The primary hazard with ice is degraded aircraft performance.
As ice accumulates on the aircraft, the aircraft’s weight increases. As ice accumulates on rotor systems, the shape of the airfoil changes, reducing its effectiveness. Due to centrifugal force, it is likely that some of the ice will shed from the rotor system. When this happens, it will likely shed unevenly. This uneven sheading of ice can cause significant imbalances in the rotor system, resulting in severe vibrations that may damage the helicopter.
In addition to structural icing, there is potential for carburetor icing for normally aspirated piston engines and visibility could be significantly reduced.
Related to icing conditions, any frost on airfoil reduces an aircraft’s lift capacity as the frost causes the airflow to separate from the airfoil. As such, a pilot should ensure there is no frost on any airfoil prior to flight.
FAA AC 00-6B Aviation Weather pg. 18-1