Without Answers, 787 Probe Could Stretch Into 'Weeks' Safety systems 'did not work as intended,' says NTSB official By Mark Russell, Newser Staff Posted Jan 25, 2013 12:17 PM CST Updated Jan 25, 2013 1:08 PM CST 4 comments Comments The burnt blue casing that contained a total of 8 battery cells from the Boeing 787 Dreamliner that caught fire at in Boston on Jan. 7 is seen on a cart at the NTSB lab in Washington. (AP Photo/Manuel Balce Ceneta) (Newser) – The bad news keeps coming for Boeing, whose 787 Dreamliner fleet remains grounded—US investigators still don't know what caused the battery fire in a Jan. 7 fire in Boston, reports Reuters. The National Transportation Safety Board says it has found a series of "symptoms" in the battery, but are nowhere near knowing the underlying cause. The NTSB chair would not say how long the investigation might take, but a former NTSB chair predicts, "It's going to take them longer. Weeks, not days." Investigators are concerned that back-up protections designed to prevent a "thermal runaway"—a chain reaction causing the battery to overheat—did not work, reports the Los Angeles Times. "There are multiple systems to protect against a battery event like this," says the current NTSB chair. "Those systems did not work as intended."