ET-AF07 M1 Ice Rain Note Final R0 PDF

ET-AF07.1 Ice and Rain Protection  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Airc...

ET-AF07.1 Ice and Rain Protection  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Table of Contents 1. Ice and Rain Protection (Level 3)........................................................... 1 1.1 Purpose of Ice and Rain Protection.............................................................. 1 1.2 Ice Formation and Its Effects...................................................................... 1 1.2.1 Factors Affecting Ice Formation....................................................................... 1 1.2.2 Ice Types...................................................................................................... 2 1.2.3 Aircraft Areas Subjected to Ice Formation......................................................... 4 1.2.4 Ice Formation Effects on Aircraft...................................................................... 4 1.3 Ice Control Systems.................................................................................. 5 1.3.1 Ice Detector System...................................................................................... 5 1.3.2 Ice Protection.............................................................................................. 10 1.4 Typical Anti-Icing Systems....................................................................... 14 1.4.1 Thermal Pneumatic Anti-icing........................................................................ 14 1.4.2 Thermal Electric Anti-Icing System................................................................ 23 1.4.3 Portable Water Tank Ice Prevention............................................................... 25 1.4.4 Chemical Anti-Icing...................................................................................... 26 1.5 Typical De-Icing Systems......................................................................... 28 1.5.1 Wing and Stabilizer Deicing Systems.............................................................. 28 1.5.2 De-icing System for Turboprop Aircraft........................................................... 30 1.5.3 Propeller De-icing System............................................................................. 31 1.5.4 Deicing System Components......................................................................... 33 1.6 Ground De-icing of Aircraft....................................................................... 37 1.6.1 Frost Removal............................................................................................. 38 1.6.2 Ice and Snow Removal................................................................................. 39 1.7 Rain Protection....................................................................................... 39 1.7.1 Windshield Wiper Systems............................................................................ 39 1.7.2 Chemical Rain Repellant............................................................................... 40 1.7.3 Pneumatic Rain Removal Systems................................................................. 42 1.8 Windshield Frost, Fog, and Ice Control Systems.......................................... 43 1.8.1 Electric....................................................................................................... 43 1.8.2 Pneumatic.................................................................................................. 44 Issue No. 0 ET-AF07.1 Page 2 of 4  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.8.3 Chemical.................................................................................................... 45 1.9 Maintenance & Troubleshooting................................................................ 45 1.9.1 Inspection and Testing................................................................................. 45 1.9.2 Troubleshooting........................................................................................... 46 1.9.3 Removal and Installation.............................................................................. 47 Issue No. 0 ET-AF07.1 Page 3 of 4  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Introduction This is the first module of ET-AF07: Aircraft Auxiliary Systems Course. It deals with aircraft ice and Rain Protection system. This module comprises lessons on ice types, its formation and effects together with ice detection, protection and removal systems such as wing anti-ice system, engine anti-ice system, probe heat, ice detectors, windshield wiper system, and flight deck window heat, and drain and water line heating system. Thermal pneumatic system, thermal electric, chemical, and pneumatic systems would be introduced. The module winds up the course with a sample discussion on ice and rain protection component inspection/troubleshooting and units removal/installation. At the end of the topic the trainee will be able to:  Describe the layout, location, operation, inspection and maintenance of anti-ice and de- ice systems.  Describe the layout, location, operation, inspection and maintenance of rain repellent/removal systems Issue No. 0 ET-AF07.1 Page 4 of 4  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1. Ice and Rain Protection (Level 3) Aircraft icing is the accretion of supercooled liquid onto an airplane during flight. Water droplets in the air can be supercooled to below freezing without actually turning into ice unless they are disturbed in some manner. This unusual occurrence is partly due to the surface tension of the water droplet not allowing the droplet to expand and freeze. However, when aircraft surfaces disturb these droplets, they immediately turn to ice on the aircraft surfaces. Accreted ice adversely affects flight. 1.1 Purpose of Ice and Rain Protection The operation of aircraft in the present day necessitates flying in all weather conditions and it is essential that the aircraft is protected against the build-up of ice which may affect the safety and performance of the aircraft. Aircraft designed for public transport and some military aircraft must be provided with certain detection and protection equipment for flights in which there is a probability of encountering icing (or rain) conditions. In addition to the requirements outlined above, certain basic standards have to be met by all aircraft whether or not they are required to be protected by the requirements. These basic requirements are intended to provide a reasonable protection if the aircraft is flown intentionally for short periods in icing conditions. The requirements cover such considerations as the stability and control balance characteristics, jamming of controls and the ability of the engine to continue to function. 1.2 Ice Formation and Its Effects 1.2.1 Factors Affecting Ice Formation Ice formation on aircraft in flight is the same as that on the ground; it can be classified under four main headings, i.e. Hoar Frost, Rime, Glaze Ice and Pack Snow. Dependent on the circumstances, variations of these forms of icing can occur and two different types of icing may appear simultaneously on parts of the aircraft. Ice in the atmosphere is caused by coldness acting on moisture in the air. Water occurs in the atmosphere in three forms, i.e. invisible vapour, liquid water and ice. The smallest drops of liquid water constitute clouds and fog, the largest drops occur only in rain and in between these are the drops making drizzle. Icing consists of crystals, their size and density being dependent on the temperature and the type of water in the atmosphere from which they form. Snowflakes are produced when a number of these crystals stick together or, in very cold regions, by small individual crystals. Issue No. 0 ET-AF07.1 Page 1 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.2.2 Ice Types There are four main types of icing: hoar frost, rime, clear or glaze and mixed. Each type is associated with different meteorological conditions, which are dependent on temperature and precipitation. Following is a brief explanation of each type and the basics of their formation. Hoar Frost Hoar frost occurs on a surface which is at a temperature below the frost point of the adjacent air and of course, below freezing point. It is formed in clear air when water vapour condenses on the cold airframe surface and is converted directly to ice and builds up into a white semi- crystalline coating; normally hoar frost is feathery. When hoar frost occurs on aircraft on the ground, the weight of the deposit is unlikely to be serious, but the deposit, if not removed from the airframe, may interfere with the airflow and attainment of flying speed during take-off, the windscreen may be obscured and the free working control surfaces may be affected. Hoar frost on aircraft in flight usually commences with a thin layer of glaze ice on the leading edge, followed by the formation of frost which gradually spreads over the whole surface. Again the effects are not usually serious, though