(c)
SSFD faults are inhibited on the ground and cannot be duplicated during ground test.
(d)
SSFD faults can be generated for the following conditions. 1) ILS data fail during ILS capture; diagnostic codes 218,
219. 2) Localizer or glideslope deviation disagrees with data receiver on cross channel; diagnostic codes 236, 237.
3) IRU data faulty or missing; diagnostic codes 114 thru 118, 122 thru 125, 132, 215, 216, 230, 231, 238, 240, 241, and
249. 4) LRRA data faulty; diagnostic codes 176, 221. 5) Elevator surface position data fault; diagnostic codes 142,
143. 6) Aileron surface position data fault; diagnostic codes 211,
214. 7) Rudder surface position data fault; diagnostic codes 212,
217. 8) Feel computer data fault; diagnostic codes 222, 223. 9) Stabilizer position data error; diagnostic codes 213, 229. 10) Flap position data error; diagnostic codes 210, 224.
D. Yaw Damper Module BITE
(1)
The yaw damper module BITE consists of a number of monitors that check critical data, and of test routines designed into the module.
(a)
Power-up testing occurs when power is applied to the module. Testing consists of fault disengage, servo loop monitor, command coincidence monitor, and memory read/write tests.
(b)
Preflight testing occurs when the YDM test switch on the P61 panel is set to L or R. Testing causes the inertial reference system to self test, moves the rudder and checks rudder position, and check IRU inputs.
(c)
Continuous inflight testing of data inputs and internal operation is performed by monitor circuits.
(2)
AIRPLANES WITHOUT YDM -122 AND SUBSEQUENT YDM DASH NUMBERS; faults detected by yaw damper monitor circuits results in setting faultballs on the face of the module.
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(3)
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757 MAINTENANCE MANUAL
(a)
The ADC input monitor checks ADC output bus 1 data for activity, parity, SSM, and data reasonableness. The monitor output sets the ADC fault ball.
(b)
The IRU input monitor checks IRU data bus 3 data for activity, parity, SSM, and SSFD. The monitor output sets the IRU fault ball.
(c)
The air ground input monitor compares data from three air ground relays. If any one input disagrees with the other two a fault is declared. The monitor output sets the AIR/GRD fault ball.
(d)
The hydraulic pressure monitor checks hydraulic pressure switch high pressure and low pressure inputs. Monitor output sets the HYD PRESS fault ball.
(e)
A common mode monitor checks LVDT voltage. Low voltage is declared a fault. Monitor output sets the LVDT fault ball.
(f)
A command/response monitor compares yaw damper servo position to commanded position. A fault is declared if a disagree is detected. Monitor output sets the YD ACT fault ball.
(g)
Monitor microprocessor output is compared to control
microprocessor output. A disagree sets the YDM fault ball.AIRPLANES WITH YDM -122 AND SUBSEQUENT YDM DASH NUMBERS; faults detected by the yaw damper monitor circuits are shown on the yaw damper display. The faults are divided into FAULTS NOW and LAST LEG FAULTS. FAULTS NOW are faults that occurred during the last air/ground transition. LAST LEG FAULTS are faults that occurred before the last air/ground transition. The messages that follow can be shown by the yaw damper module.
(a)
NO FAULTS - There are no FAULTS NOW and no LAST LEG FAULTS.
(b)
NO FAULT NOW - There are no FAULTS NOW but there are LAST LEG FAULTS.
(c)
NO LEG FAULT - There are FAULTS NOW but there are no LAST LEG FAULTS.
(d)
FAULTS NOW - There are one or more FAULTS NOW faults, and they are displayed by pressing the DISPLAY button on the faceplate of the yaw damper module.
(e)
LAST LEG - There are one or more LAST LEG FAULTS, and they are the DISPLAY button on the faceplate of the yaw damper module.
(f)
TEST RUNNING - Power Up Test (PUT) or Pre-Flight Test (PFT) is running on the yaw damper module.
(g)
ACCEL - The yaw damper module has determined that there is a fault with the modal suppression accelerometer.
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