After dedicating 300,000 hours of engineering and lab time to analyzing potential problems with lithium-ion batteries carried on its 787 Dreamliners, Boeing is confident it has a comprehensive solution that will enable an early return to routine flight operations. The solution does not require identification of the root cause for two overheating incidents that led to the grounding of all fifty 787s that have been delivered, because it would preclude the kind of combustion event that might endanger aircraft safety. Some features of the solution are similar to fixes employed on Boeing 747s following the ignition of fuel-tank vapors on TWA Flight 800 in 1996; the precise cause of that incident was never pinpointed, but the solutions adopted prevented any repetition.
Boeing officials are careful to emphasize that the final decision on a return to flight will rest with the Federal Aviation Administration, which approved the company’s plan for a 19-task certification process that should resolve safety concerns. However, it expects to have completed all 19 tasks before the end of March, and is already assembling teams and kits for the installation of fixes as soon as FAA gives the go-ahead. Each of the 50 planes already delivered will require three days of downtime to install and test modifications. The on-board modifications include eliminating potential sources of short-circuiting in the battery, tightening the performance specifications on the battery charger, and creating an air-tight containment system that would vent any vapors while also removing oxygen that could feed a fire.
Most of the 15 design changes being introduced probably are not needed. But because the root cause of the two heating incidents earlier this year has not been identified, Boeing has chosen to address every conceivable source of difficulty. A team of 350 engineers and 150 lab technicians has narrowed the range of possible causes from 80 to about five, however there is no guarantee the one true cause will ever be found. Ironically, that has led the company to make more extensive improvements to the battery system than would have been the case if a single-point failure leading to the two incidents had been isolated. The battery system thus ends up being far more resistant to a wide range of improbable upsets. In fact, it will now be one of the most carefully studied and designed subsystems on any commercial airliner.
The battery already had quadruple redundant protections against overcharging — the sole possible cause of a “thermal runaway event” — and thus investigators have concluded something more obscure caused the two heating incidents. But because Boeing could not publicly discuss much of what its engineers were finding while it was party to the investigation, some misconceptions about the battery problem have taken hold. First, the batteries do not generate an independent source of oxygen when overheated that could sustain combustion. Second, the “smoke” that the planned venting system will remove from the plane is actually vapor generated by electrolytes, rather than a by-product of fire. And third, the batteries in question do not play a central role in the functioning of the 787; they exist mainly to support operations on the ground such as refueling.
Now that the company and regulatory authorities can speak more freely about what they have found, the flying public will be able to better understand the nature of the battery issue and how it has been resolved. A year from now, the problem likely will have been forgotten as carriers clamor to operate the most fuel-efficient jetliner ever built. A passenger survey conducted by early operator ANA before the grounding found very high levels of satisfaction with the Dreamliner’s on-board air quality, oversized windows, cabin space and other amenities. It appears that Boeing is well on its way to resolving the latest glitch that has delayed making these features available to the global market.
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