some change in the landing characteristics of the aircraft can be expected. Rime Ice Rime ice is the term given to a rough opaque white structure. This ice can form at ground level or at altitude. At ground level, it forms when the air temperature drops to the dew point causing fog, then falls below 0°C creating freezing fog. Droplets of water that are super cooled (water that has a temperature below freezing but not frozen), form the fog. However, any cold object that these droplets touch causes the droplets to freeze on contact, building up an opaque, white rime, which has an open structure and is porous. It has the same consistency as the frost build- up that forms around the icebox of a refrigerator/deepfreeze. If the fog is moving with a breeze, the windward side of the object gets the thickest coating. In flight, this type of ice formation forms on the leading edges of an aircraft when it flies through a low-density cloud of small super cooled water droplets. The initial droplets freeze on contact with the LE, and subsequent droplets freeze on contact with the ice that has formed, trapping air between them. This gives the opaque white effect and forms a very rough surface that disrupts the airflow. Issue No. 0 ET-AF07.1 Page 2 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.1 Rime Ice Build Up on Leading Edge of Wing Glaze Ice Glaze ice, also known as clear or rain ice, forms when the aircraft encounters large water drops in clouds or in freezing rain (or super-cooled rain) with the air temperature and the temperature of the airframe below freezing point. On contact with the airframe, the water droplet starts to freeze but not instantaneously. This allows the air to bubble to the surface and dissipate forming a transparent or opaque coating of ice with a glassy surface. Glaze ice may be mixed with sleet or snow. It will form in greatest thickness on the leading edges of aerofoils and in reduced thickness as far aft as one half of the chord. Ice formed in this way is dense, tough and sticks closely to the surface of the aircraft, it cannot easily be shaken off and if it breaks off at all, it comes away in lumps of an appreciable and sometimes dangerous size. The main danger of glaze ice is still aerodynamic but also the weight of the ice produces unequal loading and propeller blade vibrations. Glaze ice is the most severe and most dangerous form of ice formation on aircraft because of its high rate of catch. Figure 1.2 Glaze Ice Build Up on Top Surface and Leading Edge of Wing Mixed Icing Issue No. 0 ET-AF07.1 Page 3 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Mixed icing is the term given to the formation of both glaze and rime ice. This is formed when the aircraft is flying in the transition phase between the two conditions. The surface is rough and predominantly opaque white but with clear patches. 1.2.3 Aircraft Areas Subjected to Ice Formation The following areas are critical areas on the aircraft where ice forms and where protection is essential Wing leading edges Horizontal and vertical stabilizer leading edges Engine cowl leading edges Propellers Propeller spinner Air data probes Flight deck windows Water and waste system lines and drains Antenna 1.2.4 Ice Formation Effects on Aircraft The buildup of ice on the aircraft is known as 'ice accretion'. If ice continues to be deposited on the aircraft one, or more, of the following effects may occur. a. Decrease in Lift This may occur due to changes in wing section resulting in loss of streamlined flow around the leading edge and top surfaces. b. Increase in Drag Drag will increase due to the rough surface, especially if the formation is rime. This condition results in greatly increased surface friction. c. Increased Weight and Wing Loading The weight of the ice may prevent the aircraft from maintaining height. d. Decrease in Thrust With turbo-prop and piston engines, the efficiency of the propeller will decrease due to alteration of the blade profile and increased blade thickness. Vibration may also occur due to uneven distribution of ice along the blades. Gas Turbine engines may also be affected by ice on the engine intake, causing disturbance of the airflow to the compressor. Furthermore, ice breaking away from the intake, may be ingested by the engine causing severe damage to the compressor blades and other regions within the engine. e. Inaccuracy of Pitot Static Instruments Ice on the pitot static pressure head causes blockage in the sensing lines and produces false readings on the instruments. f. Loss of Inherent Stability This may occur due to displacement of the centre of gravity caused by the weight of the ice. g. Radio antennae Issue No. 0 ET-AF07.1 Page 4 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Reduced efficiency h. Loss of Control Loss of control may occur due to ice preventing movement of control surfaces. (This is not usually a problem in flight but may occur on the ground). Figure 1.3 effects of structural icing The effects of ice accretion on the ground are similar to those occurring in flight but the following additional effects may be caused. a. Restriction of the controls may occur if ice is not removed from hinges and gaps in the controls. b. The takeoff run may be increased because of the increase in weight and drag. c. The rate of climb may be reduced because the weight and drag are increased. 1.3 Ice Control Systems 1.3.1 Ice Detector System As ice forms on thin edges first, each aircraft has points, such as the windscreen wiper arms, where the formation of ice indicates that the aircraft has entered into icing conditions. Locations on the airframe where ice build-up affects the controllability or stability of an aircraft are termed critical points, such as the leading edge of the wings, tailplane, and fin. Pilots must be aware of Issue No. 0 ET-AF07.1 Page 5 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems the effect of icing. There are several different types of ice detector that can be fitted to aircraft to assist the pilot in identifying icing conditions. These operate in different ways and are listed below: 1. Icing conditions exist: a. Temperature/moisture probes 2. Icing has formed: a. Visual i. Ice detection light ii. Hot rod detector b. Pressure i. Smiths ice detector c. Torque i. Serrated rotor d. Vibration frequency i. Vibrating rod ice detector Temperature/Moisture Probes Figure 1.4 Temperature and Moisture Probes Unlike the other detectors, this Ice Detector works on the principle of detecting when icing conditions exist, not when ice has actually formed. Working on the principle that ice cannot form unless there is moisture and freezing temperature, the detector system consists of two separate units. These are a moisture detector and a temperature sensor termed a thermal switch. The moisture detector consists of a unit that has two cylindrical rods that are mounted close together. When they protrude into the free stream airflow, the forward rod screens the rear rod. Both rods are heated resistance bulbs. As the forward bulb shields the rear bulb, it cools more quickly than the rear bulb. Any moisture in the free stream airflow impinges on the forward bulb only. This acts to cool the forward bulb down even more. Issue No. 0 ET-AF07.1 Page 6 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems A controller built into the base of the moisture probe senses the temperature difference between the two probes. If it drops to a predetermined value, it sends a signal to the thermal switch. The temperature sensor of the thermal switch is exposed to the ambient temperature of the free stream airflow. While the OAT remains above freezing, the switch remains open and prevents the signal from being sent to the flight deck. As soon as the temperature drops, the switch closes, and any moisture signal illuminates an amber ice warning light on the flight deck. Ice Detection Light Unless an aircraft is not certified to operate at night, or is prohibited from night operations, it must be equipped with a light that illuminates those parts of the wing that are deemed critical for ice accumulation. The lighting must not cause glare or reflection that would interfere with the flight crew. For large air transport aircraft, this is achieved by mounting a spot lamp in the wing root fillet panel ahead of the leading edge of the wing, so that it illuminates the length of the wing. Hot Rod Ice Detector Figure 1.5 Hot Rod Ice Detector The Hot Rod Ice Detector is a visual indicator. It consists of a thin rod with an aerofoil cross section with a heater element running down its centre, which is controlled by an on/off switch on the flight deck. The rod is angled backward and protrudes into the airflow. A small lamp Issue No. 0 ET-AF07.1 Page 7 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems mounted in the unit’s housing illuminates the rod for nighttime operations. Either one rod is mounted where both pilots can observe it or two rods are fitted. Each is located where a pilot can see it but so that it does not interfere