Investigators Are Now Looking At Boeing Subcontractors In The Dreamliner Probe

US safety investigators will visit Boeing subcontractors this week to test components linked to the battery of a Japan Airlines 787 Dreamliner that caught fire in Boston earlier this month.

A National Transportation Safety Board spokeswoman said Monday that investigators would travel to the southwestern state of Arizona for testing at Securaplane in Tucson and Pratt & Whitney Power, formerly Sundstrand, in Phoenix.

The NTSB investigators will test the charger and start power on the JAL B-787 battery.

The battery "will be functionally tested and the memory will be downloaded" at its manufacturer Securaplane, while the same work will be performed on the controller for the auxiliary power unit at Pratt & Whitney, the spokeswoman added.

Investigators probing the fire on the JAL plane after it landed in Boston on January 7 have nonetheless ruled out an overcharged battery as the cause, as the powerpacks undergo further tests.

Meanwhile, aviation regulators were focusing on the lithium-ion batteries as the cause of a glitch that forced an All Nippon Airways (ANA) flight into an emergency landing in Takamatsu, Japan last week.

In Tokyo, Japanese and American safety inspectors were probing GS Yuasa, which also manufactures the batteries for the Dreamliner's advanced electronics systems, after the aircraft's worldwide fleet was grounded over safety fears.

Despite the investigation, GS Yuasa shares were up 0.95 percent to 318 yen in afternoon Tokyo trade.

The Japanese firm is just one of many contractors in a complex global chain that led to three years of delays before Boeing delivered its first 787 to ANA in 2011.

Boeing's cutting-edge new planes suffered a series of glitches earlier this month, prompting a global alert from the FAA that led to the worldwide grounding of all 50 operational 787s.

Here's the full history of the problems with the Dreamliner >