The Dreamliner's Battery Fire
I'll bet the broadband video conference lines between Boeing, Yuasa and Thales are getting overtime use this week following Monday's ground fire in a Boeing 787-8 Dreamliner at Boston's Logan airport. The instant I saw the video of it, with smoke curling out of the after hatch, I thought to myself, that better not be a battery issue. But it now appears that this is exactly what it was.
This is serious stuff for Boeing and could put a significant dent in the airplane's certification basis if they can't figure out a solution. When Boeing proposed the Dreamliner a decade ago, it spec'd lithium-ion batteries for the airplane's innovative electrical power conversion system, which is made by Thales, with batteries from Yuasa. The airplane can also use conventional NiCad cells but either way, batteries provide starting energy for the APU and back-up power for other systems. At the time, the hazards of Li-ion were known, but Boeing wanted the weight savings and power density that only Li-ion can offer. Working with the FAA, it developed new certification standards for batteries under so-called special conditions. That required sophisticated electronics to provide overcharge and charge imbalance protection and physical thermal containment. Taken together and on paper, those precautions look more than robust enough to meet the stringent safety requirements of a modern airliner.
Well, maybe not. When I was researching Li-ion batteries for aircraft last year, I heard real concerns that the Li-ion main ship/starting battery risk wasn't yet well understood. As I reported, Cessna already lost one Citation to an Li-ion ground fire and withdrew Li-ion batteries as an option, at least temporarily. Now comes the 787 incident that might have gone the same way if it hadn't been caught early. It's also possible that the fire wouldn't have gotten any worse and that despite the smoke, the thermal containment worked. The airport fire crew showed up with the correct chemicals to fight an Li-ion blaze, but it still took 40 minutes to contain it completely. Early reports suggest the battery pack was well into progressive thermal runaway, with one failed cell torching off another. We'll see what the investigation reveals and I suspect it won't be long because Boeing isn't going to want the risk exposure if the problem is significant. The 787 is an ETOPS-330 airplane, meaning it can legally fly routes more than five hours from a diversion airport. That's a long time to have a smoke-filled cabin. Or worse.
The 787's flaws have been well publicized and the industry has made cooing noises that this is just normal teething pains that every airplane has experienced. That may be correct, although it's hard to compare the 787 to other airplanes because it's such leap forward in terms of all-electric sophistication. It's bound to have bugs. But I wouldn't consider an Li-ion battery fire a bug, so much as a confirmation that those who think Li-ion isn't ready for commercial airplanes could very well have a point.
Li-ion batteries runaway for three main reasons: They're sensitive to charging imbalance between cells, cells themselves short and external heat can ignite the highly flammable electrolytes. Once burning, they're hard to put out. Li-ion batteries are finding their way into vehicle markets, driven by the hybrid and electric vehicle push, but also as standard starting batteries in some new models. The record for these early adoptions seems good, both in performance and safety. But the Li-ion battery universe is still small. Flooded cells and AGM have been implicated in a few fires, too, but there are orders of magnitudes more of them out there.
I have five motorcycles in my garage, each with a blinking battery tender. I could replace the flooded cells with Li-ion, get more starting capacity for less weight, albeit at three times the cost. I haven't done that yet because I don't think the technology is quite ready for prime time and I don't care about the weight. Plus, I'm cheap.
Boeing obviously felt differently. I sure hope they're proven right.
Friday a.m. addition: The FAA is expected to announce a major review of 787-8 electrical systems and wiring complaint incidents.