with normal vision. When flying in possible icing conditions, the pilot keeps a regular watch on the rod. Ice forms on its thin edge before forming on the lifting surfaces of the aircraft. When ice is observed, the rate of accretion indicates the severity of the conditions. The pilot can apply heat to the rod or mast to clear it, then switch the heat off, and watch how quickly the ice reforms. Smiths Ice Detector Figure 1.6 Smiths Pressure-Operated Ice Detector The Smiths ice detector, shown in figure 1.6, is a pressure-operated unit that detects the presence of ice. In this design, a detector housing mounts inside the fuselage with a probe protruding into the free stream airflow. The probe, a hollow cylindrical tube with one end sealed and heater element core has four small holes facing forward and two large holes facing aft. In non-icing conditions, the positive air pressure (pitot and static) in the detector unit holds the switch in the open condition. In icing conditions, the formation of ice on the front edge quickly blocks the four small holes. This results in a reduction of pressure in the detector (static only), which results in the switch closing. As the switch closes, an amber ice indication light on the flight deck illuminates and power is applied to the heater in the probe. The power is supplied to both the heater and the ice warning light until the ice melts and the positive pressure is re- established. The severity of icing is indicated by the frequency at which the ice warning light illuminates. Issue No. 0 ET-AF07.1 Page 8 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Serrated Rotor Ice Detector Figure 1.7 Serrated Rotor Ice Detector The serrated rotor ice detector consists of a housing mounted inside the airframe with a protruding serrated rotor and fixed knife, which is mounted at right angles to the aircraft’s skin with the rod in front of the knife. During flight, an electric motor inside the housing rotates the serrated rotor at a constant rate toward the leading edge of the knife. These have a minimum clearance. In non-icing conditions, the torque required to turn the rotor is at a low level. However, as ice forms on the rotor, the torque increases as the knife shaves the ice off. The increased torque makes a micro switch and illuminates an ice warning light on the flight deck. This remains on as long as ice is forming on the rotor and is shaved off. Vibrating Rod Ice Detector The Vibrating Rod is the most modern of the ice detection systems and consists of a rod that protrudes into the free stream airflow from a detector unit housing. These are normally mounted on the underside of the fuselage. The rod is vibrated by an electrical impulse at a set frequency of 40 kHz. In non-icing conditions, the rod maintains this frequency. However, as ice forms on the rod, its mass increases and vibration frequency decreases. A drop in frequency activates the ice warning light on the flight deck and applies power to a heater element within the rod. When the ice has been cleared, the vibration frequency of the rod is restored and power to both the warning light and the indication is removed. The rod continues to vibrate at 40 kHz until ice forms on the rod again. Severity of icing is determined by the frequency at which the warning light illuminates. Issue No. 0 ET-AF07.1 Page 9 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.8 Vibrating rod ice detector 1.3.2 Ice Protection There are several different systems for protecting aircraft from ice build-up, which can be classified into two groups, de-icing systems and anti-icing systems: Pneumatic de-icing Liquid de-icing Electrical de-icing Electrical anti-icing Thermal anti-icing The areas to be protected are: Leading edges of the wings, tailplane, and fin Jet engine air intakes Windshield Pitot probes Propellers a. Anti-Icing Ice is prevented from forming by ensuring that the ice protection system is operating whenever icing conditions are encountered or forecast. i. Purpose and Operation TO BE FILLED ii. Hot air Anti-Icing Issue No. 0 ET-AF07.1 Page 10 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems TO BE FILLED iii. Electrical Anti-Icing TO BE FILLED b. De-Icing In this method of ice protection, ice is allowed to form on the surfaces and is then removed by operating the particular system in the specified sequence. i. Purpose and Operation Pneumatic (or mechanical) systems are used for de-icing only, It is not possible to prevent ice formation and works on the principle of cyclic inflation and deflation of rubber tubes on aerofoil leading edges. Details of pneumatic systems operation will be discussed in the following section. ii. Pneumatic De-Icing Pneumatic boots, often referred to as just boots, are a mechanical de-icing system fitted to the leading edge of the aircraft’s wings, tailplane, and fin. The boots consist of a shaped rubber sleeve (boot) that conforms to the leading edge of the surface to which it is attached. Within the boot are a series of tubes that can be inflated. For narrow wing profiles such as light aircraft and outer wing sections of larger aircraft, these tubes are orientated with the wing’s span and are termed spanwise. For thicker cross sections, the tubes are orientated at right angles to the wingspan and termed chordwise. The tubes are connected to the air supply by short lengths of flexible hose secured by hose clips. Depending on the type specified, a boot may be attached to the leading edge either by screw fasteners or by cementing them directly to the leading edge skin. The external surfaces of the boots are coated with a film of conductive material to bleed off accumulations of static electricity. Figure 1.9 Pneumatic De-Icing Boots Issue No. 0 ET-AF07.1 Page 11 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems The tubes in the boots are inflated by air from the pressure side of an engine driver vacuum pump or, in some types of turbo-propeller aircraft, from a tapping on the engine compressor. At the end of the inflated stage of the operating sequence, and whenever the system is switched off, the boots are deflated by vacuum derived from the vacuum pump or from the venturi section of an ejector nozzle in systems using the engine compressor tapping. The method of distributing air supplies to the boots depends on the system required for a particular type of aircraft. In general three methods are in use: Shuttle valves controlled by a separate solenoid valve Individual solenoid valves direct air to each boot Motor driven valves The controls and indication required for the operation of a system will depend on the type of aircraft and on the particular arrangement of the system. In a typical system a main ON-OFF switch, pressure and vacuum gauges or indicating lights form part of the controlling section. Pressure and vacuum is applied to the boots in an alternating, timed sequence and the methods adopted usually vary with the methods of air distribution. In most installations, however, timing control is affected by an electronic device. Figure 1.10 Pneumatic De-icing System Layout Issue No. 0 ET-AF07.1 Page 12 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Operation - When the system is switched on, pressure is admitted to the boot sections to inflate groups of tubes in sequence. The inflator weakens the bond between ice and the boot surfaces and cracks the ice that is carried away by the airflow. At the end of the inflation stage of the operating sequence, the air in the tubes is vented to atmosphere through the distributor and the tubes are fully deflated by the vacuum source. The inflation and deflation cycle is repeated whilst the system is switched on. When the system is switched off, vacuum is supplied continually to all tubes of the boots to hold the tubes flat against the leading edges thus minimizing aerodynamic drag. iii. Alcohol De-Icing (Fluid De-Icing System) Figure 1.11 Fluid De-Icing System Figure 1.11 is a schematic representation of a T-tailed aircraft’s fluid de-icing system. These systems are also referred to as weeping or wet wings. The system consists of a fluid reservoir, an electrical pump, filter, head-compensating valve, NRVs, micro porous panels, and pipe work. The pilot’s controls consist of a rotary timing switch, which times from 0 to 8 minutes, a chime that sounds when the switch reaches zero, a contents warning light that illuminates when the tank’s capacity has 30 minutes of fluid left, and a low pressure warning light. When ice has formed, the pilot selects the appropriate amount of fluid to be dispensed by using the timer. This activates the pump, and Isopropyl Alcohol is pumped to the panels where it oozes or weeps out of the micro pores onto the skin’s surface. A head-compensating valve is fitted to the aircraft to ensure that fluid is supplied to the fin and, if used, T-tail, as well as the wings. Issue No. 0 ET-AF07.1 Page 13 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems The pilot must be aware of the effect of the airflow across the aircraft’s wings at different angles of attack, as this alters the distribution pattern of the fluid. The system suffers from the pores becoming blocked by impact with insects and fine airborne particles. To overcome this, the system has to function regularly to clean the pores. 