NTSB spokesman Peter Knudson said investigators would carry out functional testing and memory downloads of the auxiliary power unit, or APU, built by Pratt & Whitney Power, known as Hamilton Sundstrand until United Technologies took over Goodrich last year. He said he did not have a date for that trip.

The safety board earlier ruled out excess voltage as the cause of a battery fire on the 787 at the Boston airport this month. It said investigators would travel on Tuesday to Tucson, Arizona, where the maker of the battery charger, Securaplane, a unit of Britain's Meggitt Plc is based.

(Reporting By Andrea Shalal-Esa; Editing by Maureen Bavdek)