundation.

Japan’s Kyodo News agency quoted transport ministry investigator Hideyo Kosugi as saying that the liquid leaked through the electrical-room floor to the outside of the aircraft.

The transport ministry said the leak could have led to an accident. ANA, which operates 17 Dreamliners, and Japan Airlines, which has seven, said they wouldn’t fly their 787s until they complete safety checks.

The 787 is the first plane to make extensive use of lithium-ion batteries, which have raised concerns in the past for their potential to catch fire. The FAA has given the batteries extra scrutiny and issued a special rule for their use in the 787. The plane has two batteries, the main one near the front and a second one in the rear.

Boeing and the airlines will need to move quickly to determine whether the problem is a flaw in the batteries themselves, in the plane’s wiring or in some other area that is fundamental to the plane’s electrical system.

The FAA said in a statement that it issued its grounding order because both incidents “resulted in release of flammable electrolytes, heat damage and smoke. ... These conditions, if not corrected, could result in damage to critical systems and structures, and the potential for fire in the electrical compartment.”

Popular plane

Boeing has booked orders for more than 800 of the planes from airlines around the world attracted by its increased fuel efficiency and improved passenger experience.

The jet is fuel-efficient because of its light weight, which derives in part from its use of electricity to do things that other airplanes do with hot air vented through internal ducts.

Before it carried paying passengers, the 787 was closely reviewed by inspectors from Boeing and the FAA.

Mike Sinnett, chief engineer on the 787, said last week that the plane’s batteries have operated through a combined 1.3 million hours and never had an internal fault.

He said they were built with multiple protections to ensure that “failures of the battery don’t put the airplane at risk.”

The lithium-ion design was chosen because it is the only type of battery that can take a large charge in a short amount of time.

Sinnett said Boeing was not considering replacing the lithium-ion design with another type of battery.

Neither GS Yuasa Corp., the Japanese company that supplies the batteries for the 787, nor Thales, which makes the battery charging system, would comment on the recent troubles.

All Nippon Airways and Japan Airlines were the 787’s first two customers — more than three years late — and remain among its biggest. But other 787s have had problems as well.

Back on Jan. 9, ANA canceled a domestic flight to Tokyo after a computer wrongly indicated there was a problem with the 787’s brakes. Two days later, the carrier reported two new problems with the aircraft — a minor fuel leak and a cracked cockpit windscreen.

Many of the 787s problems are typical of well-established planes around the world, many analysts have said, Hiatt said, adding that he would have no qualms about flying aboard a 787.

“That airplane is the most scrutinized plane in the air,” he said. “I would get on the airplane tomorrow.”

Transportation Secretary Ray LaHood dismissed any doubts that the FAA was not as diligent as it should have been when certifying the plane.

“Our people are the best, but we need to work with Boeing and to make sure everything we’ve done has been done correctly,” he said at a luncheon Wednesday in Washington.

Boeing was already under scrutiny for last week’s fire, which was also tied to the battery in the back of the plane.

That fire prompted investigations by the National Transportation Safety Board and the FAA, and the FAA later said it would review the design and manufacture of the plane, focusing on its electrical systems.

The NTSB said Wednesday that it would send an investigator to Japan to join the latest probe, and that representatives from the FAA and Boeing were on their way, too.

United frequent flier Josh Feller said he changed his plans to fly a United 787 from Los Angeles 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 email. “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.”

The Associated Press contributed to this report.