Text-only reference. Published from the recorded official FAA Airframe Chapter 15 PDF. Diagrams, photographs, and figure artwork are not reproduced here; use the official FAA PDF for those materials.
Pressurized can Clamp release Nozzle Solenoid valve Time delay module Bracket Can connection Shutoff valve Visual reservoir Shroud FWD Can replacement level Hydrophobic coating Glass window layer Plastic window layer The rain removal system shown in Figure 15-43 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.
Windshield Frost, Fog, & 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. 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 windshield assembly. These are critical features 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 15-28 LH windshield blower actuator cable MADC (air data computer) T-duct assembly Drain line Bell mouth duct assembly Windshield blower RH windshield blower actuator cable LH nozzle assembly RH nozzle assembly Windshield blower actuator FWD ply. Windshields are typically bonded together by the application of pressure and heat without the use of cement.
aircraft 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 flight deck switches. Separate circuits for pilot and co-pilot are common to ensure visibility in case of a malfunction. Consult Inner glass ply Center glass ply Outer glass ply Vinyl plies Conductive coating on the inner face of the outer glass ply 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 15-29 levels. On these aircraft, NORMAL heating supplied heat to the broadest area of windshield. HIGH heating supplies a 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 15-45 illustrates a simplified windshield heat system of this type. 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 released 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 repellent systems achieve some anti-icing effects from operating this system although electric windshield heat is usually used. 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 15-46 shows a set of spray tubes for application of chemical anti-ice on an aircraft windshield.
Water & Waste Tank Ice Prevention Transport type aircraft have water and waste systems on board, and electrical heaters are often used to prevent the formation of ice in the water lines of these systems. Water Temperature controller 5A 50A Normal High heat relay Windshield Low heat relay High 15-30 Waste tank drain line (3) heater blanket Waste tank drain valve (3) heater blanket AFT wall of compartment Waste tank FWD lines carry water from the potable tanks to the lavatories and galleys. The waste water tanks collect the gray water from the galleys and lavatories. Heater blankets, inline heaters, or heater boots are often used to heat the water supply lines, water tank drain hoses, waste drain lines, waste tank rinse fittings, and drain masts. Thermostats in the water lines supply temperature data to the control unit that turns the electrical heaters on and off. When the temperature falls below freezing, the electrical heaters turn on and stay on until the temperature reaches a safe temperature. Figure 15-47 is a schematic of a water supply line heater system, and and heater blankets. Figure 15-48. Waste water tanks and heater blankets.
Controller Water supply in-line heater (SAT 2129, WL 189, LBL 8) Remote temp sensor (SAT 2171, WL 200, LBL 52) Controller Water supply in-line heater (SAT 2133, WL 189, LBL 8) Remote temp sensor (SAT 2171, WL 200, LBL 52) Controller Water supply in-line heater (SAT 2079, WL 155, RBL 49) Water tank drain heater Controller Water supply in-line heater (SAT 2127, WL 189, LBL 3) Remote temp sensor (SAT 2144, WL 203, LBL 80) P320 ground service/handling power panel Note: Heater off when temperature is > 60 °F (15 °C) Heater on when temperature is < 45 °F (7 °C) 115V AC ground service bus Water supply Line heaters 15-31