Boeing outlines fix for 787 batteries
Venting batteries produced 'smoke' that wasn't, no fire, performed as planned
Boeing has outlined plans to improve the performance and safety features of the batteries used in its 787 aircraft, after two of the planes infamously experienced on-board incidents at Takamatsu and Boston, but has stopped short of offering a thorough explanation for just what went wrong.
What is known is that something caused the batteries on two 787s to become very hot. Why that happened isn't known, but the company hinted, during a 90-minute presentation and Q&A session in Tokyo, that a “deep discharge” event occurred in one cell of the planes' batteries, heating it to the point at which it vented so much hot electrolyte that an adjacent cell warmed and also vented. A manufacturing fault seems to be the reason such an event was able to occur and the company has outlined three key improvements to stop this happening again.
Mike Sinnett, a Boeing vice president and chief project engineer for the battery fix, was at pains to point out that losing batter power won't mean a nasty end for a 787 flight, as the batteries operate for mere seconds in flight and even then only as bridges between other multiply-redundant power sources in the event the main power source isn't working. The batteries do the bulk of their work on the ground, powering systems when the in-flight generators aren't available.
On the contentious flights, “the cells vented,” Sinnett explained, “and the venting is a protective measure that when something happens in a battery cell the pressure and the heat can build up inside that cell. We vent the cell to prevent the pressure from building up too high and to keep the temperature down.”
“This is what happened in the [Japanese] Takamatsu and the [Boston's airport] Logan event. The heat from the cell propagated to other cells and they vented as well. This is a protective mechanism that is designed into the battery cells.”
But when the batteries vent, they leak vaporised electrolyte which looks like smoke. Sinnett insisted the visible vapours were “not the product of combustion [and] not the result of a fire.” Once the batteries vented, he said, all other systems worked as planned with flight crews notified after smoke detectors worked. The vaporised electrolyte was jettisoned overboard, so never posed a risk to passengers or crew.
Sinnett said the event cannot be considered a “thermal runaway”, and that Boeing's batteries have four levels of protection against the only known catalyst of such an event, namely overcharging. Sinnett said he is “very confident” Boeing has “never seen overcharging” in the 787 fleet. He also said he is content that Boeing's suppliers - GS Yuasa makes the batteries and Thales the charger – aren't at fault.
Both have nonetheless redesigned their contributions to the 787. GS Yuasa will “develop and institute enhanced production standards and tests to further reduce any possibility for variation in the production of the individual cells as well as the overall battery.” The battery box will acquire a, pardon the pun, battery of new insulation and isolation features and reside in a new stainless steel enclosure. All components will work in a newly-narrowed “acceptable level of charge for the battery” that will be achieved “both by lowering the highest charge allowed and raising the lower level allowed for discharge.”
The new and improved design for the Boeing 787 battery box
Another change will see “The battery charger … adapted to soften the charging cycle to put less stress on the battery during charging.”
All of these changes need to be certified before the 787 will fly again. Boeing says it's working to earn those certifications as fast as is practicable.
Senior executives said that once the changes are signed off, they'll happily board a 787, on the first flight if possible.
Boeing's almost-explanation of the incident is available as a PDF. ®
Not an explosion - just a "prompt exothermic disassembly"
Talk about a load of PR spin.
The statement was just a 'Don't you worry about it - we know what we're doing' pat on the head to the authorities. I hope the FAA have the cojones to stand up to this blithering and see it for what it is - a bandaid solution to a problem that Boeing has admitted not knowing the cause of.
Fire (sorry, shouldn't use the F word) is the ultimate no-no on board an aircraft. Building a big strong box around something that Boeing said could never catch fire in the first place is not an elegant solution.
If these things get recertified, I will not be wanting to experience their 330 minutes ETOPS certification capability in the next few years. I'd rather stick with either a 380 or 777 or ever a 747 for my long haul jaunts.
Note that the icon does not represent fire.
Re: insulation/electrical tape
Individual voltage monitors per cell is an absolute must!! Without that capability, the cells WILL drift apart over time, and one cell will get overdischarged or overcharged.
NiMH, NiCd and Pb batteries tolerate overcharge (within reason), so those packs ae always slightly overcharged, to ensure that the individual cells stay balanced. LiIon has zero tolerance for both overcharge and overdischarge. When charging, individual cells must all be monitored, if a cell reaches max voltage beforr others, the battery management system must tell the charger to slow down, and also start draining power away from that cell.
Without this, the batterypack is a ticking timebomb.
Re: The vaporised electrolyte was jettisoned overboard, so never posed a risk to passengers or crew
Except that in the Boston incident, the failure of the battery caused the APU to stop (because the APU control unit is directly powered from the battery bus). This removed power from the fans intended to ventilate the equipment bay and keep fumes out of the cabin.
Re: I put my money on...
I don't think Boeing would point the finger at anyone else whether or not they can. Right now they will be mega focussed on trying to twist the facts to their world-view where "no fire occurred" and the 'smoke' was a planned safety release. They need everyone to believe this message so they can recertify the planes and get them back in the air before the airlines start cancelling orders/demanding refunds/suing.