Boeing warned 15 carriers to avoid flying the 747 and 787 near “high level thunderstorms” because of a risk of engine-icing problems. Six incidences of GEnx engines losing thrust at high altitude because of a buildup of ice crystals behind the front fan led to Boeing issuing a notice probating flying at high altitude within 50 miles of thunderstorms.
In the meantime, GE and Boeing are working to control the problem.