a) All pitot-static probe heaters remain off and indicator lights remain illuminated.
(b)
Position PITOT-STATIC A to OFF.
(c)
Position PITOT-STATIC B to ON. 1) Check for following results: a) F/O P/S 2 AUX STATIC indicator light goes out; all other indicator lights
remain on. b) Upper right pitot-static probe radiates heat; all other heaters remain off.
(d)
Open F/O - UPPER R circuit breaker and check F/O P/S 2 AUX STATIC indicator light illuminate.
(e)
Position PITOT-STATIC B switch to OFF.
(4)
Repeat step (3) for lower right pitot-static, right elevator pitot; right temperature probe heater, using F/O's LWR R and UPPER R circuit breakers and indicator light and PITOT-STATIC B switch.
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D. Restore Airplane to Normal.
(1)
Close applicable circuit breakers.
(2)
Remove electrical power if no longer required.
(3)
Install protective caps or covers as required.
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CONTROL CABIN WINDOW ANTI-ICING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. Windows No. 1, 2, 4 and 5 on each side of the control cabin are provided with electrical heating for window anti-icing and defogging (Fig. 1). Heating of the control cabin windows also improves the impact strength of the windows and is used for birdproofing the windows when flying at altitudes where bird strikes are possible. Power to the left No. 1, 4 and 5 windows and the right No. 2 window is supplied from the left generator and the right No. 1, 4 and 5 and left No. 2 window is supplied from the right generator. In the event of a power failure from one generator, the No. 2 window on that side and the No. 1, 4, and 5 windows on the other side will still be supplied power from the other generator, thus ensuring that reasonable forward vision from each side will be maintained.
B. The forward No. 1 windshield and the No. 2 sliding window on each side of the cabin have a separate control system for each window (Fig. 2). The control system maintains its respective window at the required temperature by the use of automatic controls. Each system consists of the heated window, a window heat sensor, a control switch, a heat control unit, a power indicating light, and an overheat indicating light. A power and overheat test switch is used in common with all four systems. The No. 4 and 5 windows receive power through the side window heat switch. Power to windows No. 4 and 5 is regulated by a thermal switch located in the circuit between the two windows. While the system is in operation, the temperature of the windows is regulated at 107 + 7/-7°F for the No. 1 and 2 windows and from 80-120°F for the No. 4 and 5 windows. The control system turns off the power to the No. 1 and 2 windows when an overheat condition of approximately 145°F is detected.
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C. When the system is first energized, a ramp function in the heat control unit causes the power delivered to the No. 1 and No. 2 windows to increase gradually from zero to full power in approximately 3 minutes, unless it is controlled at a lesser level by the window reaching control temperature before the ramp time runs out. This reduces the thermal shock to the pane when the power is applied to a cold window. A power interruption of 5 seconds or more will cause the ramp function to start over from zero, while for lesser interruptions, the ramp will start over at a fraction that is proportional to the time off. The window heat sensor provides a temperature control signal to the heat control unit, which in turn modulates the amount of power to the window to maintain the window at the required operating temperature. The power indicating light will be illuminated when power is being supplied to the window. If an overheat condition is detected, the heat control unit will cutoff power to the windows, turn off the power indicating light, illuminate the overheat indicating light and the master caution and anti-ice lights of the master caution system (Refer to Chapter 33, Master Warning and Caution Lights). While the system is in operation, the heat control unit may be functionally tested by the use of the system test switch. Holding the test switch in the POWER position will force the control unit to supply power to the window and illuminate the power indicating light. If the operational confidence check is performed under conditions where the window temperature is within the overheat cutoff range, whether by outside environment or by excessively long testing, an overheat cutoff will occur. An overheat condition can be simulated by holding the test switch in the OVERHEAT position. The system is returned to normal by momentarily placing the control switch in the OFF position. The temperature of the No. 4 and 5 windows is controlled by the thermal switch on the No. 5 window.
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