http://avherald.com/h?article=463508bb&opt=1An Air China Boeing 757-200, registration B-2856 performing flight CA-4307 from Chengdu to Guangzhou (China), was climbing through FL260 when a large bang was heard from the nose section of the aircraft and the aircraft performance worsened. The crew stopped the climb and returned to Chengdu for a safe landing with a "slightly rearranged radome".