By Keith Laing - 02/07/13 05:55 PM EST
National Transportation Safety Board (NTSB) Chairwoman Deborah Hersman said Thursday that the FAA should reconsider the exemptions granted to the Boeing 787 "Dreamliner" during certification testing before the plane is allowed to return to flight.
Hersman said the 787 was certified by the Federal Aviation Administration (FAA) after it was granted nine exemptions for "novel or unusual design features," including the use of lithium-ion batteries that have now sparked at least one electrical fire.
"Boeing assessed that the likelihood a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours," Hersman said during an update at the NTSB's headquarters in Washington.
"The 787 fleet has accumulated less than 100,000 flight hours, yet there have now been two battery events, results in smoke, less than two weeks apart, on two different aircrafts," she continued. "The assumptions that were used to certify the battery must be reconsidered."
The 787 was grounded by the FAA after a fire broke out on an airplane that was being operated by Japan Airlines at Boston's Logan International Airport. Other worldwide aviation agencies quickly followed the FAA's lead, resulting in a worldwide grounding of the Dreamliner that has lasted for nearly a month.
Hersman said Thursday that the NTSB's investigation of the battery that was involved has revealed that it experienced a short circuit that led to accelerated temperature increases known as "thermal runaway."
Hersman said that too was different than Boeing's initial projections.
"Boeing indicated that ... tests that were conducted before certification showed no evidence of cell-to-cell propagation or fire in the battery," she said. "However, our investigative findings with respect to the event battery showed that when a short circuit did occur, it resulted in cell-to-cell propagation ... and the fire."
The NTSB identified the special conditions that were placed on Boeing's use of lithium batteries by the FAA included maintaining safe cell temperatures and pressures; preventing uncontrolled temperature increases; stopping the emission of explosive or toxic gases; preventing fluids from damaged structures surrounding the battery; controlling the charge-rate of the battery to prevent overheating and installing monitoring and warning features on the battery.
Hersman said the NTSB's investigation, which she stressed is still incomplete, has revealed that "[T]here are nine special conditions; there are nine factors that they need to take a look at.
"What we have seen is with respect to a number of those special conditions, and also the assumption that they would not have a smoke event but less than once every 10 million flight hours, we have not seen that in the fleet performance," she added.
The Hill is checking with the FAA and Boeing for a response to the NTSB's concerns.