>>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". Boeing counted a

>>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". 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.