WASHINGTON (AP) - Boeing is alerting airlines about possible engine icing problems on some of its new planes. It is recommending that planes with a specific General Electric engine avoid flying near thunderstorms that might contain ice crystals. Boeing spokesman Marc Birtel said Saturday that Boeing issued the advisory after ice crystal formation in some instances diminished engine performance. Airlines with planes affected include United, Japan Airlines, Lufthansa and Air India. Models affected are the 747-8 and the 787, which Boeing Co. calls the Dreamliner. "To reduce chances of ice crystal conditions, Boeing recommends that operators fly at least 50 nautical miles from thunderstorms that may contain ice crystals," Boeing said in its statement. The advisory covers Boeing planes with General Electric Co.'s GEnx engine. In its statement, Boeing said that GE is "working diligently" to deal with the issue and that corrective changes "will be introduced into the fleet as soon as they are available." It's the latest problem to confront the 787. Earlier this year, the 787 was grounded after two planes suffered from smoldering batteries. Flights resumed after Boeing redesigned the battery system.