* Still uncertain when 787 will restart flights - ANA
* ANA expects installation of new batteries will take a month
* No plans to change order for 66 Dreamliners
* ANA expects 10 Dreamliner deliveries in year from April 1
By Tim Kelly and Kentaro Sugiyama
TOKYO, March 19 (Reuters) - Boeing Co's goal to have its grounded 787 Dreamliner jets back in the air within weeks is a best-case scenario and too uncertain for the aircraft's biggest customer to plan the plane's operational return to service.
All 50 of the technologically-advanced 787s in service have been idled since mid-January following two battery incidents at a U.S. airport and on a domestic flight in Japan. Boeing last week unveiled a new battery system and predicted the 787 would fly again within weeks rather than months.
Asked whether Boeing was presenting a best-case scenario, Osamu Shinobe, the architect of All Nippon Airways' strategy to put the fuel-efficient 787 at the centre of the airline's fleet planning, said "That's what we understand it to be."
"The problem is we don't know how long the Federal Aviation Administration (FAA) will take to finish its checks (on the new battery system)," he told Reuters in an interview. Shinobe, who joined ANA from college in 1976, will run the carrier from April following a switch to a holding company structure.
For Boeing to meet its target, Shinobe explained the planemaker needs to complete certification testing this week, gain quick FAA approval followed by an airworthiness directive soon after. It would then have to transport all the parts and equipment to 787s parked around the world to begin installing the new batteries. Boeing has said that could take a week per plane.
"If that happens, then what Boeing is saying is not a lie," said Shinobe, 60, noting it could take a month to put the new battery systems on all ANA's 17 Dreamliners, with Boeing likely to work on three jets at a time.
Twelve of ANA's 787 planes are parked in Tokyo, with another four at regional airports in Japan and one in Frankfurt. Each will be fixed at its current location. ANA has canceled more than 3,600 domestic and international flights since the 787 was grounded through to end-May.
On Friday in Tokyo, Boeing unveiled a new fire-proof battery packed with added insulation, heat-resistant material and spacers and encased in a steel box. The aircraft maker has also added a specialized pipe to vent gases produced by any overheating directly outside the aircraft.
The FAA last week approved Boeing's plan to test its new battery for certification. Boeing said it finished three tests of the new system and was performing three more in cooperation with the FAA, allowing it to estimate when the plane would be back in the air. The head of Boeing's commercial aircraft company, Ray Conner, briefed Shinobe on the battery fix in Tokyo on Thursday.
Boeing's prediction drew scepticism from some regulators and industry experts, who said it was too early to say when the Dreamliner would fly again with the root cause of the battery overheating still unknown.
Boeing also faces public hearings next month on the safety of its batteries. The U.S. National Transportation Safety Board is looking into what caused the battery failures and the original process used to certify the power packs.
Japan's Civil Aviation Bureau said it was "inappropriate" for Mike Sinnett, the 787's chief engineer, to have said the cause of the overheating may never be discovered.
Once regulators approve the battery fix, Boeing plans to install the new system in its 787s in the order they were delivered, with ANA heading the queue.
Shinobe said ANA has no plans to change its outstanding orders for another 66 Dreamliners, and expects to take delivery of 10 new planes in the next 12 months. Rival Japan Airlines Co has seven Dreamliners, with another 38 on order. (Editing by Ian Geoghegan)