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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) The input data fault logic is a continuous input monitoring system. The input data is determined invalid if an ADC watchdog, parity or SSM bus fault is set. When an ADC input or comparison fault is detected, a corresponding fault message is sent to the CMC. Fault latching is inhibited on ground or if the air/ground discrete is invalid. The latch can be reset by the power-up reset, maintenance reset, or ADC automatic reset.
2) The ADC autoreset is generated with the airplane in air. If sensor data within monitor threshold is detected for 10 seconds continuously, the ADC fault latch is reset, provided there have been no more than 4 resets since the airplane was last on ground.
(6) IRU Input Signal Processing (Fig. 11)
(a) Input Monitor
1) The IRU input monitor consists of a watchdog monitor, parity monitor, and Sign Status Matrix (SSM) monitor, comparison monitor, and input data fault logic. The watchdog monitor input fault is set when no IRU information is received for 300 msec. The parity monitor input fault is set if a parity error is detected in ten out of twenty 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 in ten out of twenty successive samples. For all samples indicating FAILED, TEST, or NCD, the incoming values are discarded and the last previous valid values are used. If a ground speed sample is indicated as FAILED, TEST, or NCD, 423.3 knots is substituted for the sample value.
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(b) Signal Selector 1) The comparison monitors use the incoming parameter values and compares them to the respective signal selector output. 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 are used for median selection. With only one IRU remaining valid, median selection is avoided and that single input is used by the median selector. Also, a second IRU fault is set and the yaw damper disengages. Differences exceeding specified amounts for more than 1 second result in a comparison fault latch and the affected IRU being declared failed. The comparison monitors are inhibited if either of the two remaining IRUs is invalid, the air/ground discrete is invalid, or until 200 milliseconds after the ground-to-air transition. 中國航空網 m.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：747-400 AMM 飛機維護手冊 空調 AUTO FLIGHT(158)
