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IRU
IRU
IRU
ADC
IRU
ADC
IRU
ADC

A/GRELAY
HARDWARE YAW DAMPER MODULE

SERVOCMD
SERVOFEEDBACK
DEFAULT VALUES & AUTHORITY LIMITING

Yaw Damper Control Law Schematic
Figure 9 (Sheet 1)

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 (c) Output Command Processing
 1)  The output command is authority limited to fixed or variable amounts, depending on the availability of ADC and IRU inputs. Authority is in accordance with the table shown. The variable authority is programmed as a function of true airspeed. True airspeed is used when both ADCs are valid and at least one IRU is valid. For other combinations, ground speed is substituted for true airspeed. The authority is either variable, |3.0 degrees, or |0.3 degrees rudder as shown in the table. Commands are applied through an easy-on/easy-off gain schedule (5 second, ramp) when the air/ground discrete indicates in-air (takeoff), or on-ground (landing), respectively.
 2)  Default values for indicated angle of attack (AOA), impact pressure, and true airspeed are used depending upon ADC and IRU availability. As an example, with one ADC and two IRUs available, indicated AOA becomes a constant 7.88 degrees, impact pressure becomes a constant 270 millibars, and ground speed is substituted for true airspeed.
 (5) ADC Input Signal Monitoring (Fig. 10)
 (a) Input Monitor
 1)  The ADC input monitor consists of a watchdog monitor, parity monitor, and Sign Status Matrix (SSM) monitor. The watchdog monitor transmits an input fault signal if no air data information is received for 400 msec when required by the YDM. The parity monitor transmits a fault signal if a parity error is detected in 4 out of any 8 successive samples. For all samples with parity error, the incoming values are discarded and the last previous valid values are used.
 2)  The SSM monitor provides an input fault signal if incoming data is indicated as FAILED for 4 out of 8 successive samples. For all samples indicating FAILED, the incoming values are discarded and the last previous valid value is used. A fault signal is also provided if impact pressure is indicated as No Computed Data (NCD) for 4 out of 8 successive samples. For all samples indicating NCD, the incoming value is discarded and the last previous valid value is used. If any indicated angle of attack sample is indicated as NCD, 0.0 degrees is substituted for the sample value. If a true airspeed sample is indicated as NCD, 100 knots is substituted for the sample value. If incoming data is indicated as TEST for 4 out of 8 successive samples, a fault signal is transmitted. For all samples indicating TEST, the incoming values are discarded and the last previous valid value is used.
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