United Airlines said Thursday it expected to keep its six Boeing 787s out of service until May 12, as the cutting-edge airplane remained grounded worldwide due to battery problems.
United, the only US airline with the 787 Dreamliner, just two days ago announced it would keep them on the ground through March 30.
United has "tentatively" scheduled a 787 on its Denver route to Tokyo's Narita International Airport on May 12, UAL spokeswoman Christen David said in an emailed response to a query.
"We are taking the 787 out of our schedule through June 5, except for Denver-Narita," she said.
A person close to the airline's situation noted the Federal Aviation Administration (FAA) investigation of overheated lithium-ion batteries on the 787 was ongoing and schedule adjustments were necessary.
All 50 787s in service around the world have been banned from flight since January 16 after a battery fire on a parked plane and battery smoke on another one forced an emergency landing.
US and foreign investigators have reported progress in the probe of the lithium-ion batteries but have yet to pinpoint the cause of the problems.
Boeing is set to propose temporary fixes to the battery problems to US air-safety regulators Friday and could have them back in the air in two months, The New York Times reported.
The Times, citing industry and federal officials, said Boeing had narrowed down the ways in which the lithium-ion batteries could fail, concluding they would be safe to use after making changes such as adding insulation between the battery cells.
Boeing commercial airplane division chief Raymond Conner will unveil the proposals in a meeting Friday with FAA chief Michael Huerta, according to the Times.
Federal officials told the newspaper the aircraft could be back in the air by April if the fixes are approved.