Aircraft icing encompasses a range of conditions during which frozen precipitation forms on an aircraft. It is usually separated into two broad classifications, ground icing and in-flight icing. Icing can compromise flight safety by affecting the performance, stability, and control of the aircraft, and as a result the ability of the pilot to maintain the desired flight path. The primary effect of icing is its adverse impact on the aerodynamics of the airplane. Ice accretion results in increased drag and reduced maximum lift which reduce the performance and safety of the flight. While ice does add weight to the aircraft, the amount is usually a very small percentage of the aircraft gross weight, and its effects are insignificant compared to the aerodynamic effects.