Three incidents of trouble involving Boeing 787 aircraft operated by All Nippon Airways Co. in January have been traced to poor quality components, while a fuel leak on a Japan Airlines Co. Dreamliner occurred due to improper valve coating, the transport ministry said Friday. The Ministry of Land, Infrastructure, Transport and Tourism, quoted by Japanese Kyodo news agency, said it has found no problems undermining the safety of the ANA aircraft and it will continue to monitor efforts by Boeing Co. and relevant component makers to improve their product quality. The latest findings by the ministry do not cover the ANA B-787 that made an emergency landing in western Japan in January due to smoke in the cockpit. The incident prompted aviation authorities around the world to ground Dreamliners.