1.4 Typical Anti-Icing Systems 1.4.1 Thermal Pneumatic Anti-icing Thermal anti-ice uses a very large quantity of hot air. Only aircraft with large turbine engines (or dedicated heaters) can use this system, as the air drawn off from the HP compressor results in less thrust as it reduces the engine pressure ratio (EPR) and raises the exhaust gas temperature (EGT), which has to be considered at high altitude and when flight planning. These systems must have an overheat sensor in the supply and shut off valve as the temperature could damage the structure of the leading edge. In flight, the airflow across the wings and any moisture in the atmosphere dissipates the heat in the leading edge structures. When the aircraft is on the ground, this cooling airflow is not available. To prevent structural damage, the air/ground logic circuit closes the anti-icing valves. Figure 1.12 Thermal Anti-Icing Issue No. 0 ET-AF07.1 Page 14 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems It is standard for leading edge anti-icing to be selected “on” prior to take-off. To prevent the engines from losing thrust during the initial climb as the air/ground logic switches to air logic, a 12-second time delay operates. This keeps the valves closed until the aircraft has stabilized. In modern systems, this is also linked to the radio altimeter and cuts out if the aircraft reaches 400 ft radio altitude before the 12 seconds has elapsed. a. Wing Anti-Ice (WAI) System Thermal wing anti-ice (WAI or TAI) systems for business jet and large-transport category aircraft typically use hot air bled from the engine compressor. Relatively large amounts of very hot air can be bled off the compressor, providing a satisfactory source of anti-icing heat. The hot air is routed through ducting, manifolds, and valves to components that need to be anti-iced. Figure 1.13 shows a typical WAI system schematic for a business jet. The bleed air is routed to each wing leading edge by an ejector in each wing inboard area. The ejector discharges the bleed air into piccolo tubes for distribution along the leading edge. Fresh ambient air is introduced into the wing leading edge by two flush-mounted ram air scoops in each wing leading edge, one at the wing root and one near the wingtip. The ejectors entrain ambient air, reduce the temperature of the bleed air, and increase the mass airflow in the piccolo tubes. The wing leading edge is constructed of two skin layers separated by a narrow passageway. The air directed against the leading edge can only escape through the passageway, after which it is vented overboard through a vent in the bottom of the wingtip. Issue No. 0 ET-AF07.1 Page 15 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.13 Thermal WAI system When the WAI switch is turned on, the pressure regulator is energized and the shutoff valve opens. When the wing leading edge temperature reaches approximately +140 °F, temperature switches turn on the operation light above the switch. If the temperature in the wing leading edge exceeds approximately +212 °F (outboard) or +350 °F (inboard), the red WING OV HT warning light on the annunciator panel illuminates. Issue No. 0 ET-AF07.1 Page 16 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.14 Heated wing leading edge The ducting of WAI systems usually consists of aluminum alloy, titanium, stainless steel, or molded fiberglass tubes. The tube, or duct, sections are attached to each other by bolted end flanges or by band-type V-clamps. The ducting is lagged with a fire-resistant, heat-insulating material, such as fiberglass. In some installations, thin stainless steel expansion bellows are used. Bellows are located at strategic positions to absorb any distortion or expansion of the ducting that may occur due to temperature variations. The joined sections of ducting are hermetically sealed by sealing rings. These seals are fitted into annular recesses in the duct joint faces. When installing a section of duct, make certain that the seal bears evenly against and is compressed by the adjacent joint’s flange. When specified, the ducts should be pressure tested at the pressure recommended by the manufacturer of the aircraft concerned. Leak checks are made to detect defects in the duct that would permit the escape of heated air. The rate of leakage at a given pressure should not exceed that recommended in the aircraft maintenance manual. Air leaks can often be detected audibly and are sometimes revealed by holes in the lagging or thermal insulation material. However, if difficulty arises in locating leaks, a soap-and water solution may be used. All ducting should be inspected for security, general condition, or distortion. Lagging or insulating blankets must be checked for security and must be free of flammable fluids, such as oil or hydraulic fluid. b. Leading Edge Slat Anti-Ice System Issue No. 0 ET-AF07.1 Page 17 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Aircraft that utilize leading edge slats often use bleed air from the engine compressor to prevent the formation of frost on these surfaces. On a modern transport category aircraft, the pneumatic system supplies bleed air for this purpose. WAI valves control the air flow from the pneumatic system to WAI ducts. The WAI ducts carry the air to the slats. Holes in the bottom of each slat let the air out. The airfoil and cowl ice protection system (ACIPS) computer card controls the WAI valves, and pressure sensors send duct air pressure data to the computer. The aircrew can select an auto or manual mode with the WAI selector. In the auto mode, the system turns on when the ice detection system detects ice. The off and on positions are used for manual control of the WAI system. The WAI system is only used in the air, except for ground tests. The weight on wheels system and/or airspeed data disarms the system when the aircraft is on the ground. [Figure 1.15] Figure 1.15 Wing leading edge slat anti-ice system WAI Valve The WAI valve controls the flow of bleed air from the pneumatic system to the WAI ducts. The valve is electrically controlled and pneumatically actuated. The torque motor controls operation of the valve. With no electrical power to the torque motor, air pressure on one side of the Issue No. 0 ET-AF07.1 Page 18 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems actuator holds the valve closed. Electrical current through the torque motor allows air pressure to open the valve. As the torque motor current increases, the valve opening increases. [Figure 1.16] Figure 1.16 A wing anti-ice valve. WAI Pressure Sensor - The WAI pressure sensor senses the air pressure in the WAI duct after the WAI valve. The ACIPS system card uses the pressure information to control the WAI system. WAI Ducts - The WAI ducts move air from the pneumatic system through the wing leading edge to the leading edge slats. Figure 1.17a shows that only leading edge slat sections 3, 4, and 5 on the left wing and 10, 11, and 12 on the right wing receive bleed air for WAI. Sections of the WAI ducting are perforated. The holes allow air to flow into the space inside the leading edge slats. The air leaves the slats through holes in the bottom of each slat. Some WAI ducts have connecting “T” ducts that telescope to direct air into the slats while 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 1.17 a & b] Issue No. 0 ET-AF07.1 Page 19 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.17 WAI ducting 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 Issue No. 0 ET-AF07.1 Page 20 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 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. 