C. These two switches in the antiskid system are operated when the landing gear lever is placed in the UP position. One switch interrupts power to the antiskid module. The other switch opens the circuit to the antiskid inoperative lights. The light circuit is opened to prevent a false antiskid inoperative condition to register when the antiskid power is cut off during the landing gear retraction cycle.
6. Antiskid Test Circuit
A. The antiskid test circuit is a continuous function during operation of the antiskid system. An inoperative light (inboard or outboard) will illuminate with any power loss to the system (e.g. an open valve or a faulty transducer circuit). If an inoperative light comes on, that particular channel can be switched off and the inoperative light will remain on. This is a constant reminder that antiskid protection is off and that manual braking techniques should be used.
Transducer 543
32-42-0Page 6 Figure 2 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Oct 20/83
531 Antiskid Control Valve Schematic
Feb 15/71 Figure 3 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 32-42-0 Page 7
Antiskid System Block Diagram 591
32-42-0 Figure 4 Jun 20/85
Page 8
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
B. Ground test features are built into the antiskid control shield. Two test switches and four indicator lights are located on the front of the antiskid control shield. Thje antiskid control shield is located in the equipment compartment and is accessible to the ground crew for trouble shooting. The two test switches are marked SYSTEMS TEST and COMPONENT TEST. During a systems test, the SYSTEMS TEST switch is held in either the momentary left or right position and a simulated wheel speed signal of 400 CPS is injected in either the left or right gear control circuit. If the switch is held in the left position and the system operates properly, the right indicator lights will come in indicating that more than 75% of full brake release voltage has been sent to the right valves. If the switch is held in the right position, the left indicator lights should come on. If during the systems test one light or a pair of lights fail to show, the component switch is used to localize trouble in either the antiskid control valve, transducer or antiskid control shield.
C. The COMPONENT TEST switch is a 4-position (XDCR, OFF, VALVE, AUTOBRAKE) switch which is spring-loaded to the center (off) position. This switch is used to isolate failures indicated by the antiskid inoperative lights on the center panel in the control cabin. If an inoperative light on the center instrument panel is on, the lights on the face of the antiskid control shield are checked. Any light that is illuminated on the control shield (LO, RO, LI or RI) indicates a fault in that channel. If the component test switch is positioned to VALVE and the fault light goes out, it is an indication of an open valve circuit. If the switch is positioned to XDCR and the light goes out, the associated transducer circuit is either shorted or open. If the fault light remains on with the switch in both the XDCR and VALVE positions, then the fault is located in the control shield. The illumination of two inoperative lights on the center instrument panel accompanied by all four fault lights on the front of the antiskid control shield is an indication of a problem in the parking brake valve or switching circuit, or a loss of primary power to both outboard and inboard antiskid channels. The AUTOBRAKE position of the TEST switch provides functional check of the automatic braking system (Ref 32-43-0).
7. Operation
A. Normal Antiskid Mode
(1)
Wheel speed transducers, one driven by each wheel, produce electrical frequency outputs which are proportional to wheel speed. The signals are processed by individual wheel circuit cards in the antiskid control shield to control brake pressure to the applicable wheel. The transducer frequency output signal is accepted by a converter circuit on the wheel circuit card where it is converted to a dc voltage which is proportional to wheel speed (Fig. 4).
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