Fifteen airlines have been warned about the risk of ice forming on Boeing’s new 747-8 and 787 Dreamliner planes.The issue - affecting some types of engines made by General Electric when planes fly near high-level thunderstorms - prompted Japan Airlines to cancel two international routes.There have been six incidents since April when aircraft powered by General Electric engines lost power at high altitude.These are the latest technical issues to hit the Dreamliner. They saw the entire fleet being grounded earlier this year following battery problems. The Boeing 747-8 series and the new 787 Dreamliner are the only types of aircraft affected by the high-altitude icing issue.The new warning was given to airlines, including Lufthansa, United Airlines and Japan Airlines, saying aircraft with the affected engines – General Electric’s GEnx – must not be flown within 50 nautical miles of thunderstorms that may contain ice crystals.