The Federal Aviation Administration is close to approving tests of Boeing's approach to fixing the batteries on its 787 jets, and the tests could begin next week, federal and industry officials said Wednesday.
The FAA could still demand changes in Boeing's proposed new battery design if problems develop in the laboratory and flight tests, which will take several weeks. But the decision to start the tests will be a major step in Boeing's efforts to get the innovative jets, which have been grounded since mid-January, back in the air.
The federal approvals are expected late this week or early next week, even though some battery specialists remain concerned that investigators have not found the precise cause of two incidents in which the jetliner's new lithium-ion batteries emitted smoke or fire.
The National Transportation Safety Board has found that a short-circuit in one cell caused a battery in a jet parked at Logan Airport in Boston to overheat and burst into flame on Jan. 7. The board plans to release a preliminary report on that incident on Thursday.
But investigators in Japan have suggested that something else may have caused the battery on an All Nippon Airways 787 to emit smoke on a flight on Jan. 16. They said the battery may have been hit by a surge of electrical current from another part of the plane.
Donald R. Sadoway, a professor of materials chemistry at the Massachusetts Institute of Technology, said the Japanese data suggested that temperatures might have shot much higher in that battery than in the one on the plane in Boston. If that is true, he said, Boeing and the FAA might need to add more steps to the safety plan.
The FAA's Seattle office on Wednesday was completing its recommendation to approve Boeing's plan for the tests, which are needed to certify that its proposed fixes would work, federal officials said. The plan is still subject to approval by Michael P. Huerta, the head of the FAA, and Ray LaHood, the transportation secretary, who will be briefed on it over the next several days.
LaHood said in January that the planes ''won't fly until we're 1,000 percent sure they are safe to fly.'' Department officials said LaHood and Huerta had been kept informed of the details of the proposal as it was created, and they are expected to sign off on it.