NTSB: Boeing Dreamliner blaze probe needs more time
An interim report from the National Transportation Safety Board offers insight into the state of the battery in a Japan Airlines fire in January, but there's still more work to be done.
The organization noted that the report was strictly factual in nature and based on initial findings. That meant it didn't detail a clear-cut reason for the fire, provide analysis, or make any conclusions or recommendations.
The NTSB said its investigation into the probable cause of the 787 battery fire is continuing. It's also continuing to review the design, certification, and manufacturing process for the 787 lithium-ion battery system.
The Federal Aviation Administration ordered airlines to ground their fleets of the much-hyped Dreamliner in January after a series of fires involving the aircraft's lithium-ion batteries. The action came on the heels of Japanese carriers All Nippon Airways and Japan Airlines grounding their 787s after a battery fire forced the evacuation of an ANA flight.A similar incident, the one detailed today by the NTSB, occurred January 7 when a JAL 787 on the ground at Boston's Logan International Airport caught fire. The blaze was discovered by staff while the plane was parked at the airport for cleaning.
In response, the FAA announced it would conduct a comprehensive review of the aircraft, which features innovative use of composite materials.
A month ago, the NTSB said the January 7 fire originated with the short-circuiting of a single cell in the battery that then spread to other cells. Charred battery components indicated that the temperature inside the battery case exceeded 500 degrees Fahrenheit.
At that time, it was unclear what caused the battery to short-circuit. The NTSB said potential causes of the initiating short circuit being evaluated included battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
Despite the ongoing investigation, the FAA last month granted Boeing permission to resume test flights, but those flights have been subject to a number of restrictions. That includes limiting the flights to specific airspace over unpopulated areas and conducting preflight testing and inspections and in-flight monitoring.
The NTSB noted today that a maintenance manager in the JAL cockpit on the day in question observed that the auxiliary power unit (APU), the sole source of airplane power at the time, had automatically shut down. Shortly thereafter, a mechanic opened the aft electronic equipment bay and found heavy smoke and fire coming from the front of the APU battery case.
The APU battery provides power to start an APU during ground and flight operations, the NTSB said. Flight data recorder data showed that the APU was started about 10:04 while the airplane was being taxied to the gate after arrival in Boston. The FDR data also showed that, about 36 seconds before the APU shut down at 10:21:37, the voltage of the APU battery began fluctuating, dropping from a full charge of 32 volts to 28 volts about 7 seconds before the shutdown.
Within the APU battery are eight lithium-ion cells connected in series and assembled in two rows of four cells. Looking at the external casing of the battery showed that the right side of the case had the most extensive damage, and disassembly of the battery revealed that to be the case. Most of the cells were found to be electrically short-circuited except for one, cell No. 8.
Here's the full executive summary:
The National Transportation Safety Board (NTSB) notes that the information discussed in this interim factual report is based on initial findings from the investigation of this incident. Because the investigation is continuing, no conclusions or recommendations are being made at this time. Readers are encouraged to access the public docket for this incident (DCA13IA037) for further details about the information presented in this report. In addition, readers are advised that the information presented in this report could change if new evidence becomes available.
On January 7, 2013, about 1021 eastern standard time, smoke was discovered by cleaning personnel in the aft cabin of a Japan Airlines (JAL) Boeing 787-8, JA829J, which was parked at a gate at General Edward Lawrence Logan International Airport (BOS), Boston, Massachusetts. About the same time, a maintenance manager in the cockpit observed that the auxiliary power unit (APU)--the sole source of airplane power at the time--had automatically shut down. Shortly afterward, a mechanic opened the aft electronic equipment (E/E) bay and found heavy smoke and fire coming from the front of the APU battery case. No passengers or crewmembers were aboard the airplane at the time, and none of the maintenance or cleaning personnel aboard the airplane was injured. Aircraft rescue and firefighting personnel responded, and one firefighter received minor injuries. The airplane had arrived from Narita International Airport, Narita, Japan, as a regularly scheduled passenger flight operated as JAL flight 008 and conducted under the provisions of 14 Code of Federal Regulations Part 129.
The APU battery provides power to start an APU during ground and flight operations. Flight data recorder (FDR) data showed that the APU was started about 1004 while the airplane was being taxied to the gate after arrival at BOS. The FDR data also showed that, about 36 seconds before the APU shut down at 1021:37, the voltage of the APU battery began fluctuating, dropping from a full charge of 32 volts to 28 volts about 7 seconds before the shutdown.
The APU battery consists of eight lithium-ion cells that are connected in series and assembled in two rows of four cells. Each battery cell has a nominal voltage of 3.7 volts. The cells have a lithium cobalt oxide compound chemistry and contain a flammable electrolyte liquid.
External observations of the battery involved in this incident showed, among other things, that the right side of the battery case appeared to have the most extensive damage of the four battery sides. Disassembly of the battery revealed that the cells that were located in the left side of the battery (cells 1 through 4) generally exhibited the least thermal and mechanical damage and that the cells that were located in the right side of the battery (cells 5 through 8) generally exhibited the most thermal and mechanical damage. Thermal damage was the most severe near cell 6. Continuity measurements using a digital volt meter indicated that all of the cells were found to be electrically short circuited except for cell 8.
The APU battery was configured so that each cell's vent disc, which is a plate that ruptures when the internal pressure in a cell reaches a predetermined level, would be oriented toward the exterior of the battery. Disassembly of the battery showed that the vent discs on cells 1 through 3 were opened slightly, the cell 4 vent disc was intact (although weight measurements indicated that the cell lost some electrolyte), and the vent discs on cells 5 through 8 had opened more completely, leaving a ruptured appearance.
The NTSB is examining the certification and testing of the 787 battery system as part of its investigation of this incident. According to the Federal Aviation Administration (FAA), the 787 incorporated "novel or unusual design features," including the use of lithium-ion batteries. Because the FAA determined that applicable airworthiness requirements did not address lithium-ion batteries, the agency issued nine special conditions regarding the use of these batteries on the 787. These nine special conditions were intended to ensure that this new technology would not pose a greater safety risk than other technologies addressed in existing airworthiness regulations.
During the 787 certification process, Boeing performed a safety assessment (known as functional hazard assessment) to determine the potential hazards that various failure conditions of electrical system components could introduce to the airplane and its occupants. Boeing also determined that the probability that a battery could vent was once in every 10 million flight hours. As of January 16, 2013, the in-service 787 fleet had accumulated less than 52,000 flight hours, and during this period two events involving smoke emission from a 787 battery (the BOS event and a second event in Japan being investigated by the Japan Transport Safety Board) had occurred on two different 787 airplanes.
The NTSB's investigation into the probable cause of the 787 battery fire at BOS is continuing. The NTSB is also continuing to review the design, certification, and manufacturing processes for the 787 lithium-ion battery system.