The specified load may be expected in terms of aerodynamic  forces, as in turns. In level flight in undisturbed air, the  wings are supporting not only the weight of the aircraft, but  centrifugal force as well. As the bank steepens, the horizontal  lift component increases, centrifugal force increases, and the  load factor increases. If the load factor becomes so great that  an increase in AOA cannot provide enough lift to support  the load, the wing stalls. Since the stalling speed increases  directly with the square root of the load factor, the pilot  should be aware of the flight conditions during which the  load factor can become critical. Steep turns at slow airspeed,  structural ice accumulation, and vertical gusts in turbulent  air can increase the load factor to a critical level. One of the greatest hazards to flight is aircraft icing. The  instrument pilot must be aware of the conditions conducive to  aircraft icing. These conditions include the types of icing, the  effects of icing on aircraft control and performance, effects  of icing on aircraft systems, and the use and limitations of  aircraft deice and anti-ice equipment. Coping with the hazards  of icing begins with preflight planning to determine where  icing may occur during a flight and ensuring the aircraft is  free of ice and frost prior to takeoff. This attention to detail  extends to managing deice and anti-ice systems properly  during the flight, because weather conditions may change  rapidly, and the pilot must be able to recognize when a change  of flight plan is required. Structural icing refers to the accumulation of ice on the  exterior of the aircraft. Ice forms on aircraft structures and  surfaces when super-cooled droplets impinge on them and  freeze. Small and/or narrow objects are the best collectors  of droplets and ice up most rapidly. This is why a small  protuberance within sight of the pilot can be used as an “ice  evidence probe.” It is generally one of the first parts of the  airplane on which an appreciable amount of ice forms. An  aircraft’s tailplane is a better collector than its wings, because  the tailplane presents a thinner surface to the airstream. Ice in the induction system can reduce the amount of air  available for combustion. The most common example of  reciprocating engine induction icing is carburetor ice. Most  pilots are familiar with this phenomenon, which occurs when  moist air passes through a carburetor venturi and is cooled. As  a result of this process, ice may form on the venturi walls and  throttle plate, restricting airflow to the engine. This may occur  at temperatures between 20 °F (–7 °C) and 70 °F (21 °C).  The problem is remedied by applying carburetor heat, which  uses the engine’s own exhaust as a heat source to melt the  ice or prevent its formation. On the other hand, fuel-injected  aircraft engines usually are less vulnerable to icing but still  can be affected if the engine’s air source becomes blocked  with ice. Manufacturers provide an alternate air source that  may be selected in case the normal system malfunctions. In turbojet aircraft, air that is drawn into the engines creates  an area of reduced pressure at the inlet, which lowers the  temperature below that of the surrounding air. In marginal  icing conditions (i.e., conditions where icing is possible),  this reduction in temperature may be sufficient to cause ice  to form on the engine inlet, disrupting the airflow into the  engine. Another hazard occurs when ice breaks off and is  ingested into a running engine, which can cause damage to  fan blades, engine compressor stall, or combustor flameout.  When anti-icing systems are used, runback water also can  refreeze on unprotected surfaces of the inlet and, if excessive,  reduce airflow into the engine or distort the airflow pattern in  such a manner as to cause compressor or fan blades to vibrate,  possibly damaging the engine. Another problem in turbine  engines is the icing of engine probes used to set power levels  (for example, engine inlet temperature or engine pressure ratio  (EPR) probes), which can lead to erroneous readings of engine  instrumentation operational difficulties or total power loss. The type of ice that forms can be classified as clear, rime, or  mixed, based on the structure and appearance of the ice. The  type of ice that forms varies depending on the atmospheric  and flight conditions in which it forms. Significant structural  icing on an aircraft can cause serious aircraft control and  performance problems. A glossy, transparent ice formed by the relatively slow  freezing of super cooled water is referred to as clear ice.  [Figure 4-17]  The terms “clear” and “glaze” have been used  Icing Types of Icing Structural Icing Induction Icing Clear Ice Figure 4-17.  Clear ice. 4-13