With 787 Dreamliners grounded around the world, Boeing is scrambling to devise a technical fix that would allow the planes to fly again soon, even as investigators in the United States and Japan are trying to figure out what caused the plane's lithium-ion batteries to overheat.
Ray LaHood, the transportation secretary, made it clear on Friday that a rapid outcome was unlikely, saying that 787s would not be allowed to fly until the authorities were "1,000 percent sure" they were safe.
"Those planes aren't flying now until we have a chance to examine the batteries," Mr. LaHood told reporters. "That seems to be where the problem is."
The Federal Aviation Administration on Wednesday took the rare step of grounding Boeing's technologically advanced 787s after a plane in Japan made an emergency landing when one of its two lithium-ion batteries set off a smoke alarm in the cockpit. Last week at Boston's Logan Airport, a battery ignited in a parked 787.
The last time the government grounded an entire fleet of airplanes was in 1979, after the crash of a McDonnell Douglas DC-10.
The grounding comes as the United States is going through a record stretch of safe commercial jet flying: It has been nearly four years since a fatal airline crash, with nearly three billion passengers flying in that period. The last airliner crash, near Buffalo, N.Y., came after a quiet period of two and a half years, which suggests a declining crash rate.
Investigators in Japan said Friday that a possible explanation for the problems with the 787's batteries was that they were overcharged — a hazard that has long been a concern for lithium-ion batteries. But how that could have happened to a plane that Boeing says has multiple systems to prevent such an event is still unclear.
Given the uncertainty, it will be hard for federal regulators to approve any corrective measures proposed by Boeing. To lift the grounding order, Boeing must demonstrate that any fix it puts in place would prevent similar episodes from happening.
The government's approach, while prudent, worries industry officials who fear it does not provide a rapid exit for Boeing.
The F.A.A. typically sets a course of corrective action for airlines when it issues a safety directive. But in the case of the 787, the government's order, called an emergency airworthiness directive, required that Boeing demonstrate that the batteries were safe but did not specify how.
While the government and the plane maker are cooperating, there are few precedents for the situation.
"Everyone wants the airplane back in the air quickly and safely," said Mark V. Rosenker, a former chairman of the National Transportation Safety Board. "But I don't believe there will be a corner cut to accomplish that. It will happen when all are confident they have a good solution that will contain a fire or a leak."
Boeing engineers, Mr. Rosenker said, are working around the clock. "I bet they have cots and food for the engineers who are working on this," he said. "They have produced a reliable and safe aircraft and as advanced as it is, they don't want to put airplanes in the air with the problems we have seen."
The government approved Boeing's use of lithium-ion batteries to power some of the plane's systems in 2007, but special conditions were imposed on the plane maker to ensure the batteries would not overheat or ignite. Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.
Even so, after the episode in Boston, the federal agency said it would review the 787's design and manufacturing with a focus on the electrical systems and batteries. The agency also said it would review the certification process.
The 787 has more electrical systems than previous generations of airplanes. These systems operate hydraulic pumps, de-ice the wings, pressurize the cabin and handle other tasks. The plane also has electric brakes instead of hydraulic ones. To run these systems, the 787 has six generators with a capacity equivalent to the power needed by 400 homes.
The 787's two main batteries, each about twice the size of a car battery, serve several functions. One, in the front of the plane, provides power for the plane's start-up and ground operations like refueling, and is a backup power for the electrical brakes. The second battery, in the back of the plane, is used to start the auxiliary power unit — a small engine that is used on the ground — and serves as a backup power source. Both batteries have had malfunctions.
It is not uncommon, of course, for new aircraft types to encounter problems. Last year, small cracks were found in the wings of the double-decker Airbus A380, which entered service in 2007. Regulators required inspections and, later, fixes that Airbus ultimately devised.
Airbus executives have expressed sympathy for their rival's current woes and said they were confident Boeing would get to the bottom of the problem. But some acknowledged that an extensive review of the battery technology could set off costly delays in Airbus's rival program, the A350-XWB, which uses the same type of batteries and is scheduled to enter service in late 2014.
Problems with lithium-ion batteries in the aviation world are not new and have contributed to dozens of fires aboard airplanes in recent years. Cessna was forced to replace lithium-ion batteries on its CJ4 business jet with nickel-cadmium after a battery fire on the plane in 2011. The CJ4 was certified under special conditions similar to the 787's.
It is possible that regulators will allow flights to resume before the safety board completes its investigation, which could take months, experts said.
"It's a real conundrum," said Kevin Hiatt, president and chief executive of the Flight Safety Foundation, an aviation research firm. "The question is how amenable is the F.A.A. right now before we know all the details of what's gone bad."
Experts said that regulators are ready to act more quickly, and that this has helped the industry's safety record.
"It took five major accidents before we grounded the de Havilland Comet," said John Cox, a longtime safety expert. "It took four before they grounded the DC-10, and with the Concorde, one before they grounded the airplane," he said. "With the 787, even without a major accident, there was enough concern that they grounded the airplane."
Mr. Rosenker, the former safety board chairman, agreed that regulators had reacted more swiftly than they once might have.
"Bad things can happen if you don't operate out of an abundance of caution," he said. "We've learned this over the years."
—Nicola Clark and Christopher Drew contributed reporting.