Boeing engineers and federal regulators appear to have vastly underestimated the possibility of a lithium-ion battery fire before the 787 Dreamliner was certified.
An interim report released last week by the National Transportation Safety Board said Boeing engineers believed an incident like the Jan. 7 fire on a Japan Airlines plane at Boston's Logan International Airport had a probability of happening just once in a billion flight hours. So far, the 787 fleet has logged approximately 52,000 hours and has already had two incidents in which batteries were burned.
A fire captain who responded to the Boston fire "reported that the battery was hissing loudly and that liquid was flowing down the sides of the battery case," the NTSB said in its 48-page report. "He heard a 'pop' sound," and smoke began pouring out of the electronics equipment bay. The captain "received a burn on his neck when the battery, in his words, 'exploded.'"
Click on the image below to see different views of the charred battery.
The auxiliary power unit (APU) battery area showed damage consistent with smoke, hot gases, and discharged electrolyte. (Source: NTSB)
The incident occurred while the aircraft was being cleaned after a flight. A mechanic told the NTSB that he found heavy smoke in the electronics equipment compartment and then discovered two small flames at the connectors on the front of the battery case. After trying unsuccessfully to douse the flames with a fire extinguisher, he called the airport's fire department, which used a handheld thermal imaging camera to discover what a firefighter called "a white glow about the size of a softball" amid the smoke. The temperature of the battery reached 1,250F, the NTSB told Design News.
That fire was the first of two battery-related incidents for the 787. Nine days later, a 787 operated by All Nippon Airways Co. made an emergency landing at Takamatsu Airport in Japan. Though the batteries sustained heat damage, it's not yet clear whether a fire was involved in that incident.
The two incidents appear to contradict Boeing's original functional safety hazard assessment of the 787 electrical power system. That assessment, made before certification, identified two potential hazards pertaining to the aircraft's main and auxiliary power unit (APU) batteries. The first hazard, "battery vents smoke/fire," was assessed with an average probability of 1 x 10-9 per flight hour, according to the NTSB report. The probability for the second, "battery vent and/or smoke without fire," was classified as 1 x 10-7 per flight hour. The assessment now appears to make the events about 20,000 times less likely than what has occurred at this point.
Boeing evaluated the probabilities by puncturing a battery cell with a nail to induce short circuiting. "This test resulted in cell venting with smoke but no fire," the report said. The company's engineers then combined those results with information from other manufacturers to determine that the likelihood of cell venting (without fire) would be about once per 10 million flight hours.
The NTSB still does not know what caused the JAL fire. It examined the battery and its eight cells. "All of the cells were found to be electrically short circuited except for cell 8," and four of the cells "exhibited a darkened, charred appearance."
Still, no one as yet knows exactly why the short circuit occurred. Before certification, Boeing's analysis determined that overcharging was the only failure mode that could cause a cell to vent fire. However, NTSB investigators have said the JAL battery was not overcharged.
The agency is "continuing to review the design, certification, and manufacturing processes for the 787 lithium-ion battery system."
Lots of misunderstandings here (the dangers of a little knowledge, and all that jazz). Firstly the certification data does not cite the RELIABILITY of the battery system, it cites the HAZARD RATE of the battery system - the instantaneous probability of failure at any moment in time (which is why it's quoted in a "per flying hour" figure rather than an MTBF). These are very different characteristics and cannot be related to eachother directly.
Secondly two arrisings in 52,000 hours does not mean that the MTBF is 26,000 hours; it means that the MTBF probably lies somewhere in the range 1,200 hours to 10^10 hours. Assuming the batteries had been through burn-in/PRAT programmes (which it's rather difficult to NOT do for aircraft equipment) then they'd be in the "random" or (as often misnamed) "constant failure rate" region of the bathtub curve. In this region it's the spaces between the failures that are random, and you need a decent population of samples to draw any conclusions about failure rates. Two is far too small a number from which to deduce ANYTHING.
Finally there's comment about the "driving the nail through test" as if it was the only test performed. Again, I don't know about this specific system but I *do* have experience of qualifying equipment onto aeroplanes, and I would be very surprised if the battery system didn't get exactly the same set of basic qualification tests as every other significant part of the avionics - thermal, vibration, shock, bump, humidity, mould etc etc.