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 1.18] Figure 1.18 WAI inhibit logic schematic 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 Issue No. 0 ET-AF07.1 Page 21 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems  Air-driven hydraulic pump operation  Engine start  Bleed air temperature less than 200 °F (93 °C). WAI Indication System The aircrew can monitor the WAI system on the onboard computer maintenance page. The following information is shown:  WING MANIFOLD PRESS—pneumatic duct pressure in PSIG  VALVE—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 (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. c. Engine Inlet Anti-Icing System Part of the certification process for jet engines for use in aviation is an ice ingestion test, as the effect of a block of ice hitting a high-speed rotor off centre is to put it out of balance. The most likely place for ice to form on an engine’s nacelle is the intake lip where the airflow stagnates, allowing ice to form easily. Ice also forms on the tip of the engine’s rotating bullet, inlet guide vane (IGV), and at the root end of the first/second row(s) of compressor blades. Apart from the hazard of lumps of ice forming on the lip, then breaking off and being ingested, ice formations disrupt the airflow into the engines. This can lead to the engines stalling in certain flight conditions such as high pitch angles. There are two systems for protecting air intakes. For large turbine aircraft, this is normally done using bleed air anti-icing. For smaller turboprop engines, this is normally achieved by a mixture of electrical anti-icing and de-icing. Issue No. 0 ET-AF07.1 Page 22 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.19 Intake Bleed Air Anti-Icing Figure 1.19 shows how the intake lip of a turbine engine is anti-iced using bleed air. When engine anti-icing is selected, the anti-icing valves open, allowing bleed air to enter the bleed air manifold. Where IGVs are fitted, some air is passed down through them to prevent ice from forming on them. This air can be used to anti-ice the bullet. A piccolo tube behind the intake lip heats the lip structure preventing the formation of ice. If the air used for anti-icing is exhausted overboard, there is reduction in EPR. However, if the bleed air is exhausted back into the intake (close to the blade roots), it ensures that ice does not form at the blade roots but raises the temperature of the intake air, which reduces its density. Engine anti-icing can be selected and operated on the ground due to the large volume of airflow passing over the intake lips, even when the aircraft is stationary and the engines are at ground idle. 1.4.2 Thermal Electric Anti-Icing System 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 Issue No. 0 ET-AF07.1 Page 23 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 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. Data probes that protrude into the ambient airstream are particularly susceptible to ice formation in flight. Figure 1.20 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. Figure 1.20 Probes with thermal electric anti-icing on one commercial airliner. 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 1.21 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. Issue No. 0 ET-AF07.1 Page 24 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.21 Pitot probe heat system. 1.4.3 Portable Water Tank Ice Prevention One water heater is installed in each lavatory and in each galley. Water pipes, where icing conditions can occur are insulated and heated by tape electrical heaters. The potable water service panel is heated to prevent ice formation. Optionally, the fill/drain nipple and overflow nipple are also electrically heated. These heating elements are controlled automatically by anti- ice control units. In winter conditions, the potable water system must be drained during night stops. Issue No. 0 ET-AF07.1 Page 25 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.22 Potable Water Heating and Ice Protection 1.4.4 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 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, 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 1.23 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 nonperforated stainless steel rear panels and bonded to wing and stabilizer leading edges. As fluid is delivered Issue No. 0 ET-AF07.1 Page 26 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 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. Figure 1.23 Chemical deicing system. Issue No. 0 ET-AF07.1 Page 27 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.5 Typical De-Icing Systems 1.5.1 Wing and Stabilizer Deicing Systems GA aircraft and turboprop commuter-type aircraft often use a pneumatic deicing system to break off ice after it has formed 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. a. 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 cockpit are used to control the flow of source air to the system. b. Deice Boot System for Light Aircraft Figure 1.24 shows de-icer boots fitted to a light twin piston-engine aircraft. This system is manually operated with a momentary switch when the pilot detects that the ice has built up to the correct depth. The boots are pneumatically connected to the instrument air vacuum manifold downstream of the instruments, and the exhaust air from the engine-driven vacuum pumps via an inflation-deflation valve. When not in operation, the valve applies the vacuum pressure of 2.2 psi from the instrument manifold to the boots. When the pilot selects the de-ice, the valve closes the suction side and diverts the exhaust air from the vacuum pump into the pneumatic system to inflate all the spanwise boots simultaneously. Issue No. 0 ET-AF07.1 Page 28 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.24 De-icer Boots on a Light Twin Figure 1.25 De-Icing Control Panel for a Light Aircraft The boots are inflated to a nominal pressure of 18 psi. At this pressure, a pressure switch then closes the inflation valve and opens the deflation valve. To confirm to the pilot that they are functioning correctly, a green light illuminates at 8 psi and remains illuminated until the pressure drops below 8 psi. A timer unit starts to count down to prevent them from remaining inflated should the pressure not reach 18 psi, or the pressure switch fails as the inflation valve opens. If the inflation sequence has not started before the timer unit reaches zero, it automatically opens the deflation valve and closes the inflation valve. The whole operation from start of inflation to Issue No. 0 ET-AF07.1 Page 29 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems complete deflation should not exceed 34 seconds. If the pilot notices that the green 8 psi light remains illuminated, the circuit breakers for the surface de-icer should be pulled. 1.5.2 De-icing System for Turboprop Aircraft Figure 1.26 shows a pneumatic deice system used on a turboprop aircraft. The source of pneumatic air is engine bleed air, which is used to inflate two inboard wing boots, two outboard boots, and horizontal stabilizer boots. Additional bleed air is routed through the brake deice valve to the brakes. A three-position switch controls the operation of the boots. This switch is spring loaded to the center OFF position. When ice has accumulated, the switch should be selected to the single-cycle (up) position and released. Pressure-regulated bleed air from the engine compressors supply air through bleed air flow control units and pneumatic shutoff valves to a pneumatic control assembly that inflates the wing boots. After an inflation period of 6 seconds, an electronic timer switches the distributor in the control assembly to deflate the wing boots, and a 4-second inflation begins in the horizontal stabilizer boots. After these boots have been inflated and deflated, the cycle is complete, and all boots are again held down tightly against the wings and horizontal stabilizer by vacuum. The spring-loaded switch must be selected up again for another cycle to occur. Each engine supplies a common bleed air manifold. To ensure the operation of the system, if one engine is inoperative, a flow control unit with check valve is incorporated in the bleed air line from each engine to prevent the loss of pressure through the compressor of the inoperative engine. If the boots fail to function sequentially, they may be operated manually by selecting the DOWN position of the same deice cycle switch. Depressing and holding it in the manual DOWN position inflates all the boots simultaneously. When the switch is released, it returns to the (spring-loaded) off position, and each boot is deflated and held by vacuum. When operated manually, the boot should not be left inflated for more than 7 to 10 seconds, as a new layer of ice may begin to form on the expanded boots and become un-removable. If one engine is inoperative, the loss of its pneumatic pressure does not affect boot operation. Electric power to the boot system is required to inflate the boots in either single-cycle or manual operation. When electric power is lost, the vacuum holds the boots tightly against the leading edge. Issue No. 0 ET-AF07.1 Page 30 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.26 Wing deice system for turboprop aircraft. 