(Reuters) — Boeing and All Nippon Airways are investigating a landing gear problem on the 787 Dreamliner, the first technical glitch reported since the new jetliner entered service less than two weeks ago, the airline said on Monday. Pilots on the first of two aircraft delivered so far to ANA were forced to deploy the landing gear using a manual backup system, after an indicator lamp suggested the wheels were not properly down. They landed at Okayama at the second attempt following the incident which happened on Sunday, the airline said. "We are not yet sure what the problem was, but we are investigating," an airline spokesman said, adding that Boeing is also involved in the investigation. Kyodo news agency linked the problem to a hydraulic valve. A Boeing spokesman in Europe said: "We are aware of this matter and are on site in Japan with ANA offering whatever assistance they require." The 787 Dreamliner is a revolutionary lightweight aircraft built mainly of carbon composites designed to save fuel.