747-400 AMM 飞机维护手册 导航 NAVIGATION 3(154)

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 (TMMDB) to perform the thrust limit calculations. The control TMMDB provides the interface between the TMMDB and the TLC as well as determines what data from the TMMDB will be used for the calculations.
 2)  This process also maintains any data required by the TMMDB to perform the thrust limit calculations. Data such as pressure altitude, static air temperature, total air temperature, standard day temperature and mach number.
 (f)  The foreground rating computations monitor ensures that the thrust limit is valid. This is done by comparing the reference thrust limit computed by the foreground processor and the selected thrust rating from the task processor. If the the difference between these two limits is greater than a predetermined value, the monitor will send the last used limit from the TLC. If this difference exists for more than 2 seconds, the TLC is considered failed. Two exceptions for the above failure logic exist: 1) When a new ADC channel is selected, or 2) ADC channel discrepencies.
 (6)  The task processor TLC includes three major processes: process air data, compute reference thrust rating and monitor thrust limits. In addition, it also detects latent software and hardware failures and allows filtering of intermittent and periodic failures.
 (a)  
The air data processing receives ADC data through the autothrottle servo card. This data must first be selected through a selection process. It is then decoded and filtered.

 (b)  
The compute reference thrust rating process receives the filtered data from air data processing and computes the reference thrust limit. The computations are performed in the TMMDB (as in the foreground process) but the data received for this process comes from the autothrottle servo card.

 (c)  
The rating computations monitor determines the status of the computed reference limit. It compares its value to that from the foreground processor and if the difference is greater than the tolerance difference, it will signal the foreground monitor to use the last thrust limit value. When the difference between the two values become acceptable, the task monitor will signal the foreground monitor to resume transmition of the computed limits.

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747-400 MAINTENANCE MANUAL
 (d)  The task processor rating computations monitor also has the capability to directly access the BITE, independent of the foreground processor, for signaling any failures within the rating computations process.
 10. Failure Detection_________________
 A. General
 (1)  
The FMC will monitor the integrity of the program and the data base memory as well as monitor the processor operation, overflow protection and the validity of interface data.

 (2)  
All input signals will be monitored and if a fault is found, the FMC will respond in accordance to the type of fault. The FMC will detect wiring failures whenever the internal monitoring and LRU interfaces allow such an isolation to be acheived.

 B. ARINC 429 Input Fault Monitoring
 (1)  
The SSM (Sign Status Maxtix) of the ARINC 429 input signals will be monitored for Fail/Warn (F/W), No Computed Data (NCD), Functional Test (F/T) and normal states.

 (2)  
Faults resulting from activity logic will be coded as ACT Fail for the corresponding source. Faults resulting from SSM status shall be coded SSM FAIL for the corresponding source. ARINC 429 input failures shall be reported on the general purpose busses by dedicated discretes.

 C. Fault Processing for ARINC 429 Inputs
 (1)  
Three types of fault processing exist. These are inactivity, NCD and F/W fault processes.

 (2)  
Inactivity fault processing monitors signals which are received at a certain rate. If this rate is inactive for 2 seconds the corresponding LRU is considered failed. During the delay, the last received valid data will be used.

 (3)  
No computed data (NCD) faults determined by the SSM status will not be considered for computational purposes, although this is true for most cases there are several exceptions. These exceptions are shown below.

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