Seattle - Boeing advised airlines on Friday about a risk of engine icing problems on its new 747-8 and 787 Dreamliner planes with engines made by General Electric, urging 15 carriers to avoid flying them near high-level thunderstorms.The warning led Japan Airlines to pull 787 Dreamliners from two international routes. Other affected airlines include Lufthansa, United Airlines, an arm of United Continental Holdings and Cathay Pacific Airlines ."Boeing and JAL share a commitment to the safety of passengers and crews on board our aircraft. We respect JAL's decision to suspend some 787 service on specific routes," a Boeing spokesperson said.The move followed six incidents from April to November involving five 747-8s and one 787 when aircraft powered by GE's GEnx engines suffered temporary loss of thrust while flying at high altitude.The problem was caused by a build-up of ice crystals, initially just behind the front fan, which ran through the engine, said a GE spokesperson, adding that all of the aircraft landed at their planned destinations safely.Boeing on Friday issued a notice prohibiting the affected aircraft from flying at high attitude within 50 nautical miles of thunderstorms that may contain ice crystals.Japan Airlines said on Saturday it will replace Dreamliners on its Tokyo-Delhi and Tokyo-Singapore flights with other types of aircraft while also dropping a plan to use 787s for its Tokyo-Sydney route from December.JAL will continue to fly 787s for other international and domestic routes, which are unlikely to be affected by cumulonimbus cloud for the time being, a company spokesperson said."The aviation industry is experiencing a growing number of ice-crystal icing encounters in recent years as the population of large commercial airliners has grown, particularly in tropical regions of the world," the GE spokesperson said.GE and Boeing are working on software modifications to the engine control system, which they hope will eliminate the problems, he added.All 747-8s are powered by GEnx engines while 787s are powered either by GE's engines or the rival Trent 1000 made by Rolls-Royce.