CAUTION: RELEASE TEST SWITCH AS SOON AS THE OVERHEAT LIGHT ILLUMINATES AS WINDOW MAY BE DAMAGED.
(7)
Position test switch to OVHT. Check that all OVERHEAT indicator lights illuminate and that master caution and warning ANTI-ICE indicator light illuminates.
(8)
Return all window heat control switches to OFF. The amber OFF LIGHT for the applicable window will illuminate.
(9)
Remove electrical power if it is no longer required.
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30-09-111 Page 402 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/98
WING THERMAL ANTI-ICING SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY
AIRPLANES WITHOUT WING TAI SYSTEM GROUND OPERATION CAPABILITY
1. General
A. The wing thermal anti-icing (TAI) system prevents the formation of ice on the wing leading edge slats. The system receives regulated hot air (pneumatic air) from the engine bleed air distribution system and is operable only when air is available from that system (Ref Chapter 36, Engine Bleed Air Distribution System). The flow of pneumatic air is controlled by a shutoff valve for each wing. Both valves are operated by a single control switch on the pilot's overhead panel. When the system is in operation, the valves direct the hot pneumatic air through a distribution system to the wing leading edge slats. The system consists of supply and distribution ducting, two control valves, electrical control components, and indicating components (Fig. 1 and 2).
2. Wing Anti-Ice Ducting
A. The pneumatic air duct is connected to each of the wing leading edge supply ducts through a control valve located in the wing leading edge just outboard of the engine strut on each side of the airplane (Fig. 1). The wing supply ducts are connected to each of the wing leading edge slats by telescoping ducts. The telescoping ducts consist of two tubes, one of which slides within the other as the slats are extended or retracted, and are sealed by an O-ring between them. The inner telescoping duct is connected to the wing TAI supply manifold ducts by a swivel T-connection to allow rotational movement of the telescoping duct around the wing supply duct. The T-connection is sealed by an O-ring between each end of the T and the supply duct. The outer telescoping duct is connected to a slat anti-icing spray duct by a swivel T-connection to allow rotational movement of the telescoping duct about the slat anti-icing spray duct. A support bracket in the slat leading edge supports the ends of the slat spray ducts and the telescoping duct and prevents the TAI air from flowing back through the telescoping duct cutout in the slat beam. The slat anti-icing spray duct runs the full length of the slat and has perforations to direct the air towards the slat leading edge. The air then flows between the slat upper skin and the slat beam where it is exhausted overboard through openings in the slat inner skin.
Jan 20/83 30-11-0 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
B. To compensate for wing flexing, duct misalignment, and thermal expansion the ducts inboard of approximate wing station 159 are rigidly held and pre-stressed on installation by the use of threaded couplings to stretch the ducting. The ducts outboard of wing station 159 use slip type expansion joints. Duct movement is also absorbed by the swivel joints at each telescoping duct connection and by expansion bends in the duct routing.
3. Wing Anti-Ice Control Valves
A. The flow of air into the wing TAI system is controlled by a wing TAI shutoff valve for each wing supply duct. The valves are located in the wing leading edge just outboard of each engine strut, (Fig. 1) and are 2-1/2-inch diameter electric motor-driven butterfly valves, which operate on 115-volt ac power. The valves are equipped with limit switches to prevent overrunning of the motor, and valve position indicator switches, which are used in the valve position indicator circuits. Each valve is also equipped with an external valve position indicator to verify valve position. The valves are controlled by the valve control relay.
4. Wing Anti-Ice Control Components
A. The operation of the wing anti-ice control valves are governed by the following electrical control components; a pair of contacts on the landing gear safety relay, a wing TAI control switch, a valve control relay, two ground overheat thermal switches, and two transistorized circuit cards (Fig. 2).
B. The safety relay is energized by the main gear safety sensor when the airplane is on the ground. Refer to Chapter 32, Landing Gear Miscellaneous Electrical Components. The relay is used to direct power to the appropriate side of the control switch for operation of the system during testing.
C. The wing TAI control switch is located on the P5 overhead panel. The switch is a three position six pole toggle switch; two poles are used in the valve control circuit and the other four poles are used in the valve position indicating circuits. It has an ON position, an OFF position and a momentary TEST position. The control switch is used to control the operation of the wing anti-ice system.
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