A safety regulator on Thursday released hundreds of pages of details from its probe of a battery fire aboard Boeing's 787 Dreamliner, but the information did not reveal what caused the January blaze, and a call for hearings on the matter could slow efforts to get the plane back in the air.
The National Transportation Safety Board said it would hold two public meetings in April, one on the design and certification of Boeing 787's battery system, and a second on general lithium-ion battery technology the same month.
The NTSB is poring over the entire system, from the burned battery carcass to the certification and testing by the Federal Aviation Administration and Boeing.
Some experts were surprised by the hearings, given that there was no loss of life from the battery that caught fire aboard a parked jet shortly after it landed at Boston's Logan International Airport in January. A second incident in Japan a few days later prompted regulators worldwide to ban the 787 from commercial flight on January 16, a restriction costing Boeing and airlines millions of dollars a day.
"It's unusual to have hearings when you haven't had a major incident," said John Hansman, co-chairman of an FAA advisory committee and a professor of aeronautics at the Massachusetts Institute of Technology
Such "unprecedented public scrutiny" of the battery, he said, tends to slow down the process and make people behave more conservatively. "They don't want to look like they're being rash."
The NTSB's 39-page "interim factual report," part of 499 pages of studies released on Thursday, provides extensive detail on the testing performed on the battery. It also makes clear that investigators remain a long way from understanding why the battery caught fire in the first place.
Boeing called the report a "positive step" toward completing the investigation and a spokesman Marc Birtel said the company had worked closely with the NTSB to understand what happened.
The FAA did not respond to a request for comment.
Greg Feith, a former NTSB investigator, said the NTSB reports spread blame for the failure beyond Boeing by highlighting how many organizations were involved in the system.
The report also suggests that the NTSB is looking at whether the FAA, and its designees who work at Boeing, had the technical knowledge to critically question test data used to show the failure rate for the battery was acceptably low.
"The FAA will be under scrutiny to demonstrate that the guys responsible for signing off on these things at Boeing had the levels of knowledge to be able to identify shortcomings for correction prior to the airplane being certified," said Feith, a partner at Media and Communications Strategies consulting firm in Washington, D.C.
Over the past eight years, the FAA has outsourced much of its oversight of Boeing and other aircraft makers to so called "designees" who work for the companies but have the power to certify work on the FAA's behalf.
Jim Hall, who was chairman of the NTSB from 1995 to 2000, said it was appropriate for the board to exercise oversight of the FAA's certification process, given the changes to the system.
"Essentially, now Boeing is designating their own representatives rather than the federal government," he said. "It raises in my mind a number of issues that I hope the investigation will answer with regard to the certification process."
SMOKE IN THE CABIN
While the report did not determine what sparked the battery fire, it revealed new details about the battery system.
For example, a system designed to vent smoke from the plane during a battery fire failed to function because it lacked power after the battery caught fire. The system's auxiliary power unit (APU), a gas-driven engine in the tail of the plane, also was shut off at the time, and the battery is used to start that system.
"As a result, smoke generated by the APU battery could not be effectively redirected outside the cabin and aft (electrical equipment) bay," located in the fuselage behind the right wing of the 787.
Boeing had said that the venting system failed because the plane was on the ground and lacked cabin pressure to use in expelling fumes from the cabin.
The NTSB report, while marking a milestone in the probe of the Boston fire, also signaled that the NTSB has significant additional work to do in its investigation.
The NTSB said a group focused on system safety and certification was going through records of testing and analysis performed by Boeing and its suppliers, system maker Thales SA of France, and battery maker GS Yuasa Corp of Japan.
The NTSB report also revealed abnormal function of the battery shortly before the fire was reported. It said a flight data recorder showed that the voltage and current in the battery fluctuated sharply, though never exceeded 32 volts, its rated level. Overcharging has been associated with fire.
About 21 minutes after the plane landed at Logan, the battery voltage dropped to zero and rebounded to 28 volts three times in three seconds.
About three minutes later, a ground crew member "reentered the cockpit and reported smoke in the cabin," the report said.