1.5.3 Propeller De-icing System The formation of ice on the propeller leading edges, cuffs, and spinner reduces the efficiency of the powerplant system. Deice systems using electrical heating elements and systems using chemical deicing fluid are used. a. Electrothermal Propeller Device System Many propellers are deiced by an electrically heated boot on each blade. The boot, firmly cemented in place, receives current from a slip ring and brush assembly on the spinner bulkhead. The slip ring transmits current to the deice boot. The centrifugal force of the spinning propeller and air blast breaks the ice particles loose from the heated blades. Issue No. 0 ET-AF07.1 Page 31 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.27 Electro thermal propeller deice system components. On one aircraft model, the boots are heated in a preset sequence, which is an automatic function controlled by a timer. This sequence is as follows: 30 seconds for the right prop outer elements; 30 seconds for the right prop inner elements; 30 seconds for the left prop outer elements; and, 30 seconds for the left prop inner elements. Once the system is turned on for automatic is activated, it cycles continuously. A manual bypass of the timer is incorporated. Figure 1.28 Propeller electrical deice system schematic. b. Chemical Propeller Deice Issue No. 0 ET-AF07.1 Page 32 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Some aircraft models, especially single-engine GA aircraft, use a chemical deicing system for the propellers. Ice usually appears on the propeller before it forms on the wing. The glycol-based fluid is metered from a tank by a small electrically driven pump through a microfilter to the slinger rings on the prop hub. The propeller system can be a stand-alone system, or it can be part of a chemical wing and stabilizer deicing system such as the TKS™ weeping system. 1.5.4 Deicing System Components Several components are used to construct all deice boot systems. The components may differ slightly in name and location within the system depending on the aircraft. Components may also combine functions to save space and weight. The basic functions of filtering, pressure regulation, distribution, and attachment to a vacuum when boots are not in use must all be present. Check valves must also be installed to prevent back flow in the system. Manifolds are common on multiengine aircraft to allow sourcing of low pressure air from both engine pumps. Note that air- pump pressure is typically expelled overboard when not needed. Bleed air is shut off by a valve when not needed for deice boot operation on turbine engine aircraft. A timer, or control unit with an automatic mode, exists on many aircraft to repeat the deice cycle periodically. a. Engine-Driven Air Pump To provide pressure for the deice boots; older aircraft may use a wet-type engine-driven air pump mounted on the accessory drive gear case of the engine. Some modern aircraft may also use a wet-type air pump because of its durability. The pump is typically a four vane, positive displacement pump. Engine oil passes from the accessory case through the pump mounting base flange to lubricate the pump. Some of the oil is entrained in the output air and must be removed by an oil separator before it is sent through other components in the deice system. When installing a wet-type pump, care should be taken to ensure that the oil passage in the gasket, Pump and mounting flange are aligned to ensure lubrication. Most modern GA aircraft are equipped with a dry-type engine-driven air pump. It is also mounted on the engine accessory drive case; however, it is not lubricated with engine oil. The pump is constructed with carbon rotor vanes and bearings. The carbon material wears at a controlled rate to provide adequate lubrication without the need for oil. This keeps output air oil- free; thus, the use of an oil separator is not required. Caution should be used to prevent oil, grease, or degreasing fluids from entering the pump or the air system to ensure proper pump and system operation. Dry-type and wet-type pumps are virtually maintenance free. Mounting bolts should be checked for security as should all hose connections. Wet-type pumps have a longer time before requiring overhaul, but dry-type pumps give the assurance that the deice system will not be contaminated with oil. b. Oil Separator An oil separator is required for each wet-type air pump. Pump output air flows through the separator where most of the oil is removed and sent back to the engine though a drain line. Some systems may include a secondary separator to ensure oil free air is delivered to the deice system. There are no moving parts in an oil separator. A convoluted interior allows the air to Issue No. 0 ET-AF07.1 Page 33 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems pass, while the oil condenses and drains back to the engine. The only maintenance required on the separator is flushing the interior of the unit with a specified solvent. This should be done at intervals prescribed in the applicable maintenance manual. c. Valves i. Control Valve A control valve is a solenoid operated valve that allows air from the pump to enter the deice system. When energized by the deice switch in the cockpit, the valve opens. The control valve dumps pump air overboard when the deice system is not in use. Many control valves are built in combination with pressure relief valves that keeps the deice system safe from over pressure. Figure 1.29 A solenoid operated deice control valve. ii. Distributor Valve A distributer valve is a type of control valve used in relatively complex deice boot systems. It is an electrically-operated solenoid valve controlled by the deice boot system timer or control unit. On some systems, a distributor valve is assigned to each set of deice boots it controls. It differs from a control valve in that it has the deflate valve function built into it. Therefore, the distributor valve transfers connection of the boots from the pressure side of the air pump to the vacuum side of the pump once the proper inflation time has elapsed. The valve also dumps the unneeded air from the pump overboard. Another type of distributor valve exists that handles the inflation and deflation of numerous sets of deices boots in a single unit. It also connects the boots to vacuum and dumps pump air when deice is not needed. A servo motor is used to position the multi-position valve. These centralized units are controlled by a timer or control unit. They inflate and deflate all of the boots on the aircraft. The timer may be built into the unit on some models. iii. Regulators and Relief Valves Issue No. 0 ET-AF07.1 Page 34 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Both the pressure and vacuum developed by an air pump must be regulated for use in the deice boot system. Typical boot inflation air pressure is between 15 and 20 psi. Vacuum pressure is set for the requirements of the gyroscopic instruments operated by the vacuum side of the air pump. Measured in inches of mercury, normal vacuum pressure (suction) is 4.5 to 5.5 "Hg. Deice boot system air pressure is controlled by a pressure regulator valve located somewhere in the system downstream of the pump or oil separator, if installed. The regulator may be a stand- alone unit, or it may be combined into another deice system component. Regardless, the spring loaded valve relieves pressure overboard when it exceeds the limit for which the system is designed. A vacuum regulator is installed in the vacuum manifold on the suction side of the air pump to maintain the vacuum at the designed level. Also known as a suction regulating valve or similar, the spring loaded valve contains a filter for the ambient air drawn through the valve during operation. This filter must be changed or kept clean per manufacturer’s instructions. Figure 1.30 A vacuum regulator. d. Timer/Control Unit All but the simplest of deice systems contain a timer or control unit. This device controls the action of the distributor valve(s) to ensure all boots are inflated in the proper sequence and for the correct duration. Six seconds of inflation is common to break off accumulated ice. The boot then must be immediately deflated so that ice does not adhere to the inflated geometry of the boot. This could cause it to fail to deflate or break off ice when the boot is re-inflated. The timer, or control unit, can also be made to cycle through the inflation and deflation of all boots periodically, thus relieving the flight crew of repetitive manual activation of the system. The function and capabilities of timers and control units vary. Consult the manufacturer’s maintenance information for the performance characteristics of the timer/control unit on the aircraft in question. The timer, or control unit, may be an independent Issue No. 0 ET-AF07.1 Page 35 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems device, or it may be built-in as part of another deice system component, such as a central distribution valve. e. Manifold Assembly In all pneumatic deice boot systems, it is necessary for check valves to be installed to prevent backflow of air in the system. The location(s) depend on system design. Sometimes, the check valve is built into another system component. On twin-engine aircraft, it is common to unite the air supplied from each engine-driven pump to provide redundancy. Check valves are required to guard against backflow should one pump fail. A manifold assemble is commonly used to join both sides of the system. It contains the required check valves in a single assembly. Figure 1.31 A manifold assembly used in multiengine aircraft deice systems. f. Inlet Filters The air used in a deice boot system is ambient air drawn in upstream of the gyroscopic instruments on the suction side of the engine-driven air pump. This air must be free of contaminants for use spinning the gyros, as well as for inflation of the deice