Japan's Civil Aviation Bureau said on Friday that preparations are not yet complete for any test flight of Boeing Co's grounded 787 Dreamliner this week.
"It's Thursday (in the United States) and nothing has been set," said Shigeru Takano, a senior safety official at the Civil Aviation Bureau (CAB). "There are a number of steps it needs to take before a test flight," he said at a news briefing.
Boeing Co plans to conduct two flight tests of its revamped 787 battery system, as soon as the end of the week, three sources familiar with the matter told Reuters on Wednesday. The aircraft maker has predicted the Dreamliner could return to operation within weeks.
Test flights would mark a step toward Boeing's goal of returning the jet to service in weeks, after it was grounded worldwide in January because batteries overheated on jets owned by All Nippon Airways Co Ltd <9202.T> and Japan Airlines Co Ltd <9201.T>.
Japan's aviation regulator last week criticized as inappropriate remarks made by Boeing executives at a March 15 press briefing in Tokyo who said that the cause of the battery fault may never be found. The CAB also said it was too early to estimate that the 787 would return to operation within weeks.
The U.S. National Transportation Safety Board (NTSB) said Boeing did not inform investigators of what it planned to say about the Dreamliner jets during last week's briefing in Tokyo.
Boeing's position was "inconsistent with our expectations" from a company involved in an accident probe, NSTB general counsel David Tochen wrote in a letter.
The letter points out that NTSB policy prohibits parties to an investigation from releasing information about it or drawing any conclusions.
At the March 15 press conference in Tokyo, Boeing said that the NTSB had ruled out the possibility that fire had erupted inside the metal battery container in the JAL incident, and that flames only occurred outside the box.
NTSB spokesman Peter Knudson later said it was too early in the investigation to rule out fire inside the box.
"We have received the correspondence and remain fully committed to support the NTSB and other regulatory authorities in their investigations into the cause of the 787 battery incidents, and also continue our around-the-clock efforts to return the 787 fleet to service," said Boeing spokesman Marc Birtel.
(Reporting by Tim Kelly Sakthi Prasad and Alwyn Scott; Editing by Ken Wills, Daniel Magnowski and Steve Orlofsky)