All batteries re dangerous because they store energy, and if the energy gets out through an unintended back door that leads to "bad stuff"(tm). Aircraft batteries tend to be big, and so there is a lot of stored energy, that's all. Now the only difference between the LithiumCobalt (as these are) technology and the previous Nickel or lead-based technologies is that the Lithium cells have a self-oxidising electrolyte that will burn in the absence of air, so it's difficult to extinguish. So the trick is to stop them getting hot in the first place. For this reason all non-trivial lithium charging systems use single-cell charging techniques (monitoring the voltage of each cell throughout the charge). This is proven technology, and we really need to wait to find out what the ACTUAL failure mode was, rether than getting hysterical about the subject before we know what really happened.
I'm(was) an aircraft design engineer. In my old times we didn't implement systems not able to work at -50 deg C. the planes are not flying or landing only in California....
I cannot help but wonder how much experience the battery box engineers have with lithium cells. Without mechanical endplates and tiebars, the batteries will physically swell at about 90SOC, gradually fracturing the internal structure.
Eventually they will short, typically during the end of the charge cycle. This feature is well known, yet completely lacking in the sheetmetal Boeing housing.
Easy there, ghost rider. The nature of a blog is armchair quarterbacking. If the premise is that the lithium battery suffers inherent dendrite growth, then you've answered the mail, the chemistry is not suitable for aircraft safety. My premise was something wasn't passively managed properly external to the battery. Charge rate, temperature, discharge, short circuit or load test. The main premise here is not to bang the square error into the historical round past failure mode. It is more about questioning whether the solution is to properly compartmentalize the potential for fire or prevent a runaway condition or detect and countermand a defective battery when bad conditions can be sensed. Even those simple nicad packs on power drills have basic circuits that detect when one cell has reached max charge condition. I think the Boeing/Yuasa course will work in the short run to get dreamliner out of money black-hole limbo. Those batteries will be the best maintained in the fleet, while something else smolders and degrades. And I don't think this is about incompetence or deliberate malfeasance, either. Flying is a balancing act, between money, time and safety. But most birds don't think about that.
Ha, well the NY Times usually reports things quite accurately (give or take a few missteps along the way). Well then the FAA was asleep at the wheel, too! But you're right, both Boeing and the FAA must shoulder the blame for this and hopefully won't make the same mistake again.
From what I've read in the past the FAA approved the design of the batteries before production. However I read this in the New York Times so might not be totally accurate. If true Boeing can't get all of the blame. But I agree with you I would expect more from both groups.
Ignorance and gone is the hubris about aeronautical engineers being superior to automotive engineers.
How old is the Volt design? They knew about the problem and designed means to handle it and even had to strengthen that later.
Ignorance costed out the sway bar on hte Corvair... people running around with fancy degrees assuming that they have superior knowledge.
If this isn't handled with a cooling system, I suspect that a crash will ignite things far more quickly. Superhazardness. Looks like hte battery should be jettisoned before impact.
I am not a member of the psychic community so I will not pretend to know the cause of the fire. I am troubled by the information that is missing from reports that I have read. If I was in the position of determining reliability, I would have decades of historical data that could be used directly, or by extrapolation, for most critical components - except for the batteries. A casual criticality analysis would also point to the batteries as a potential danger area. This being the case, I would cover my butt with a barrage of different empirical testing and ensure adequate monitoring was in place. The bottom line is that there is circumstantial evidence that adequate testing was not performed, internal Boeing review processes did not catch it, and the Feds went along with everything.
The major item of concern for me is that some number of Boeing engineers 'touched' this project without a serious level of concern. IMO, the "we drove a nail" test should have been plural and emphasized - "We ran 37[?] long term tests involving shorts, vibration, load changes,...". During my career I have observed that companies in defensive mode after a disaster are usually determined to deflect responsibility by doing a data dump of techno-babble like "we calculated that this would last forever based on manufacturer's data and we confirmed this by running 5,000 different tests that simulated 600 years of operation, blah, blah,...".
The simple question in my mind is "Are these failures due to cover up or incompetence"??
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