boots. To ensure clean air, an inlet filter is installed as the air intake point for the system. This filter must be regularly maintained as per manufacturer’s instructions. shows a typical inlet air filter. Figure 1.32 shows the relationship of the vacuum regulator and inlet air filter to other system components. Issue No. 0 ET-AF07.1 Page 36 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.32 Air filter for vacuum system. g. De-icing Boots Deicer boots are made of soft, pliable rubber, or rubberized fabric, and contain tubular air cells. The outer ply of the deicer boot is of conductive neoprene to provide resistance to deterioration by the elements and many chemicals. The neoprene also provides a conductive surface to dissipate static electricity charges. These charges, if allowed to accumulate, would eventually discharge through the boot to the metal skin beneath, causing static interference with the radio equipment. On modern aircraft, the deicer boots are bonded with an adhesive to the leading edge of wing and tail surfaces. The trailing edges of this type boot are tapered to provide a smooth airfoil. Elimination of fairing strips, screws, and rivnuts used on older types of deicing boots reduces the weight of the deice system. The deicer boot air cells are connected to system pressure and vacuum lines by non-kinking flexible hose. When gluing the deice boots to the leading edge of wings and stabilizers, the manufacturer’s instruction must be strictly followed. The glue is typically a contact cement normally spread on both the airfoil and the boot and allowed to become tacky before mating the surfaces. Clean, paint-free surfaces are required for the glue to adhere properly. Removal of old boots is performed by re-softening the cement with solvent. 1.6 Ground De-icing of Aircraft The presence of ice on an aircraft may be the result of direct precipitation, formation of frost on integral fuel tanks after prolonged flight at high altitude, or accumulations on the landing gear following taxiing through snow or slush. In accordance with the Federal Aviation Administration (FAA) Advisory Circular (AC) 120-60, the aircraft must be free of all frozen contaminants adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces before takeoff. Issue No. 0 ET-AF07.1 Page 37 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Any deposits of ice, snow, or frost on the external surfaces of an aircraft may drastically affect its performance. This may be due to reduced aerodynamic lift and increased aerodynamic drag resulting from the disturbed airflow over the airfoil surfaces, or it may be due to the weight of the deposit over the whole aircraft. The operation of an aircraft may also be seriously affected by the freezing of moisture in controls, hinges, valves, microswitches, or by the ingestion of ice into the engine. When aircraft are hangared to melt snow or frost, any melted snow or ice may freeze again if the aircraft is subsequently moved into subzero temperatures. Any measures taken to remove frozen deposits while the aircraft is on the ground must also prevent the possible refreezing of the liquid. 1.6.1 Frost Removal Frost deposits can be removed by placing the aircraft in a warm hangar or by using a frost remover or deicing fluid. These fluids normally contain ethylene glycol and isopropyl alcohol and can be applied either by spray or by hand. It should be applied within 2 hours of flight. Deicing fluids may adversely affect windows or the exterior finish of the aircraft, only the type of fluid recommended by the aircraft manufacturer should be used. Transport category aircraft are often deiced on the ramp or a dedicated deicing location on the airport. Deicing trucks are used to spray the deicing and/or anti-icing fluid on aircraft surfaces. Figure 1.33 aircraft deicing a. Alcohol Spraying Frost deposits can be removed using a frost remover or deicing fluid. These fluids normally contain ethylene glycol and isopropyl alcohol and can be applied either by spray or by hand. b. Hot water Spraying The water is heated to a maximum temperature of 95°C and pressure sprayed onto the airframe to melt and blast away the snow/ice. After a surface has been de-iced, it must either be dried or treated within three minutes. Issue No. 0 ET-AF07.1 Page 38 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.6.2 Ice and Snow Removal Probably the most difficult deposit to deal with is deep, wet snow when ambient temperatures are slightly above the freezing point. This type of deposit should be removed with a soft brush or squeegee. Use care to avoid damage to antennas, vents, stall warning devices, vortex generators, etc., that may be concealed by the snow. Light, dry snow in subzero temperatures should be blown off whenever possible; the use of hot air is not recommended, since this would melt the snow, which would then freeze and require further treatment. Moderate or heavy ice and residual snow deposits should be removed with a deicing fluid. No attempt should be made to remove ice deposits or break an ice bond by force. After completion of deicing operations, inspect the aircraft to ensure that its condition is satisfactory for flight. All external surfaces should be examined for signs of residual snow or ice, particularly in the vicinity of control gaps and hinges. Check the drain and pressure sensing ports for obstructions. When it becomes necessary to physically remove a layer of snow, all protrusions and vents should be examined for signs of damage. Control surfaces should be moved to ascertain that they have full and free movement. The landing gear mechanism, doors and bay, and wheel brakes should be inspected for snow or ice deposits and the operation of unlocks and microswitches checked. Snow or ice can enter turbine engine intakes and freeze in the compressor. If the compressor cannot be turned by hand for this reason, hot air should be blown through the engine until the rotating parts are free. 1.7 Rain Protection There are several different ways to remove the rain from the windshields. Most aircraft use one or a combination of the following systems: windshield wipers, chemical rain repellent, pneumatic rain removal (jet blast), or windshields treated with a hydrophobic surface seal coating. 1.7.1 Windshield Wiper Systems In an electrical windshield wiper system, the wiper blades are driven by an electric motor(s) that receive (s) power from the aircraft’s electrical system. On some aircraft, the pilot’s and copilot’s windshield wipers are operated by separate systems to ensure that clear vision is maintained through one of the windows should one system fail. Each windshield wiper assembly consists of a wiper, wiper arm, and a wiper motor/converter. Almost all windshield wiper systems use electrical motors. Some older aircraft might be equipped with hydraulic wiper motors. Maintenance performed on windshield wiper systems consists of operational checks, adjustments, and troubleshooting. An operational check should be performed whenever a system component is replaced or whenever the system is suspected of not working properly. During the check, make sure that the windshield area covered by the wipers is free of foreign matter and is kept wet with water. Adjustment of a windshield wiper system consists of adjusting the wiper blade tension, the angle at which the blade sweeps across the windshield, and proper parking of the wiper blades. Issue No. 0 ET-AF07.1 Page 39 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Figure 1.34 Electric Windshield Wiper System Figure 1.35 Hydraulic wiper system 1.7.2 Chemical Rain Repellant Water poured onto clean glass spreads out evenly. Even when the glass is held at a steep angle or subjected to air velocity, the glass remains wetted by a thin film of water. However, when glass is treated with certain chemicals, a transparent film is formed that causes the water to Issue No. 0 ET-AF07.1 Page 40 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems behave very much like mercury on glass. The water draws up into beads that cover only a portion of the glass and the area between beads is dry. The water is readily removed from the glass. This principle lends itself quite naturally to removing rain from aircraft windshields. The high-velocity slipstream continually removes the water beads, leaving a large part of the window dry. A rain repellant system permits application of the chemical repellant by a switch or push button in the cockpit. The proper amount of repellant is applied regardless of how long the switch is held. On some systems, a solenoid valve controlled by a time delay module meters the repellent to a nozzle which sprays it on the outside of the windshield. Two such units exist — one each for the forward glass of the pilot and copilot. Figure 1.36 Cockpit rain repellant systems This system should only be used in very wet conditions. The rain repellant system should not be operated on dry windows because heavy undiluted repellant restricts window visibility. Should the system be operated