By Matt Tomsic
Published Feb. 7, 2013
The fire aboard a Boeing 787 in January began in the airplane’s auxiliary power unit battery’s sixth cell, said Deborah Hersman, chairman of the National Transportation Safety Board during a news conference today.
“We believe that the evidence points to a single cell,” Hersman said. “We do know that the short circuit came first, the thermal runaway followed in cell No. 6, and it propagated into the other cells.”
The NTSB is investigating a Jan. 7 fire aboard a Japan Airlines 787 at Logan International Airport in Boston, and the safety board provided updates today on the investigation and the incidents that predicated the fleet’s grounding.
After passengers and crew disembarked from the Japan Airlines 787, maintenance and cleaning personnel found smoke in the cabin and called firefighters, who put out the fire about 40 minutes after arriving on scene. The fire damaged the auxiliary power unit, or APU, battery.
During today’s news conference, Hersman also said the battery’s certification process needed to be reviewed.
Certification focuses on safety to ensure equipment meets minimum standards, she said, and the Federal Aviation Administration found that Boeing used novel or unusual design features that weren’t addressed by the FAA’s airworthiness regulation, so the administration issued special conditions with its certification.
Hersman said the NTSB is interested in how the FAA’s special conditions relate to the battery incident. Boeing studied possible battery failures and performed several tests, including tests designed to short-circuit the battery, Hersman said.
“Boeing has indicated that these tests showed no evidence of cell-to-cell propagation or fire in the battery,” Hersman said. “Boeing assessed that the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours.”
But the 787 fleet has accumulated fewer than 100,000 flight hours, Hersman said, and “there have now been two battery events resulting in smoke less than two weeks apart on two different aircrafts.”
The second event happened on an All Nippon Airways 787 in Japan about a week after the fire in Boston. Japanese regulators are leading that investigation, and the battery incident forced the emergency landing of an All Nippon Airways 787. The ANA flight was climbing at 30,000 feet when the crew noticed smoke and fumes in the cabin and flight deck. Japanese regulators haven’t characterized the issue as a “fire event,” Hersman has said.
“The assumptions used to certify a battery must be reconsidered,” she said.
The NTSB’s next steps include examining the methods for certifying the batteries, conducting tests on field replacement batteries and providing an interim report within 30 days.
“We are looking at a number of different scenarios,” Hersman said. “And obviously certification is over all of those issues.”