full text of the classic FAA guide
Icing of the pitot tube as seen in figure 96 reduces ram air pressure on the airspeed indicator and renders the instrument unreliable. Most modern aircraft also have an outside static pressure port as part of the pitot-static system. Icing of the static pressure port reduces reliability of all instruments on the system—the airspeed, rate-of-climb, and the altimeter.
FIGURE 96. Internal pitot tube icing. It renders airspeed indicator unreliable.
Ice forming on the radio antenna distorts its shape, increases drag, and imposes vibrations that may result in failure in the communications system of the aircraft. The severity of this icing depends upon the shape, location, and orientation of the antenna. Figure 97 is a photograph of clear ice on an antenna mast.
FIGURE 97. Clear ice on an aircraft antenna mast.