The senior US air safety official said Wednesday that even if his agency accepts Boeing's plan to fix batteries on its 787, the plane will need a slew of tests before it is allowed to fly again.
Federal Aviation Administration chief Michael Huerta was speaking after a report that Boeing might be able to make test flights as early as next week, but he seemed to suggest that the process might take time.
In testimony to the House of Representatives aviation subcommittee, said he expected to have an FAA report next week on Boeing's proposal.
"What Boeing has presented to us is a proposal that identifies a handful of probable causes that are all in the battery itself," he said.
"Once we approve the plan we have to go through the process of actually implementing the plan which will involve a great deal of testing, a great deal of further analysis and re-engineering before these planes are back in the air."
All 50 of the world's 787s were grounded on January 16 after the lithium-ion batteries on the cutting-edge plane overheated, causing a fire on one parked in Boston and smoke on another that forced an emergency landing in Japan.
The eight-cell battery was manufactured by GS Yuasa of Japan, which was hired for the project by Thales, a French subcontractor for the 787 Dreamliner, an all-new plane built largely with lightweight composite materials.
The lithium-ion batteries are significantly more powerful and lighter than the nickel-cadmium batteries used in other planes.
Huerta said that Boeing had presented a "comprehensive" plan that offers three levels of fixes, including design and re-engineering, to make sure that fire and smoke do not reoccur.
Boeing's plan focuses on a problem on a single cell, a problem that migrates to another cell and a problem that affects the entire battery, thus affecting the aircraft.
"We're working on the cell level, the battery level and the plane level," Huerta said, without providing details on the processes.
The Wall Street Journal reported this week that US government regulators have been working to give Boeing approval for test flights of its proposed battery fixes as early as next week, citing people familiar with the situation.
The people said Boeing had told some airline customers that if testing were conducted in early March, the jets could be carrying passengers by the end of the month, the Journal said.
The FAA gave Boeing approval earlier this month for two 787 test flights so the aerospace giant could collect data on the battery problems.
"I don't have an application in front of me for any other test flight," Huerta said.