FAA Grounds 787s

[RR_NDB]

Li Ion as main battery in 787 and APU battery use

Hi,

Maintenance and flt crew check list items will determine if bat state is ok for dispatch. This is standard on all big jets.

And with Li Ion there is another reason for this. It can increase itīs voltage (during charging) providing a false indication of "health" and not be able to deliver the required energy (to the bus) if an emergency situation requires it (bus voltage below, i estimate ~ 30 V). A cell that fall below a given threshold very probably will never recover. Lead Acid in this aspect can go to zero, exhibit a high internal resistance and FULLY RECOVER. I faced this situation and after charging (longer time was required) it returned to the same (anti) capability.

In flight the APU Bat will only be used to start the APU if NO OTHER SOURCE IS AVAILABLE.

Question:

JAL in BOS probably started the APU using the battery? If so the runaway probably started with hot cells (after high current use starting APU) and when receiving high current (with regime to recharge "fast")