The NTSB is investigating if the recent Boeing 787 battery issues could be linked to the formation of small build-ups, known as dendrites, inside lithium-ion batteries.

The acknowledgement confirms Aviation Week reports last week that dendrites have been suspected among the possible causes of two battery incidents that prompted the grounding of all 50 787s in operation.

Dendrites build up in lithium batteries, usually through uneven absorption and desorption of lithium ions, and can penetrate the inner membranes that divide the anode and cathode. The dendrites, which also can be triggered by foreign object particles on the surfaces, introduce a physical contact between the positive and negative electrodes, generating a short circuit.

Boeing, meanwhile, completed initial flight tests of the 787 aimed at assessing the performance of the main and APU batteries as part of the investigation. Boeing test captains Mike Bryan and Randy Neville together with a crew of 11 flight test personnel completed a second battery monitoring test flight Feb. 11 on board 787 test aircraft ZA005. The uneventful 1 hr. 29 min. flight was completed when the aircraft returned to Boeing Field at 11:46 a.m.

The aircraft also was used for an initial flight on Feb. 9, which lasted 2 hr. 19 min.

Analysis of the test results “will continue in the days ahead,” says Boeing.