The NTSB said it was still a mystery why the systems designed to prevent such an event on the 787 failed, apparently in two cases, despite authorities having cleared the Dreamliner as a safe aircraft more two years ago.
Sequence of Events a Mystery
Subsequent testing showed clear evidence of a short circuit, a thermal runaway, and a fire, but scientists still did not know what the sequence of events was.
"We are early in our investigation," she said. "We are working very hard to determine what happened and why it happened."
The NTSB and other major aviation regulators last week ordered all 50 Dreamliners in global service grounded after the two battery incidents.
Boeing (IW 500/16) has since halted deliveries of the 787, introduced into service in October 2011 as an ambitious, energy-efficient aircraft designed with extensive use of lightweight composite materials and pioneering electrical systems.
Hersman said it was still a mystery why the systems designed to prevent such an event on the 787 failed, apparently in two cases, despite authorities having cleared the Dreamliner as a safe aircraft more two years ago.
"What we have seen from these two events does not comport with any of the risk analysis that we would expect to see with respect to reliability or smoke or a fire event in these batteries," she said.
"These events should not happen as far as design of the aircraft. There are multiple systems to protect against a battery event like this. Those systems did not work as intended. We need to understand why."
Copyright Agence France-Presse, 2013
