Pneumatic Deicing Boots

ACIPS control ACIPS control card—EAI (right) Ice detector (right) WOW ADIRU ASCPC ECSMC WES L&R systems ARINC 629 buses Engine bleed air 8 9 10 11 12 13 14 Heated slats card—WAI OPAS AIMS ACIPS control card—EAI (left) Ice detector (left) Anti-ice/lighting panel (P5) APU bleed air Engine bleed air 1 2 3 4 5 6 7 Heated slats WAI valve WAI pressure sensor WAI duct WAI valve WAI pressure sensor WAI duct AUTOOFF ON Electrical connector Locking crank and position indicator Actuator Body Torque motor Locking screw extended. The telescoping section attached to the slat on one end, slides over the narrow diameter “T” section that is connected into the WAI duct. A seal prevents any loss of air. This arrangement allows warm air delivery to the slats while retracted, in transit, and fully deployed. [Figure 15-11] WAI Control System Modern aircraft use several onboard computers to control aircraft systems. The WAI system is controlled by the ACIPS computer card. The ACIPS computer card controls both WAI valves. The required positions of the WAI valves change as bleed air temperature and altitude change. The left and right valves operate at the same time to heat both wings equally. This keeps the airplane aerodynamically stable in icing conditions. The WAI pressure sensors supply feedback information to the WAI ACIPS computer card for WAI valve control and position indication. If either pressure sensor fails, the WAI ACIPS computer card sets the related WAI valve to either fully open or fully closed. If either valve fails closed, the WAI computer card keeps the other valve closed.

15-6 Inner telescoping duct Telescoping duct door Wing front spar Pneumatic duct Wing TAI supply manifold duct Wing TAI supply manifold Ground overheat thermal switch Wing anti-ice control valve SlatSlat anti-icing spray ducts Slat inner skin Outer telescoping duct TAI airflow between beam and slat upper skin Spacers between skin and beam Slat beam A 15-7 There is one selector for the WAI system. The selector has three positions: auto, on, and off. With the selector in auto and no operational mode inhibits, the WAI ACIPS computer card sends a signal to open the WAI valves when either ice detector detects ice. The valves close after a 3-minute delay when the ice detector no longer detects ice. The time delay prevents frequent on/off cycles during intermittent icing conditions. With the selector on and no operational mode inhibits, the WAI valves open. With the selector off, the WAI valves close. The operational mode for the WAI valves can be inhibited by many different sets of conditions. [Figure 15-12] The operational mode is inhibited if all of these conditions occur: • Auto mode is selected.

• Takeoff mode is selected. • Airplane has been in the air less than 10 minutes. With auto or on selected, the operational mode is inhibited if any of these conditions occur: • Airplane on the ground (except during an initiated or periodic built-in test equipment (BITE) test). • Total Air Temperature (TAT) is more than 50 °F (10 °C) and the time since takeoff is less than 5 minutes. • Auto slat operation. • Air-driven hydraulic pump operation. • Engine start. • Bleed air temperature less than 200 °F (93 °C). The WAI valves stay closed as long as the operational mode inhibit is active. If the valves are already open, the operational mode inhibit causes the valves to close.

WAI Indication System The aircrew can monitor the WAI system on the onboard computer maintenance page. [Figure 15-13] The following information is shown: • WING MANIFOLD PRESS—pneumatic duct pressure in PSIG. Right WAI valve Right WAI pressure sensor Left WAI pressure sensor Left WAI pressure sensor Set valve positions according to flow schedule OPAS AUTO WING OFF ON ACIPS control card— EAI (2) ASG cards (2) WAI selector (P5) Ice detector (2) WOW ADIRU WES ASCPC ECSMC AIMS FMCS Left, Right Arinc 629 systems buses P210 right power management panel ACIPS control card—WAI Flow schedule example P84 right systems card file On Auto & wing ice Takeoff mode Air < 10 minutes Ground mach < 0.18 In air < 5 min Auto slat ADP operation Engine start Bleed temp < 200 °F (93 °C) Wing ice Wing ice Air 28V DC right main bus WAI CTRL TAT > SOF (10 °C) 240 °F 310 °F 380 °F450 °F Precooler out temp Altitude Flow rate 15-8 Ice Protection Al titude 10,000 Eng T ype - - 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 13 13 Wing anti-ice: Wing manifold pressure 50 50 Valve Regulating Regulating Air pressure 19 19 Air flow 85 85 • V ALVE—WAI valve open, closed, or regulating.

• AIR PRESS—pressure downstream of the WAI valves in PSIG. • AIR FLOW—air flow through the WAI valves in pounds per minute. WAI System Built-In Test Equipment (BITE) Test BITE circuits in the WAI ACIPS computer card continuously monitor the WAI system. Faults that affect the dispatch of the aircraft cause status messages. Other faults cause 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. 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.

Thermal Electric Anti-Icing 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. 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. thermal electric heat on one airliner. A pitot tube, for example, contains an internal electric element that is controlled by a switch in the flight deck. 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 to safely determine functionality.

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 controls are used for other probe heaters.

