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MAINTENANCE MANUAL
b) Successful fault recovery and subsequent re-engagement c) Sensor loss recovery to at least one IRU d) Upon landing
2) During this mode, the yaw damper control law computes commands. However, the airplane on ground status causes the control law output to convert commands to zero. Even though no output commands are possible, the INOP lamps do not illuminate during the ground operational mode. The sensor cross-comparison monitors are also disabled during this mode. The ground operational mode is exited when the airplane becomes airborne, all IRUs are lost, or when the preflight test is initiated.
(e) Preflight Test 1) The preflight test is entered when the ground operational mode is valid and the YAW DMPR test switch on P61 is activated. The INOP indicator is illuminated throughout the test. The preflight test also initiates the IRS self-test. During the IRS self-test, the four annunciator lights for each IRS channel illuminate. The preflight test has the following automatic test sequence: a) Moves the rudder to 3 degrees each direction and returns to center. b) The rudder holds in each of the three positions for one second and a position test is performed. The position test determines the difference between the commanded position and the feedback position. The position test fails if the difference exceeds 0.5 degree. c) AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; After 10 seconds, the test verifies proper IRU input to the system. If any IRU input is not within limits, the IRU faultball is set d) AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS; After 10 seconds, the test verifies proper IRU input to the system. If any IRU input is not within limits, the corresponding IRU fault message is recorded
2) If all the position tests and any one IRU data are satisfactory, the INOP indication is cancelled and the system returns to the ground operation mode. If any position test or all three IRU data tests fail, the INOP indication persists and the auto-disengage relay is actuated. If any IRU channel self-test fails, the FAULT annunciator light for that channel remains illuminated.
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(f) Fade-In
1) The fade-in mode is entered from the power-up mode or ground operational mode. The mode is entered if the airplane is airborne when power is first applied or after the airplane becomes airborne. The mode prevents a sudden rudder transient response. The easy-on control law provides a linear rise in gain from zero to one in 5 seconds. When a gain of one is reached, the full flight mode is engaged.
(g) Flight Mode 1) The full flight mode is entered when the airplane is airborne and the fade-in function is completed. The flight mode performs turn coordination and yaw damping. Yaw correction and turn coordination are computed from yaw rate, lateral acceleration, indicated angle of attack, roll angle, roll rate, and true airspeed (or ground speed when true airspeed is not available). The flight mode also provides fault monitoring, self checks, command limiting, degraded operation as required, auto-disengage, and fault indications.
2) When no IRU data is available or a servo loop fault is detected, a YDS fault is latched and the associated channel automatically disengages. Each channel may also be engaged and disengaged by the YDS manual controls. The flight mode automatically exits to the ground operational mode upon landing via the fade-out function.
(h)
Fade-Out
1) The fade-out mode is entered directly upon airplane landing. The mode prevents a sudden stop of rudder control. The easy-off control law provides a linear decrease in gain from one to zero in a 5-second time period. The transition begins as soon as a ground state is established.
(i)
Fault
