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b) Yaw damper command coincidence c) Activity monitor d) Transient watchdog faults
2) The YDM fault latch resets if all YDM monitors exhibit no failures for 10 seconds continuously and within 15 seconds of detecting a YDM fault. Autoreset is limited to a maximum of four resets per flight. There is no limit on autoreset when the airplane is on ground.
3) The following faults are incapable of automatic recovery: a) Power-up reset YDM fault b) Ground test YDM fault c) Background Read Only Memory (ROM) fault d) Watchdog faults caused by total loss of CPU or
erroneous sum check values.
(4) Yaw Damper Control Law Schematic (Fig. 9)
(a)
Yaw Damping Command
1) Yaw damping is provided by a combination of yaw rate, roll rate, roll attitude, lateral acceleration, angle of attack, impact pressure, and true airspeed. Feedback gain is scheduled as a function of impact pressure.
(b)
Modal Accelerometer Command
1) The modal accelerometer command is provided by forward and aft accelerometers which sense body lateral acceleration. Fore body and aft body gain is scheduled as a function of impact pressure.
(c)
Turn Coordination Command
1) The turn coordination gain is scheduled as a function of impact pressure. Turn coordination signal is scheduled as a function of roll attitude and true airspeed.
(d)
Control Law Command
1) The control law 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 impact pressure. True airspeed is used when both ADCs are valid and at least one IRU is valid or when one ADC and one IRU is valid. For other combinations, ground speed is substituted for true airpseed. The authority is either variable, | 4.0 degrees, or | 1.0 degree 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.
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2) Default values for indicated angle of attack (AOA), impact pressure, and true airspeed are used depending upon ADC and IRU availability. With one or zero ADCs and two or three IRUs available, indicated AOA becomes a constant -8.1 degrees, impact pressure becomes a constant 167.5 millibars, and ground speed (constant 423.3 KTS) is substituted for true airspeed.
(5) ADC Input Signal Processing (Fig. 10)
(a) Input Monitor
1) The ADC input monitor consists of a watchdog monitor, parity monitor, Sign Status Matrix (SSM) monitor, comparison monitor, and input data fault logic. The watchdog monitor transmits an input fault signal if no ADC data is received for 400 msec when required by the YDM. The parity monitor transmits a fault signal if a parity error is detected in four out of nine 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, No Computed Data (NCD), or TEST in four out of nine successive samples. For all samples indicating FAILED, NCD, and TEST, the incoming values are discarded and the last previous valid value is used. If the angle of attack or impact pressure sample is indicated as NCD, that data will be accepted as valid data. If a true airspeed sample is indicated as NCD, 100 knots is substituted for the sample value. If the overspeed sample is indicated as NCD, the incoming value is discarded and the previous valid value is used.
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