SEATTLE The National Transportation Safety Board raised serious questions Thursday about the certification of Boeing s 787 with lithium ion batteries.

NTSB Chairman Deborah Hersman said Boeing certification tests of the battery showed that any failure in one of the eight cells inside the battery case would not spread to adjacent cells. However, fire and thermal runaway did spread inside the battery of a Japan Airlines 787 in Boston on January 7.

Hersman said the fire began in cell No. 6, then spread to other cells. The plane s flight data recorder showed a sudden drop of four volts, which is an indication one of the eight cells had failed.

The NTSB still does not know for sure what triggered the failure of the cell and continues to look for signs of contamination that might have been built into the cell in the factory, or occurred while the battery was in service. The 787 in Boston had only been flying for three weeks.

The NTSB says that the battery needs to be redesigned to prevent any spread of fire or breakdown between cells.

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