Boeing provided a briefing on the 787 battery solution, which includes a new charger for the revised battery with additional spacing and shielding, and the new case and venting system that has been nicknamed the “fireplace and chimney” by some industry observers.
The slides from Boeing’s presentation can be found here.
Boeing indicated with certainty that in neither event was there a fire in the battery, nor a thermal runaway, but instead cell venting, a safety mechanism. In this case, such cell venting spread to other cells. They indicate that the only mechanism that could lead to thermal runaway is overcharging, and that data from the flight data recorded indicated that an overcharge situation did not occur. Therefore, a thermal runaway could not have occurred, despite both the NTSB and JTSB indicating that it had. Mike Sinnett from Boeing indicated that it was a matter of perspective. Reminds me of “newspeak” as it remains a fact that a “cell venting” runaway did occur, and when one cell vented, it caused others to vent as well to the point that the containment case was damaged, hot flammable electrolyte leaked into the aircraft, and the nice clean batteries ended up a charred mess that no longer worked.
Clearly, something created significant heat, as illustrated by the burnt battery and difficulty for firefighters at Logan had in putting out what they described as a fire, which did spread from one cell to other cells and engulf the whole battery. Is that “cellular venting runaway” rather than “thermal runaway?” Who cares if an airplane can still catch fire over an ocean?
The re-design of the battery system improves the battery, the charging system, the containment vessel, and the venting system, and even condensation removal, and provide enough protection to bring the airplane to a safe landing at an airplane level. For an airplane with 330 minute ETOPS capability, and emergency landing is often not very easy. They are betting that a robust solution set, but one that does not include fire suppression, will be sufficient to eliminate further risk. Let’s hope they are right – but some of us remain unconvinced.