Ice Shedding
It is common in most turbo-fan jet engines to have ice buildup on fan blades during startup and taxi to the runway. It occurs when the air temperature is very near freezing and it is raining. The water quickly freezes when coming in contact with the fan blades as the air mass is cooled with the fan rotating and builds up. It isn't a problem with snow, e.g., below freezing temperatures. The engine run up schedule will normally shed the ice outward to prevent it from entering the core of the engine, having it pass through the fan bypass to prevent compressor damage. The Trent 500, 700 and 800 are susceptible to this as are the CF6-80 series the GE90 and P&W engines. In the Trent 800, ice can build up all the way into the first stages of the IP compressor according to some people.
The real danger, however, is operating in ice fog. Here, the ice buildup is very rock solid due to the fine water particles and not easily shed no matter what you do. It is dangerous as it changes the efficiency of the fan, disturbs the air entering the core and results in less thrust than what may be expected. Also, if it sheds during TO, it can really damage the compressor.
Turbine D