Boeing is getting closer to figuring out the cause of battery problems plaguing the 787 Dreamliner, KING 5 reports.
The company has reportedly narrowed the cause to four or five possibilities, a source tells KING 5.
The company is seeking FAA approval to resume flights of one of its 787's to test its theories, which include temperature inside electrical bays where the lithium ion batteries are stored, and the effects of vibration.
Reuters reports the FAA has approved a one-time flight to ferry a grounded 787 from Texas to Washington state.
The plane would be staffed with a small crew that would have to continuously monitor the plane's battery and land immediately if it gets any warning messages.
The Wall Street Journal reported Wednesday the company is proposing a series of design changes to the batteries to minimize fire risks on 787's and allow for the resumption of flights while it seeks more permanent fixes.
NTSB Chair Deborah Hersman said Wednesday investigators were still likely weeks away from determining a cause.
Hersman told the Wall Street Journal investigators continue looking into the "assessments that were made" by the Federal Aviation Administration in approving the 787 plane and the steps that need to be taken before flights can resume. Hersman says regardless of the cause, the risks from the lithium ion batteries need to be "mitigated."
In another potential complication, CBS news reports the lithium ion batteries in use on the 787 don't meet federal guidelines instituted in 2008, because they were essentially "grandfathered" an exemption to the current regulations.
"Now the question is since the batteries have been called into question will Boeing be required to meet the current standard and could it meet the current standard," said CBS correspondent Sharyl Attkisson.
The NTSB has schedule a news conference Thursday to further detail its investigation.