With 787 Dreamliners grounded around the world, Boeing is scrambling to come up with 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 Friday that a rapid outcome was unlikely, saying 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," 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 triggered a smoke alarm in the cockpit. Last week at Boston's Logan Airport, a battery caught fire 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 3 billion passengers flying in that period. The last airliner crash, near Buffalo, N.Y., came after a quiet period of 21 2 years, suggesting 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 incidents from happening.
The government's approach, while prudent, worries industry officials who fear it does not provide a rapid exit for Boeing.
The FAA 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 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, 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 catch fire. Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.
Even so, after the incident 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 power needed by 400 homes.
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' rival program, the A350-XWB, which uses the same type of batteries and is scheduled to enter service in late 2014.