Well this is certainly a troubling development in your excellent continued coverage of this, Chuck. Considering the number of battery incidents that occurred so quickly in succession, I would say this was a gross underestimation on their part. I would expect more from a company like Boeing, especially when lives are at stake. It's not like they started making airplanes yesterday.
I'm sure that NTSB will implement a test with a "thermal runaway battery state" to check B787 for the worst scenario again.
There was a lot of information about the battery but nothing about the plane maintenance procedures. The Li-ion batteryes require complex electronics control which are in standby or switched off during " while the aircraft was being cleaned after a flight".
It also seems that more questions keep coming up about these incidents and the initial testing/certification. At this point, I would be very worried at Boeing as this seems to be an issue that will not go away with some simple changes!
Thank you Charles for keeping us at DN updated regularily!
I can't imagine the number of ways a battery can be induced to malfunction, let alone create a test to demonstrate the batteries vulnerability. A brief perusal of on-line battery certification references suggests the air-worthiness qualification requirements for any system is extensive. For Lithium-ion batteries it would be doubly so. These incidents seem to represent an aspect of this technology not previously seen which explains why there is so little information being presented to the press.
I think the NTSB and Boeing would get a whole lot more frequent flyer mileage with the general public if they gave just a bit more disclosure on the cause and effect of the fire. Driving nails thru cells to sim shorts and desktop analysis of fault probabilities doesn't go too far with road warriors. Either excess load or unregulated charge made those batteries fail unless they really are unreliable chemistry. They weren't that old. So either the electrons going inny or outy weren't being properly managed and that's outside the battery; not where the fire happened. The longer the answer isn't focused on, the more people lose confidence in the whole design. Not fair but reputation and confidence in equipment is 98% perception and only 2% direct experience.
When our Li-Ion battery failed in our aftermarket radio several years ago, many of the symptoms were the same as with the 787... much heat, vapor, venting, smoke... These were NOT the result of poor charging, overloading of the circuit... none of that! You say that shorting the cell with a nail is not a satisfactory test... What do you suggest is a more appropriate test? Easy to armchair quarterback this... For us, it turned out that the nail test was a fairly accurate predictor of the results of a short circuit... And gee, guess what? Our issue turned out to be the result of an internal cell short circuit... Really, the 787 issue sounds exactly like ours, only a scale difference... I would be looking very carefully at dendrite growth causing out-gassing internal to the cell, making the cell swell. internal parts can then slide and cause unforseen shorts and it is all downhill from there!
Interestingly dendrites have cropped up as the cause of the above system's failure. In the case of Cell#6 in the Boeing cluster an internal short was indicated in earlier posts. If this was caused by dendrite growth inside the cell then any evidence of that would be completely destroyed.
Dendrite growth leads to soft shorts to begin with, then as time progresses the condition worsens and if the cell is in a battery cluster, the other cells overwhelm the faulty cell to an extent where temperatures rise.
In Duracell we could detect zinc dendrite growth by x-raying the cell...it would show as a blurred outline penetrating the separator.
There are several research papers on the subject of dendrite growth in Lithium systems
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.
I don't know, Charles - first, this article seems nothing more than a rehash of stuff we've been seeing for weeks; second, it shows a lack of sophistication about how MTTFs (Mean Time To Failure) are determined and what they mean.
It's only possible to calculate a meaningful MTTF when a statistically significant number of cases have been run through the period in question - then you have real failures over real time to base the number on. In this case, where an unusual technology (lithium-cobalt) is being applied in a completely new application, all that can be done is to try to guesstimate an MTTF by imagining some specific failure modes, how often they might occur, and cranking to get a number. Would a company with integrity do this, you ask? Sure, if they were compelled to do the impossible by some inane government bureau to satisfy some inane regulation! If you need an example, look at our EPA requiring fuel providers to blend in ethanol in amounts that don't exist! Your government hard at work in fantasyland.
In other words, these MTTFs are often fantasy numbers, and we shouldn't be surprised when the reality turns out far different.
If some fault happens that was not considered in the calculation, then of course the actual failure will occur much sooner. This doesn't mean there was anything wrong with the calculation itself. Take the suggestion by an EE on this blog some days ago - that the problem was that individual cells shorted to the battery enclosure. As an EE myself, I can tell you that we can really build perfect insulation systems - that is, that their MTTF would be ~infinite. But if one is installed badly - or designed poorly - it might fail in a few hours. The original analysis might assume - duuh - that the cells would be insulated. But if this unanticipated problem occurred, a failure would happen much earlier than the calculated MTTF. Of course, this would also be a very easy problem to correct, which is why I doubt it's the cause; this would have been triumphantly announced already.
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.
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.
About a year ago, I was scheduled to fly back to Melbourne, FL from Jackson MS in a 7 am flight. We had boarded the plane and were sitting comfortably when the pilot came on the intercom and stated that the plane had a problem and would not be departing as scheduled. After about 45 minutes, he announced we should deplane and make other arrangements. After I rescheduled for a late afternoon flight, I was walking out to catch a ride. I ran into the pilot and crew. He stated that someone had left some switches in the cockpit in the wrong position and discharged the batteries. As we chatted I discovered they had to replace the ones in the plane which turned out to be Lithium Ions. Since they could not fly the replacement batteries on passenger aircraft, they had to send them to New Orleans via a cargo flight and then a technician had to drive them up to Jackson and replace them. I laughed because they could fly the INSTALLED batteries but could not fly the "loose" replacement batteries on commecial passenger airplanes. When I departed that evening about 5 pm the aircraft was still sitting there and as I understood it, it departed the next day, empty, back to Atlanta...
I think you have hit it one the head. As a veteran road warrior I have followed this subject with a combination of consternation and amusement.
Since their inception LiPo cell batteries have been variously considered
too hazardous for passengers to carry in their laptops
unsafe to carry spares
unsafe to carry spares unless especially caped
Some of the makers have had severe problems with battery failures resulting in burned users.
Yet suddenly (when the airplane makers want them) they are safe to use even when vital for flight.
I think both Boeing and NTSB have badly missed the mark on the hazard analysis here. One thin spot in the polymer spells a cascading short. Electable batteries might be a good solution if and only if the plane can fly safely without them. The military can supply the technology for the ejectors.
Sorry if I seem too firm here but we are dealing with a lot of people's lives, including mine.
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"??
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.
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.
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