airworthiness factual report error
In the airworthiness factual report there appears to be an error on page 16 concerning the JAL APU start power consumption.
The Flight Data Recorder report shows measurement DCBus_APU_Battery_Current (A) in figure B-12 on page 10B-13 only discharging an average of about 20 amps for the APU start with a momentary spike up to 30 amps during the 35-second discharge.
This would only be 640 watts average with the spike at 960 watts, not the 9.6 kW (32V x 300A) mentioned in the airworthiness report. Some of the other power figures in that paragraph appear incorrect also and should be re-checked.
In addition I wanted to point out that same FDR current data also shows that the APU battery was constantly being overcharged by trickle-charging at 1 to 2 amps during the 14 minutes between Last Engine Shut Down and the APU Shuts Down event.
The Securaplane battery charging patent #5,780,994 is based upon a Ni-Cd battery charging profile and assumes a trickle-charging phase of indefinite length following the fast-charge phase.
GS Yuasa does not include trickle-charging in the CC/CV charging procedure found in the LVP10-66.pdf data sheet for the cells, nor does any other manufacturer of Lithium chemistry batteries.
The CT Scan report also provides evidence of overcharging in the scans of the "normal undamaged" Main battery. The cell walls are clearly seen to be bulging outward and there may be cell-to-cell wall contact. This swelling of the cells is also seen in the CT scans shown in the JTSB reports for the "undamaged" APU battery of the ANA aircraft.
I have a mechanical load analysis which shows that only a couple of psi delta-pressure is necessary to deform the 0.031" stainless steel material used as the cell case. A deformed cell case would likely cause internal short-circuit contact of the current collector bars to the case leading to cell thermal runaway such as was experienced in both battery incidents.
The source of the pressure delta could be internal due to overcharging, and/or external due to operation at reduced atmospheric pressure such as in high altitudes (e.g. 6000 ft).