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R R For isolation, these BITEs use the snapshots for internal variables and also use for the MCDU and FCU the maintenance
R words received respectively by FM and FG.
R R 1_ FAC, FG and FM snapshots - The snapshot contains the state (0 or 1) of a certain number of application software functional variables (a maximum of 76). - Each time a trigger event is detected, a snapshot is taken. - The snapshot is specific to the triggering event. - The snapshot contains the data enabling the system to analyse the fault and isolate the faulty LRU(s). - Snapshots are displayed within TSD (trouble shooting data) in menu mode (words W1 to W5).
2_ The information transmitted by the FCU and the MCDU is considered by the FG and FM BITEs as ordinary snapshots.
R 3_ Analysis(Ref. Fig. 003)
4_ Analysis (FAC, FG (COMMAND and MONITOR), and FM BITE levels)
R R R R R R a_ 1 st phase analysis(Ref. Fig. 006) The 1st phase analysis is made by the side of the computer which detected the triggering event. The result of this analysis is named RESANAC (result of analysis in COM lane) or RESANAM (result of analysis in MON lane). Composition is as follows:
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| | TYPE / SYMETRY CODE | | | | ERROR CODE | | | EVENT |||
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R R - Event: triggering event - Error code: calculated from the state of the variables of
R R R R R the snapshot and, if applicable, the maintenance word transmitted by the FCU. - Type/symetry code Type: Area where fault context is recorded (ground, flight, AFS TEST, LAND TEST). Symetry: coded to 1 when the failure must be symmetrical i.e. detected by both sides of the computer. In this case, an additional analysis is made at the computer command side (2nd phase analysis).
R R 1st Phase Analysis - FAC, FG and FM BITE levels Figure 006
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b
_
The RESANAM is transmitted to the COMMAND side if the fault was detected on the MONITOR side (not available for FM BITE analysis).
2nd phase analysis (not available for FM BITE analysis)
The second phase analysis is made by the COMMAND side of
the computer following a triggering event. It is triggered
on reception of a RESANAC or a RESANAM.
The 2nd phase analysis computes:
-A RESANA (result of analysis of the second phase in lane COM) which has the same composition as the RESANAC or the RESANAM and is displayed within TSD in menu mode (C/M result of analysis).
-Two codes, CLRU1 and CLRU2, which designate two LRUs suspected as being the origin of the analyzed fault. CLRU1 is allocated to the LRU with the higher probability of failure.
The general computation principle is as follows:
-The 2nd phase analysis is only performed if RESANA C or M, computed by the 1st phase analysis, comprises a bit S coded to 1 (Ref. RESANA composition).
-If this analysis is effective, a 2 second correlation window is opened to take into account, if applicable, the result of the 1st phase analysis transmitted by the other part of the computer. If the fault is correlated, bit CD=0, the 3rd phase analysis will not be made at FIDS level (CD = Correlation Demand). If not, bit CD=1 when fault isolation cannot be performed at the level of the computer which detected the fault, then an additional analysis is made at FIDS level (3rd phase analysis).
-The LRU failure codes are computed from RESANA or RESANAC and RESANAM.
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