inadvertently, do not operate the windshield wipers or rain clearing system as this tends to increase smearing. Also, the rain repellant residues caused by application in dry weather or very light rain can cause staining or minor corrosion of the aircraft skin. To prevent this, any concentrated repellant or residue should be removed by a thorough fresh water rinse at the earliest opportunity. After application, the repellant film slowly Issue No. 0 ET-AF07.1 Page 41 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems deteriorates with continuing rain impingement. This makes periodic reapplication necessary. The length of time between applications depends upon rain intensity, the type of repellant used, and whether windshield wipers are used. 1.7.3 Pneumatic Rain Removal Systems Windshield wipers characteristically have two basic problem areas. One is the tendency of the slipstream aerodynamic forces to reduce the wiper blade loading pressure on the window, causing ineffective wiping or streaking. The other is in achieving fast enough wiper oscillation to keep up with high rain impingement rates during heavy rain falls. As a result, most aircraft wiper systems fail to provide satisfactory vision in heavy rain. The rain removal system shown in Figure 1.37 controls windshield icing and removes rain by directing a flow of heated air over the windshield. This heated air serves two purposes. First, the air breaks the rain drops into small particles that are then blown away. Secondly, the air heats the windshield to prevent the moisture from freezing. The air can be supplied by an electric blower or by bleed air. Figure 1.37 Pneumatic Rain Removal Systems Issue No. 0 ET-AF07.1 Page 42 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.8 Windshield Frost, Fog, and Ice Control Systems In order to keep windshield areas free of ice, frost, and fog, window anti-icing, deicing, and defogging systems are used. These can be electric, pneumatic, or chemical depending on the type and complexity of the aircraft. A few of these systems are discussed in this section. 1.8.1 Electric High performance and transport category aircraft windshields are typically made of laminated glass, polycarbonate, or similar ply material. Typically clear vinyl plies are also included to improve performance characteristics. The laminations create the strength and impact resistance of the wind-shield assembly. These are critical feature for windshields as they are subject to a wide range of temperatures and pressures. They must also withstand the force of a 4 pound bird strike at cruising speed to be certified. The laminated construction facilitates the inclusion of electric heating elements into the glass layers, which are used to keep the windshield clear of ice, frost, and fog. The elements can be in the form of resistance wires or a transparent conductive material may be used as one of the window plies. To ensure enough heating is applied to the outside of the windshield, heating elements are placed on the inside of the outer glass ply. Windshields are typically bonded together by the application of pressure and heat without the use of cement. Figure 1.38 illustrates the plies in one transport category aircraft windshield. Figure 1.38 Cross-section of a transport category windshield. Whether resistance wires or a laminated conductive film is used, aircraft window heat systems have transformers to supply power and feedback mechanisms, such as thermistors, to provide a window heat control unit with information used to keep operating temperature within acceptable limits. Some systems are automatic while others are controlled by cockpit switches. Separate circuits for pilot and co-pilot are common to ensure visibility in case of a malfunction. Consult the manufacturer’s maintenance information for details on the particular window heat system in question. Some windshield heating systems can be operated at two heat levels. On these aircraft, NORMAL heating supplied heat to the broadest area of windshield. HIGH heating supplies a Issue No. 0 ET-AF07.1 Page 43 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems higher intensity of heat to a smaller but more essential viewing area. Typically, this window heating system is always on and set in the NORMAL position. Figure 1.39 illustrates a simplified windshield heat system of this type. Figure 1.39 Electric windshield heat schematic. 1.8.2 Pneumatic Some laminated windshields on older aircraft have a space between the plies that allows the flow of hot air to be directed between the glass to keep it warm and fog free. The source of air is bleed air or conditioned air from the environmental control system. Small aircraft may utilize ducted warm air, which is release to flow over the windshield inner surface to defrost and defog. These systems are similar to those used in automobiles. The source of air could be ambient (defog only), the aircraft’s heating system, or a combustion heater. While these pneumatic windshield heat systems are effective for the aircraft on which they are installed, they are not approved for flying into known icing conditions and, as such, are not effective for anti-ice. Large aircraft equipped with pneumatic jet blast rain repellant systems achieve some anti-icing effects from operating this system although electric windshield heat is usually used. Issue No. 0 ET-AF07.1 Page 44 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.8.3 Chemical As previously mentioned in this chapter, chemical anti-ice systems exist generally for small aircraft. This type of anti-ice is also used on windshields. Whether alone or part of a TKSTM system or similar, the liquid chemical is sprayed through a nozzle onto the outside of the windshield which prevents ice from forming. The chemical can also deice the windshield of ice that may have already formed. Systems such as these have a fluid reservoir, pump, control valve, filter, and relief valve. Other components may exist. Figure 1.40 shows a set of spray tubes for application of chemical anti-ice on an aircraft windshield. Figure 1.40 Chemical deicing spray tubes. 1.9 Maintenance & Troubleshooting Maintenance and Troubleshooting may be carried out using tasks, subtasks and charts in the aircraft specific Maintenance Manual (Chapter 30 in the ATA100 Scheme). The following is a sample maintenance activity taken from a light aircraft maintenance manual. 1.9.1 Inspection and Testing Windscreen Wiper Issue No. 0 ET-AF07.1 Page 45 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Inspection a. Examine the system for cleanliness, security, damage, connections and locking b. Examine blades for security, damage and contamination. Blades should be replaced at regular intervals. c. Check level of fluid in pump reservoir (electro-pneumatic system) d. Examine hydraulic pipes for leakage and electrical cables for deterioration and chafing Operational Check Before carrying out an operational check, the following precautions must be taken: a. Ensure that the windscreen is free of foreign matter b. Ensure that the blade is secure and undamaged During the check ensure that the windscreen is kept wet with water. NEVER operate the windscreen wipers on a dry screen. It may cause scratches. 1.9.2 Troubleshooting Deice Boot Issue No. 0 ET-AF07.1 Page 46 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Table 1.1 1.9.3 Removal and Installation Removal and installation procedures are given in component maintenance manual (sample pages) Issue No. 0 ET-AF07.1 Page 47 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Issue No. 0 ET-AF07.1 Page 48 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems Condition Replacement Criteria Recommended Action Issue No. 0 ET-AF07.1 Page 49 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1. Foreign Object Any damage beyond allowable Replace Deicer Damage (FOD) repair limits per manual 2. Surface Exposed stitch line threads or Replace Deicer Erosion excessive leakage 3. Cut, tear or Cut, tear or rupture exceeding Temporary rupture the limit Repair or Replace Deicer 4. De-bonding/ Area De-bonded or the surface Replace Deicer swelling due to swollen tubes unable to pull leaky integral vacuum to flat condition fuel tank (Wet Wing) 5. Excessive Repairs exceeding repair limits Replace Deicer Repairs as prescribed per maintenance manual 6. Pinholes in Multiple pinholes on leading Replace Deicer — boot at leading edge surface Ensure edge replacement deicer has an electrical path from conductive surface of the deicer to the aircraft wing 7. Bulge or stitch Any Bulge located in inflatable Replace Deicer line failure area of deicer 8. Improper Multiple surface cracks/splits Replace Deicer — Maintenance Perform proper (Use of maintenance per unauthorized manual additives, adhesives, waxes or polishes) Table 1.2 Issue No. 0 ET-AF07.1 Page 50 of 51  Ethiopian Aviation Academy Revision No. 0 Aviation Maintenance Training September 2017 ET-AF07 : Aircraft Auxiliary Systems 1.9.4 Deice Boot Maintenance TO BE FILLED Issue No. 0 ET-AF07.1 Page 51 of 51