* ANA cancels another 78 Dreamliner flights
* ANA and JAL say sticking to orders for 87 Boeing 787s
* Transport Minister: maybe time to reinforce the investigation
* Boston, Japan batteries made on different dates - ministry
* Japan probe snagged as battery data recorder burnt
By Tim Kelly and James Topham
TOKYO, Jan 25 (Reuters) - Japan's leading airlines are firmly behind Boeing Co's 787 Dreamliner, saying they have had no second thoughts on orders for several dozen more of the planes - even as they have $5 billion worth of the futuristic aircraft sitting idle pending a complex investigation into unexplained battery problems.
All Nippon Airways Co and Japan Airlines Co Ltd have been the biggest customers to date for the technologically advanced 787 jetliner, which has a list price of $207 million and is about one third made by Japanese companies - from fuselage and engine parts to batteries and toilets.
U.S. safety officials said on Thursday they were nowhere close to completing their probe into a battery fire on a JAL-operated 787 at Boston airport almost three weeks ago. And investigators in Japan, looking into a later incident that prompted an ANA 787 to make an emergency landing on a domestic flight, have made little headway in finding out what caused a lithium-ion battery to overheat, triggering alarms in the plane's cockpit.
All 50 Dreamliners in service were grounded on Jan. 17.
The painstaking reconstruction effort - which Japanese authorities are running in tandem with U.S safety officials - and the lack of key performance data, suggests it could be months before the 787 can return to commercial service - a potentially costly setback for both Boeing and the airlines banking on the plane for growth.
U.S., Japanese and Boeing representatives have spent time this week at the Kyoto headquarters of GS Yuasa Corp, which makes batteries for the Dreamliner, looking at everything from manufacturing quality to technical standards. The charred battery remains the focus of the probe.
Critical circuit boards that control and monitor the performance of the battery unit were so badly burnt in the Japan incident that they may yield little data to help investigators, said a person involved in the probe, who didn't want to be named as it is ongoing and findings are only preliminary.
As a result, investigators have been poring over other components in the plane's complex electronics systems for clues as to how the battery was performing at the crucial time it began to overheat, the person said.
"The circuit board (system) is badly damaged. We'll see how much we can learn from examining it, but we'll also have to look at other recording devices on the aircraft to try to find out what happened," the person told Reuters.
That relatively inexpensive circuit boards may be keeping $10 billion worth of high-tech aircraft idle underscores how dependent the Boeing jet is on advanced electronics rather than more traditional, but less fuel-efficient, parts, experts said.
The Japanese investigators have said it doesn't appear the damaged battery was overcharged, echoing similar findings in the Boston incident. And on Friday, another potential lead - that the batteries could just be part of a 'bad batch' - was ruled out when Japan's transport ministry said the two batteries were made on different dates.
After checks, investigators plan to send the damaged battery monitoring unit to its manufacturer, Fujisawa-based Kanto Aircraft Instrument, for further tests. The battery's charger will also at some stage be returned for detailed inspection by the firm that makes it, Arizona-based Securaplane Technologies Inc.
The investigation is proving more problematic as this is the first time many of the investigators have seen a 787, which is not just an unfamiliar new plane, but is full of new technology.
Japanese Transport Minister Akihiro Ota told reporters on Friday: "I feel we might have come to the stage where it is time to consider whether it is necessary or not to try to reinforce (the investigation) structure."
NO CHANGE ON ORDERS
Both ANA and JAL said that comments from the National Transportation Safety Board (NTSB), the U.S. safety regulator - that the probe could be long and the concerns over air safety were "very serious" - would not affect their 787 orders.
"We have no plans at the moment to change our order," said Sze Hunn Yap, a spokeswoman for JAL, which has 7 Dreamliners with another 38 on order. Ryosei Nomura, a spokesman for ANA, which has 17 of the 787s and another 49 ordered, told Reuters: "We are currently not considering a change to our order. We are looking forward to seeing an even safer 787 back in the air."
ANA cancelled more flights scheduled to use the Dreamliner, bringing the carrier's total cancellations since the Jan. 16 emergency landing to 459. The carrier, which says it flies around 3.7 million passengers each month, said the cancellations so far - and it will announce more on Saturday - had affected more than 58,000 passengers. At this time of the year, ANA normally offers more than 780 domestic flights and over 170 international flights a day.
While Japan's airlines remain firmly committed to the Dreamliner, Poland's LOT has raised the prospect of seeking compensation for its losses. Another customer, China's Hainan Airlines Co Ltd, said it was disappointed in the 787 delays, which would impact its expansion plans.
Investors, for now, seem unfazed. Since the Jan. 7 fire at Boston, shares in Boeing have dropped 3 percent, while shares in ANA and JAL are down 2.7 percent and 2.5 percent respectively.