NTSB identifies origin of JAL Boeing 787 battery fire
ntsb.gov
ntsb.gov
> the majority of evidence from the flight data recorder and both thermal and mechanical damage pointed to an initiating event in a single cell. That cell showed multiple signs of short circuiting, leading to a thermal runaway condition, which then cascaded to other cells.
> Boeing ... determined that the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours ... there have been two critical battery events on the 787 fleet with fewer than 100,000 flight hours.
Seems like Musk was right in his guess after all (http://www.flightglobal.com/news/articles/elon-musk-boeing-7...), but it is shocking how badly Boeing got its estimates wrong. Does anyone know exactly how they came up with these numbers?
Have any pointers on the switch from engineering-driven to whatever they are now? I'd love to read more.
Long before any incidents, Boeing estimated a smoke event as once in 10 million hours. The measured rate of fire events is much higher than Boeing's pre-certification estimate of the rate of smoke events. There is absolutely no implication that Boeing's definition of smoke event doesn't include fires.
Edit: as mentioned below, the real problem seems to be that you're assuming smoke implies fire, when smoke merely suggests fire.
> During the 787 certification process, Boeing studied possible failures that could occur within the battery. Those assessments included the likelihood of particular types of failures occurring, as well as the effects they could have on the battery. In tests to validate these assessments, Boeing found no evidence of cell-to-cell propagation or fire, both of which occurred in the JAL event. The NTSB learned that as part of the risk assessment Boeing conducted during the certification process, it determined that the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours.
So, to summarize, in the certification process, Boeing claimed:
a: no evidence of a fire.
b: a 10-million-hour estimate for a "smoke event".
My original question was merely from a statistical/technical perspective: how is this figure calculated if they have no evidence of the event they are supposed to measure? From my understanding, automobiles undergoing similar certification are tested under abnormally rigorous conditions, and the chances of those conditions happening are taken into account when calculating failure rates. But if Boeing claims it had no evidence of a fire happening at all, what is the reasoning behind the number? Is it just a convenient way to say probability=0?
http://en.wikipedia.org/wiki/Fault_tree_analysis
It sounds like one of their incoming assumptions--a probability, a manufacturing spec, something like that--didn't match up with reality. That happens. They're probably going over the fault tree, madly trying to figure out which one and by how much.
Boeing counted a malfunction as a "smoke event" which is a release of emissions from a battery overheating, not necessarily a fire. The no evidence of a fire is a claim that regardless of a battery failure, there is no plausible failure chain that leads to a fire beginning in the battery.
>>But if Boeing claims it had no evidence of a fire happening at all, what is the reasoning behind the number? Is it just a convenient way to say probability=0?
In the case of a fire, yes. But this just means that the battery fault alone won't cause a fire. If other systems fail all bets are off. I suspect you are conflating smoke event with a fire.
>>My original question was merely from a statistical/technical perspective: how is this figure calculated if they have no evidence of the event they are supposed to measure? From my understanding, automobiles undergoing similar certification are tested under abnormally rigorous conditions, and the chances of those conditions happening are taken into account when calculating failure rates.
As I explained above, Boeing claimed that it was possible that a battery could malfunction(one in ten million hour), but they had no plausible scenario that could lead to a fire. In this case, battery malfunctioning does not necessarily equal a fire. The smoke event is calculated from a number of probabilistic factors such as the confluence of the possibility of electrical overcharging and arcing and simple faults with the battery. It is a made up number that doesn't take into account that this is a new design that introduces other possibilities of failure.
If smoke doesn't imply fire then P(smoke) > 0 doesn't imply P(fire) > 0.
Eh, I don't think that means much. You can't put odds on an unknown failure mode.
Unless Boeing's subcontractors have made ground breaking advances in the design of lithium-ion cells then these criticisms are enormously well founded. And as we've seen those subcontractors have not, in fact, found a magical escape from the fundamental problems of thermal runaway and chain-reaction in lithium-ion cells.
A good engineer doesn't need to see detailed diagrams, etc, pop open a couple files and you've got a pretty good idea of whether a project is good, or is fucked.
Yeah, some luck that guy has...
That said, if this is the proximate cause of the smoke and fire then it points to some ways to fix the problem that don't involve completely re-designing the way the plane is built which is good news for Boeing.
As for the 'other chemistry' arguments, one of the challenges of various battery chemistry is the rate of charge and the rate of discharge. My Battlebot team went through a number of battery packs for our robots[1] and found that the energy-density, charge rate, and discharge rate was one of those "pick any two" scenarios. A pain to work around.
Boeing and Lockheed are pretty much the only space flight companies working with the government. Musk has an issue with this which is why his battery predictions are so enjoyable.
http://articles.washingtonpost.com/2011-10-16/business/35279...
http://www.ntsb.gov/investigations/2013/boeing_787/boeing_78...
Further reading: http://en.wikipedia.org/wiki/Auxiliary_power_unit
Edit: after further research, it seems compressed air is not used on the 787. It's all electric (two generators on the APU and on each engine):
"The power source for APU starting may be the airplane battery, a ground power source, or an engine-driven generator. The power source for engine starting may be the APU generators, engine-driven generators on the opposite side engine, or two forward 115 VAC ground power sources. The aft external power receptacles may be used for a faster start, if desired."[1]
1. http://www.boeing.com/commercial/aeromagazine/articles/qtr_4...
Evidently adding the APU saves enough money to justify its significant weight.
- backup power for emergencies - allowing attempted engine restarts in the air - allowing the airplane to be self-sufficient should it be forced to land somewhere without ground equipment (or big enough ground equipment)
As investigators work to find the cause of the initiating
short circuit, they ruled out both mechanical impact damage
to the battery and external short circuiting.
Chairman Hersman said that potential causes of the initiating short circuit currently being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
They don't know the precise cause, but they have narrowed it down to a few possibilities.
Paraphrase:
"The thing we built doesn't work properly, and we think it could be because of how it works, how we designed it, or how we built it".
Sounds like a useful assessment.
They've just learned what areas to focus on.
Chairman Hersman said that potential causes of the initiating short circuit currently being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
You buy some electronic/hobby equipment while traveling, put in your luggage among your clothes. In mid-flight those things get shorted and everybody is doomed.
Those batteries can ignite when shorted due to shock or tearing - which is pretty much what happens to some luggage on every flight.
Presumably such a blanket ban would come in the wake of a single high profile incident, so in fact I am saying quite the opposite of "we should only take precautions against things that have already caused problems." Taking precautions against things that happened, instead of things which are likely to happen in the future is irrational.
Box cutters took down a few planes, so we banned them. This is an irrational ban, because box cutters now have an infinitesimally small chance of taking down planes. Whether box-cutters took down 4 planes or 100 planes in the past really doesn't matter since it does not indicate future performance.
When new information becomes available we are able to update our risk assessment, it isn't necessary for us to wait for more plane crashes. I don't see any new information here though, the risks posed by Li-ion batteries and fires on airplanes have been well understood for quite some time.
[edit] Originally I said lithium primary cells only, but I was wrong.
Chairman Hersman said that potential causes of the initiating short circuit currently being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
Maybe you should tweet to Boeing's CEO, let them run to CVS or Radio Shack to buy a few US made batteries and call it a day.
[Japanese companies outsource all their cheap goods manufacturing to other countries.]