Figure 15-13.  Ice protection onboard computer maintenance page.  Altitude 10,000  Eng Type - - TAT -2 L  R Ice detection:  Engine/wing Engine/wing Engine anti-ice: Fincase duct leak signal  Normal  Normal Valve Regulating Regulating Supply air temp  884  884 Air pressure  13  13 Air flow  Wing anti-ice: Wing manifold pressure  50  50 Valve Regulating Regulating Air pressure  19  19 Air flow  85  85 Ice Protection In devices that use thermal electric anti-ice, current flows  through an integral conductive element that produces heat.  The temperature of the component is elevated above the  freezing point of water, so ice cannot form. Various schemes  are used, such as an internal coil wire, externally wrapped  blankets or tapes, as well as conductive films and heated  gaskets. A basic discussion of probe heat follows. Windshield  heat and portable water heat anti-ice are discussed later in this  chapter. Propeller deice boots, which also are used for anti- ice, are also thermal electric and discussed in this chapter. Data probes that protrude into the ambient airstream  are particularly susceptible to ice formation in flight.  Figure 15-14  illustrates the types and location probes  that use thermal electric heat on one airliner. A pitot tube,  for example, contains an internal electric element that is  controlled by a switch in the cockpit. Use caution checking  the function of the pitot heat when the aircraft is on the  ground. The tube gets extremely hot since it must keep ice  from forming at altitude in temperatures near -50 °F at speeds  possibly over 500 miles per hour. An ammeter or load meter  in the circuit can be used as a substitute to touching the probe,  if so equipped. central maintenance computer system (CMCS) maintenance  messages. The BITE in the WAI ACIPS computer card  also performs automatic power-up and periodic tests. Faults  found during these tests that affect dispatch cause status  messages. Other faults cause CMCS maintenance messages.  The power-up test occurs when the card gets power. BITE  does a test of the card hardware and software functions and  the valve and pressure sensor interfaces. The valves do not  move during this test. Simple probe heat circuits exist on GA aircraft with a switch  and a circuit breaker to activate and protect the device.  Advanced aircraft may have more complex circuitry in which  control is by computer and flight condition of the aircraft  is considered before thermal electric heaters are activated  automatically.  Figure 15-15  shows such a circuit for a pitot  tube. The primary flight computer (PFC) supplies signals  for the air data card (ADC) to energize ground and air heat  control relays to activate probe heat. Information concerning  speed of the aircraft, whether it is in the air or on the ground,  and if the engines are running are factors considered by the  ADC logic. Similar control is use for other probe heaters. The periodic test occurs when all these conditions are true: •  The airplane has been on the ground between 1 and  5 minutes. •  The WAI selector is set to auto or on. •  Air-driven hydraulic pumps are not in intermittent  operation. •  Bleed pressure is sufficient to open the WAI valves. •  The time since the last periodic test is more than  24 hours. •  During this test, the WAI valves cycle open and  closed. This test makes sure that valve malfunctions  are detected. Chemical Anti-Icing Thermal Electric Anti-Icing 15-10 Electricity is used to heat various components on an aircraft  so that ice does not form. This type of anti-ice is typically  limited to small components due to high amperage draw.  Effective thermal electric anti-ice is used on most air data  probes, such as pitot tubes, static air ports, TAT and AOA  probes, ice detectors, and engine P2/T2 sensors. Water lines,  waste water drains, and some turboprop inlet cowls are also  heated with electricity to prevent ice from forming. Transport  category and high-performance aircraft use thermal electric  anti-icing in windshields. Chemical anti-icing is used in some aircraft to anti-ice the  leading edges of the wing, stabilizers, windshields, and  propellers. The wing and stabilizer systems are often called  weeping wing systems or are known by their trade name of  TKS™ systems. Ice protection is based upon the freezing  point depressant concept. An antifreeze solution is pumped  from a reservoir through a mesh screen embedded in the  leading edges of the wings and stabilizers. Activated by a  switch in the cockpit, the liquid flows over the wing and  tail surfaces, preventing the formation of ice as it flows.  The solution mixes with the supercooled water in the cloud,  depresses its freezing point, and allows the mixture to flow  off of the aircraft without freezing. The system is designed  to anti-ice, but it is also capable of deicing an aircraft as  well. When ice has accumulated on the leading edges, 