Chemical Anti-Icing 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 15-9 TAT probe Left AOA sensor Right AOA sensor Right pitot probe Right ice detector Center pitot probe Left pitot probe Left ice detector P2/T2 probe 115V AC left XFR bus Pitot probe HTR L 28V DC left main bus Ground heat control relay Air heat control relay Probe heat sensor relay Left pitot probe Probe/vane HTR ctrl L P110 left power management panel NOTE: Left pitot probe heat system shown Right and center systems similar See AOA probe heat 1 1 1 1 On Off AIMS AFDC ADIRUPFC SAARU Flight controls ARINC 629 bus Left pitot ADM Pitot heat indication • Failed On • Failed Off In air or > 50 knots On GND and One or both engines on 15-10 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 flight deck, 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, the antifreeze solution chemically breaks down the bond between the ice and airframe. This allows aerodynamic forces to carry the ice away. Thus, the system clears the airframe of accumulated ice before transitioning to anti-ice protection. Figure 15-16 shows a chemical anti-ice system. The TKS™ weeping wing system contains formed titanium panels that are laser drilled with over 800 tiny holes (.0025-inch diameter) per square inch. These are mated with non-perforated stainless-steel rear panels and bonded to wing and stabilizer leading edges. As fluid is delivered from a central reservoir and pump, it seeps through the holes.

Aerodynamic forces cause the fluid to coat the upper and lower surfaces of the airfoil. The glycol-based fluid prevents ice from adhering to the aircraft structure. Some aircraft with weeping wing systems are certified to fly into known icing conditions. Others use it as a hedge against unexpected ice encountered in flight. The systems are basically the same. Reservoir capacity permits 1- 2 hours of operation. TKSTM weeping wings are used primarily on reciprocating aircraft that lack a supply of warm bleed air for the installation of a thermal anti-ice system. However, the system is simple and effective leading to its use on some turbine powered corporate aircraft as well.

Wing & Stabilizer Deicing Systems GA aircraft and turboprop commuter-type aircraft often use a pneumatic deicing system to break off ice after it has formed Slinger ring in spinner Proportioning unitProportioning unit High pressure switch Vent Low pressure switch Porous panel on vertical stabilizer Windshield pump Proportioning unitPorous panel on stabilizer Porous panel on wing Filter Solenoid valve Metering pump Spray bar Tank 3/16" OD nylon 5/16" OD nylon 1/2" OD nylon 3/16" OD stainless steel 15-11 on the leading-edge surfaces. The leading edges of the wings and stabilizers have inflatable boots attached to them. The boots expand when inflated by pneumatic pressure, which breaks away ice accumulated on the boot. Most boots are inflated for 6 to 8 seconds. They are deflated by vacuum suction. The vacuum is continuously applied to hold the boots tightly against the aircraft while not in use.

Sources of Operating Air The source of operating air for deice boot systems varies with the type of powerplant installed on the aircraft. Reciprocating engine aircraft typically use a dedicated engine-driven air pump mounted on the accessory drive gear box of the engine. The suction side of the pump is used to operate the gyroscopic instruments installed on the aircraft. It is also used to hold the deice boots tight to the aircraft when they are not inflated. The pressure side of the pump supplies air to inflate the deice boots, which breaks up ice that has formed on the wing and stabilizer leading edges. The pump operates continuously.

Valves, regulators, and switches in the flight deck are used to control the flow of source air to the system. Turbine Engine Bleed Air The source of deice boot operating air on turbine engine aircraft is typically bleed air from the engine compressor(s). A relatively low volume of air on an intermittent basis is required to operate the boots. This has little effect on engine power enabling use of bleed air instead of adding a separate engine-driven air pump. Valves controlled by switches in the flight deck deliver air to the boots when requested. Pneumatic Deice Boot System for GA Aircraft GA aircraft, especially twin-engine models, are commonly equipped with pneumatic deicer systems. Rubber boots are attached with glue to the leading edges of the wings and stabilizers. These boots have a series of inflatable tubes.

During operation, the tubes are inflated and deflated in an alternating cycle. [Figure 15-17] This inflation and deflation causes the ice to crack and break off. The ice is then carried away by the airstream. Boots used in GA aircraft typically inflate and deflate along the length of the wing. In larger turbo prop aircraft, the boots are installed in sections along the wing with the different sections operating alternately and symmetrically about the fuselage. This is done so that any disturbance to airflow caused by an inflated tube is kept to a minimum by inflating only short sections on each wing at a time.

GA System Operation aircraft with reciprocating engines. In normal flight, all of the components in the deice system are de-energized. Discharge air from the dry air pumps is dumped overboard through the (top) and inflated (bottom). deice control valves. The deflate valve is open connecting the deice boots to the suction side of the pump through the check valve manifold and the vacuum regulator. The gyroscopic instruments are also connected to the vacuum side of the dry air pump. The vacuum regulator is set to supply the optimum suction for the gyros, which is sufficient to hold the boots tightly against the airfoil surfaces.

When the switch shown in Figure 15-19 is pushed ON, the solenoid-operated deice control valves in each nacelle open and the deflate valve energizes and closes. Pressurized air from the discharge side of the pumps is routed through the control valves to the deice boot. When the system reaches 17 psi, pressure switches located on the deflate valve de-energize the deice control valve solenoids. The valves close and route pump air output overboard. The deflate valve opens and the boots are again connected to vacuum. On this simple system, the pilot must manually start this inflation/deflation cycle by pushing the switch each time deice is required. Larger aircraft with more complex systems may include a timer, which will cycle the system automatically until turned OFF. The use of distributor valves is also common. A distributor valve is a multi-position control valve controlled by the timer. It routes air to different deice boots in a sequence that minimizes aerodynamic disturbances as the ice breaks of the aircraft. Boots are inflated symmetrically on each side of the fuselage to maintain control in flight while deicing occurs. Distributor valves are solenoid operated and incorporate the deflate valve function to reconnect the deice boots with the vacuum side of the pump after all have been inflated.

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