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(b) Signal Selector 1) A median value of parameters from both ADCs is selected for use in the control law computations. Incoming parameter values are compared to the respective signal selector output. If the difference is greater than the specified values shown below for one second, the compare fault is set. (Airplane must be 200 milliseconds after the ground to air transition, A/G discrete valid, and neither ADC invalid.) Following a ADC fault, data from the remaining valid ADC may be used.
2) The maximum deviation allowed between the ADC input values and the median ADC value follows: a) True airspeed - 60 knots b) Angle of attack - 5 degrees c) Impact pressure - 27 millibars
(c) Fault Annunciation 1) AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; Any ADC input or comparison fault sets the DADC faultball indicator and software monitors. 2) AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS; Any ADC input or comparison fault causes an ADC fault message to be recorded. 3) If the airplane is in the air and the air/ground (A/G) discrete is valid, input faults are latched. The latch is reset by the power-up reset, maintenance reset, or ADC automatic reset. 4) AIRPLANES WITH YDM DASH NUMBERS -101 THRU -121; The faultball is not reset by the power-up reset.
5) The ADC auto-reset is generated with the airplane in air and the yaw damper not in an INOP status. If sensor data within monitor threshold is detected for 10 seconds, the ADC fault latch is reset, provided there have been no more than four resets since the airplane was last on ground. Maintenance reset is generated by pressing the RESET switch on the yaw damper module.
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(6) IRU Input Signal Processing (Fig. 11)
(a) Input Monitor
1) The IRU input monitor consists of a watchdog monitor, parity monitor, preflight test monitor, and Sign Status Matrix (SSM) monitor. The watchdog monitor input fault is set when no IRU information is received for 300 msec when required by the YDM. The parity monitor input fault is set if a parity error is detected in four out of any 8 successive samples. For all samples with a parity error, the incoming values are discarded and the last previous valid values are used.
2) The SSM monitor input fault is set when incoming data is indicated as FAILED, TEST or NCD for 4 out of 8 successive samples. For all samples indicating FAILED, TEST or NCD, the incoming values are discarded and the last previous valid values are used. The preflight test inputs monitor fault is set if the test values from the IRUs are incorrect. The monitor is active only during the airplane preflight test.
(b) Signal Selector
1) A median value of parameters from all three IRUs is selected for use in control law computations. If one IRU fails, that input is not used. The two remaining IRU inputs and the last valid median value are used for median selection. With only one IRU remaining valid, median selection is avoided and that single input is used. Each parameter input value is compared to the selected median value. Differences exceeding specified amounts for more than one second result in a comparison fault latch and the affected IRU being declared failed. (The airplane must be 200 milliseconds after the ground to air transition, no input fault for that IRU and A/G discrete valid).
2) The maximum deviation allowed between IRU input values and the median IRU value follows: a) Roll attitude - 5 degrees b) Body axis roll rate - 2.5 deg/sec c) Body axis yaw rate - 2.5 deg/sec d) Body axis lateral acceleration - 0.1 g e) Ground speed - 60 knots
(c) Fault Annunciation
1) AIRPLANES WITH YDM NUMBERS -101 THRU -121; If any IRU input, comparison, or preflight test monitor fault is detected, the IRU fault ball is set.
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