The US National Transportation Safety Board's conclusion about the battery on board the JAL-owned Dreamliner seems to be at odds with the statement made by the Japanese official that "excessive electricity may have overheated the battery in the ANA-owned Dreamliner".
NTSB will examine the battery charger (made by UK's Securaplane Technologies Inc) and the auxiliary power unit (by US's United Technologies).
From Reuters (1/20/2013; emphasis is mine):
Dreamliner probe widens after excess battery voltage ruled out
(Reuters) - U.S. safety investigators on Sunday ruled out excess voltage as the cause of a battery fire this month on a Boeing Co 787 Dreamliner jet operated by Japan Airlines Co (JAL) and said they were expanding the probe to look at the battery's charger and the jet's auxiliary power unit.
Last week, governments across the world grounded the Dreamliner while Boeing halted deliveries after a problem with a lithium-ion battery on a second 787 plane, flown by All Nippon Airways Co (ANA), forced the aircraft to make an emergency landing in western Japan.
A growing number of investigators and Boeing executives are working around the clock to determine what caused the two incidents which the U.S. Federal Aviation Administration says released flammable chemicals and could have sparked a fire in the plane's electrical compartment.
There are still no clear answers about the root cause of the battery failures, but the U.S. National Transportation Safety Board's statement eliminated one possible answer that had been raised by Japanese investigators.
It also underscored the complexity of investigating a battery system that includes manufacturers across the world, and may point to a design problem with the battery that could take longer to fix than swapping out a faulty batch of batteries.
"Examination of the flight recorder data from the JAL B-787 airplane indicates that the APU (auxiliary power unit) battery did not exceed its designed voltage of 32 volts," the NTSB said in a statement issued early Sunday.
On Friday, a Japanese safety official had told reporters that excessive electricity may have overheated the battery in the ANA-owned Dreamliner that was forced to make the emergency landing at Japan's Takamatsu airport last week.
"The NTSB wanted to set the record straight," said one source familiar with the investigation who was not authorized to speak publicly.
U.S. investigators have already examined the lithium-ion battery that powered the APU, where the battery fire started in the JAL plane, as well as several other components removed from the airplane, including wire bundles and battery management circuit boards, the NTSB statement said.
On Tuesday, investigators will convene in Tucson, Arizona to test and examine the charger for the battery, and download non-volatile memory from the APU controller, with similar tests planned at the Phoenix facility where the APUs are built. Other components have been sent for download or examination to Boeing's Seattle facility and manufacturer facilities in Japan.
Securaplane Technologies Inc, a unit of Britain's Meggitt Plc that makes the charger, said it will fully support the U.S. investigation.
Officials with United Technologies Corp, which builds the plane's auxiliary power unit and is the main supplier of electrical systems on the 787, said they would also cooperate with the investigation.
(Full article at the link)
Meanwhile, The Seattle Times reports that the top management at Boeing secretly says the US regulators are overreacting.
30-Day free trial by following the link.
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11 comments:
secretly says they're overreacting? electrical fires on a plane? #brownsferryftw
Overreacting...
Let's all collectively remember the Toyota overreacting debacle.
and NRC is overreacting for wanting filtered vents installed.
The two statements are not in conflict as they appear to be, but they fail to highlight an aspect of the battery design.
The battery has 8 cells wired together to give the desired voltage. Each cell however is a little battery in its own right and must be managed as such. So while the overall voltage may have been within specifications, as the NTSB said, that does not prove that each cell was ok. It is quite possible that if one cell was out of spec and drawing too little power, the system could overcharge the others, as the JTSB suggested, while the battery voltage still looked good, as the NTSB said. Afaik, the battery controllers are not on a one per cell basis, but rather on each monitors multiple cells, so catching a discrepancy is not guaranteed.
Either way, it is clear that the current setup is not satisfactory and that Boeing was lucky to have avoided a disastrous in flight fire.
The grounding may wind up being longer than people generally hope, because if no clear cause can be found, this battery design will have to be scrapped.
We all know Silver is a monetary metal, but it's about time people switched from lithium batteries to Silver-Zinc batteries that are safer and more environmentally friendly. There is a reason that NASA uses Silver-based batteries as opposed to lithium-based batteries that are known to be a fire hazard...
NASA has the luxury of rescheduling when there are glitches and of treating the systems gently until they have to deliver. Those parameters do not apply to a commercial airline operation, where the schedule drives and delays mean losses.
The 787 batteries have very high charge/discharge rates in normal service from a very compact package, more than any other battery chemistry can deliver. A direct substitute does not exist currently, afaik. Hence the return to operations of the 787 may be slower than hoped for.
BA thinks the FAA overacted grounding the fleet but BA can't tell you what is wrong with the battery packs, sounds like a conflict to me (still could be a wiring/wire problem if they are lucky).
I believe if the battery backup/aux power design is found faulty then the entire 787 has to be re-certified because this is a core piece of engineering, the plane is built around it. Re-cert could take years including the rewiring for new battery packs.
This is why BA is standing behind the current and original design, anything else is back to the drawing board.
Silver/Zinc battery applications:
NASA: Launch-vehicle guidance and control, telemetry, NASA vehicles Lunar Rover and Mars Rover, space shuttle payload launch and power for the life-support equipment used by the astronauts during EVA’s.
Military: Missle systems, Navy: mines, buoys, deep submergence and rescue vehicles, torpedo propulsion, drones and submarines.
If the most critical applications rely on it, why doesn't Boeing and the civil aviation industry do the same? Is it a matter of putting more priority on cost-savings over safety?
While the use of Li-ion batteries in space is new they are used on space craft because of economy and high energy density to weight ratios.
http://www.clyde-space.com/products/spacecraft_batteries
http://aiaa.kavi.com/apps/group_public/download.php/3238/Attachment%2035-9,%20%20SC14_WG1%20LIB_ISO_20110523.pdf
The fact that the battery terminal voltage never exceeded 32 volts doesn't vindicate the charging system. Over-voltage is one way to murder a battery, but under the right circumstances, the job can be done without exceeding the maximum rated battery voltage.
Consider a battery with multiple cells. If one of those cells were to short, IR losses during charging would cause localized heating of the shorted cell. It will also cause the voltage drop across the remaining cells to increase above their nominal charging value. Each cell in the battery would then successively fail due to heating until the battery caught fire.
Since the overall battery resistance is lower with the shorted cell, it will attempt to draw more charging current. If the charging system doesn't have appropriate current limiting and/or a means of sensing battery temperature, the charger will cheerfully bring the battery to ignition temperature.
Other interesting areas to look into include the voltage/current profile used to charge the battery and the load (discharge) profile.
RE: "Meanwhile, The Seattle Times reports that the top management at Boeing secretly says the US regulators are overreacting."
The Seattle Times have been cheer-leading for Boeing since since the early days of aviation, so it's good to see that they still support our (former) home-town company.
With regards to the regulator's "over-reacting", Boeing is right. Some of the FAA regulators that have had 1st hand experience with exploding components, smoke-filled cockpits, and oxygen mask deployment become absolutely paranoid about safety. From that point on, you just can work with them. I'm sure that's the case here.
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