LITTLE HEADWAY

Under aviation inspection rules, airlines are required to perform detailed battery inspections once every two years.

Officials are carrying out detailed tests on the batteries, chargers and monitoring units in Japan and the United States, but have so far made little headway in finding out what caused the battery failures.

Japan’s transport ministry said the manufacturing process at the company which makes the 787 battery’s monitoring unit did not appear to be linked to the problem on the ANA Dreamliner that made the emergency landing.

The NTSB said on Tuesday it was carrying out a microscopic investigation of the JAL 787 battery. Neither it nor the Japan Transport Safety Board has been able to say when they are likely to complete their work.

The global fleet of 50 Dreamliners - 17 of which are operated by ANA - remain grounded, increasing the likely financial impact to Boeing, which is still producing the aircraft but has stopped delivering them, and the airlines that fly the Dreamliner.

Boeing said on Wednesday that its 2013 financial forecast assumes no significant impact from the grounding. Boeing shares rose slightly in early trading and are down just 0.5 percent since the 787 was grounded.

ANA posts its earnings on Thursday. ANA shares rose 0.56 percent on Wednesday.