Excuse the tortured metaphor, but the old advice
about not putting all your eggs in one basket applies to engineering as well as
to other fields. The implication
is that if the basket with all your eggs slips and falls, you’ve lost everything. Boeing hasn’t lost everything, but the
battery troubles besetting its new 787 Dreamliner could not have come at a
worse time.
The 787, the latest-model wide-body jetliner from
Boeing that seats up to 290 passengers, has been in commercial service since
October 2011, less than a year and a half. It boasts the latest high-tech advances such as a mainly
carbon-fiber airframe for reduced weight and fuel consumption, and mostly
electrical control systems, rather than the older pneumatic or hydraulic actuators. Consequently, its electrical power
requirements are about triple that of earlier comparable airliners, and so the
electrical power system of the 787 was boosted accordingly. Like a car, the engines (or
turbogenerators driven by engines) provide most of the electrical power in
flight, but for emergencies and times when the generators aren’t running, the
787 needs batteries, also like a car.
But lead-acid or even nickel-cadmium batteries were seen to be too heavy
for the advanced jet, so designers chose to use two 60-some-pound auxiliary
power units (battery banks) that employed lithium-cobalt batteries.
Now, lithium batteries have both virtues and
vices. Their main virtue is that
they have the best energy-weight ratio of just about any commercial type of
battery, meaning you get more stored energy in a 60-pound lithium battery than
you would in the same weight of nickel-cadmium or lead-acid batteries. So far, so good. But lithium is one of the more reactive
metals, and the chemistry of lithium batteries is very touchy with regard to
storage temperatures, charging rates, and defects such as little metal needles
that sometimes grow through insulating layers and short the things out. When any of these problems happen to a
severe enough degree, the battery can catch fire. And once a lithium battery is on fire, there’s very little
you can do except to wait till it burns itself out, because all the ingredients
for the fire are already inside the battery. Even the FAA recognizes this because it doesn’t require any
fire-fighting equipment to put out lithium-battery fires—just adequate
ventilation to make sure the hazardous fumes from the fire don’t harm
passengers or crew, and don’t spread the fire to other parts of the plane.
But there is evidence that in the two
lithium-battery fires that occurred on 787s in the last couple of months, even
these safety systems didn’t work properly. After these fires in Boston and Japan, the FAA and most
other national air-safety agencies grounded the entire fifty-plane fleet of
787s until the battery problem is resolved.
This problem clearly could have been worse. The planes could have crashed, but in
the incidents so far, the pilots discovered the problem in enough time to land
the planes safely. In the past,
lithium-battery fires in a plane’s cargo compartment have caused the loss of
the plane, and that is why you are not allowed to carry loose non-rechargeable
lithium-ion batteries in checked luggage on air flights. (Didn’t know that, did you?) But anybody who owns or leases a
multi-million-dollar investment like a 787 knows that every day you can’t fly
it is a big hole in your pocket, and also seriously disrupts flight schedules
that were made assuming the new 787s would be available.
It looks like the planes were designed almost in
the expectation that the batteries would
catch fire some time or other, even though the ventilation systems apparently
didn’t work as well as planned. The
fix is likely to be a challenge, because the plane’s entire electrical system
is designed around lithium batteries.
Substituting an older type of battery is feasible, but will involve a
major redesign, adding weight and probably space and a lot of certification tests
to ensure that the fixes aren’t worse than the original problem.
We may be getting ahead of the game if we assume
the lithium batteries are going to come out of the 787s altogether. The fact that the fires happened so
close in time, after over a year of service, says to me that there may have been
some kind of well-controlled slipup either in the manufacture of those
particular batteries, or the design of those particular planes. If engineers and investigators can
isolate—and ideally, reproduce—the cause of these fires, and it turns out to be
fixable, then it may be a simple matter of making sure those particular
conditions don’t happen again, and the planes can fly safely again with the
lithium batteries they were originally designed for.
The trouble with these investigations is that once
you get a lithium fire going, there isn’t a lot left to pick through to see
what started it. In the “Sources”
section at the end of this blog, I’ve put a URL for a little video that I must
say about at the outset, “Kids, don’t try this at home.” It shows a guy taking apart an ordinary
consumer lithium battery and setting fire to it. After you watch that video, you may have second thoughts
about buying a lithium anything, though most people don’t go around taking
propane torches to their batteries.
We can be thankful that the battery incidents did not result
in any fatalities, and I for one hope that the problem turns out to be
discoverable, reproducible under controlled conditions, and fixable. But in any case, Boeing has some
lithium-colored egg on its face for the time being, and has about fifty
reasons—equal to the number of 787s sold—to get to the bottom of the problem
and solve it to everyone’s satisfaction.
Sources: I referred in the preparation of this
piece to an article in the Tacoma, Washington News-Tribune by John Gillie published online on Jan. 27, 2013 at http://www.thenewstribune.com/2013/01/27/2451132/787-battery-fire-correction-may.html. I also referred to the Wikipedia
articles on Boeing and the Boeing 787 Dreamliner. The lithium-fire-from-battery video can be viewed at http://www.youtube.com/watch?v=BliWUHSOalU.
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